Agmatine

Agmatine is a molecule (specifically, a biogenic amine,^[1]) which is a decarboxylated form of L-Arginine and has the molecular name of 4-(aminobutyl)guanidine;^[2] prior to its naming as Agmatine, it was referred to as 'Clonidine-displacing substance' as it was discovered to displace bound Clonidine from receptors.^[3]

Agmatine is a small biogenic amine that can serve as a signalling molecule in the human body; it is a decarboxylated form of the amino acid L-arginine

Agmatine is a bacterial byproduct (due to expression of the enzyme that makes agmatine from arginine being expressed in bacteria) and as such it is found in fermented foods including:^[4]

• Wine at up to 6.5ppm in white and 22ppm in red^[5][6]
• Beer at 0.5–42ppm^[7][8][9]
• Sake at 114ppm^[10]
• Coffee (instant) at 0.4–5.3ppm^[11]
• Terrestrial meat products (3.1ppm normally, increased to 27ppm after cooking and up to 42ppm if fermented)^{[12][13][14][15]}
• Fish (highly variable at undetectable up to 401ppm)^[16][17][18]

Food products that have failed to have a detectable agmatine concentration include green and roasted coffee,^[19] flour,^[20] and both soy sauce and cabbage juice.^[21]

Agmatine is found in a variety of food products alongside other polyamines, but the concentrations found in food is significantly lower than standard supplemental dosages and likely not biologically relevant

Agmatine is a biogenic amine with one or two positive charges, which prevents it from passively transporting across membranes (requiring transporters).^[22] The molecule is a strong base (alkaline) normally,^[23] is diprotonated form dominates at a pH of 7.2 (near physiological concentrations) and is the most stable (1325kJ/mol) followed by the monoprotonated (1070kJ/mol) and neutral (705kJ/mol)^[24] with a pK_a of 8.93.^[25]

Due to its lipophilicity and high level of hydrogen bonds, it is hypothesized to be poorly absorbed.^[25]

The enzyme expression of Arginine Decarboxylase (ADC) in human tissues^[26] appears to differ from bodily areas where Agmatine naturally accumulates,^[27][28] with this discord through to be due to most bodily Agmatine not being due to biosynthesis via ADC.^[2]

In general, the mRNA of the ADC enzyme is relatively highly expressed in the liver and kidneys with detectable levels in skeletal muscle, the small intestine,^{[29][30][31][32]} and brain (higher in hypothalamus, medulla oblongata, and hippocampus; comparatively lower in the striatum and cerebral cortex with the PVN being noted.^[33] Mostly on neurons, with the highest immunohistology appearing on neocortical and hippocampal interneurons^[33]); some in immune cells such as macrophages^[34] and lymphocytes.^[35]

When looking at where Agmatine accumulates in the body, rat studies suggest that the highest levels appear to be in the stomach, small intestine and adrenal gland^[27][28] with some presence in smooth muscle and endothelial cells^[36] with comparatively lower concentrations detected in heart, spleen, aortic and brain tissue.^[27][28] When looking at areas of the brain that are comparatively higher in Agmatine, the rat hypothalamic paraventricular and supraoptic nuclei appear to have high concentrations^[37] usually in terminals of neurons forming excitatory synapses with pyramidal neurons.^[38] Comparatively concentrated areas in the lower brainstem (visceral relay nuclei the nucleus tractus solitarii and pontine parabrachial complex, and periventricular areas including the laterodorsal nucleus, locus coeruleus and dorsal raphe^[39]), midbrain (ventral tegmental area and periaqueductal gray^[39]), and forebrain (preoptic area, amygdala, septum, bed nucleus of the stria terminalis, midline thalamus, and the hypothalamus^[39]) have been reported. A few sources suggested that not only neurons have Agmatine, and that astrocytes^[40] and the chromaffin cells of the adrenal medulla^[41] have expressed Agmatine concentrations.

Four other sources of Agmatine are currently known including gut microflora and dietary sources.^[42] Enterohepatic circulation may also account for preserving Agmatine concentrations in the body.^[2][42]

Although L-Arginine directly converts into nitric oxide (via conversion into L-citrulline and giving off NO as a byproduct after being subject to the nitric oxide synthase enzyme), agmatine is unable to be a substrate for nitric oxide.^{[43][44][45][46]} Although agmatine may influence nitric oxide metabolism, it is not due to being converted into nitric oxide.

Agmatine is not a metabolic precursor of nitric oxide

One possible pathway of metabolism of agmatine is being subject to the diamine oxidase (DAO) enzyme,^[3] which also handles metabolism of histamine and is known as histaminase,^[47][48] and when agmatine is subject to DAO, the product is 4-guanidinobutyrate.^[49]

This pathway has been suggest to account for up to 50% of agmatine metabolism (in rat hepatocytes),^[49] and inhibiting this enzyme approximately doubles plasma agmatine in rats (0.7 to 1.3µM in this study).^[47] DAO is expressed in high levels in kidney tissue, gastrointestinal and epithelial tissue, and smooth muscle cells of the endothelium yet does not appear to be present in skeletal or cardiac muscle, liver, brain, or adrenals.^[47]

Agmatine can convert to 4-guanidinobutyrate via the DAO enzyme, which is possibly the main catabolite of agmatine. This enzyme appears to be expressed in high levels in mucus membranes, kidneys, and endothelium

Agmatine is able to convert into the polyamine putrescine, and can do this directly via the agmatinase enzyme, which gives off urea as a byproduct^[43][50] or indirectly via conversion into carbamoyl putrescine (agmatine deiminase enzyme), which gives off ammonia as a byproduct, and is then converted into putrescine itself (carbamoyl phosphate as byproduct) via the putrescine transcarbomylase enzyme.^[51] Regardless of the pathway, around 10% of agmatine appears to be metabolized into polyamines.^[49]

Agmatine has been noted to increase activity of the protein known as antizyme,^[52] which can suppress intracellular accumulation of polyamines^[52] and polyamine synthesis from ornithine via inhibition of L-ornithine decarboxylase;^[53] this enzyme is induced by polyamines themselves, and agmatine is the only known molecule to induce this enzyme that is not a polyamine.^[54]

Agmatine is an intermediate in polyamine synthesis between arginine and the polyamine known as putrescine, and the conversion of agmatine into putrescine can take one of two pathways to produce either urea or ammonia. Despite this, however, agmatine may be inhibitory on polyamine bioactivity by reducing the amount of polyamines in cells

One in vitro study has also noted that approximately 1-3% of agmatine incubated in rat hepatocytes was converted into GABA,^[49] which is much less than polyamines (10%) and guanidinobutyraldehyde (50%); 30% of agmatine was not metabolized in this study.

Likely not practically relevant

If the latter pathway is chosen and carbamoyl phosphate is produced, it can be metabolized into carbamate via the carbamate kinase enzyme, which simultaneously converts ADP into ATP. This pathway, known as the deiminase pathway, is a way for bacteria to produce ATP from arginine and agmatine.^[55][56][57]

The above mechanism is common to transcarbomylase enzymes (that produce carbamoyl phosphate), as both ornithine transcarbomylase^[58][59] and oxamate transcarbamylase^[60][61] have been linked to bacterial ATP production through carbamate production.

In bacteria at least (human relevance not known and probably doubtful), agmatine can be used to create ATP

Serum concentrations of agmatine have been detected in the ranges of 6.8+/-0.6ng/mL^[62] and 6.8-16.9ng/mL^[63] in rats, but appear to be significantly higher in humans such as 47ng/mL,^[64] 33.8+/-16.6ng/mL,^[65] or 79.42-82.44ng/mL.^[66]

Cerebrospinal fluid (CSF) concentrations of agmatine in rats are in the range of 6.1-23.5ng/mL,^[63] while those in humans range from 24.3-54.0ng/mL.^[65] The latter study noted a possible correlation between CSF and serum agmatine concentrations.^[65]

Neural concentrations in rats have been noted to be in the range of 15.3+/-2.4ng/g,^[62] while bovine brain has higher concentrations (1.5-3.0nmol/g or 0.2-0.4µg/g).^[67] The concentrations in the bovine brain are correlated with those of catecholamines, as 0.2-0.4µg/g of agmatine in cow brain is similar to 0.5µg/g concentrations seen for both noradrenaline and dopamine.^[67]

Agmatine has a regulated serum concentration and it appears to be in the range of 50ng/mL or higher for humans than it is for rats. Its concentrations are similar to those seen with catecholamines

Plasma agmatine levels (independent of supplementation) have been noted to be significantly reduced in metabolic syndrome (by 3.7%)^[66] and significantly elevated in both schizophrenia^[68] and depression.^[69]

Agmatine appears to be reduced in metabolic syndrome (by a small amount) and elevated in some neurological disorders such as depression and schizophrenia

Agmatine has been found to be absorbed following oral ingestion^[70] and oral ingestion appears to influence cognition^[71] (suggesting that it can reach the brain).

When looking at the distrubution, low doses (9nmol in rats) is able to increase bodily concentrations of agmatine in all tested organs (stomach, intestines, liver, spleen, lungs, brain, colon, kidneys, adrenals, heart, and skeletal muscle) with 64+/-7% being detected in the liver after 3 hours.^[70]

Appears to be absorbed following oral ingestion and readily distributed to tissues; it appears to reach the brain following oral ingestion

In systemic circulation, agmatine appears to have a half-life of less than 10 minutes^[72][73] although in the brain it appears to have a half-life exceeding 12 hours.^[72]

There appears to be a fairly short half-life in systemic circulation (not the brain), while the half-life in the brain itself appears to be much longer

Agmatine cannot passively cross plasma membranes due to being protonated at physiological pH, and thus requires transporters. It does appear to be readily taken up by rat hepatocytes (rate of 0.37+/-0.04nmol/h/mg protein).^[49] Uptake into cells appears to have some overlap with putrescine transportation, as high concentrations of putrescine can inhibit agmatine uptake^[70][74] and vice versa.^[49] Transportation is energy dependent.^[74]

The Extraneuronal Monoamine Transporter (EMT) and Organic Cation Transporter 2 (OCT2) transporters can accept agmatine with similar capacities, with the OCT1 transporter being significantly (9-fold) less active.^[75] These receptors are saturatable at 1-2mM (K_m) with a V_max of 8-16nmol/min/mg protein (11.5+/-1.1 for OCT2 and 15.9+/-3.5 for EMT).^[75]

Agmatine appears to be taken up by transporters into cells and tissue, and the transporters used have overlap with putrescine transporters. EMT and OCT2 are suspected of being the transporters

When looking at specific brain regions, agmatine in basal conditions (without supplementation) has been detected in the brains of rats in the cortex (14.9-16.6ng/g), hypothalamus (19.5-23.9ng/g), medulla (22.2-25.9ng/g), cerebellum (20.6-37.0ng/g), and hippocampus (23.6-33.1ng/g).^[62] An overall immunohistological approach notes that most agmatine concentration is present in the cerebral cortex and subiculum (inferior portion of the hippocampus), but can be detected in other brain regions when an axon transport inhibitor is used (such as the forebrain and brainstem); there is no detectable agmatine containined neurons in the cerebellum nor spinal cord.^[39]

Agmatine concentrations in the brain are correlated with imidazoline receptor concentrations^[64] and with concentrations of the enzyme that creates agmatine (arginine decarboxylase);^[67][76] the enzyme that degrades agmatine (agmatinase) appears to also be well expressed in the hypothalamus and hippocampus but not in the cortex.^[50]

Agmatine is expressed in various brain regions, and is particularly rich in the inferior portion of the hippocampus and the cerebral cortex

Agmatine is known to cross the blood brain barrier where 10, 50, and 300mg/kg injections of agmatine into mice noted that the highest dose was able to increase neural agmatine to approximately 800ng/g (700% higher than baseline) and in monkeys injected with 25-200mg/kg agmatine it was found that the rise in cerebral agmatine (11.3μM or 1,469ng/mL) was approximately 16% that of the plasma rise in agmatine (70.2μM or 9,126ng/mL).^[63] There appears to be a rather long elimination phase from the brain (between 24-72 hours).^[77]

In both mice and monkeys, L-arginine injections failed to increase brain agmatine.^[63]

Agmatine can increase brain agmatine concentrations at high doses, and can cross the blood brain barrier. Plasma agmatine rises to a larger degree than does neural agmatine concentrations, and administering L-arginine does not increase agmatine concentrations

Agmatine is a ligand for imidazoline receptors with most affinity towards the I₁ receptor subset followed by I_2b.^[91] Its affinity is greater enough to displace idazoxan from the receptor, similar to how it can displace clonidine from the α2A receptor^[92] and has been calculated (EC₅₀ values) at 0.7µM and 1µM for I₁ and I₂ receptors, respectively.^[67]

Agmatine is an Imidazoline receptor agonist (activator) with fairly high affinity

Downstream of the imidazoline receptor lays an increase in β-endorphin secretion.^[93]

Activation of imidazoline receptors underlies an increase in endorphins (and the effects of that, likely analgesia and blood glucose reductions)

Agmatine is known to interact with the alpha-2 (α2) subsets of the adrenergic receptors, and has affinity for all four subsets (variable K_i between 0.8–164μM^{[67][86][94][94][95]} and an EC₅₀ of 4µM has been noted to be lower than noradrenaline at 0.8µM, the main ligand of adrenergic receptors,^[67]) while having poor or no significant affinity for the alpha-1 (α1) subset nor β-adrenergic receptors.^[67][86] In regards to its affinity for the α2A receptors, it can displace clonidine from the binding site.^[67][91]

One study has noted that 10µM agmatine has shifted the concentration-response curve to the left (indicative of enhancing the signalling of noradrenaline and the agonist moxonidine with IC₅₀ values of 7.76 and 6.86), while 100-1,000µM agmatine had the opposing effect and hindered signalling; the authors concluded that at low doses agmatine is a positive allosteric modulator of α2A signalling while at higher concentrations it inhibits signalling competitively.^[86]

Agmatine has high affinity for the alpha-2 adrenergic receptors, with little to no affinity for the alpha-1 subsets nor the entire class of beta-adrenergic receptors. It appears to be a positive allosteric modulatory at low concentrations (enhancing the signals of other ligands without inherently activating the receptor), while at higher concentrations it can act as a competitive inhibitor

Numerous studies in vitro have failed to find a per se agonistic property of agmatine on these receptors (in line with the role of an allosteric modulator, which does not inhernetly act on the signalling of a receptor),^[95][96] while those in living models have noted that some effects of agmatine can be abolished with α2A receptor inhibitors (yohimbine and rauwolscine most commonly).^[97][98]

Agmatine definitely appears to signal through α2A receptors in living models, possibly due to the allosteric modification mentioned earlier. This is not always seen in vitro, possibly due to not introducing other ligands into the medium (as agmatine would enhance the signalling of other ligands, it presumes another ligand is present)

Agmatine has its concentrations correlated with catecholamines in the bovine brain (0.2-0.4µg/g for agmatine, 0.5µg/g for dopamine and noradrenaline)^[67] and is known to influence a subset of catecholamine receptors (the α2 adrenergic receptors) while not significantly influencing the others (α1 adrenergic, β-adrenergic, and dopamine D2 receptors).^[67]

Agmatine is thought to interact with monoamine oxidase (MAO) enzymes as imidazoline ligands usually have this property since MAO enzymes are structurally similar to imidazoline receptors.^[99][100] Agmatine has been found to be a ligand for MAOA near the flavin site (somewhat weak in preventing kynuramine from being oxidized, IC₅₀ at 1,000µM^[24]) and elsewhere has been noted to have an IC₅₀ value of 168µM but not be significantly active in vivo.^[100]

Agmatine has its concentrations correlated with catecholamine levels, and is known to interact with the MAO enzymes as well although weakly (MAO inhibition is likely not a practical concern with supplemental agmatine due to the high concentration needed)

It shows positive regulation such as a concentration-dependent release of adrenaline and noradrenaline from adrenal chromaffin cells with an EC₅₀ of 5µM^[67] (these cells express imidazoline but not α2A receptors,^[101] so this was thought to be indicative of acting on imidazoline receptors which induce catecholamine synthesis^[102]) and elsewhere has been noted to increase the actions of noradrenaline secondary to α2A receptors (in endothelial cells).^[103] This potentiation is cocaine-sensitive (prevented by cocaine, an inhibitor of the noradrenaline transporter) yet agmatine does not modify the noradrenaline transporter per se.^[103]

However, activation of the α2A receptors in endothelial cells has been shown to suppress synthesis of catecholamines,^[103] while imidazoline receptor activation may also suppress catecholamines.^[104]

Agmatine appears to have a regulatory role for catecholamines, and has been implicated in both inducing and suppressing their release. Practical implications of supplemental agmatine are not currently known

Agmatine has affinity for the NMDA receptors (IC₅₀ value in the 100-300μM range^[105]) as the guanidine group of agmatine interacts with the NMDA channel pore,^[106] and has been noted to bind to both the MK-801 binding site^[107] and the polyamine binding site (K_i of 15μM)^[88] but not the glutamate nor glycine binding sites.^[105] As agmatine does not have the ability to activate the receptor up to 100μM^[106] and can displace MK-801, which is a noncompetitive antagonist and channel blocker of the NMDA receptor.^[108] Though there is evidence for inhibition of the receptor and protection from neurotoxic stressors that signal via the NMDA receptor^{[71][109][109][109]} but those that act on the same signalling pathway but circumvent the receptor (calcimycin and staurosporin) are unaffected.^[109]

Kainate and AMPA receptors are mostly unaffected, with 3,000μM concentration only inhibiting 15-20% of activity,^[106] and four heterodimers (ε1ζ1 through ε4ζ1) are equally inhibited with agmatine.^[105]

The binding of agmatine to the polyamine binding site^[88] is able to inhibit NMDA signalling from other polyamines such as spermidine from signalling through the receptor^[106] via competitive inhibition.^[88] This may also extend to histamine, which is thought to bind to the polyamine binding site^[110] (not fully confirmed, but may be a unique site^[111]) which agmatine can antagonize.^[112]

Agmatine binds to two sites of the NMDA receptor (neither of which bind glutamate) and functions as a noncompetitive inhibitor. It can competitively inhibit polyamines from activating the receptor, and the inhibition of NMDA receptors does not extend to the other two glutaminergic receptors (AMPA and kainate)

Due to the role of agmatine as an NMDA inhibitor, it shows protective effects against glutamate excitotoxicity (19-51% reduction of cytotoxicity with 10-1,000µM^[109]) and NMDA excitotoxicity with similar potency (46% at 1,000µM)^[109].

Lower concentrations of agmatine (1-10µM agmatine) have been found to be bioactive, attenuating the reduction in catecholamines seen during glutamate excitotoxicity^[71]

These protective effects in vitro with 1,000µM are comparable to 1,000µM desipramine^[71] and to 20µM MK-801.^[109]

Inhibition of NMDA appears to be present in vivo following intraspinal or intrathecal injections of low dose agmatine^[111][113]

Appears to be neuroprotective against excitotoxicity (from glutamate and NMDA) likely due to blocking the receptor that they signal through, the NMDA receptor. This has been noted in living systems following standard dosing, and although its maximal potency is at a very high concentration likely not attainable with supplementation it does appear to be active at even physiological concentrations

The interactions of agmatine with NMDA receptors in an inhibitory manner is thought to play roles alcohol^[114][115] and cocaine dependence,^[116] and general neuroprotection against excitotoxicity mediated via the NMDA receptor. Some anti-depressive effects (ultimately influencing potassium and calcium signalling) may also be tied back into NMDA receptor antagonism.

NMDA inhibition appears to be sought after mostly for its antiaddictive and neuroprotective properties, with the latter referring mostly to excitatory toxins (such as excessive glutamate or stimulant usage)

Nitric oxide is covered more in depth in the cardiovascular health section, due to its interactions with blood flow and cardiovascular health. This section solely discusses neurology

Agmatine has been noted to be a neuronal nitric oxide synthase (nNOS) inactivator with a K_i of 29µM secondary to increasing the activity of the NADPH oxidase subunit.^[117] L-Arginine is known to hinder the activity of this subunit^[118][119] and has been noted to reduce the inactivation of nNOS induced by agmatine.^[117]

Inactivation of nNOS either directly (or indirectly via NMDA inhibition as NMDA activation causes an increase in nNOS activity^[120]) is thought to underlie the interactions of agmatine and opioids, since NOS inhibitors tend to attenuate tolerance to opioids^{[121][122][123]} and NMDA inhibitors have been implicated as well.^[123][124]

Agmatine is able to inhibit the activation of the neuronal isoform of the nitric oxide synthase enzyme (nNOS) in many instances, either directly via inactivation or secondary to the NMDA receptor being inhibited. For any neurological phenomena that involves nNOS suppression, supplemental L-arginine is possible antagonistic

1mM agmatine has been found to inhibit the nicotinic acetylcholine receptor's response to the agonist dimethylphenylpiperazinium (DMPP) by 67+/-11% (showing signs of both competitive and non-competitive inhibition)^[125]

May be an antagonist of nicotinic acetylcholine receptors, but needs to be investigated more to confirm

Agmatine does not appear to interact with serotonin per se too much, as it does not influence serotonin release from PC12 neurons (1-100µM)^[71] and when serotonin is depleted (70%) the antidepressant effects of agmatine are unaffected.^[126] That being said, the antidepressant effects of agmatine appear to be dependent on serotonin receptors as blocking either the 5-HT_1A,^[90] 5-HT_1B,^[87] 5-HT_2A,^[87][90] or 5-HT_2C^[87] serotonin receptors inhibits antidepressant effects.

Blocking the 5-HT₃ receptor does not appear to abolish the antidepressant effects of agmatine^[90] perhaps since it has been implicated for being an antagonist itself,^[38][127] and agmatine does not appear to be a direct ligand for the 5-HT₂ receptors.^[67]

Agmatine appears to enhance signalling through the serotonergic receptor, but does not appear to modify synaptic (extracellular) serotonin concentrations nor is it really dependent on them. This augmentation of serotonergic signalling appears to underlie antidepressant effects

Due to the above mechanisms and due to synergism between agmatine and serotonergic antidepressants,^[98][128] it is thought that agmatine enhances serotonin signalling. It is not known whether this is due to postsynaptic protein modifications or allosteric modification of the receptor (it appears to be independent of influencing synaptic serotonin concentrations) and it is unclear exactly what mediates these effects as NMDA antagonism^[129] and NOS inhibition^[130] are both implicated in enhancing serotonergic signalling, while inhibition of both the imidazoline^[128][131] and α2A receptors^[98] prevent antidepressant effects.

It is unclear how agmatine enhances serotonergic signalling, but signalling through one of the four classical pathways of agmatine (or, likely, some combination of them) appears to then beneficially modify serotonin signalling

Endocannabinoids are naturally occurring ligands of the cannabinoid receptors (CB1 and CB2; the former more involved with neurology) and are named after the first discovered ligand, THC from marijuana. The CB1 receptors are expressed in a pattern in the midbrain^[132][133] that is very similar to the pattern of imidazoline receptors^[134] and agmatine localization,^[28] and in cardiac tissue at least they have been found to beneficially influence one another.^[135]

While agmatine (50-100mg/kg injections) are ineffective at reducing thermal pain perception (hot plate test in rats), 50mg/kg agmatine was able to synergistically increase the pain killing efficacy of two cannabinoidergic drugs by 300-440% via acting on imidazoline receptors,^[136] although the effect is also abolished when CB1 antagonists are used.^[136] It seems that signalling through imidazole receptors (seen elsewhere when agmatine augmented cannabinoid induced hypothermia^[137][138] ) from agmatine will enhance the actions of the CB1 receptor, but still requires an agonist, and it is unlikely that other mechanisms are at play since yohimbine failed to abolish the synergy (excluding α2A receptors^[136]) while NDMA antagonism is known to reduce analgesia from CB1 signalling^[139] and NOS inhibition is fairly ineffective.^[139][140]

It has been noted elsewhere that activation of imidazoline receptors is able to inhibit binding of the CB1 antagonist SR 141716A from its binding site,^[141] which suggests imidazoline-induced allosteric modification of the CB1 receptor.

Via signalling through imidazoline receptors, agmatine appears to enhance the pain killing effects of cannabinoids against heat. There appears to be general synergism between the two, and agmatine's role appears to be an indirect positive modulator (possibly by changing the structure of the receptor to better encourage signalling) of CB1 receptors

Potential unexplored synergism for relieving neuropathic pain, as marijuana is well known to do so

The activation of imidazoline receptors (specifically I₂ receptors) in the adrenal glands appears to induce the release of β-endorphin (a naturally produced opioidergic pain killer)^[93] which has central and peripheral implications.

Enhancement of opioidergic analgesia^[124] and the attenuation of tolerance development^[142] have been noted with NMDA antagonists before (possible role of Agmatine) although one study has noted that the prevention of tolerance was reliant on activation of imidazoline receptors.^[143]

Agmatine is able to release some opioids inherently by activating imidazoline receptors in the adrenal glands. So in regards to the following information of how agmatine interacts with opioids (which should apply to β-endorphin as well), it is somewhat synergistic with itself in persons with functioning adrenals

The acute analgesic (pain killing) effects of morphine are augmented when coadministered with agmatine,^[144] which is mediated by α2A receptors^[145] and appears to extend to oxycodone^[146] and fentanyl (two other opioidergic drugs similar to morphine).

For acute analgesia, agmatine appears to be synergistic with opioids

Agmatine has been found to potently inhibit tolerance to μ-opioid agonists (Endo-2 and DAMGO-AG) with intrathecal injections of 4nmol^[113] which appears to be effective for up to 48 hours following a single dose.^[113] This has also been noted in rhesus monkeys given oral agmatine (40-80mg/kg).^[147]

Tolerance to opioidergic drugs has been noted to be reduced in research animals.^[121][144]

Tolerance to opioids (the reduction of efficacy that comes with prolonged usage) appears to be attenuated when agmatine is coadministered, which would synergistically preserve the analgesic effects of opioids

Adrenergic receptors are involved with opioid receptors, with activation of the α2A receptor^[148][149] and inhibition of β-adrenergic receptors being able to attenuate morphine withdrawal symptoms;^[150] conversely, yohimbine (inhibitor of α2A) negatively augments withdrawal symptoms.^[151][152]

In studies that measure addictive properties (self-administration usually what is investigated) or withdrawal symptoms of opioidergic drugs, agmatine has been noted to reduce self-administration of fentanyl.^[153][154]

In regards to conditioned place preference (CPP; a preference for one place over another thought to be a biomarker of addictive behaviour^[155]), agmatine cotreatment with morphine is able to augment morphine-induced conditioned place preference.^[156]

Agmatine appears to be synergistic with opioid drugs such as morphine or fentanyl, preventing their tolerance and possibly reducing the addictive potential thereof. Agmatine appears to be quite potent at this effect

Agmatine appears to be a nonproton ligand for ASIC3^[157][158] which is one of six acid sensing ion channels^[159] that are usually activated by acidity (protons);^[160] ASIC3 is somewhat unique since it is not readily desensitized in response to acidity^[161][162] and is present in sensory neurons where its activation is associated with the perception of pain.^[163][164]

Agmatine can induce signalling at neutral pH (7.4), and is classified as a nonproton ligand since it does not bind to where protons do on the channel (during acid sensing).^[158] This activation was unique to agmatine (not seen with polyamines nor arginine), and agmatine was also found to sensitize receptors to acidity (pH 7.0).^[158] However, the authors noted that the low potency paired of signalling paired with low concentrations of agmatine normally may mean that this is not a significant concern under normal conditions^[158] although pain can be induced with agmatine in mice via ASIC3 dependent means.^[157]

Conditions in which acid-induced pain is relevant (blood pH of around 7.0) include inflammation, infection, ischemia, hematomas, and exercise^[159] while conditions where agmatine is elevated (alongside increases in percieved pain) include cancer and trauma patients.^[34][165]

Agmatine is able to activate the ASIC3 receptor which is involved in percieving pain associated with acidity, and via this mechanism it is theoretically pain causing. Practical significance of this pathway is not known, but at this moment in time it is plausible that agmatine normally does not signal pain but unnormally high concentrations can augment acid-induced pain

In an acetic-acid writhing test (visceral pain model), agmatine has weak analgesic properties.^[143] In tests of inflammatory or neuropathic pain, agmatine produces dose-dependent pain reduction.^[166][167]

Agmatine by itself has been found to either have no activity in pain relief^[136] or to have a short lasting activity (10-30 minutes, only against thermal hyperalgesia) in rats.^[72] The short lasting effects may be related to agmatine's short half-life (less than 10 minutes^[72]) and secretion of β-endorphin from the adrenal glands.^[93]

Agmatine does not appear to be effective against heat pain and fairly weak against visceral pain. Despite that, agmatine appears to have dose-dependent pain relieving properties on inflammatory and neuropathic pain

One double-blind study (partly funded by Trimarco Medical Division, conducted by patent holders) using 2.67g of Agmatine Sulfate for 14 days in patients with lumbosacral spine degenerative pathologies associated with radiculopathy (n=61) noted that after 14 days there were reductions in pain as assessed by the VAS rating scale, the McGill pain questionnaire, but no significant improvement on the Oswestry Disability Index.^[168] These benefits appeared to still be statistically significant after Agmatine sulfate was discontinued for 60-65 days.^[168]

Agmatine in isolation appears to be effective in reducing the perception of pain in this particular disease state, and requires more research on it since the degree of pain reduction was remarkable

The α2A receptors are somewhat central to addiction, where its activation is thought to be helpful for addiction (as seen with clonidine and nicotine addiction^[169][170]) and its inhibition thought to be a negative influence (augmentor) of addiction (some limited evidence for yohimbine acting in a pro-addictive manner).

α2A receptors are also upregulated in response to addictive drugs such as nicotine^[171] which augments stimulation (assessed by locomotion in rats) and addiction with subsequent dosages relative to a single dose.^[172] Preventing this upregulation is currently hypothesized to be the mechanism by which agmatine prevents nicotine-induced conditional hyperlocomotion^[173] and the increase in locomotion seen over a week of chronic dosing.^[172]

Agmatine appears to prevent the increase in hyperlocomotion with chronic nicotine ingestion, which is possibly due to preventing upregulation of α2A receptors (which prevents nicotine from releasing more catecholamines with repeated dosages)

Symptoms of alcohol withdrawal such as wet dog shakes/tremors^[174] and anxiety^[175] are attenuated with agmatine administration. Although the mechanism for this is not yet known, it is thought to be related to NMDA receptor antagonism since polyamines are known to activate the NDMA receptor in a neurotoxic manner during alcohol withdrawal^[176][177] and agmatine is an established inhibitor.

May be useful during alcohol withdrawal, and despite nicotine and opioids being related to α2A receptor upregulation the interactions with alcohol are possibly mediated by another mechanism (NMDA antagonism)

Cocaine addiction has been noted to be aided by NMDA inhibition in vitro^[116] (with not so promising evidence in humans^[178][179]) and by NOS inhibition in planarians (non-mammalian model of animals with mammalian-like neurotransmission),^[180] which are two currently hypothesized links between cocoaine addiction and agmatine.

Coadministration of agmatine in a dose sufficient to prevent fentanyl-induced addictive behaviour has failed to modify cocaine related addictive behaviour in rats.^[154] Practical relevance of this data is uncertain since it is known that cocaine is not overly addictive to rats^[181] and is lower on the reward ladder than is intense sweetness;^[181][182] there is currently no evidence in humans.

Evidence for the anti-addictive properties on cocaine are limited and not overly promising in rat models, but due to known species differences between rats and humans in this regard it is uncertain how agmatine will practically influence cocaine addiction

In general, research animals pretreated with agmatine prior to an experimentally induced stroke show neuroprotection with injections of around 100mg/kg.^{[183][184][185][186][187][188]}

In general, agmatine pretreatment before experimentally induced strokes is highly neuroprotective in research animals and quite reliable as well

Nitric oxide synthase (NOS) enzymes, which agmatine is known to inhibit, differential modulate strokes (iNOS appears to contibute to excessive nitric oxide production and harm^[189][190] while eNOS is protective via vasodilation;^[191] nNOS is also a bit neurotoxic^[192]) and it is thought this is one of the targets of agmatine in stroke prevention, as its inhibition towards iNOS (220μM) is 34-fold more potent than that of eNOS (7500μM)^[117] and it has been noted that the typical changes in NOS enzyme content after a stroke (increase in iNOS and acute suppression of eNOS) are attenuated with agmatine pretreatment, with iNOS reduced by 13.35% (6 hours) and 46.30% (24 hours)^[193] and normalization appears to occur within 4 days.^[183]

Perhaps secondary to reduced iNOS production of nitric oxide (has been confirmed),^[188] a reduction in peroxynitrate concentrations have also been detected.^[184]

There appears to be beneficial modulation of nitric oxide metabolism in response to agmatine supplementation, where the proinflammatory changes in iNOS are reduced and the protective effects of eNOS preserved. This reduces levels of nitric oxide and peroxynitrate, which in the context of a stroke their abnormal elevations are harmful

The aquaporin-4 receptor is a receptor expressed on astrocytes that selectively uptakes water,^[194] and reducing (or abolishing) expression of this receptor enhances survival in brain edema^[195] which is induced after ischemia stroke.^[196] Agmatine (100mg/kg) has been noted to attenuate the increased expression of aquaporin-4 seen during experimental stroke^[185] and possibly secondary to that brain edema from stroke is almost normalized.^[183][185]

The expression of aquaporin-4 is significantly reduced with agmatine pretreatment, and due to this less edema occurs following experimental stroke. This is likely an effect of agmatine that is secondary to another target

When looking at neurons and glial cells, astrocytes (glial cell) appear to be preserved with agmatine pretreatment at 100mg/kg injections in vivo^[183][197] and in isolated cells (100µM).^[186]

The in vitro study confirmed increased NF-kB translocation into the nucleus associated with more activation of IκBα and IKKα/β,^[186] which is a cellular protective effect.^[198] Although it is not confirmed what mediates this process, agmatine has been noted to activate PI3K/Akt elsewhere^[199][200] and this is known to be a cellular survival pathway (Akt signalling via NF-kB to survivin).^{[201][202][203]}

Agmatine appears to protect cells from ischemia/hypoxic death, which may be due to increasing activity of NF-kB which then increases survivin

The arginine decarboxylase enzyme has been noted to be induced (increased in activity) by acidity in both plants^[204] and bacteria^[205] and has been shown to be responsive to osmotic^[206] and copper-induced oxidative stress.^[207]

Due to the above, and the fact that in mammals subject to cold stress an increase in cerebral (15.3+/-2.4ng/g to 57.4+/-19.6ng/g; 275%^[62]) and plasma (6.8+/-0.6ng/mL to 58.1+/-12.8ng/mL; 754%^[62]) agmatine is seen, it appears that the arginine decarboxylase enzyme is stress responsive and increases agmatine in periods of stress (although the authors of at least one paper suggest other mechanisms may be at play, since a plasma rise in agmatine was detected in 4 hours which may have been too quick to place causation on the enzyme^[62]).

The enzyme that creates agmatine from arginine (known as arginine decarboxylase) appears to be increased under periods of stress, and due to this the stress response is met with a large increase in agmatine. It is thought that this is a protective response to stress

An increase in arginine decarboxylase activity has been noted during hypoxia.^[188]

Mechanistically, an intrathecal infusion of agmatine (10-40mcg) can cause concentration dependent increases in the firing of neurons in the locus coeruleus (via nitric oxide signalling^[208]). This brain region appears to be involved in the bodily response to stress, particularly anxiety and depression,^[209] and thus this is thought to be related to agmatine's actions.

There are a few interactions with alcohol as well, as anxiety caused from alcohol withdrawal is abolished^[175] and the anxiety reduction by alcohol is actually agmatine dependent (depleting agmatine prevents it from occurring).^[175]

Agmatine is involved in anxiety processing in the brain, and alcohol appears to reduce anxiety via influencing agmatine concentrations

In studies using an elevated maze plus test (EPM; standard anxiety test for rats), 20-40mg/kg injections of agmatine^[210] and 40mg/kg^[211] have efficacy in reducing anxiety with comparable (nonsignificantly more potent) effects relative to 30mg/kg Imipramine.^[211] One study using oral intake of agmatine (10-40mg/kg) noted reduced anxiety in a social conflict test in rats comparable to diazepam, with no effect from 80mg/kg nor 5mg/kg.^[212]

In a light-dark test of anxiety, agmatine at similar doses has either failed to have an effect^[126] or it was only notable at 80mg/kg injections in mice or 10mg/kg oral intake; both being less potent than the reference drug (diazepam).^[212]

100mg/kg has been found to either have no effect^[211] or actually worsen anxiety.^[210]

Agmatine appears to be able to reduce anxiety at a dosage similar to that where depression is reduced, although there is a demonstratable bell curve with agmatine and double the dose does not have anxiolytic effects. The overall anxiolytic effect at maximal efficacy is either less than or comparable to reference drugs (Valium)

Agmatine kinetics (without supplementation) appear to be altered in persons with depression, as there are higher serum concentrations^[69] but also higher breakdown as assessed by agmatinase activity in both depressed and bipolar persons.^[33] Agmatine is also influenced by pharmaceutical depressants, being reduced in concentration by bupropion (Wellbutrin)^[69] while SSRI drugs increase agmatine concentrations.^[128] Depression also appears to be associated with perturbed imidazoline receptor signalling.^[213]

Depression is associated with altered agmatine kinetics and function, although not really in a predictable manner. Pharmaceutical antidepressants seem to have differing effects on agmatine as well (either decreasing or increasing) despite both being able to treat depression

When used by itself, agmatine appears to reduce immobility time in a forced swim test at 10-40mg/kg oral ingestion (human equivalent being 1.6-6.4mg/kg)^[71] which has been confirmed elsewhere with 5-40mg/kg^[90] or 10mg/kg oral ingestion^[71] and various doses of injections (anywhere between 0.01-100mg/kg; with more efficacy in the 10-50mg/kg range).^{[98][126][211]} For studies using active controls, it was found that agmatine (50mg/kg) is slightly less effective than 15mg/kg imipramine^[126] or 10-100mg/kg are all comparable to 30mg/kg imipramine.^[211]

Antidepressant effects have also been noted in tail suspension tests^[71][98] with 40-80mg/kg oral ingestion being of similar potency as 10mg/kg imipramine.^[71]

By itself, agmatine has been noted to have antidepressant effects with moderate dosages and these antidepressant effects have been confirmed following oral ingestion into rats. The potency seems either comparable to or weaker than the reference drug imipramine, but comparisons between the two are not that consistent. The estimated human dose for the rats 10-40mg/kg is 1.6-6.4mg/kg (or 217-435mg for a 150lb person)

Agmatine has been found to work synergistically with numerous antidepressants such as bupropion (at 10-20mg/kg agmatine injections, dependent on imidazoline receptors^[131]), imipramine (0.01-50mg/kg,^[98] although a failure noted elsewhere^[128]), SSRIs (5-10mg/kg agmatine injections, dependent on imidazoline receptors),^[128] and oddly putrescine (a polyamine) is synergistic with agmatine on depressive symptoms (0.001mg/kg agmatine injection).^[85]

The antidepressant effects are abolished by L-arginine,^[98][98] yohimbine (α2A receptor blocker),^[90][98][98] and GMP itself;^[98] another study noted that potassium channel inhibitors (which appears to be the mechanism that agmatine works via) are inhibtied by PDE5 inhibitors such as Viagra.^[214] Blocking either the 5-HT_1A,^[90] 5-HT_1B,^[87] 5-HT_2A,^[87][90] or 5-HT_2C^[87] serotonin receptors blocks the effects as does blocking the delta and mu subunits of opioid receptors (but not kappa)^[215] and opening potassium channels appears to prevent the effects of agmatine.^[216]

The effects are not affected by prazosin (an α1A receptor blocker),^[98] serotonin depletion,^[126] blocking the beta-adrenergic system (propanolol),^[87][90] or 5-HT₃ receptors.^[90]

The inhibition of potassium channels may underlie synergism,^[216] as the classical antidepressants mentioned earlier tend to have the ability to inhibit potassium channels^{[217][218][219][220]} as does adenosine (endogenous neurotransmitter)^[221] and folic acid^[222] while opening potassium channels appears to be a pro-depressant effect.^[223][224] It was mentioned earlier that blocking a variety of serotonin receptors inhibits synergism, and serotonin likely mediates potassium channels via its receptor.^[225] Finally, despite agmatine not per se inhibiting potassium channels at up to 500µM^[226] its antidepressant effects are abolished with potassium channel openers.^[216]

The anti-depressant effects of agmatine appear to be via augmenting other agents. While agmatine itself cannot inhibit potassium channels, it (somehow) increases the ability of other agents to inhibit potassium channels which adds to their antidepressant effects. This synergism requires that signalling through serotonin receptors is preserved (which the active molecules likely signal through) and that signalling through the α2A receptors is preserved (which agmatine likely signals through)

One pilot study in human subjects with depression (major depressive disorder and unipolar/bipolar distinctions) and no antidepressant resistance who were given 2-3g agmatine orally without any other pharmaceutical drug noted that the three tested subjects all reported remission of depression^[227] which was not reversed by administration of PCPA;^[227] suggesting that similar to animal studies^[126] agmatine's antidepressive effects are unrelated to serotonin.

One very small pilot study suggests that agmatine is able to induce remission of depression (ie. a curative effect)

Neuropeptide Y is a peptide neurohormone that positively regulates hunger and due to this is known as an 'orexigenic' (hunger increasing or appetite stimulating) hormone^[228] and its injections into the paraventricular nuclei (PVN) of the hypothalamus induces food intake.^[229] Neuropeptide Y is highly associated with α2-adrenergic receptors^{[230][231][232]} and their activation (usually via clonidine in studies) increases NPY concentrations;^[233][234] this is thought to explain why antagonists (yohimbine and rauwolscine) suppress appetite.^[235][236]

Administration of agmatine has been demonstrated to increase food intake in satiated rats, but not hungry rats^[237] and infusions of agmatine into the hypothalamus cause increases in food intake (10-20nmol causing 45-54% over 24 hours) associated with increased neuropeptide Y activity,^[97] thought to be mediated by α2-adrenergic activation as yohimbine attenuated the effects.^[97] Intraperitoneal injections of agmatine (40-80mg/kg) were also effective at increasing food intake (44-49% over 24 hours) while 20mg/kg was ineffective.^[97]

Agmatine is somewhat opposite of yohimbine, and via the α2A receptors agmatine infusions can increase appetite, but only in rats that are 'full' rather than already hungry rats. The practical relevance of this information is not known, although promising for those unable to gain weight due to not being able to eat enough

Agmatine is known to be stored to high levels in the hippocampus, specifically CA1 pyramidal neurons.^[38] It is thought to be co-released with glutamate vesicles^[64][238] via a synaptic Ca2+-dependent exocytotic process^[239] and the levels of agmatine in the synpase increase with hippcampal action potentials (neuronal activation)^[239] and the process of learning (60-85% in water maze testing in rats);^{[238][240][240][241]} although higher increases have been reported (210-573%) but only for 85-95 minutes;^[242] baseline agmatine does appear to increase, but in the aforementioned lower range.^[242] Agmatine appears to attenuate subsequent hippocampal discharges^[243]

Agmatine has also been found to be elevated in the stratum radiatum and both prefrontal and perirhinal cortices^[244] during the learning process, and is also elevated in the locus coeruleus^[39] which has neuronal activity enhanced by agmatine infusions.^[208] The locus coeruleus is involved in agmatine's benefits on inhibitory avoidance tasks,^[245] the prefrontal cortex is involved in behavioural learning and executive functioning,^[246][247] and the perirhinal cortex (as well as the hippocampus) beneficially influence displaced object recognition.^[248]

Agmatine's role of a neurotransmitter is involved in memory formation. During learning tasks agmatine is elevated in the hippocampus, prefrontal cortex, stratum radiatum, and perirhinal cortiex and it appears to be a negative regulator of glutaminergic signalling that is coreleased with glutamate (NMDA receptor antagonism likely is involved here as well)

One study (albeit in human mesenchymal stem cells rather than neurons) has noted that increasing activity of the arginine decarboxylase enzyme is able to cause an increase in agmatine (2-fold) which was thought to be the cause for the increase seen in BNDF secondary to phosphorylation of Akt and CREB.^[199] BNDF is downstream of CREB^[249] which is downstream of Akt^[250] which agmatine is known to activate;^[200] this pathway is seen as prosurvival in these stem cells^[251] but positively regulates synaptic plasticity and memory formation in neurons.^[252]

Beyond the possible increase in BDNF (which would play a role in memory formation), oral intake of 20mg/kg agmatine for 2 weeks has increased adenylate cyclase activity in the prefrontal cortex.^[90]

Agmatine may have a role in memory formation secondary to enhancing synaptic formation or increasing cAMP activity, the two appear to be regulated by independent means

Conversely, agmatine possesses some amnesiac mechanisms such as antagonism of NMDA receptors^[253][254] and the negative regulation on nitric oxide metabolism^[255] as they both positively mediate memory formation. Inhibition of NOS has indeed been noted with 40mg/kg injections (as evidenced by a decrease in L-citrulline, indicative of less arginine-citrulline conversion via NOS).^[256] Interestingly, an elevation of citrulline is detectable in the dentate gyrus and prefrontal cortex during the learning process.^[244]

Although agmatine is co-released with glutamate (agonist of NMDA receptors) under normal non-supplemental conditions, it is not likely a concern; learning tasks increase basal synaptic agmatine from 0.25µM to 0.75µM in the rat brain^[242] while the IC₅₀ for inhibiting the NDMA receptor is in the 100-300µM range.^[105][106] However, it is plausible that high supplemental levels may inhibit NMDA receptors in the hippocampus.

There are some mechanisms which may be suspicious for being amnesiac, as both NDMA and NOS (which agmatine inhibits) can positively modulate memory formation. Practical relevance of this information is not known

For studies using water-mazes to assess spatial learning, microinjections directly into the hippocampus have failed to augment memory formation^[257] and this failure is also seen with intraperitoneal injections of 10-50mg/kg.^{[258][259][260][261]} Agmatine does not appear to modify spatial learning, and one study assessing exploratory learning has found a similar failure.^[260]

Contextual fear conditioning and learning has twice been noted to be impaired with agmatine injections (20-40mg/kg intravenously)^[258][259] while inhibitory avoidance tasks^[245][245] and behavioural learning appear to be enhanced.^[260] Displaced object recognition (but not novel object recognition) appears to be enhanced with agmatine infusions as well in the standard dosage range (either 10mcg intrathecal infusion^[261] or 40mg/kg intravenous^[261]).

Incidentally, the tasks that get benefit with memory formation from agmatine are those where the brain regions normally see pulses of agmatine during the learning process (independent of supplementation). This includes the perirhinal cortex and hippocampus (displaced object recognition)^[248] and the prefrontal cortex (behavioural learning),^[246][247] whereas the locus coeraleus is known to react to agmatine supplementation and is associated with inhibitory avoidance tasks.^[245] The benefits seen with agmatine appear to be both task and delay dependent, and are hypothesized to be associated with more complex rather than simplistic tasks.^[262]

Agmatine appears to increase cognition in the brain regions that are eithe responsive to agmatine or are known to release agmatine into the synapse in high concentrations when activated. Due to this agmatine is able to benefit inhibitory avoidance tasks, displaced object recognition, and behavioural learning; it does not appear to influence spatial learning, and may be adverse towards contextual fear conditioning (learning to avoid or fear negative stimuli)

It is likely that there is a bell curve effect and that higher doses are not better, and there is still no evidence that working memory is enhanced with agmatine supplementation.

Nitric oxide signalling is known to be a positive mediator of seizures^[263] where L-arginine increases seizure susceptability (when other things start them) in a manner attenuated by NOS inhibition.^[264] It is thought that agmatine signals via the α2A receptor to reduce nitric oxide production (via downregulating iNOS) to reduce seizure frequency and magnitude.^[265]

When a seizure occurs, nitric oxide signalling is enhanced and excessive NO signalling exacerbates the sequelae of the seizure. Agmatine is thought to be protective of seizures by reducing the amount of NO signalling that occurs secondary to acting on its adrenergic receptor, the α2A receptor

Agmatine itself (100mg/kg injection 45 minutes prior to seizure induction) is able to augment phenobarbitol (ED₅₀ reduced from 22.54 to 16.82mg/kg) and valproate (256.1 to 210.6mg/kg) seizure inhibition despite failing to per se protect rats from electroshock (MES) induced seizures^[266] and other tested antiepileptics (carbamazepine, lamotrigine, phenytoin, oxcarbazepine, and topiramate) were unaffected by agmatine.^[266] Elsewhere, injections of comparable doses (80-160mg/kg, but not lower) were anticonvulsive against MES^[267] while lower doses of agmatine (30mg/kg oral ingeston) have been noted to be effective in reducing MES induced seizures within 15 minutes and extending for six hours (most efficacy at four hours^[265]) and 60-120mg/kg were not significantly more effective than 30mg/kg.^[265]

Lower doses of agmatine (5-40mg/kg; most efficacy from 10-20mg/kg at 30-45 minutes before the seizure) prior to pentylenetetrazole (PTZ) induced seizures have been shown to have anticonvulsive effects^[264] in a manner attenuated by yohimbine and nitric oxide induction, but augmented with the NOS inhibitor L-NAME.^[264]

Agmatine appears to be active in rodents in suppressing seizures following multiple stimuli (PTZ and MES) and this has been confirmed to occur in rats within 15-360 minutes of acute oral dosing; estimated human equivalent being 5mg/kg bodyweight

Agmatine has a few interactions with calcium signalling. Firstly, NMDA receptor activation tends to increase intracellular calcium which can then activate nNOS^[268][269] and via being an NDMA antagonist^[106] agmatine can limit the increase in calcium (agmatine can act on nNOS in more than just this way, however). Furthermore, agmatine has been noted to block calcium channels directly on hippocampal neurons in a reversible manner with an IC₅₀ value of 0.79-1.57µM and recorded 21+/-4% inhibition at a concentration of 100nM^[226] but elsewhere has been noted to displace the calcium channel blocker known as Diltiazem.^[270]

Agmatine has failed to have any influence on sodium or potassium channels at concentrations of up to 500µM.^[226] That being said, nitric oxide has been noted to increase the activity of calcium-activated potassium channels^[271][272] which is downstream of NMDA activation;^[273] this presumes an inhibitory effect of agmatine on potassium channels (as it is an NMDA antagonist), which is thought to at least in part contribute to antidepressant effects.^[216]

Overall, it seems that agmatine is antagonistic to calcium signalling (both by preventing NMDA signalling, and by directly inhibiting influx at physiological concentrations) and may indirectly be inhibitory to potassium channel signalling (also via NMDA antagonism)

Low dose agmatine (5-10mg/kg injections) for 30 days in mice who had memory deficits induced by the diabetic toxin streptozotocin was able to reduce both blood glucose and improve memory^[274] although the memory improving effect was independent of the I₂ (imidazoline) receptor,^[274] which is required for glucose reduction (suggesting two independent mechanisms).^[275]

Agmatine has also shown protective effects against memory impairment induced by beta-amyloid pigmentation,^[276] the MPTP toxin,^[277] scopolamine,^[278][279] and inflammation (using lipopolysaccharide to cause inflammation).^[280][281]

Agmatine appears to be able to protect the brain from research toxins that induce amnesia and for conditions that may be negative towards memory formation (inflammation and an elevation of blood glucose)

Two studies have noted that agmatine has an ability to disrupt the prepulse inhibition (PPI; a phenomena where a 'prepulse', usually a neuronal action potential, weakly occurs prior to the desired action potential or pulse and due to desensitization attenuates the signal^[282]). When PPI is high active action potential are exagerrated and when PPI is low active they are dampened somewhat. Disrupted prepulse inhibition is thought to be related to schizophrenia^[283][284] and other neurological ailments such as anxiety and PTSD;^[282] agmatine concentrations in the serum of schizophrenia patients is also reliably elevated.^[68]

Agmatine injections into research animals have noted that agmatine is able to attenuate PPI in response to sound^[285] and the drug phencyclidine.^[286] It is additive with apomorphine in this regard,^[285] and administration of agmatine to rats is able to attenuate apomorphine induced climbing and amphteamine/ketamine induced hyperlocomotion.^[287]

There are interactions with agmatine and prepulse inhibition, a neurological phenomena where a smaller 'prepulse' occurs and suppresses the magnitude of the subsequent 'pulse' due to short-term desensitization

During the aging process, there appears to be dysregulation in the nitrenergic (nitric oxide related) system as total NOS activity (not enzyme count) is increased in the prefrontal cortex^[288] while agmatine is decreased in the prefrontal cortex and hippocampus (CA1 cells)^[289] alongside an increase in polyamines.^[290] It is thought that the increase in NOS and decrease in agmatine are related to age-related behavioural impairments.^{[291][292][293]}

Agmatine injections (40mg/kg) daily for 4-6 weeks in aged rats appears to normalize the increased NOS activity in the dentate gyrus and prefrontal cortex without affecting eNOS or nNOS protein content (not significantly affected by the aging process either),^[294] which works well with the aformentioned theory as agmatine is also known to correct age-related behavioural impairments at this dose.^[260]

Agmatine may be useful in normalizing age-related behavioural deficits

Agmatine is a vasorelaxing agent, and at 10µM can increase nitric oxide production in endothelial cells^[295] and can increase cGMP concentrations in cells (a normal consequence of nitric oxide acting upon its receptor).^[296] This direct stimulation of nitric oxide production (similar to both L-Arginine and D-Arginine) has been found to be secondary to the α2A receptor, and is blocked by rauwolscine at the level of the receptor.^[295]. Arginine activates this receptor at 1mM concentration, while the concentration of agmatine required to 100-fold lower.^[295]

Mainly due to acting on the α2A receptor, agmatine induces nitric oxide synthesis. This is a similar mechanism to L-arginine (and by extension, L-citrulline) but agmatine appears to be 100-fold more potent at activating this receptor

The overall production of nitric oxide is dependent on G-protein signalling (G_i/o; coupled to the α2A receptor)^[295] and NOS enzymes, as inhibitors of NOS enzymes abolish the nitric oxide production.^[297] Calcium channel activation^[92][295] and ryanodine receptors (RyR) which modulate calcium channels^[298] are also involved. The interaction of agmatine and RyRs (which are mediated by nitric oxide) may be due to nitric oxide increasing cyclic ADP-ribose (cADPr) activity;^[299][300] cADPr is a positive regulator of the RyR^[301][302] and although agmatine does not influence its levels or its binding^[303] abolishing the actions of cADPr prevents nitric oxide formation.^[303] From there, the increase in calcium can increase activity of eNOS enzymes^[304][305] due to activating the protein known as calmodulin.^[306]

Increasing nitric oxide via activating the α2A receptor requires that the G-protein coupled to the α2A receptor influences a molecule known as cADPr which then increases the activity of the ryanodine receptor. The ryanodine receptor releases calcium, and this calcium then activates calmodulin which can activate endothelial nitric oxide synthase (eNOS) and subsequent production of nitric oxide

A problem above is that ryanodine receptors (RyRs) are both dependent on and induce nitric oxide formation, which suggest it is both upstream and downstream of NOS enzymes;^[307] inhibiting NOS enzymes actually prevents agmatine from acting on RyRs.^[303] Interestingly, the effects of agmatine on nitric oxide have also been noted to be impaired by blocking the imidazoline receptors,^[92] phospholipase C (PLC),^[295] and PI3K^[200] which are independent of NOS inhibition (L-NAME has no effect).^[296] It is known that there exists signalling from imidazoline^[308] and α2A receptors^[309] towards PI3K and PLC, there exist a signalling pathway from PI3K via Akt that activates eNOS^[310][311] and agmatine has been shown to signal via this pathway.^[312]

Activation of the ryanodine receptor actually requires nitric oxide (being both upstream and downstream of NOS enzymes) and this can be rationalized by signalling through both the α2A or imidazoline receptors causing activation of the PI3K/Akt/eNOS pathway, which can also boost production of nitric oxide.

It is plausible that activation of the PI3K/Akt/eNOS pathway causes a short boost in nitric oxide synthesis, while the increased nitric oxide then activates the RyR/Calmodulin pathway to provide a more sustained boost

There are some pro-contractile properties of agmatine as well. It has been noted that high concentrations of agmatine (1mM) are able to slightly augment the ability of noradrenaline to contract arteries (EC₅₀ value changef from 2.2µM to 1.5µM) while suppressing the procontractile properties of clonidine (0.9µM to 2.6µM) and methoxamine (1.6µM to 2.8µM).^[103]

Agmatine may be able to enhance the contractile properties of noradrenaline at high concentrations

There appears to be weak competitive inhibition on all isoforms of NOS with K_i values of 220μM (iNOS), 660μM (nNOS), and 7500μM (eNOS).^[117] Other studies have found inhibition of nNOS with an IC₅₀ of 160μM^[43] and iNOS with 260μM^[313] although the latter study failed to find inhibition of nNOS and eNOS.^[313] Other studies have mostly failed to find per se inhibitory effects on NOS enzymes (especially eNOS, which does not appear to be inhibited much if at all)^[44][45][46] which is probably due to the high concentration required for inhibition.

Agmatine is able to inhibit the activity of NOS enzymes, but this occurs at fairly high concentrations; while inhibition of iNOS and nNOS are likely not possible without supplementation (but feasible with supplementation) the inhibition of eNOS seems to be irrelevant (too high of a concentration to matter)

Despite the weak competitive inhibition, agmatine is known to be an irreversible nitric oxide synthase (NOS) enzyme inactivator with a K_i of 29μM.^[117]

The mechanism appears to be from a 3-fold increase in the activity of the NADPH oxidase subset of NOS (this study used nNOS) which caused a large spike of H₂O₂ and oxidative inactivation of the enzyme.^[117] This was dependent on calmodulin (which transfers an electron from the NADPH oxidase subunit to the heme group of the NOS enzyme; calmodulin itself can reduce NOS activity via inactivation^[117]) and after one hour activity was reduced to 30+/-1.2%, omitting NADPH had no effect on the first 20 minutes but significantly inhibited inactivation between 20-60 minutes.^[117]

This overall profile of negative regulation (weak competitive inhibitor but an oxidative inactivator) is similar to other NOS inhibitors such as aminoguanidine^[314][315] and guanabenz.^[316] It is unsure how biologically relevant this is due to the short plasma half-life of agmatine, but unlike the inhibition of the enzyme the inactivation is at a physiologically relevant concentration.

Agmatine can inactivate NOS enzymes, and this occurs at a much more reasonable dosage (three-fold that which activates eNOS). It is not exactly sure how this inactivation affects nitric oxide production in a living system

In isolated ventricular myocytes, agmatine (0.1-10mM) has been noted to inhibit calcium uptake into cells^[317] and reduce peak amplitude of the L-type calcium channel in a concentration dependent manner.^[318]

High concentrations have a calcium blocking effect in isolated cells. Practical relevance of this information is not yet known

Vasorelaxation has been noted in kidney cells (causing an increase in glomerular filtration rate)^{[297][303][319]} and cardiac cells (aortic rings)^[320][321] which appear to be nitric oxide dependent (hindered by NOS inhibitors and endothelial-dependent).^[297]

Agmatine infusions have failed to modify vascular tone in the rat arterial tail vein.^[103]

Has some demonstratable relaxing properties in vitro which are dependent on nitric oxide

One study assessing bleeding time (increased by blood thinners) in rats given 300μg/kg agmatine noted an increase in blood pressure following bleeding which improved survival, and that this effect was abolished by yohimbine and arginine (suggesting that it is α2A dependent and relies on a reduction of nitric oxide).^[322]

Appears to reduce bleeding associated with an increase in blood pressure, suggesting an overall modulatory role on blood flow rather than a unilateral increase in blood flow

Agmatine is known as clonidine displacing substance since it appears to displace clonidine at both α2A receptors and imidazoline receptors^[67] and clonidine is known to act as an antihypertensive (blood pressure reducing) drug via the imidazoline receptor^[323][324] which is a property shared by agmatine.^[325] Oddly, despite displacing clonidine from the imidazoline receptor agmatine does not interfere with its actions.^[73]

Acting on imidazoline receptors is known to reduce blood pressure

In anaesthesized rats, injections of agmatine appear to reduce blood pressure^{[73][326][327]}

Activation of the imidazoline receptors localized in the adrenal gland is known to reduce blood glucose in streptozotocin-induced diabetic rats and agmatine has been found to activate these receptors.^[93][275] The reduction of blood glucose appears to be associated with an increase in β-endorphin,^[93][275] and β-endorphin is known to increase tissue glucose uptake into skeletal muscle^[328][329] independent of whether it is exercised or at rest;^[330] possibly due to an increase in GLUT4 mRNA content.^[275]

β-endorphin has elsewhere been noted to inhibit hepatic glucose production^[331] while inducing insulin secretion from the pancreas;^[332] however, it is unsure how agmatine supplementation influences these parameters.

Agmatine can act upon the adrenal glands (via the imidazoline receptors) to release β-endorphin, an opioid that can dispose of glucose from the blood into skeletal muscle tissue. Due to this, agmatine can reduce blood glucose via adrenal gland-dependent means

Agmatine, secondary to activating imidazoline receptors upon the adrenal glands, can release β-endorphin into the plasma.^[275]

β-endorphin (induced by agmatine) is known to increase skeletal muscle glucose uptake in diabetic rats^[93][275] independent of whether the muscle is at rest or exercise^[330] possibly via GLUT4 mRNA upregulation^[275] yet β-endorphin (per se, not induced by agmatine in this study) does not appear to modify adipocyte glucose uptake;^[333] this suggest a possible nutrient partitioning effect, but needs to be investigated further to confirm.

Agmatine can reduce blood glucose acutely in diabetic animals, and it is plausible that this is due to a selective disposal of glucose into muscle rather than fat which is due to an increase in β-endorphin. More studies are needed to assess whether or not this actually occurs following oral supplementation

Injections of agmatine into the hypothalamus appear to dose-dependently cause secretion of luteinizing hormone, thought to be secondary to activating imidazoline receptors.^[334]

In vitro, agmatine is able to protect retinal ganglion cells from apoptosis^[335] and this has been noted with topically applied agmatine (reducing 55.44% cell death down to 18.65%) which appears to be associated with a reduction in intraocular pressure.^[336] This protective effect appears to extend to ischemic ocular injury as well.^[337]

Agmatine, applied topically, appears to be protective of the eyes; the implications of oral supplementation is not yet known

Agmatine is normally expressed in stomach tissue at a concentration of around 71ng/g wet weight, which is one of the highest non-brain organ concentrations of agmatine in rats (ahead of the spleen and intestines).^[27] It is stored in mucus membranes of the stomach (in parietal cell canaliculi), where its strong alkalinity likely buffers stomach acid from damaging parietal cells.^[23]

Agmatine appears to be inhernetly gastroprotective due to its alkalinity, where it protects parietal cells of the stomach from stomach acid

Agmatine at 100mg/kg (injection) has shown protective effects against gastric ischemia (PI3K dependent)^[338] but elsewhere has augmented damage on alcohol-induced ulceration^[339] and stress-induced ulceration^[340][341] via acting on imidazoline receptors in the 20-25mg/kg dosage range; it is not clear if the reason for the difference is due to the dosage or the context of the injury.

α2A receptors appears to induce gastric contractions when activated with imidazoline receptors having no significant role.^[342]

Agmatine has been noted to both protect the stomach from damage (against ischemia) yet augment damage done by chemical and stress induced damage

Agmatine is involved with the intestines as it is produced by colonic bacteria (also gastric bacteria^[343]) and can accumulated in the intestines following oral administration of agmatine.^[70]

Agmatine is produced within the kidney where it can enhance glomerular filtration rate in kidney tissues possibly via I₂ imidazoline receptors (a selective I₁ agonist was ineffective)^[319] and elsewhere has been found to be dependent on NOS enzymes;^[297] the alpha-2-adrenergic receptors do not appear to be required,^[297][319] but activation of a class of receptors known as ryanodine receptors (activates calcium signalling) may explain the effects of agmatine.^[303] Regardless of the mechanism, it appears that neurons are not required (as innervated and denervated kidneys have similar effects).^[319]

Na+/K+ ATPase has also been noted to be increased in renal cells.^[344]

Preliminary evidence suggests an increase in glomerular filtration rates, which is supposedly a renoprotective effect. This may be related to a relatively novel mechanism, acting upon ryanodine receptors

Agmatine is known to interact with the α2A receptors in the vas deferens^[95] both presynaptically and postsynaptically^[345] where it is able to enhance electricity-induced twitches thought to be associated with blocking potassium channels at 10-1,000µM.^[345][346] It was later noted that this enhancement occured in the prostatic portion of the vas deferens but not epididymal portion, and reached maximal enhancement at 1mM (207.1+/-14.2% of control).^[346]

L-Arginine and L-Citrulline are two amino acids that raise plasma arginine concentrations

Agmatine's oxidative inactivation of the nitric oxide synthase enzyme (seen in this study with nNOS with a K_i of 29µM) is due to increasing the activity of the NADPH oxidase subunit^[117] which arginine is known to hinder for nNOS^[118][119] yet appears to increase activity for iNOS and eNOS.^[118][347] In this sense, arginine is antagonistic to the effects of agmatine towards nNOS (a possible reason why supplemental arginine inhibits many neurological effects) but does not affect eNOS in the same manner.

It is not sure whether pairing either of these two agents with arginine will enhance systemic nitric oxide production (via eNOS; the mechanism underlying most of the blood pressure effects) or be antagonistic; both are plausible, with the former being due to increased nitric oxide production from eNOS and the latter due to quicker inactivation of the enzyme.

Arginine (and by extension, citrulline) are inhibitory to some of the neurological effects of agmatine supplementation such as reducing opioid tolerance. The interaction between agmatine and arginine in regards to blood vessels (and 'the pump' for physical exercise) is not clear

Agmatine is involved with alcohol on both a gastric and neurological level, and overall it can be said that agmatine is good for rehabilitating alcohol withdrawal but probably not the best supplement to coingest.

Alcohol's reduction of anxiety (anxiolysis) is prevented by inhibition of the arginine decarboxylase enzyme, suggesting that it works via agmatine.^[175] The increase in anxiety seen during alcohol withdrawal is also normalized with agmatine.^[175]

Additionally, the analgesic (pain killing) effects of alcohol appear to be augmented with agmatine injections in rats thought to be due to imidazoline receptor signalling^[348] and agmatine has been noted to block the alcohol induced hyperactivity seen in rats (male only) at 5-20mg/kg without affecting locomotion inherently.^[349] There does not appear to be any interaction between agmatine and conditioned place preference (CPP), thought to be indicative of no alterations on motivation/addiction.^[350]

On a negative side, agmatine is known to be a gastroprotective agent (aids in protecting parietal cells from stomach acid^[23]) but has counterintuitively enhanced ulcer formation from alcohol consumption in rats.^[339]

At this moment in time, agmatine appears to be useful for alcohol withdrawal. The usage of agmatine alongside alcohol might not be prudent as one study noted an enhancement of stomach ulceration, so timing of agmatine and alcohol consumption would be prudent

With acute doses of caffeine that are able to induce locomotion (in caffeine naive mice), agmatine at 5-20mg/kg is able to block the increase in locomotion but only in male mice.^[351]

Marijuana is the prototypical cannabinoid drug, which signals through two receptors known as endocannabinoid receptors (CB1 and CB2); the following information should apply to all CB1 agonists (so possibly anandamide from arachidonic acid metabolism and oleamide) with uncertain interactions with CB2 agonists (echinacea).

The CB1 receptors are expressed in a pattern in the midbrain^[132][133] that is very similar to the pattern of imidazoline receptors^[134] and agmatine localization,^[28] and in cardiac tissue at least they have been found to beneficially influence one another.^[135]

Endocannabinoid receptors are intimately expressed alongside imidazoline receptors and they appear to positively influence one another; marijuana is a potent activator at CB1 receptors, whereas agmatine is a potent activator of imidazoline receptors

Agmatine has been found to synergistically enhance hypothermia^[137][138] and augment the potency of two cannabinoidergic drugs by 300-440% in regards to reducing heat pain (agmatine alone is inactive on this type of pain).^[136] This effect is independent of α2A receptors^[136] and unlikely to be associated with NOS or NMDA inhibition^[139][140] while it was inhibited by both imidazoline antagonists (blockers) and CB1 receptor antagonists.^[136] Due to both receptors being required and the ability of imidazoline activation to modify binding of the CB1 receptor antagonist SR141716A to its receptor^[141] it is plausible that activation of imidazoline receptors will augment signalling through the CB1 receptor via positive allosteric modification of the receptor (changing the structure of the receptor to modify signalling, positive refers to an increase in signalling relative to baseline).

There appears to be synergism between CB1 receptor signalling and imidazoline receptor signalling. It is not 100% sure how it works right now, but both receptors seem to be important and it is possible that structural changes occur to the CB1 receptor after the imidazoline one is activated (which then enhances signalling). While synergism is only noted for heat pain right now, agmatine has potential to be synergistic with marijuana on a wide variety of mechanisms (most excitingly, neuropathic pain)

Although the trials cannot be found, an MSDS reports that the acute LD₅₀ of agmatine is 300mg/kg after oral ingestion in mice, 980mg/kg in rats, and 3200mg/kg in rabbits.^[352]

A study conducted over 51 days assessing dose tolerability that used 1.335g (10 days), 2.67g (subsequent 10 days), 3.56g (subsequent 10 days followed by 21 days of maintenance) with the dose divided into thrice daily doses with meals in patients with lumbosacral spine degenerative pathologies associated with radiculopathy did not note any significant health effects of supplementation aside from sparse gastrointestinal discomfort when the dose was increased to 3.56g which faded after a few days.^[168]

Limited evidence in humans, but currently there are no known side-effects. Insufficient evidence to conclude its level of safety, however