Multiple Direct Effects of the Dietary Protoalkaloid N-Methyltyramine in Human Adipocytes.

Dietary amines have been the subject of a novel interest in nutrition since the discovery of trace amine-associated receptors (TAARs), especially TAAR-1, which recognizes tyramine, phenethylamine, tryptamine, octopamine, N-methyltyramine (NMT), synephrine, amphetamine and related derivatives. Alongside the psychostimulant properties of TAAR-1 ligands, it is their ephedrine-like action on weight loss that drives their current consumption via dietary supplements advertised for 'fat-burning' properties. Among these trace amines, tyramine has recently been described, at high doses, to exhibit an antilipolytic action and activation of glucose transport in human adipocytes, i.e., effects that are facilitating lipid storage rather than mobilization. Because of its close structural similarity to tyramine, NMT actions on human adipocytes therefore must to be reevaluated. To this aim, we studied the lipolytic and antilipolytic properties of NMT together with its interplay with insulin stimulation of glucose transport along with amine oxidase activities in adipose cells obtained from women undergoing abdominal surgery. NMT activated 2-deoxyglucose uptake when incubated with freshly isolated adipocytes at 0.01-1 mM, reaching one-third of the maximal stimulation by insulin. However, when combined with insulin, NMT limited by half the action of the lipogenic hormone on glucose transport. The NMT-induced stimulation of hexose uptake was sensitive to inhibitors of monoamine oxidases (MAO) and of semicarbazide-sensitive amine oxidase (SSAO), as was the case for tyramine and benzylamine. All three amines inhibited isoprenaline-induced lipolysis to a greater extent than insulin, while they were poorly lipolytic on their own. All three amines-but not isoprenaline-interacted with MAO or SSAO. Due to these multiple effects on human adipocytes, NMT cannot be considered as a direct lipolytic agent, potentially able to improve lipid mobilization and fat oxidation in consumers of NMT-containing dietary supplements.

Inhibition of indoleamine 2,3-dioxygenase 1/2 prevented cognitive impairment and energetic metabolism changes in the hippocampus of adult rats subjected to polymicrobial sepsis.

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection that may affect the brain. We investigated the role of indoleamine 2,3-dioxygenase (IDO-1/2) inhibition on long-term memory and energetic metabolism after experimental sepsis by caecal ligation and perforation (CLP). Experimental sepsis increased the activity of complexes I, II-III and IV at 24h after CLP, and IDO-1/2 inhibition normalized the activity of these complexes in the hippocampus. Wistar rats presented impairment of habituation and aversive memories 10days after CLP. Adjuvant treatment with the IDO inhibitor prevented long-term cognitive impairment triggered by sepsis.

Species differences in the metabolism of ritobegron in vitro and assessment of potential interactions with transporters and cytochrome P450 enzymes.

Ritobegron, a selective ß3-adrenoceptor agonist, is the prodrug of the active compound, KUC-7322. We investigated species differences in its metabolism in vitro and the potential for drug-drug interactions with ritobegron. In rat, dog, monkey, and human liver microsomes, ritobegron was not metabolized by cytochrome P450 enzymes (CYPs). KUC-7322 was the only metabolite observed. Hydrolysis of ritobegron to KUC-7322 was likely catalyzed by carboxylesterases in human liver microsomes. The maximum velocity of the reaction (V(max))/Michaelis-Menten constant (K(m)) for hydrolysis of ritobegron to KUC-7322 was much higher in rat serum than those in other species. There were also species differences in the conjugation of KUC-7322. Sulfate conjugates of ritobegron were detected in all species, whereas glucuronide and glutathione conjugates of KUC-7322 were only observed in rat liver subcellular fractions. Ritobegron and KUC-7322 did not affect the CYP-mediated metabolism of probe substrates in human liver microsomes and organic anion transporter 1 (OAT1)-, OAT2-, OAT3-, organic cation transporter 2 (OCT-2)-, OCT3-, or organic cation/carnitine transporter 1 (OCTN1)-mediated uptake of probe substrates in S2 cells. Ritobegron, but not KUC-7322, inhibited P-glycoprotein-mediated digoxin transport in Caco-2 cells. Significant uptake of KUC-7322 was observed in OAT3-expressing S2 cells. Therefore, CYP-mediated drug-drug interactions are not likely when ritobegron is administered with CYP substrates or inhibitors. Ritobegron may increase the plasma concentrations of P-glycoprotein substrates, such as digoxin, and the plasma concentration of KUC-7322 may increase when it is administered in combination with OAT inhibitors such as probenecid.

Functional investigation of ß-adrenoceptors in human isolated detrusor focusing on the novel selective ß3-adrenoceptor agonist KUC-7322.

This study aimed to characterize the ß-adrenoceptor (ß-AR) subtype mediating relaxation of isolated human bladder strips and to explore relaxation by the novel ß3-AR-selective agonist KUC-7322 for its relaxant effect on the human isolated detrusor and for its effect on the carbachol (CCh)-induced contractile response. In two parallel studies, relaxation of isolated human bladder strips was tested for the ß-AR agonists isoproterenol, clenbuterol, BRL 37344, and KUC-7322. For the isoproterenol and KUC-7322 responses, antagonism by CGP 20712A, ICI 118551, and SR59230A was determined. The potency and efficacy of the reference agonists for detrusor relaxation was in line with their known ß3-AR activity. KUC-7322 relative to isoproterenol was a full agonist with a pEC(50) of 5.95 ± 0.09 and 5.92 ± 0.11 in the two studies. SR59230A exhibited antagonism of the expected potency against isoproterenol (apparent pK (B) 7.2) but not against KUC-7322. Neither isoproterenol nor KUC-7322 nor forskolin significantly attenuated CCh-induced contraction. These results suggest that KUC-7322 displays full agonistic activity in relaxing the human detrusor without inhibiting the contraction induced by cholinergic stimulation. These characteristics, if proven in vivo, may be beneficial for the treatment of overactive bladder, as increased bladder capacity with a negligible effect on voiding contractions may be anticipated.

Bladder selectivity of the novel ß3-agonist ritobegron (KUC-7483) explored by in vitro and in vivo studies in the rat.

We performed in vitro and in vivo experiments to evaluate the pharmacological profile of ritobegron and its effects on the bladder in rats. ß(3)-AR selectivity was assessed using CHO cells expressing various subtypes of the human ß-adrenoceptor (AR). Effects on isolated organs were evaluated using the organ-bath method. Effects on intravesical pressure, heart rate, and mean blood pressure were evaluated in urethane-anesthetized rats. Ritobegron increased cAMP accumulation in a concentration-dependent manner in CHO cells expressing any one of three human ß-AR, its selectivity for ß(3)-AR being 301-fold and 32-fold higher versus ß(1)-AR and ß(2)-AR, respectively. Ritobegron decreased the resting tension of the isolated bladder in a concentration-dependent manner (EC(50), 7.7 × 10(-8) mol/L; maximal relaxation, 97.0 %), and the ß(3)-AR antagonist SR58894A produced a parallel rightward-shift of this concentration-response curve without altering the maximal response [pK(B) value, 6.43]. Ritobegron concentration-dependently increased atrial rate and decreased myometrial contractions in vitro, and its selectivity for the bladder was 2,078-fold higher versus the atria and 14-fold higher versus the uterus. In vivo, ritobegron induced a dose-dependent decrease in intravesical pressure (ED(50) 0.4 mg/kg), without affecting heart rate and only slightly lowering mean blood pressure. Thus, ritobegron displayed potent and selective ß(3)-AR agonistic activity toward transfected human ß-AR and exhibited a high selectivity for the bladder versus other organs in rats. Moreover, it decreased intravesical pressure with minimal effects on the cardiovascular system in anesthetized rats. These results suggest that ritobegron shows promise as a potential agent for the treatment of overactive bladder.

Effects of ritobegron (KUC-7483), a novel selective ß3-adrenoceptor agonist, on bladder function in cynomolgus monkey.

We evaluated the pharmacological profile of ritobegron [KUC-7483; (-)-ethyl 2-[4-(2-{[(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino}ethyl)-2,5-dimethylphenyloxy]acetate monohydrochloride] and its effects on the bladder in cynomolgus monkeys by in vitro and in vivo experiments. In vitro, ritobegron decreased the resting tension of the isolated bladder in a concentration-dependent manner (EC(50) 8.2 ± 2.3 × 10(-7) M; maximal relaxation 88.7 ± 3.7%). The ß(3)-adrenoceptor (AR) antagonist 3-(2-allylphenoxy)-1-[(1S)-1,2,3,4-tetrahydronaphth-1-ylamino]-(2S)-2-propanol hydrochloride (SR58894A) produced a rightward shift of this concentration-response curve without altering the maximal response (pK(B) value 6.56 ± 0.35). In isolated atria, ritobegron increased the atrial rate only at high concentrations (EC(50) 6.5 ± 1.2 × 10(-5) M). Ritobegron had no effect on tracheal contraction at concentrations from 10(-9) to 10(-4) M, and even at the highest concentration tested, 10(-3) M, the maximal relaxation it induced was only 26.7 ± 8.1%. Tests of the selectivity of ritobegron for the bladder gave values of 79.3- and 1200-fold higher versus atria and trachea, respectively. In the in vivo study ritobegron significantly decreased intravesical pressure (ED(50) 1.44 mg/kg) without affecting either mean blood pressure or heart rate. In conclusion, ritobegron displayed potent and selective ß(3)-AR agonistic activity and relaxed the monkey isolated bladder, and in vivo it decreased intravesical pressure without affecting cardiovascular parameters. These results suggest that ritobegron may be a promising potential agent for the treatment of overactive bladder.

Effects of ritobegron (KUC-7483), a novel ß3-adrenoceptor agonist, on both rat bladder function following partial bladder outlet obstruction and on rat salivary secretion: a comparison with the effects of tolterodine.

The objective of this study was to investigate the effects of the ß3-adrenoceptor (AR) agonist ritobegron on rat bladder function following partial bladder outlet obstruction and on rat salivary secretion. In addition, the effects of ritobegron were compared with those of the anti-muscarinic agent tolterodine. After a 6-week partial bladder outlet obstruction (BOO), drug effects on bladder functions were evaluated using cystometrography. Effects on carbachol (CCh)-induced salivary secretion were evaluated in urethane-anesthetized rats. Ritobegron significantly decreased the frequency of non-voiding contractions (NVC), while both ritobegron and tolterodine each significantly decreased the amplitude of NVC. Ritobegron had no effect on either the micturition pressure (MP) or the residual volume (RV). In contrast, tolterodine dose-dependently decreased MP and increased RV. Ritobegron had no effect on CCh-induced salivary secretion, whereas tolterodine dose-dependently decreased it. Ritobegron decreased both the frequency and amplitude of NVC, which is similar to its effect on the contractions associated with detrusor overactivity (DO) in patients with an overactive bladder (OAB), without affecting MP, RV, or CCh-induced salivary secretion. Although tolterodine reduced the amplitude of NVC, it also markedly increased RV and significantly inhibited CCh-induced salivary secretion. These results suggest that use of ritobegron, a ß3-AR agonist, is unlikely to lead to the residual urine and dry mouth symptoms that are associated with anti-muscarinic drugs, and that ritobegron may hold promise as a safe and effective agent for OAB treatment.

p-Hydroxyamphetamine causes prepulse inhibition disruption in mice: contribution of serotonin neurotransmission.

p-Hydroxyamphetamine (p-OHA) has been shown to have a number of pharmacological actions, including causing abnormal behaviors such as increased locomotor activity and head-twitch response in rodents. We have recently reported that intracerebroventricular (i.c.v.) administration of p-OHA dose-dependently induces prepulse inhibition (PPI) disruption in mice, which is attenuated by pretreatment with haloperidol, clozapine or several dopaminergic agents. Haloperidol and clozapine have affinities for serotonergic (especially 5-HT(2A)) receptors. To investigate the involvement of the central serotonergic systems in p-OHA-induced PPI disruption, herein we tested several serotonergic agents to determine their effects on p-OHA-induced PPI disruption. p-OHA-induced PPI disruption was attenuated by pretreatment with 5,7-dihydroxytryptamine (5,7-DHT, a neurotoxin which targets serotonin-containing neurons) and p-chlorophenylalanine (PCPA, a serotonin synthesis inhibitor). p-OHA-induced PPI disruption was also attenuated by pretreatment with ketanserin (a 5-HT(2A/2C) receptor antagonist) and MDL100,907 (a selective 5-HT(2A) receptor antagonist). These data suggest that p-OHA-induced PPI disruption may involve increased serotonin release into the synaptic cleft, which then interacts with the post-synaptic 5-HT(2A) receptor.

p-Hydroxyamphetamine causes prepulse inhibition disruptions in mice: contribution of dopamine neurotransmission.

It is well known that amphetamine induces disrupted prepulse inhibition (PPI) in humans and rodents. We have previously reported that intracerebroventricular (i.c.v.) administration of p-hydroxyamphetamine (p-OHA) induces multiple behavioral responses, such as increased locomotor activity and head-twitch response in rodents. To reveal the characteristics of p-OHA on sensorimotor function in rodents, herein we tested the effects of p-OHA on PPI in mice. i.c.v. administration of p-OHA dose-dependently induced PPI disruptions for all prepulse intervals tested. This effect of p-OHA on PPI was attenuated by pretreatment with haloperidol or clozapine. p-OHA-induced PPI disruptions were also attenuated by pretreatment with L-741,626 (a selective D(2) receptor antagonist), L-745,870 (a selective D(4) receptor antagonist) or 6-hydroxydopamine (a neurotoxin which targets DA-containing neurons), but not by SCH 23390 (a selective D(1) receptor antagonist), eticlopride (a D(2)/D(3) receptor antagonist) or GBR 12909 (a DA-reuptake inhibitor). These results indicate that selective blockade of either the D(2) or D(4) receptor subtype may prevent disruption of PPI induced by p-OHA via presynaptic DA release.

Trace amine-associated receptor 1 displays species-dependent stereoselectivity for isomers of methamphetamine, amphetamine, and para-hydroxyamphetamine.

The synthetic amines methamphetamine (METH), amphetamine (AMPH), and their metabolite para-hydroxyamphetamine (POHA) are chemically and structurally related to the catecholamine neurotransmitters and a small group of endogenous biogenic amines collectively referred to as the trace amines (TAs). Recently, it was reported that METH, AMPH, POHA, and the TAs para-tyramine (TYR) and beta-phenylethylamine (PEA) stimulate cAMP production in human embryonic kidney (HEK)-293 cells expressing rat trace amine-associated receptor 1 (rTAAR1). The discovery that METH and AMPH activate the rTAAR1 motivated us to study the effect of these drugs on the mouse TAAR1 (mTAAR1) and a human-rat chimera (hrChTAAR1). Furthermore, because S-(+)-isomers of METH and AMPH are reported to be more potent and efficacious in vivo than R-(-), we determined the enantiomeric selectivity of all three species of TAAR1. In response to METH, AMPH, or POHA exposure, the accumulation of cAMP by HEK-293 cells stably expressing different species of TAAR1 was concentration- and isomer-dependent. EC50 values for S-(+)-METH were 0.89, 0.92, and 4.44 microM for rTAAR1, mTAAR1, and h-rChTAAR1, respectively. PEA was a potent and full agonist at each species of TAAR1, whereas TYR was a full agonist for the rodent TAAR1s but was a partial agonist at h-rChTAAR1. Interestingly, both isomers of METH were full agonists at mTAAR1 and h-rChTAAR1, whereas both were partial agonists at rTAAR1. Taken together, these in vitro results suggest that, in vivo, TAAR1 could be a novel mediator of the effects of these drugs.

The contribution of the metabolite p-hydroxyamphetamine to the central actions of p-methoxyamphetamine.

RATIONALE: Para-methoxyamphetamine (PMA) is a substituted amphetamine that has been responsible for a number of fatalities in Australia and North America. Previous investigators have shown that p-hydroxyamphetamine (PHA), the primary metabolite of PMA, has effects on central neurotransmitter kinetics in vitro that are similar to those of the parent compound. In order to understand the role of PHA, it is necessary to determine both the in vivo actions and the concentrations achieved relative to those of PMA. OBJECTIVES: The effects of PHA and PMA on 5-hydroxytryptamine (5HT) and dopamine kinetics in brain were determined and the concentrations of each compound measured in blood and brain. METHODS: Animals were housed at 20-22C on a standard 12/12-h light/dark cycle. High speed chronoamperometry was used to compare the ability of PMA and PHA to alter 5HT and dopamine kinetics in the rat striatum in vivo. Concentrations of PHA and PMA in blood, whole brain and striatum were determined following a dose of PMA (10 mg/kg, IP.) using HPLC with fluorescence detection. RESULTS: PHA was more effective than PMA at evoking neurotransmitter release and inhibiting the uptake of dopamine. However, both compounds were approximately equipotent 5HT uptake inhibitors. PMA and PHA concentrations in whole brain and striatum peaked within 30 min of the administered dose, whereas blood concentrations of both compounds peaked 1 h after the dose. PHA concentrations in both blood and brain were consistently much lower than PMA concentrations. CONCLUSIONS: These data indicate that although PHA is more effective than PMA at altering 5HT and dopamine kinetics in vivo, it is unlikely to achieve sufficient brain concentrations to contribute to the central effects of PMA.

Hydroxyamphetamine increases intraocular pressure in rabbits.

OBJECTIVE: To determine the effect of norepinephrine (NE) released from endogenous ocular stores on intraocular pressure (IOP) and aqueous flow in rabbits. METHODS: The IOP was measured with a pneumatonometer, the aqueous flow with a scanning fluorophotometer, and the aqueous NE by methylation with catechol-O-methyltransferase in the presence of S-adenosyl-L-[methyl-(3)H]methionine. RESULTS: Hydroxyamphetamine increased IOP in a dose-dependent fashion. Surgical removal of the superior cervical sympathetic ganglion eliminated the increase in IOP and pupil diameter; preganglionic section of the cervical sympathetic trunk did not. Hydroxyamphetamine increased the concentration of NE in the aqueous. Increased IOP was not accompanied by increased aqueous flow and was eliminated by blockade of alpha(1)-adrenergic receptors but not beta- or alpha(2)-adrenergic receptors. CONCLUSIONS: Increased IOP after hydroxyamphetamine application is consistent with earlier suggestions that the nocturnal circadian increase in IOP in rabbits is mediated in part by NE released from ocular sympathetic nerves. However, failure of hydroxyamphetamine to increase aqueous flow and of beta-adrenergic blockade to blunt the increase in IOP does not support our suggestion that the nocturnal increase in IOP results in part from NE stimulation of ciliary process beta-adrenergic receptors and increased aqueous flow. CLINICAL RELEVANCE: In addition to increasing pupil diameter, hydroxyamphetamine increases IOP.

Adrenocortical suppression blocks the memory-enhancing effects of amphetamine and epinephrine.

This study examined glucocorticoid-adrenergic interactions in modulating acquisition and memory storage for inhibitory avoidance training. Systemically (s.c.) administered amphetamine (1 mg/kg), but not epinephrine (0.1 mg/kg) or the peripherally acting amphetamine derivative 4-OH amphetamine (2 mg/kg), given to rats shortly before training facilitated acquisition performance in a continuous multiple-trial inhibitory avoidance (CMIA) task. Adrenocortical suppression with the 11beta-hydroxylase inhibitor metyrapone (50 mg/kg; s.c.), given to rats 90 min before training, did not block the effect of amphetamine and did not affect acquisition performance of otherwise untreated animals. Retention of CMIA and one-trial inhibitory avoidance was enhanced by either pre- or posttraining injections of amphetamine as well as 4-OH amphetamine and epinephrine. The finding that injections of amphetamine and epinephrine have comparable effects on memory is consistent with the view that amphetamine may modulate memory storage, at least in part, by inducing the release of epinephrine from the adrenal medulla. Metyrapone pretreatment blocked the memory-enhancing effects of amphetamine, 4-OH amphetamine, and epinephrine but did not affect retention performance of otherwise untreated animals. Posttraining injections of different doses of epinephrine (ranging from 0.0001 to 1.0 mg/kg) produced a dose-dependent memory enhancement for inhibitory avoidance training and metyrapone blocked the memory-enhancing effects of all these doses. These findings provide further evidence that the sympathoadrenal and adrenocortical systems are intimately coupled during processes of memory storage.

Increase of ocular blood flow by some phytogenic compounds.

The effects of a number of phytogenic compounds on ocular blood flow were measured by the colored microsphere technique in rabbits. Methyltyramine and coumarin increased blood flow in all eye tissues tested. The blood flow of iris, ciliary body-iris root, retina and choroid was increased by methyltyramine for 255%, 322%, 189%, and 189%, respectively, and by coumarin for 375%, 193%, 139% and 299%, respectively, at 120 minutes after drug administration. Rescinnamine, apocynin and hesperetin also increased ocular blood flow in all eye tissues except retina. The blood flow of iris, ciliary body-iris root, and choroid was increased by rescinnamine for 344%, 234%, and 199%, respectively; by apocynin for 355%, 152%, and 414%, respectively; and by hesperetin for 265%, 136%, and 204%, respectively, at 120 minutes after drug instillation. These results indicate that these compounds could be used to treat ischemic eye diseases in the future.

Involvement of hydroxylated metabolites in amphetamine-induced hypothermia in mice.

1. The hydroxylated metabolites of amphetamine, p-hydroxyamphetamine (p-OHA) and p-hydroxynorephedrine (p-OHN), were administered intracerebroventricularly in mice in order to evaluate their ability to elicit hypothermia. 2. Intracerebroventricular (i.c.v.) administration of p-OHA and p-OHN (1, 3 and 9 micrograms/mouse) induced maximal hypothermia 30 min after injection. p-OHA and p-OHN (9 micrograms, i.c.v.) produced maximal decreases in rectal temperature of -6.48 +/- 0.44 degrees C and -3.82 +/- 0.42 degrees C, respectively. Both metabolites are more effective than amphetamine (at 9 micrograms, i.c.v., -3.32 +/- 0.75 degrees C). 3. Pretreatment with haloperidol (5 micrograms, i.c.v.) suppressed the fall in temperature produced by p-OHA (3 micrograms, i.c.v.) and reduced that produced by p-OHN (3 micrograms, i.c.v.), respectively. The selective dopaminergic D1 receptor antagonist, SCH 23390, and the D2 receptor antagonists, sultopride and metoclopramide, were without effect on the hypothermia induced by either metabolite. Similarly, amphetamine-induced hypothermia was only inhibited by haloperidol. Apomorphine (0.1 mg kg-1, i.p.) did not potentiate the hypothermia induced by either metabolite, whereas the selective dopaminergic D2 agonist, quinpirole (0.2 mg kg-1, i.p.) did. Amphetamine-induced hypothermia was potentiated by apomorphine and quinpirole. 4. Neither the 5-hydroxytryptamine (5-HT) receptor blocker, cyproheptadine, nor the 5-HT receptor agonist, quipazine, modified metabolite-induced hypothermia. In contrast, amphetamine-induced hypothermia was affected by these 5-HT drugs. 5. The neuropeptide CCK-8 (0.04 mg kg-1, i.p.) and gamma-butyrolactone (40 mg kg-1, i.p.) potentiated the hypothermia produced by amphetamine and its metabolites. Conversely, desipramine (20 mg kg-1, i.p.) antagonized it.(ABSTRACT TRUNCATED AT 250 WORDS)

Superior cervical ganglionectomy in monkeys: surgical technique.

Seven cynomolgus monkeys underwent a histologically confirmed left superior cervical ganglionectomy (SCGx). Unilateral ocular sympathetic denervation persisting for at least 2 yr was confirmed by ipsilateral ptosis, miosis, supersensitivity of pupillary dilation to topical phenylephrine, and profound pupillary hyporesponsiveness to topical hydroxyamphetamine. Intraocular pressure 8-9 and 23-27 months postoperatively were identical in the denervated and contralateral control eyes. This model should facilitate studies of aqueous humor physiology and pharmacology.

Inhibition of brain MAO-A and animal behaviour induced by p-hydroxyamphetamine.

Intra- and extra-synaptosomal activity of monoamine oxidase-A (MAO-A) and -B (MAO-B), dopamine (DA) and its main metabolites were examined to clarify the mechanism of action(s) of p-hydroxyamphetamine (p-OHA) in animal behaviour mediated by central dopaminergic systems. Intrasynaptosomal DA was oxidized by MAO-A and MAO-B and this oxidation is inhibited by p-OHA. The inhibition is due to two effects: 1) uptake of DA is inhibited by p-OHA, and 2) p-OHA also inhibits intrasynaptosomal oxidation of DA by MAO-A and MAO-B. The inhibition of oxidation by MAO-A is predominant. Administration (ICV) of 80 and 160 micrograms p-OHA to mice, doses that cause various behavioural, significantly reduced striatal DA and 3,4-dihydroxyphenylacetic acid (DOPAC) levels, but greatly increased 3-methoxytyramine, without significantly changing homovanillic acid (HVA). The release of DA and blockade of DA uptake into dopaminergic neurons by p-OHA, together with preferential inhibition of the DA metabolizing enzyme, MAO-A, may contribute to p-OHA-induced behaviour mediated by the central dopaminergic systems.

Inhibition of brain type A monoamine oxidase and 5-hydroxytryptamine uptake by two amphetamine metabolites, p-hydroxyamphetamine and p-hydroxynorephedrine.

Two amphetamine metabolites, p-hydroxyamphetamine (p-OHA) and p-hydroxynorephedrine (p-OHN), selectively inhibited the A form of monoamine oxidase (MAO) in rat and mouse forebrain homogenates. Of these two metabolites, p-OHA inhibited MAO-A more strongly than p-OHN. This MAO-A-selective inhibition by p-OHA or p-OHN was found to be competitive with respect to deamination of its substrate, 5-hydroxytryptamine (5-HT). The degree of MAO-A inhibition was not changed by 90 min of preincubation of the enzyme preparations with either metabolite, and the activity inhibited by p-OHA after the preincubation recovered completely to the control level after repeated washing. Uptake of 5-HT or dopamine into mouse forebrain synaptosomes was highly reduced by both p-OHA and p-OHN. Both metabolites were more potent in reducing dopamine uptake than in reducing 5-HT uptake. In reduction of 5-HT and of dopamine uptake, p-OHA was more potent than p-OHN. These results indicate that p-OHA is a more selective inhibitor of brain MAO-A activity and 5-HT uptake than its subsequent metabolite, p-OHN. These two actions of p-OHA might, together with possible 5-HT efflux into the synaptic cleft, greatly contribute to head twitch, a brain 5-HT-mediated animal behavior induced by p-OHA.