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.

Effect of CYP2D1 inhibition on the behavioural effects of d-amphetamine.

In rats, amphetamine (AMP) conversion to 4-OH-AMP is metabolized by CYP2D1, the rat equivalent of the human enzyme CYP2D6. To determine the impact of impaired AMP metabolism on its behavioural effects, AMP-induced hyperactivity, AMP discrimination and AMP self-administration were examined in male Wistar rats with or without pretreatment with the CYP2D1 inhibitors quinine and budipine. In vivo, quinine (20 mg/kg) and budipine (10 mg/kg) increased the plasma area under the curve of AMP 4-fold and 3.6-fold respectively, and decreased the plasma levels of 4-OH-AMP, 3-fold and 8.6-fold, confirming that the doses used suppressed CYP2D1 activity. Both inhibitors prolonged AMP-induced hyperactivity (0.3 mg/kg) and prolonged the duration of AMP-appropriate responding for periods of up to 90 min post-AMP administration in a drug discrimination procedure. In rats given a preload dose of AMP (0.8 mg/kg) 3 h prior to the self-administration test session, CYP2D1 inhibition resulted in fewer AMP infusions being taken compared with rats receiving the AMP preload dose alone. These studies indicate that AMP is responsible for the behavioural effects seen in rats and that a rat phenocopy model of the human CYP2D6 deficiency state can be produced by CYP2D1 inhibitors.

Paradoxical effect of amphetamine in an endogenous model of the hyperkinetic syndrome in a hybrid dog: correlation with amphetamine and p-hydroxyamphetamine blood levels.

A telomian-beagle hybrid has been studied as a possible model for the hyperkinetic syndrome in children. Behavior tests showed that hybrids, like children, exhibit hyperactivity, impulsiveness, and impaired learning. Two groups of hybrid could be differentiated; the behaviour of one improved after amphetamine (responders) while that of the other did not (nonresponders). Moreover hybrids were less responsive than beagles to other effects of amphetamine such as stereotyped behaviour and hyperthermia. Measurement of blood levels of amphetamine and its active metabolite p-hydroxyamphetamine (pOA) showed that hybrids form less pOA. We propose that the lesser response of hybrids to toxic effects of amphetamine is due to this difference in amphetamine metabolism. Responders showed higher peak blood levels of amphetamine than nonresponders and their improvement on amphetamine correlated with blood levels of amphetamine. Therefore high levels of amphetamine appear to be necessary for its 'paradoxical' effect in this model. This suggests that amphetamine acts by activating both noradrenergic and dopaminergic neuronal systems in the CNS.

Stereotyped behavior and hyperthermia in dogs: correlation with the levels of amphetamine and p-hydroxyamphetamine in plasma and CSF.

A gas-chromatographic method for simultaneously measuring p-hydroxyamphetamine (pOA) against amphetamine (A) in plasma and CSF is presented. The time course of body temperature (Tb), stereotyped behavior (St), and A and pOA levels in plasma and CSF were studied after administration of 0.6 and 1.5 mg/kg p.o. of A to dogs. Stereotyped behavior reached maximal value 2.5 h after A, as did levels of A in CSF. The A levels in CSF decreased steadily in the following hours and simultaneously with the levels of A in plasma. St remained elevated and began to decrease after 6.5 h. The relationship between St and amounts of A was not linear but exponential. This suggest that both A and its metabolite contributed to this effect. In fact, a linear relationship was found between St and the amounts of pOA in CSF. Body temperature had a time course similar to A plasma levels, reaching peak value after 1.5 h and declining thereafter simultaneously with A. A linear relationship was found between Tb and the amounts of A in plasma. Thus Tb seems to be a peripheral A effect related to the presence of the drug in plasma.

Radioimmunoassay of amphetamines in rat parotid saliva.

Amphetamines, a commonly abused class of drugs, have been detected in various biological specimens, in particular, urine and blood. However, little information is available concerning the detection of these drugs in saliva. This investigation, utilizing the rat salivary secretions, has been attempted to establish the ability of amphetamines to be secreted in saliva and to determine the feasibility of using radioimmunoassay (RIA) for drug detection in saliva. The results of this investigation showed that (1) d-amphetamine and methamphetamine decreased salivary flow, (2) after d-amphetamine RIA tests were demonstrated in both saliva and plasma for a period of fifty minutes, and (3) positive RIA reactions were obtained by the following metamphetamine metabolites: amphetamine, 4-hydroxynorephedrine and 4-hydroxyamphetamine. Methamphetamine and 4-hydroxy-N-methylamphetamine were found to be non-reactive in the radioimmunoassay procedure. The results indicate that saliva could be radioimmunoassayed for the detection of amphetamine or amphetamine derivatives after the administration of either d-amphetamine and methamphetamine.

Kinetics and metabolism of amphetamine in the brain of rats of different ages.

The kinetics and tissue distribution of amphetamine and its metabolites p-hydroxyamphetamine (p-PH-A) and p-hydroxynorephedrine (p-OH-NE) were investigated in young adult (3-4 months) and old (20-25 months) male rats, after i.p. injection of 5 mg/kg tritium labelled D-amphetamine. The concentrations of these drugs were determined in plasma, cerebral cortex, brainstem and hypothalamus, by thin layer chromatography. 1. From 60 min up to 4 hrs after injection of amphetamine the concentration of amphetamine in plasma and brain tissue of old rats was significantly (P less than 0.05 higher than in young adult animals. In both age groups the levels of amphetamine in cerebral cortex greater than brain stem greater than hypothalamus. 2. The blood-brain barrier is permutle to p-OH-A; 10 to 20 min afer i.v. injection of 10 muCi/kg of p-OH-A (10 mCi/m mole) the ratio of brain/blood plasma was found to be 1:3. The half life of p-OH-A in blood plasma was almost identical after injection of amphetamine and p-OH-A (90 min and 98 min respectively). 3. The levels of p-OH-NE in different brain areas were significantly lower (P less than 0.05) in old animals than in young adult rats 4 hrs after application of amphetamine. This metabolite of amphetamine shows a higher concentration in the hypothalamus earlier than in other brain regions.

[Blood-brain barrier. II. Kinetics of distribution of 3H-parahydroxyamphetamine in brain structures after intravenous administration in the rat]. / Barriére hemato-encephalique II: Cinétique de distribution de la parahydroxyamphetamine 3H dans les structures du cerveau de rat aprés administration intraveineuse

Intravenously injected parahydroxyamphetamine hardly penetrates into the Central Nervous System, since, 5 minutes after injection, the tissue to plamsa concentration ratio for brain and cerebrospinal fluid amounts to 0,67 and 0,35 respectively. Its concentration in muscle is 5 times higher than in plasma. In the brain, the molecule is preferentialy taken up by the corpus striatum and the hypothalamus. Thus, parahydroxylation of amphetamine inhibits the penetration of the molecule into the brain and suppresses its cortical fixation. These characteristics could explain why this parahydroxylated amine has no psychotropic action.