Amphetamine Isomers Research Articles

Biochemical and behavioural studies of monoamine oxidase inhibition.

The effects of dl-N-propargkl ampheta-mine on monoamine oxidase in rat brain have been studied. It was found that i.p. injection of this compound produced a marked stereotyped response. It was also found to potentiate the stereotypy produced by amphetamine. Subsequent examination of monamine oxidase activity in the brains of the animals showed substantial inhibition of the B form of this enzyme (as judged by 2-phenylethylamine oxidation) but no effect on the A form. The optical isomers of N-propargyl amphetamine have been prepared and their inhibitory activityin vitro against monamine oxidase in rat liver mitochondria has been assessed. The l-isomer was found to be a better inhibitor than the d-isomer.

Kinetics, salivary excretion of amphetamine isomers, and effect of urinary pH

Amphetamine was administered to healthy subjects as the racemic mixture and as (+)- and (-)-isomers under conditions of urine acidification and alkalinization. Plasma and saliva concentration of each isomer was measured and the kinetics of the individual isomers were determined. (+)-amphetamine was eliminated more rapidly than the (-)-isomer. The difference in half-life between isomers was maximal under basic urinary pH conditions. Saliva amphetamine levels were higher than plasma levels and in the postabsorptive phase were predictably proportional to plasma drug levels.

Curare-like effects of the amphetamine isomers on neuromuscular transmission

The neuromuscular blocking effects of (+)- and (-)-amphetamine were evaluated for possible actions via the adrenergic and cholinergic systems employing the isolated rat phrenic-nerve diaphragm preparation. Dopaminergic and α- and β-adrenergic receptor blockers failed to modify the blocking effects of amphetamine on nerve-stimulated diaphragms suggesting the absence of catecholaminergic involvement. In chronically denervated diaphragms, amphetamine (2.7–4.05 × 10 −4M) and the non-depolarizing blocker (+)-tubocurarine (10 −7M) shifted the acetylcholine concentration-response curve to the right and failed to produce muscle contracture; the latter effect was produced by the depolarizing blocker succinylcholine (10 −5M). Physostigmine (1(10 −5M) and KCl (11mM) reversed amphetamine (5.4 × 10 −4M) and tubocurarine (5 × 10 −7 M) blockade, but not that elicited by succinylcholine (10 −5 M). Tetanus and post-tetanic potentiation were depressed in a concentration-dependent manner by the amphetamine isomers, with the (+)-isomer 1.8 times more potent than its (-)-enantiomer. These results indicate that amphetamine exhibits post-synaptic neuromuscular inhibition resembling curare-like nondepolarizing blockade, and that (+) -amphetamine is more potent as a neuromuscular blocker than its (-)-isomer.

Drug interactions with brain biogenic amines and the effects of amphetamine isomers on locomotor activity

Administration of single IP doses of 1.0 or 4.0 mg/kg of d-amohetamine evoked an increase in mouse spontaneous motor activity (SMA); in contrast, 1.0 mg/kg of 1-amphetamine had no significant effect, while 4.0 mg/kg caused a decreased SMA. Pretreatment with aMT or pargyline had little effect on the actions of 1-isomer, but reduced the magnitude and duration of the stimulatory effect of d-amphetamine. Pretreatment with p-chlorophenylalanine had little effect on the actions of d-amphetamine but completely abolished the depressant actions of the 1-isomer. Reserpine pretreatment markedly reduced basal SMA levels; such pretreatment caused both d- and l-amphetamine to act as stimulants of SMA.

Stimulus properties of d-amphetamine as compared to 1-amphetamine

Rats were trained to discriminate between d-amphetamine and saline. The discriminable ED 50 values for amphetamine isomers were calculated from dose-response curves and the potency ratio was 4.9. Co-administration of the ED 50 S was shown to produce synergistic effects suggesting that the amphetamine isomers may share a common site of action.

Pharmacological manipulation of hoarding: Further analysis of amphetamine isomers and pimozide

Dose-response relationships were established for the effect of d- and 1-amphetamine on hoarding latency, the time course of hoarding, and the size of the total hoard. Both isomers displayed a marked effect on hoarding latency with the d isomer approximately twice as potent as the l form. The effects of the isomers on latency were reflected in the temporal profiles and in the sizes of the accumulated hoards. In a further experiment, pimozide—a dopamine blocking agent—drastically reduced the overall level of hoarding but had only a minor effect on hoarding latency. Pimozide exerted selective action on the amphetamine isomers, markedly antagonizing the effect of d-amphetamine on latency but displaying little effect on the l form. The results indicate that pharmacological manipulation can reduce hoarding activity in the rat by means of a number of distinct mechanisms.

Equal suppression of cerebellar Purkinje cell activity by amphetamine stereoisomers

The two amphetamine isomers were compared for their ability to reduce spontaneous activity of noradrenoceptive Purkinje cells in the rat cerebellum. The drugs were applied iontophoretically to eliminate peripheral and remote central effects. Responses of Purkinje neurons were summed over several cycles of alternating (+)- and (−)-amphetamine, and poststimulus time histograms were compared. Inhibitions of Purkinje cell discharge by the two isomers were not statistically different over a wide range of pipette resistances. These data, taken together with studies showing equal effects of the two isomers on noradrenergic release and reuptake blockade and on locus coeruleus neuronal firing, indicate equipotency of the two isomers in their actions on noradrenergic mechanisms.

Quantitative determination of enantiomeric compounds. I--Simultaneous measurement of the optical isomers of amphetamine in human plasma and saliva using chemical ionization mass spectrometry.

A sensitive and specific method for the quantitative determination of the optical isomers of amphetamine from human plasma and saliva is described. Amphetamine was extracted from basified plasma or saliva with hexane and then derivatized by reaction with N-pentafluorobenzoyl-S-(-)-prolyl-1-imidazolide. The reaction of the amphetamine enantiomers with this chiral reagent yields diasteriomers which are easily resolved by gas liquid chromatography. The resolved diasteriomers upon elution from the gas chromatograph were measured quantitatively by chemical ionization mass spectrometry. Plasma and saliva levels achieved following the oral administration of 10 mg of dl-, d- and l-amphetamine in man are reported.

Comparative effects of d-amphetamine, l-amphetamine and methylphenidate on mood in man

The comparative effects of d-amphetamine, l-amphetamine, and methylphenidate were assessed in 16 normal subjects, using a double-blind, crossover placebo-controlled design. Within the dose range tested, the efficacy ratio of d-amphetamine:l-amphetamine was about 2:1, and graphic presentation of dose response scores indicated a relatively small difference in potency between the amphetamine isomers. Methylphenidate was intermediate in efficacy between d-amphetamine and l-amphetamine. The efficacy ratios for d-amphetamine:l-amphetamine on increasing euphoric mood in man were similar to the previously reported ratios of there two isomers in inducing or exacerbating psychosis in humans. These findings do not support the suggestion, made by Snyder and others, that the differential effects of d-amphetamine vs. l-amphetamine on a specific type of behavior in man could be utilized to infer the predominance of noradrenergic vs. dopaminergic mediation of amphetamine's effects on this behavior.

The effects of amphetamine isomers on rotarod performance

The amphetamine isomers impair the rotarod performance of rats in a dose-related manner, with (+)-amphetamine approximately four-times as potent as its (-)-isomer. At a rotation speed of 4 rpm, 60 min after i.p. administration, the TD50 values (mg/kg) were: (+)-amphetamine, 24 (21.9-26.4) and (-)-amphetamine, 96 (76.3-118.4), with the curves not deviating from parallelism. Coadministration of the peripheral cholinesterase inhibitor neostigmine salicylate (0.005 mg/kg) attenuated (+)-amphetamine neurotoxicity [30 (26.4-34.1)]. These results, in conjunction with previously reported effects of the drug on isolated nerve-muscle preparations, suggest that the muscle weakness produced by high doses of amphetamine may result from inhibition of transmission at the neuromuscular junction.

Dextro- and l-amphetamine are equipotent in releasing human growth hormone

(1) Peak plasma human growth hormone (HGH) response to a single intravenous administration of d- and l-amphetamine sulfate 0.1 mg/kg was evaluated in ten healthy subjects each being his own control. (2) No statistical difference was found between the mean HGH responses of the subjects to either amphetamine isomer. Also, the number of deficient HGH responses to d- and l-amphetamine was equal. (3) By analogy with similar data from studies in monkeys, the involvement of noradrenergic rather than dopaminergic mechanisms in mediating amphetamine-induced HGH release in man is tentatively suggested and possible implications for recent neuroendocrinological findings in endogenous depressives are discussed.

Catecholaminergic involvement in the effects of amphetamine isomers on seizure susceptibility

The (+)-amphetamine (2.5 mg/kg) increase in pentylenetetrazol seizure was abolished by pretreatment with reserpine, α-methyltyrosine methyl ester (α-MT), FLA-63 or 6-hydroxydopa. All treatments except reserpine antagonized the increase in seizure threshold produced by (-)-amphetamine (4 mg/kg). Only reserpine +α-MT antagonized the decrease in seizure threshold produced by (+)-amphetamine (15 mg/kg). These results indicate that amphetamine alterations in PLZ seizure susceptibility are mediated indirectly via the release of newly synthetized and/or granular stores of catecholamines.

Effects of amphetamine isomers and CNS catecholaminergic blockers on seizures in mice

The effects of (+)- and (−)-amphetamine on intravenous pentylenetetrazol(PTZ)-induced clonic seizure threshold were studied in CD-1 mice. The (+)-isomer elicited a biphasic effect, increasing seizure threshold 5–21% at low doses (1.25–2.5 mg/kg) and decreasing PTZ-induced clonic seizure threshold 15–28% at high doses (10–15 mg/kg). (−)-Amphetamine (1.25–10 mg/kg) increased PTZ-induced clonic seizure threshold 28–49%; doses of 15–45 mg/kg were without effect. Studies utilizing blockers of α- and β-noradrenergic (phentolamine, azapetine, (−)-sotalol, and (−)-INPEA), and dopa-minergic (pimozide and haloperidol) receptors suggest that the biphasic effects of (+)-amphetamine may be dependent upon α- and β-noradrenergic activation, while the decrease in PTZ-induced clonic seizure threshold possibly also involves the dopaminergic system. The increase in PTZ-induced clonic seizure threshold by (−)-amphetamine is primarily mediated by the β-noradrenergic system with α-noradrenergic and dopaminergic involvement also possible. These results show quantitative differences in the relative potency of the amphetamine isomers, [(−)- > (+)], and suggest that qualitative differences may exist as well.

Cortisol and GH responses to D- and L-amphetamine in monkeys.

Equimolar doses of D-amphetamine and L-amphetamine, and a water placebo were injected intravenously on different days into rhesus monkeys, and their plasma cortisol and GH responses were determined over a 3-hour period. D- and L-amphetamine (but not the placebo) equally suppressed plasma cortisol concentration and equally increased plasma GH concentration. Pretreatment of the monkeys with large doses of pimozide, a specific dopamine receptor blocker, did not appear to block the hormonal responses to either isomer of amphetamine. The results suggest that the hormonal responses to both D- and L-amphetamine were mediated by noradrenergic neurones stimulatory to GH and inhibitory to ACTH, and that D- and L-amphetamine exert equipotent noradrenergic effects in the neuroendocrine system.

Differential actions of d- and l-amphetamine on the metabolism of 3H-norepinephrine in rat brain

Approximately equieffective doses of d- and l-amphetamine, using suppression of operant fixed-ratio responding for food reinforcement as the determinant of potency, were compared for their ability to alter the disposition of the major and minor metabolites of NE in push-pull perfusates from rat brain lateral ventricle. While 3 mg d-amphetamine/kg and 6 mg l-amphetamine/kg both increased total 3H and the relative amounts of the minor metabolites 3H-normetanephrine and 3-dihydroxymandelic acid, only l-amphetamine caused a significant increase in the major 3H-NE metabolite, methoxyhydroxyphenylethylene-glycol. The data is discussed in relation to the abilities of the isomers of amphetamine to stereoselectively interact with noradrenergic neurons at doses that produce similar effects upon operant behavior.

Concentration of Amphetamine Isomers in Brain and Heart of Adult and Developing Mice

Abstract The levels of d‐ and 1‐amphetamine in the brain and heart of adult and developing mice aged 3–6 days and 13–16 days were studied. More d‐ than 1‐isomer was found in the brain of developing mice, except after a dose of 100 mg/kg of the drug, i. e. a dose which produces a higher level of 1‐amphetamine in the brain of 13–16‐day‐old mice. Adult brain retained 1‐amphetamine in a higher concentration than d‐amphetamine. In the youngest mice 50 mg/kg of the isomers produced equal levels of the drug in the brain and heart, whereas 100 mg/kg of the d‐form was particularly concentrated in the infant heart. In the older age groups the brain level of either isomer was generally higher than the respective heart level. The age‐ and dose‐dependent differences in the distribution of amphetamine isomers emphasize the importance of peripheral component of amphetamine action in the youngest mice and reveal a low sensitivity of the central nervous system to 1‐amphetamine in 13–16‐day‐old as well as in adult mice.

Effects of the d- and l-isomers of amphetamine on uptake, release and catabolism of norepinephrine, dopamine and 5-hydroxytryptamine in several regions of rat brain

The stereoselectivity of d- and l-amphetamine for uptake, release and catabolism of biogenic amines was studied in vitro in three regions of rat brain. The ( d-isomer was about two times more potent than the l-isomer in inhibiting uptake and releasing biogenic amines from chopped cerebral cortex labeled with norepinephrine and midbrain labeled with 5-hydroxytryptamine. On the other hand, the d-isomer was five times more potent than the l-isomer in inhibiting the uptake and releasing [ 3H]dopaminc from nerve terminals of corpus striatum. When the relative potencies of amphetamine on uptake and release were compared, it was found that approximately 11-fold higher concentrations of both isomers were required to release dopamine compared to their ability to inhibit neuronal uptake. Only 4-fold higher concentrations of both isomers of amphetamine were required to release [ 3H]nore-pinephrine compared to their ability to inhibit neuronal uptake. Approximately equal concentrations of the two isomers released and inhibited neuronal uptake of 5-hydroxytryptamine. With high concentrations (10 −3 M). the d-isomer of amphetamine was more effective than the l-isomer in inhibiting monoamine oxidase activity in synaptosome-free homogenates of cerebral cortex tissue. These results indicate that the dopamine nerve terminals of the corpus striatum possess greater stereoselectivity toward amphetamine than either the norepinephrine nerve terminals of cerebral cortex or 5-hydroxytryptaminc neurons of midbrain.

Effects of Catecholamine Receptor Blocking Agents on Toxicity and Thermal Responses Induced by Amphetamine Isomers in Adult and Developing Mice

Abstract The toxicity of d‐amphetamine was greater than that of 1‐amphetamine in adult mice with intraperitoneal dosage range of 10–50 mg/kg. In these doses neither isomer was toxic to developing mice aged 12–16 days. Both isomers of amphetamine induced a dose‐dependent hyperthermia in adults, and the response was stronger after the d‐ than the 1‐form. Ten mg/kg of d‐amphetamine increased the temperature of developing mice, while 50 mg/kg of both isomers was markedly hypothermic; p‐OH‐amphetamine (10 and 50 mg/kg) was not lethal and lacked the thermal effect in adult and developing mice. Phenoxybenzamine (20 mg/kg) completely protected adult mice against the toxicity of 50 mg/kg of d‐amphetamine. It also attenuated the d‐amphetamine‐induced hyperthermia in adult as well as hypothermia in developing mice. Propranolol (10 mg/kg) partially protected adult mice against d‐amphetamine toxicity and clearly antagonized the hyperthermia. In combination with propranolol d‐amphetamine was toxic to developing mice and potentiated the hypothermia. Metoclopramide (40 mg/kg) partially protected adult mice against d‐amphetamine toxicity and diminished the hyperthermia. In developing mice, metoclopramide increased d‐amphetamine toxicity, but decreased the hypothermia. It is suggested that amphetamine preferentially affects noradrenergic mechanisms in adult mice and dopaminergic mechanisms in developing mice. Central noradrenaline receptors seem to be mainly responsible for the mediation of amphetamine toxicity. Amphetamine‐induced disturbances in thermoregulation play a minor role in amphetamine toxicity in both adult and developing mice.

A procedure for the differentiation of the optical isomers of amphetamine and methamphetamine by thin-layer chromatography

A procedure for the differentiation of the optical isomers of amphetamine and methamphetamine by thin-layer chromatography

Sleep: Effects of d- and l-amphetamine in man and in rat

Almost identical results are reported in man and in rat for the effects of the amphetamine isomers on polygraphically recorded sleep. In both species, dextro-amphetamine produces a significantly greater increase in waking time. In both species, the two isomers have equal effects in reducing desynchronized sleep time. These findings combined with other recent data suggest that dopamine plays a direct rolw in wakefulness while norepinephrine is related inversely to amolnts of desynchronized sleep.