The pharmacology of 1-phenyl-2-propylaminopentane (PPAP), a deprenyl-derived new spectrum psychostimulant

The peculiar tyramine uptake inhibitory effect of (-)deprenyl prompted structure-activity relationship studies aiming to develop new spectrum central nervous system stimulants which are devoid of MAO inhibitory potency and operate de facto as indirectly acting, nonreleasing sympathomimetics. Of the derivatives synthesized for this purpose, 1-phenyl-2-propylaminopentane (PPAP) was selected as the reference substance and its pharmacological spectrum is presented. PPAP is taken up by the catecholamine axon terminal membrane and the vesicular membrane but it is devoid of catecholamine-releasing property. As a result, PPAP is, by interference, a potent inhibitor of the uptake of indirectly acting sympathomimetic releasers and of the catecholamine transmitters. This was proved, on the one hand, by measuring the uptake of [¹⁴C]PPAP into the catecholaminergic axon terminals and the inhibition of the uptake of [³H]noradrenaline and [³H]dopamine by PPAP in the rat brain, and, on the other hand, on the pulmonary artery strip of the rabbit and, in vivo, using the rat nictitating membrane as a detector. PPAP increases motility at 2 mg/kg and, in contrast to amphetamine, inhibits it at very high doses (50 mg/kg) only. A two-sided antagonism in the motility-increasing effect between PPAP and amphetamine and, more pronounced, between PPAP and mazindol was detected. PPAP is substantially less effective in inducing stereotyped behavior than either amphetamine or methamphetamine. PPAP facilitates learning and retention, is highly potent in antagonizing the tetrabenazine-induced depression in behavioral tests and is very effective in the forced swimming test. Whereas amphetamines facilitate performance in a very narrow range of low doses, which turns, at a modest elevation of the dose, into the opposite effect, PPAP improves performance within a reasonably broad dose range. Based on the peculiar pharmacological profile of PPAP, its potential usefulness in depression, in Alzheimer's disease and in attention-deficit-hyperkinetic disorder seems to be plausible.