PSYCHOPHARMACOLOGICAL INVESTIGATIONS OF THE 4–METHOXYINDOLE ALKALOIDS OF ALSTONIA VENENATA

Abstract

Alstovenine and venenatine, an epimeric pair of 4–methoxyindole alkaloids isolated from the bark of Alstonia venenata, showed significant psychopharmacological activity. Alstovenine, in lower doses, exhibited monoamine oxidase inhibitor activity as characterised by its ability to potentiate hexobarbitone hypnosis, amphetamine toxicity, tryptamine convulsions, prevention but not reversal of reserpine syndrome, potentiation of DOPA and 5–HTP effects, morphine analgesia and anticonvulsant effect of diphenylhydantoin. In higher doses, close to the toxic dose, it showed marked central stimulant effect as revealed by its behavioural effects (stereotypy and convulsions), antagonism to hexobarbitone hypnosis and reversal of reserpine effects. Venenatine, on the contrary, exhibited a reserpine–like profile of activity as characterised by its behavioural effects (sedation, ptosis and reduction in motor activity), potentiation of hexobarbitone hypnosis, antagonism of amphetamine toxicity, morphine analgesia and anticonvulsant action of diphenylhydantion, synergistic effect with reserpine on general behaviour and its ability to reduce the pressor effect of tyramine without affecting noradrenaline pressor response.