Polyindolinic Alkaloids from Psychotria forsteriana. Potent Inhibitors of the Aggregation of Human Platelets

Abstract

Quadrigemine B, quadrigemine A, isopsychotridine C and psychotridine, isolated from Psychotria forsteriana, are potent inhibitors of the aggregation of washed human platelets induced by ADP, collagen or thrombin. The four compounds are active in the 1-10 µM range. The quadrigemine-type alkaloids do not increase the level of platelet cyclic AMP, either alone or in the presence of 20 nM prostaglandin E, (PGE₁), an activator of adenylate cyclase. The characteristics of the pharmacological action of these compounds suggest that they act at a later stage in platelet activation, possibly through an interaction with cytoskeletal proteins.