Effects of dibutyryl cyclic adenosinemonophosphate and prostaglandin E1 on platelet aggregation and shape changes

Prostaglandin E1 (PGE1) exerted an immediate inhibitory effect upon the induction of platelet aggregation by adenosinediphosphate, epinephrine, thrombin, bovine fibrinogen, or sodium fluoride, whereas dibutyryl cyclic adenosinemonophosphate (DBcAMP) produced a delayed type of inhibition of aggregation induced by these same agents. In addition, however, both PGE1 and DBcAMP, as well as adenosinetriphosphate (ATP) and Mg++, restored, with incubation, the washed platelets to a more discoid shape. Platelet aggregability also correlated well with platelet shape. All of these findings suggest the possibility of mediation of the delayed type of inhibition through restoration of the platelet membrane by increasing the level of metabolically active ATP or the availability of cations. They tend, however, to exclude the possibility that PGE1 exerts its immediate inhibitory effect through the increase of platelet cAMP.