The influence of prostaglandin endoperoxides on platelet ultrastructure.

Prostaglandin endoperoxides produced during aggregation of blood platelets are potent promoters of platelet aggregation and the release reaction. The present investigation has studied the effects of prostaglandin endoperoxides produced by platelet microsomes after incubation with arachidonic acid on the ultrastructure of platelets. Prostaglandin endoperoxides caused platelet pseudopod formation and internal transformation associated with a contractile wave within the platelet. The contractile process was similar to that seen following incubation of platelets with collagen or thrombin but was more complete than that seen with 25 muM ADP. Platelet aggregation was more prominent in unstirred samples incubated with the prostaglandin endoperoxides than in samples similarly incubated with 25 muM ADP. Dilatation of the open canalicular system was not a prominent feature except at 45 minutes after addition of the endoperoxides to the platelets, when the platelets appeared to be in a recovery phase. We conclude that the endoperoxides promote platelet stickiness and platelet aggregation by directly or indirectly stimulating the platelet contractile system.