Aggregation of human platelets by bovine platelet fibrinogen.

Aggregation of human platelets by addition of purified bovine platelet fibrinogen is described. Bovine plasma fibrinogen showed the same but much weaker effect. Human fibrinogen produced no aggregation. No absolute requirement for divalent cations or plasma proteins could be demonstrated. The aggregation of washed platelets appeared monophasic whereas in platelet-rich plasma it was usually biphasic. The use of inhibitors of ADP-induced platelet aggregation, inhibition of intracellular ATP-production, enzyme-catalyzed removal of ADP, and direct determinations of ADP in the medium showed the second phase to be mediated by ADP released from the platelets whereas the first phase was nearly independant of ADP. While the ability of platelet fibrinogen to aggregate platelets and to clot with thrombin were otherwise intimately interconnected, some aggregation activity remained after heat-denaturation of the platelet fibrinogen.