title: Thrombin generation and secretion of platelet Factor 4 during blood clotting.
abstract: We have studied the platelet release reaction and thrombin generation during the spontaneous clotting of whole blood in vitro. Both thrombin formation and secretion of platelet Factor 4 were detected at least 12 min before clotting (clotting time, 22--26 min). Initially, at low thrombin concentrations (2--5 ng/ml), there is a small increase in plasma platelet Factor 4 (less than 1% of the amount present in serum). This is followed by a gradual increase in both platelet Factor 4 and thrombin concentrations over a 12 to 20-min interval. Finally, 5 min 5 before clotting, there is a rapid increase in both thrombin generation and platelet secretion. Thus, we have shown that the release of platelet Factor 4 is a prolonged reactoin and the extent to which it occurs parallel thrombin generation. It is only when thrombin concentrations are high (45--90) ng/ml)--during the period of clot formation--that the major part of platelet Factor 4 secretion occurs. Release of platelet Factor 4, like fibrin formation, occurs in the last step of in vitro coagulation.
mesh_terms: D001777:Blood Coagulation; D001779:Blood Coagulation Factors / Q000378:metabolism*; D001792:Blood Platelets / Q000378:metabolism; D003994:Bucladesine / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010978:Platelet Factor 4 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011458:Prostaglandins E / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism*
chemical_list: D001779:Blood Coagulation Factors; D011458:Prostaglandins E; D010978:Platelet Factor 4; D003994:Bucladesine; D013917:Thrombin