Platelets and the Triggering Mechanism of Intravascular Coagulation

S ummary The ability of platelets to trigger intravascular coagulation was studied by infusing a suspension of frozen‐thawn homologous platelets into rabbits pretreated with either saline or Thorotrast. Each animal received during a period of 30 min an amount of platelets at least equivalent to the number of circulating platelets in a normal animal of the same weight. The infusion of platelet material did not trigger fibrinogen consumption in saline‐pretreated animals. In Thorotrast‐pretreated animals, however, the platelet suspension produced significantly increased disappearance of [ 125 I]fibrinogen, moderate decreases in the fibrinogen level, significant falls in factors V and VIII, but no increase in fibrinolytic split products. None of the animals developed the generalized Shwartzman reaction. We conclude that platelets contain weak procoagulant activity which was effectively cleared by the reticuloendothelial system in the normal animal. Depression of the phagocytic capacity by Thorotrast prior to the infusion unmasked moderate intravascular coagulation.