Endogenously activated protein C is evaluated for antithrombotic activity in porcine carotid arteries subjected to mechanical trauma. Protein C is activated by intravenous administration of guanidinobenzoyl-thrombin, which binds to thrombomodulin and there deacylates to yield thrombin. The bound, transiently active thrombin yields a peak of anticoagulant activity between 5 and 10 min after infusion of the latent thrombin. Inhibition of thrombin binding in vivo by co-infusing an active-site-blocked thrombin preparation elicits acute and lethal systemic thrombosis. Nearly occlusive platelet thrombosis, which occurs within 30 min of crushing 1 cm segments of carotid arteries with a standard hemostat, is blocked by endogenous protein C activation initiated 2 min before the crush injury. It is concluded that activated protein C blocks thrombosis in deeply injured musculo-elastic arteries, and that activation of latent thrombin bound to thrombomodulin in vivo is a practical means for delivery of pharmacologically effective concentrations of activated protein C.
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