[Protein C: mechanisms of activation and anticoagulant effect]

The mechanism of functioning of protein C can briefly be presented as follows. Thrombin and factor Xa formed in the blood via coagulation, interact with endothelial thrombomodulin and thereby activate protein C circulating in the blood. The activated protein C inhibits factors V and VIII and, in so doing, blocks the further production of thrombin. In this way protein C intermediates the loop of the negative feedback and prevents excessive thrombin generation. Besides, activated protein C enhances fibrinolysis, causing the release of the tissue plasminogen activator. Activated protein C is inhibited by a heparin-dependent inhibitor and alpha 1-antitrypsin and is then excreted from the organism. Congenital deficiency of protein C gives rise to thromboses; thrombotic diseases of various etiology are accompanied by protein C decline in the blood. Injection of exogenous protein C into the blood increases the anticoagulant activity of the blood and produces an antithrombotic effect.