Relative proteolysis of the fibrinogen B beta chain by thrombin and plasmin as a determinant of thrombosis.

Thrombosis results, in part, from localized accumulation of fibrin, implying an imbalance between its rate of formation and dissolution. Astrup postulated that patency of the vascular system depended on a dynamic equilibrium between constantly active coagulation and fibrinolytic systems. Reviews of this hypothesis have concluded that neither thrombin nor plasmin proteolysis makes a major contribution to fibrinogen turnover in normal individuals and that the hypothesis of a dynamic equilibrium between clotting and lysis remains unproven. Thus, the current view is that plasmin simply serves the function of a fibrinolytic enzyme digesting fibrin in the vascular system. Here, I promote the alternative view that the relative rates of proteolysis of the B beta chain of fibrinogen by thrombin and plasmin determine the occurrence of thrombosis. This view is supported by recent data and can be used to make some readily testable predictions.