Relationship of Plasminogen Activator to Fibrin

Abstract

THERE are two principal theories of the mechanism of thrombus dissolution by the fibrinolytic system. Alkjaersig et al.¹ suggested that as fibrin polymerizes, plasminogen is adsorbed preferentially to the fibrin and is available in large quantities within a thrombus which is comparatively free of antiplasmin. When an activator enters the circulation it diffuses into the clot converting the plasminogen to plasmin in situ and so promotes lysis. Ambrus and Markus², however, proposed that when plasmin forms in the circulation naturally or during infusion of an activator it is normally bound to the excess antiplasmin present in blood. They suggested that this plasmin/antiplasmin complex is reversible and dissociates in the presence of fibrin, its preferred substrate, so allowing the plasmin to bring about fibrin dissolution by “external lysis”. Neither of these theories, however, is supported by an observed phenomena.