The significance of fibrinolysis

Abstract

The fibrinolytic mechanism is assumed to remove formed fibrin from within blood vessels and the tissues, and to play an important role in maintaining vascular patency in balance with blood coagulation and resultant fibrin formation. The conversion of the inert protein plasminogen to the active proteolytic enzyme plasmin by activator is considered to be the basic stage of this mechanism. Activator itself may be released from tissue directly or by conversion of an inert proactivator by lysokinase into an active enzymic form. When plasmin is released into the circulation it is normally bound and neutralized by antiplasmin and the actual process of fibrinolysis is thought to take place either because the plasmin antiplasmin complex dissociates as it comes in contact with fibrin (Ambrus, Back & Ambrus 1962), or because plasminogen, bound to fibrin, is converted in situ into active plasmin (Fletcher, Alkjaersig & Sherry 1962). Besides fibrin plasmin can also digest fibrinogen and other coagulation factors (VIII and V), and overactivity of the fibrinolytic mechanism is considered to lead to depletion of these factors and so promote abnormal bleeding. There is a growing opinion that conversely, the result of underactivity may be the excess formation of fibrin and an increased risk of thrombosis due to intravascular fibrin formation.