ROLE OF THE FIBRINOLYTIC SYSTEM IN THROMBOEMBOLISM

The present concept of physiologic fibrinolysis was reviewed. It was concluded that the nonspecific proteolytic activity of plasmin would essentially be limited to fibrin in vivo in view of (A) the specific adsorption of activator and of plasminogen onto the fibrin surface resulting in local generation of plasmin and (B) the fact that plasmin, adsorbed to fibrin (in contrast to plasmin in the fluid phase) largely escapes from the action of antiplasmin. The hemostatic balance in the resting condition was discussed. It was concluded that under normal conditions, systemic intravascular fibrin deposition or formation must be either nonexistent or extremely limited. On the other hand, there is considerable evidence that a limited systemic fibrinogenolysis is going on in healthy individuals and that this process can be accelerated by simple physiologic procedures, such as strenuous physical exercise. The hemostatic balance in disseminated intravascular coagulation was presented. It was concluded that there now exists both indirect and direct evidence that enhanced fibrinogen-to-fibrin conversion is counterbalanced by increased plasminogen-to-plasmin transformation. Evidence for the hypothesis that defective fibrinolytic activity leads to a tendency to thrombosis was reviewed. Situations with a low plasminogen level, a low baseline level of plasminogen activator, a reduced reserve of plasminogen activator, or an increased level of inhibitor were discussed. The evidence suggests that a reduced fibrinolytic activity may tip the hemostatic balance towards an increased tendency to thrombosis. Finally, the role of the fibrinolytic system in removing already existing thrombi was mentioned. © 1979.