Plasminogen, plasminogen activator, and platelets in the regulation of clot lysis. Reconstitution and patient studies.

Dilute clot lysis was assayed by release of soluble 125I fibrin degradation products from dPPP clots containing varying amounts of plasminogen activator and platelets. Plasminogen activator in the absence of platelets gave an approximately linear rate of lysis, with a rate proportional to its concentration. Addition of platelets to achieve normal clot retraction had little effect on the lysis rate in the absence of plasminogen activator or in the presence of very high plasminogen activator levels. However, with intermediate plasminogen activator levels, platelet-mediated clot retraction was associated with an accelerated rate of clot lysis when retraction reached 75% to 90%. The length of the lag phase before the start of the accelerated phase varied with the number of platelets and rate of clot retraction. The interaction of clot retraction and lysis was further explored in selected patients to determine (1) whether the contributions of platelet and plasma factors in these cases was similar to those seen in our studies of reconstituted plasma and (2) whether our experience with reconstituted systems could be used in the study of disorders of fibrinolysis involving platelets and fibrinolytic enzymes.