Effects of fibrin on the enhanced activation of plasminogen by urokinase and tissue plasminogen activator: Role of cross-link

Abstract

When human plasma was activated by urokinase (UK) in the presence of thrombin, thrombin plus Ca ++, Ca ++ or in their absence and the plasmin activity was measured by the hydrolysis of S-2251, plasmin activity was higher in the presence of cross-linked or non cross-linked plasma clot. The results of similar experiments utilizing plasma after severe exercise indicated that the hydrolysis of S-2251 by plasma containing tissue plasminogen activator (t-PA) was also higher in cross-linked or non cross-linked plasma clot. Fibrinolysis was faster in thrombin-induced plasma clot, but was later shown significantly in plasma clot induced by thrombin and Ca ++, whereas practically no fibrinogenolysis was shown in plasma. When Glu-plasminogen (Glu-plg) was activated by UK in the presence of cross-linked or non cross-linked fibrin and α 2antiplasmin ( α 2AP), fibrinolysis was faster in crosslinked fibrin than non cross-linked fibrin in the presence of α 2AP. No fibrinogenolysis was shown either. Plasmin activity measured by the hydrolysis of S-2251 was also higher in cross-linked or non cross-linked fibrin than in fibrinogen in the presence of α 2AP. These results indicate that enhanced activation of Glu-plg by UK or t-PA in the presence of fibrin was a more significant event than the inactivation of plasmin in the plasma clot or purified clot by α 4AP cross-linked to fibrin.