Effects of aspirin and prostaglandin E1 on in vitro thrombolysis with urokinase: Evidence for a possible role of inhibiting platelet activity in thrombolysis

Abstract

The formation of thrombi in vivo includes the activation of both platelets and the coagulation cascade. Conventional thrombolytic therapy is primarily directed toward the dissolution of fibrin. To evaluate the possibility that platelet activity impairs the lysis of thrombi, we studied the effects of aspirin and platelet-deaggregating prostaglandin E1 on thrombolysis with urokinase. Combined platelet and fibrin thrombi were produced in vitro by adding CaCl2 and collagen (1 μg/ml) to citrated platelet-rich plasma (250,000 platelets per μl). Urokinase (500-10,000 units/ml) caused a dose-dependent weight loss of the thrombi that was maximal at 2,000 units/ml. The addition of aspirin (10-200 μg/ml) to platelet-rich plasma before thrombus formation markedly enhanced thrombolysis with urokinase. This effect was most pronounced at 20 μg/ml aspirin. However, when aspirin was added after completion of thrombus formation, no significant effect on thrombolysis was noted. Prostaglandin E1 (1-100 μmol/l) improved the lysis with urokinase of the combined platelet and fibrin thrombi. This effect was maximal at 20 μmol/l prostaglandin E1. When pure fibrin thrombi were produced in platelet-free plasma, prostaglandin E1 was without effect on lysis. Thus, in vitro lysis with urokinase of combined platelet and fibrin thrombi was enhanced by the addition of platelet-deaggregating prostaglandin E1 and by pretreatment with aspirin.