[Effect of thrombolytic agents on platelets and blood coagulation system]

The effect of tissue-type plasminogen activator (tPA) on platelet aggregation and blood coagulation was investigated. Collagen-induced platelet aggregation in washed platelet suspension was significantly inhibited by the addition of tPA, but the effect was limited when platelet rich plasma was used instead of washed platelets because of the presence of alpha 2-antiplasmin in plasma. The diluted prothrombin time was significantly shortened by the addition of tPA to normal plasma, and although the levels of molecular markers of thrombin formation were increased compared to that of normal controls, the increase was diminished when factor VII-deficient plasma was used, suggesting that tPA enhances factor VII. The activated factor VII concentration was significantly increased by the addition of plasmin to factor VII solution. These findings suggest that tPA enhances the coagulation system by factor VII activation through the generation of plasmin in normal plasma. This enhancing effect of tPA on coagulation system may be partly related to vascular reocclusion after thrombolytic therapy.