Effects of PGI2 on the inactivation of thrombin,factor Xa,and plasmin by antithrombin-III and hepartin

The influence of PGI₂ on the activity and on the inactivation of enzymes participating in blood coagulation /thrombin and Factor Xa/ and fibrinolysis /plasmin/ were investigated. According to the results PGI₂ has no effect on the activity of Factor Xa and plasmin nor on the inactivation of these enzymes by antithrombin-III in the absence and presence of heparin at a concentration of PGI₂ up to 400 μg/ml. An acceleration of the inactivation of thrombin by antithrombin-III was found in the presence of PGI₂ within a concentration of 100–400 μg/ml without any effect on the heparin-accelerated inactivation of thrombin by antithrombin. We got similar results using clotting tests for the assay and the application of synthetic substrate for thrombin. This inactivation-accelerating effect of PGI₂ on thrombin was only demonstratable at a concentration five magnitudes higher than that of the anti-aggregation effect on platelets.