The Nature of Heparin Antithrombin Action

Summary Heparin accelerated the activity of isolated or unopposed antithrombin. Neither calcium, platelets nor inhibitor were required. Optimal activity was at minimal concentrations. Heparin was not consumed or altered in the process of thrombin neutralization by heparinized plasma. The full heparin activity was manifest when additional plasma antithrombin was supplied. Thrombin neutralization was noted to be a function of the plasma antithrombin concentration. It was unrelated to the heparin concentration. Heparin did not increase the total antithrombic activity in samples with either very small or large quantities of thrombin and antithrombin. The heparin influenced thrombin neutralization only in the presence of antithrombin. It did not affect the thrombin-fibrinogen reaction. Polybrene blocked the heparin effect when added to the antithrombin, but did not affect heparin action when added subsequently to the fibrinogen substrate.