Inhibition of Thrombin Induced Aggregation of Human Platelets by Antithrombin III

The influence of antithrombin III (At-III) on the thrombin induced aggregation of human platelets was studied by the aggregometer technique according to Born. When At-III was mixed with platelet suspension, subsequent addition of thrombin resulted in decreased aggregation as compared to the control. The inhibition was dependent on the At-III: thrombin ratio. Above 0.2 NIH U/ml of thrombin, no inhibitory effect was observed with physiological At-III concentrations. The effect was more pronounced at 37° C than at 20° C.