Role of activated protein C on platelet aggregation induced by thrombin

Platelets aggregate with thrombin-free activated protein C in concentrations higher than physiological levels. Aggregation was dependent on an intact release mechanism since inhibition of aggregation occurred with adenosine or EDTA. However, activated protein C reduced the sensitivity of platelets to aggregate in the presence of thrombin. Probably, activated protein C competes for membrane sites sensitive to thrombin.