The clotting time of whole blood in plastic tubes: the influence of exercise, prostacyclin and acetylsalicylic acid.

An assay for detection of a hypercoagulable state was accomplished by measuring the clotting time of whole blood (without anticoagulant present) in plastic tubes. This assay appeared to be quite sensitive to the activation state of platelets. Thus, acetylsalicylic acid (ASA) or prostacyclin (PGI2) was found to prolong significantly the whole blood clotting time (WBCT), specially under conditions where the platelet might be hyperactive. When the WBCT was carried out before and after exercise, a mean value of 12.95 min was obtained before as compared to 7.48 min after exercise. In the presence of PGI2, the WBCT after exercise was prolonged to 13.91 min. The shorter clotting time after exercise, in the absence of inhibitor, might be explained by the observation in the present study that platelet factor 3 became more readily available upon consecutive stimuli. These results suggest that platelet release may be important for the initiation of prothrombin activation in situations without already available platelet factor 3 activity.