Evidence for prothrombotic effects of exercise and limited protection by aspirin

Background-Exercise may activate platelets and leukocytes and promote thrombosis. The effects of aspirin treatment on the prothrombotic effects of exercise have not been established. Methods and Results-A total of 15 healthy men performed exhaustive exercise without and with 1 week of pretreatment with aspirin (500 mg/day). Before and immediately after exercise, platelet aggregability ex vivo was measured by filtragometry, and venous blood samples were obtained. Whole-blood flow cytometry was used to determine platelet and leukocyte activation and platelet-leukocyte aggregates. Exercise increased platelet P-selectin expression, CD11b expression in neutrophils and lymphocytes, and platelet and leukocyte responses to thrombin. ADP. platelet activating factor, and N-formyl-methionyl-leucyl-phenylalanine (fMLP) in vitro. Consistent with enhanced platelet and leukocyte activation, more circulating platelet-platelet and platelet-leukocyte aggregates were detected after exercise (P<0.001 for both). Filtragometry readings were shortened, and plasma soluble P-selectin and prothrombin fragment 1+2 were elevated. Aspirin markedly reduced the urinary excretion of 11-dehydrothromboxane B-2, decreased P-selectin expression in single platelets at rest (P<0.05), and inhibited fMLP-induced neutrophil CD11b expression, but it did not attenuate exercise-induced increases in platelet aggregability, platelet P-selectin expression, leukocyte CD11b expression, platelet-leukocyte aggregate formation, soluble P-selectin, or prothrombin fragment 1+2. Conclusions-Exercise induced platelet and leukocyte activation and platelet-leukocyte aggregation in vivo, and it increased platelet and leukocyte responsiveness to in vitro stimulation. Aspirin treatment attenuated certain signs of platelet activity in vivo at rest and fMLP-induced neutrophil activation in vitro, but it did not attenuate the prothrombotic effects of exercise.