Failure of aspirin to impair bovine platelet function

The effect of aspirin on bovine platelet function and thromboxane A2 (TXA2) production in stimulated platelets was evaluated. A single dose of aspirin (100 mg/kg of body weight) was administered orally to Holstein cows, and blood samples were obtained before and at regular intervals for 7 days after treatment. The production of TXA2 was assessed by measuring the stable metabolite thromboxane B2, using a specific radioimmunoassay. Within 4 hours of aspirin administration, the production of TXA2 was significantly (P less than 0.05) decreased, irrespective of whether collagen, adenosine diphosphate, or platelet activating factor was used to initiate platelet aggregation. Despite the inhibition of TXA2 release from the stimulated platelets, platelet function, assessed by initial rate of aggregate formation and extent of aggregation, was unaffected by aspirin administration. The extent of aggregate formation in response to collagen, adenosine diphosphate, or platelet activating factor was independent of the amount of TXA2 released from platelets before and after aspirin treatment. The results suggested that TXA2 formation is not the primary biochemical pathway involved in the aggregation of stimulated bovine platelets.