The effects of aspirin and paracetamol on the aggregation of equine blood platelets

The responses of equine blood platelets in citrated platelet-rich plasma to arachidonic acid, U44069 (prostaglandin endoperoxide analogue), adenosine 5'-diphosphate, platelet-activating factor or collagen were investigated by turbidimetric aggregometry. Pre-treatment of the platelets with aspirin (1 mmol/1) or Paracetamo1 d-3 mmol/1) abolished shape change and aggregation in response to arachidonic acid; decreased the rate of aggregation in response to collagen, with no separate effect on shape change; had no marked effect on aggregation caused by the other agonists; but in no case transformed irreversible aggregation to reversible aggregation. We conclude that thromboxane A₂ generation is of minor importance in the aggregation of equine platelets, and in particular that thromboxane A₂ is not a significant mediator of irreversible aggregation.