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/l) or paracetamol (1.3 mmol/l) 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.