Epinephrine-induced reversal of aspirin effects on platelet deformability.

The present study has evaluated the influence of epinephrine on the resistance of platelets to aspiration into micropipettes, and the effect of epinephrine on the altered deformability of aspirin treated platelets. Unlike other platelet agonists previously studied, epinephrine stimulation did not alter platelet deformability at a concentration capable of causing platelet aggregation. Aspirin caused a dramatic decrease in the resistance of platelets to aspiration. Pretreatment of platelets with epinephrine prevented aspirin from altering platelet deformability, and exposure of platelets to epinephrine after treatment with aspirin reversed the increased deformability produced by the drug. Blockade of alpha-2 adrenergic receptors with yohimbine or clonidine prevented epinephrine antagonism of the mechanical effects of aspirin. The studies provide further evidence of the novel antagonism between epinephrine and aspirin on platelet structure and function.