The potentiation of platelet aggregation by mechanical stimuli is inhibited by ethanol in vitro

Previous work on inhibition by ethanol of human platelet aggregation suggested that this was a consequence of inhibition of the activation of platelet membrane phospholipase A2 (PLA2) which precedes aggregation. In these experiments, the effect of ethanol in vitro on human gel-filtered platelets activated with A23187 or with collagen was studied at different levels of mechanical stimulus (stirring rate) in the platelet aggregometer. The dose response curve obtained by varying the concentration of aggregating agent at constant stirring rate was shifted to the right in the parallel fashion by ethanol. A23187-induced aggregation was inhibited to a greater extent than that due to collagen. When a stirring rate: response curve for platelet aggregation was obtained at a constant concentration of either chemical aggregating agent ethanol shifted the curve to the right in a non-parallel fashion, its effect being greater at greater levels of mechanical stimulus. The effects of acetylsalicylic acid, known to act at a step subsequent to PLA2 activation, were completely unlike those of ethanol. The results are consistent with an inhibitory effect of ethanol on activation of phospholipase A2 by mechanical stimuli which deform platelet membranes.