Effect of ethanol on thrombin-induced platelet phospholipid breakdown and release of [3H]-5-hydroxytryptamine.

Ethanol has been reported previously to inhibit chemically-induced platelet aggregation and the release of platelet contents. In platelet suspensions the mechanical stimulus of stirring can induce slow aggregation and the loss of endogenous arachidonic acid from phospholipids by activation of platelet phospholipases. These changes are prevented by the presence of ethanol 20-100 mM, whereas, in unstirred suspensions, ethanol alone has no effect on platelet phospholipids. Under similar conditions of reduced platelet: platelet contact, chemical stimuli, such as thrombi, although unable to produce visible aggregation, still cause the release of [3H]-5-hydroxytryptamine from platelets and also initiate the breakdown of platelet phospholipids. Ethanol does not now inhibit the thrombin-induced release of platelet contents and has little effect on phosphatidylinositol breakdown, though it inhibits phosphatidylcholine breakdown. Ethanol may therefore inhibit platelet aggregation by reducing the effect of mechanical and chemical stimuli on the activation of phospholipase A2. In contrast ethanol has rather little effect on the receptor-mediated breakdown of phosphatidylinositol which is apparently sufficient to trigger the release of platelet contents.