Inhibition of platelet aggregation in whole blood by alcohol

Our previous studies have demonstrated that addition of moderate volumes of absolute alcohol (34-170 mM final concentration) to whole blood produces concentration-dependent platelet aggregation, due to release of adenosine diphosphate (ADP) from erythrocytes. We have now investigated the effects of exposure of blood to ethanol by a more "physiologic" protocol, in which 7.8% (w/v) alcohol is added to achieve a final concentration of 1 to 85 mM in human and rat blood or platelet rich plasma (PRP). The effects of short incubation with alcohol on platelet aggregation induced by ADP, collagen and arachidonic acid were examined by the impedance method of aggregometry. Aggregation induced by collagen in PRP of either species was significantly inhibited by 85 mM ethanol, with concentrations as low as 4.25 mM inhibiting the response to collagen in rat whole blood. ADP stimulated only primary, reversible aggregation in rat PRP and whole blood, and these responses were unaffected by alcohol. Human platelets responded to ADP with irreversible aggregation, which was significantly attenuated by 85 mM ethanol in whole blood but not PRP. Arachidonic acid evoked irreversible platelet aggregation in all four preparations; this was significantly inhibited by the high dose ethanol in human and rat PRP, but not whole blood. In contrast to our earlier studies with absolute ethanol, there was no evidence of hemolysis (and therefore, ADP release from red blood cells) using the current protocol. The results of these experiments show that alcohol, at physiologically relevant concentrations, has an inhibitory effect on secondary platelet aggregation responses to some agonists in whole blood as well as PRP, possibly by its previously demonstrated effects on arachidonic acid release by phospholipases. The possibility remains to be considered that other blood cells might contribute to the effects of alcohol on platelet aggregation in whole blood.