The effect of quercetin and lithium ions on platelet aggregation.

Quercetin inhibited aggregation of porcine blood platelets induced by collagen (IC50 = 0.2 mM), ADP (IC50 = 0.5 mM), thrombin (IC50 = 0.02 mM) and ionophore A23187 (IC50 = 1.5 mM). Preincubation of platelets with 10 mM LiCl abolished the inhibitory effect of quercetin on the aggregation of these cells induced by thrombin. Lithium ions per se caused potentiation of the aggregation of platelets induced by thrombin. Neither potentiation of aggregation by Li+, nor the abolishing of the inhibitory effect of quercetin by Li+ was observed when platelets were activated by ionophore A23187. Since lithium ions inhibit activity of enzymes degradating inositol phosphate, the obtained results can be interpreted to mean that quercetin affect platelet aggregation by the inhibition of inositol phosphates production.