Inhibitory effect of glyburide on thrombin-induced platelet aggregation and phosphoinositide metabolism in normal human platelets

We previously reported the effects of diet, sulphonylureas or insulin on th rombin-induced platelet aggregation, phosphoinositide metabolism and protei n phosphorylation in non-insulin-dependent diabetes mellitus (NIDDM) patien ts. To clarify the mechanism of glyburide and insulin on platelet function, here we studied the in vitro effects of glyburide and insulin on thrombin- induced metabolic changes using normal human platelets. Platelet aggregatio n stimulated with <0.5 U/ml thrombin, 0.75-3 mu M adenosine diphosphate (AD P) or 1 mu g/ml collagen was significantly lower in glyburide-treated plate lets, but not in insulin-treated platelets, than in untreated ones (control ), Thrombin-induced incorporation of P-32 radioactivity into phosphatidic a cid (PA) in glyburide-treated platelets was lower than that in control but not in insulin-treated platelets, Phosphorylated proteins of platelets indu ced by thrombin and 12-O-tetradecanoylphorbol 13-acetate (TPA) in glyburide -treated platelets were suppressed, but not in insulin-treated platelets, c ompared with control. These results suggest that glyburide induces suppress ion of thrombin-induced activation of phospholipase C, which mediates hydro lysis of PIP and PIP2 and production of PA, and subsequently inhibits plate let aggregation.