EFFECTS OF INSULIN ON CALCIUM-METABOLISM AND PLATELET-AGGREGATION

The influence of insulin on platelets in vitro has not been exhaustive ly investigated. To clarify whether insulin affects Ca2+ metabolism in platelets directly or through alteration of other systems regulating intracellular Ca2+ homeostasis, we examined the effect of insulin both alone and in combination with prostaglandin E(1) on platelet aggregat ion and Ca2+ metabolism. Incubation of rat platelets with insulin redu ced thrombin-induced Ca2+ influx but did not change thrombin-evoked re lease of Ca2+ from internal stores or the size of internal Ca2+ stores . The interactive effects of insulin with prostaglandin E(1) were only additive, and insulin did not augment the effects of prostaglandin E( 1) on platelet Ca2+ metabolism. In contrast, insulin did not inhibit t hrombin-induced platelet aggregation but did augment inhibition of pla telet aggregation by prostaglandin E(1). Our results suggest that insu lin inhibits platelet function by both prostaglandin E(1)-dependent an d -independent mechanisms.