The relationship between glucose-induced insulin secretion and metabolism of inositol phospholipid was investigated by means of an islet perifusion method and direct measuring of inositol phosphates after sonicating the islets. The results showed that the time course of inositol phospholipid breakdown is coincident with the first phase of glucose-induced insulin secretion. Analysis of the effluent perifusate as well as the water soluble inositol-containing substance after sonication of stimulated islets revealed that most of the metabolite of inositol phospholipid is inositol-triphosphate, the hydrolysis product of phosphatidylinositol-4,5-bisphosphate. On the other hand, perifusion of islets with exogenous inositol-triphosphate showed a monophasic and dose-dependent response of insulin secretion. Thus, the initial process of glucose stimulation is accompanied with the formation of inositol-triphosphate, which is a possible candidate for the triggering of first phase insulin secretion.

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