Insulin Stimulates Hydrolysis of Plasmanylinositol-Glycan and Phosphatidylinositol-Glycan in Rat Adipocytes: Insulin-Induced Generation of Inositol Glycan, Alkylacylglycerol, and Diacylglycerol

Insulin binding to its receptor has been known to induce hydrolysis of phosphatidylinositol-glycan and release inositol-glycan and diacylglycerol, two putative second messengers of insulin actions. We metabolically labeled and purified PIG in rat cultured adipocytes. The treatment of [³H]glycerol-labeled PIG with phosphatidylinositol-specific phospholipase C released [³H]glycerol-labeled DAG and [³H]glycerol-labeled 1-alkyl,2-acyl-glycerol, suggesting that PIG has not only PIG but also plasmanylinositol-glycan moiety. Insulin induced hydrolysis of PIG/PMIG and generation of IG, DAG, and AAG in a dose-dependent manner. This report shows the first demonstration of insulin-sensitive PMIG in rat adipocytes. These results provide evidence that insulin-induced generation of IG, DAG, and AAG might be early events in the insulin-signaling mechanism in rat adipocytes, and insulin-releasable AAG seems to mediate some actions of insulin.