Insulin and Its Secretagogues Activate Ca²⁺-dependent Phosphatidylinositol Breakdown and Amylase Secretion in Rat Pancreas In Vitro

We studied the effects of insulin and insulin secretagogues on pancreatic phospholipids and the release of amylase from pancreatic fragments incubated in vitro. Insulin provoked rapid, dose-related increases in amylase release, and these were accompanied by decreases in phosphatidylinositol and increases in phosphatidic acid. Glucose and other insulin secretagogues elicited similar changes in amylase release and pancreatic phospholipids; epinephrine blocked these effects of glucose, presumably via inhibition of glucose-induced insulin secretion. Effects of insulin and glucose on phospholipids and amylase release were dependent on Ca²⁺ in the incubation medium. These findings suggest that, in the pancreas, insulin enhances Ca²⁺-dependent phosphatidylinositol breakdown, which in turn influences amylase secretion. The effects of insulin on phospholipids may also explain certain other actions of insulin.