Pyridine nucleotides in pancreatic islets during inhibition of insulin release by exogenous insulin.

In vitro addition of rat insulin (200, 400 or 800 muU/ml) to collagenase-isolated pancreatic islets of adult rats diminished glucose (3 mg/ml)-induced insulin release which was correlated with a decrease of the ratio of total NADPH/NADP and inhibition of glucose oxidation via the pentose phosphate shunt (PPS). NADH and NAD levels were not affected. It is suggested that exogenous insulin diminishes the islet total NADPH/NADP ratio by a direct or indirect decrease in PPS activity. However, it is also conceivable that insulin decreases this ratio through another mechanism than PPS. It is possible that inhibition of insulin secretion by exogenous insulin is at least in part due to the decrease of the NADPH/NADP ratio.