Effect of Methylene Blue on pyridine nucleotides and insulin secretion of rat pancreatic islets

Summary Methylene Blue, which is known to oxidise NADPH in red blood cells, was used to assess a possible role of NADPH in the glucose-stimulated secretion of insulin. When islets from rats were incubated with 3 mg/ml of glucose, Methylene Blue (0.5, 1.0, 2.0 or 5.0 g/ml) significantly decreased the concentration of NADPH, increased that of NADP⁺ and decreased the NADPH/NADP⁺ ratio in a dose-dependent manner. This effect was associated with inhibition of the glucose-induced insulin release. No significant change of NADH, NAD⁺ and ATP could be observed. It is suggested that the secretory response of the pancreatic islet to glucose stimulation depends on the NADPH/NADP⁺ ratio.