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

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 micrograms/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.