The effect of methyleneblue on insulin and glucagon release stimulated by glucose and arginine in the isolated perfused rat pancreas

Abstract

To examine the role of NADPH in the release of insulin and glucagon, isolated rat pancreata were perfused with methyleneblue, which is known to oxidize NADPH. Hormonal release was stimulated by changes in arginine or glucose concentrations as follows. After establishing the basal secretion state during perfusion at various glucose levels for 10 min., pancreata were stimulated by the addition of arginine or a change in glucose concentration of the perfusate for 15 min. Conditions for the stimulation were: (A) addition of 10 mM arginine at constant 4 mM glucose concentration; (B) increase in glucose concentration from 2.8 mM to 11.1 mM, or (C) decrease in glucose concentration from 11.1 mM to 2.8 mM. In some experiments, methyleneblue was added throughout the perfusion period at 1 or 3 micrograms/ml. The effluent from the portal vein was collected over 1 minute intervals: Insulin and glucagon concentrations in the effluent were determined by radioimmunoassay. Insulin release. Stimulation by the addition of arginine and increased glucose concentration produced a typical biphasic insulin response. In both cases, 1 microgram/ml methyleneblue reduced the second phase, and 3 micrograms/ml methyleneblue inhibited both phases almost completely. Glucagon release: Stimulation by arginine and inhibition by increasing glucose concentration were not influenced by methyleneblue; however, glucagon release induced by lowering of glucose concentration was suppressed by 3 micrograms/ml of methyleneblue. Thus, methyleneblue specifically inhibits glucose- and arginine-induced insulin release while it has no effect on arginine-induced glucagon release.(ABSTRACT TRUNCATED AT 250 WORDS)