Evidence for a limited role of NAD(P)H in the nutritional regulation of glucagon release: studies with menadione and NH4Cl.

Menadione and NH4Cl were reported to lower the islet content of reduced pyridine nucleotides. They were used to investigate the possible significance of NAD(P)H in the regulation of glucagon release by glucose and arginine. Menadione (10-25 mumol/l) enhanced arginine-stimulated glucagon release at a low glucose concentration (3.3 mmol/l), but failed both to affect glucagon secretion in the sole presence of glucose (3.3 mmol/l) and to suppress the inhibitory action of glucose 11.1 mmol/l upon glucagon output. In contrast to menadione, NH4Cl inhibited arginine-stimulated glucagon release at the low glucose concentration. The inhibitory action of glucose in high concentration upon glucagon release was not suppressed by NH4Cl. These findings do not permit to extrapolate to the A2-cell the concept that reduced pyridine nucleotides represent a major coupling factor in the nutritional regulation of hormonal release.