Effect of bicarbonate on the arginine-induced insulin and glucagon secretion in vitro

The isolated perfused rat pancreas was used to investigate the effect of extracellular bicarbonate concentration (25 and 40 mmol/l) on the arginine-induced insulin and glucagon release with or without 5.5 mmol/l glucose in the perfusate. In the absence of glucose, the insulin response to arginine was increased at 40 mmol/l bicarbonate, while no potentiation by glucose of the arginine-induced insulin release, at this bicarbonate concentration, was observed. At 40 mmol/l bicarbonate, glucose inhibition of basal glucagon release was abolished. In contrast, the glucagon response to arginine was not affected by the bicarbonate concentration in the perfusion medium. These results confirm that the bicarbonate concentration in the medium markedly influences the insulin release from the isolated perfused rat pancreas, while the glucagon response to arginine seems to be less sensitive to changes in extracellular bicarbonate concentration.