Different dynamics of insulin secretion in the perfused pancreas of mouse and rat

The dynamics of insulin release were studied in the perfused pancreas of rats and mice. Perfusion of the rat pancreas with 20 mM D-glucose resulted in the classical biphasic release of insulin with a rising second phase. However, in normal C57BL/KsJ-mice and non-inbred mice, whether fed or starved, the second phase was nearly constant. The secretory dynamics of KsJ-mice were essentially the same, whether the glucose concentration was 30 or 20 mM, whether the medium contained 2.56 or mM Ca2+, and whether or not the medium was supplemented with 5 mM pyruvate, 5 mM glutamate, and 5 mM fumarate. Insulin secretion in these mice was almost totally inhibited by omission of Ca2+, and was markedly enhanced by 3-isobutyl-1-methylxanthine. Insulin release during the constant phase was reversed by lowering the glucose concentration. A second rise of glucose from 3 to 20 mM produced a secretory pattern very similar to the first response. These studies indicate that the dynamics of insulin secretion are somewhat different in rats and mice. Since similar results were obtained with C57BL/KsJ-mice and non-inbred mice, the liability of KsJ-mice to develop beta-cell failure when stressed by the mutated db gene is not related to the constancy of the second insulin secretory phase.