In vitro pancreatic B-cell response of hyperinsulinemic rats. Differences between pregnancy and VMH-lesions.

We investigated in vitro the pancreatic B-cell response of hyperinsulinemic animals compared to that of controls with the aim of clarifying if the hyperinsulinemia is related to an alteration of the islet insulin secretion. Hyperinsulinemia was induced by pregnancy (observation at 19.5 days) and electrolytic lesions of the hypothalamic nucleus ventromedialis (2 days after lesion). The kinetics of the glucose dose/response curves (measured during a 60 min incubation period) differed markedly in the two hyperinsulinemic conditions. Whereas the islets from pregnant rats were characterized by a lowered glucose threshold, an enhanced half-maximal and maximal secretion rate, those of lesioned rats showed only an increased half-maximal and maximal secretion response in spite of a comparable islet insulin content. When culturing islets of hyperinsulinemic animals up to 6 days, the insulin secretion of those prepared from VMH-lesioned rats behaved identically to controls, whereas the islets of pregnant rats maintained their enhanced sensitivity at a glucose concentration of 5 mmol/l. These results confirm that the pancreatic B-cell response contributed significantly to the hyperinsulinemia, but different mechanisms are likely to be responsible for the altered B-cell secretion.