Insulin Secretion in the Perinatal Period of the Rat in Vivo and in Vitro Effects of Glucose and Gibenclamide (HB 419)

During the perinatal period of the rat the effect of glucose and glibenclamide (HB 419) on the secretion of insulin was studied in vivo and in vitro. In the in vitro experiments isolated islets of 21 day old fetal and 5 day old newborn rats were perifused wtih 16.7 mM glucose or 16.7 mM glucose plus 1 mug/ml glibenclamide, while in the in vivo ecperiments glucose, 0.5 g/kg of body weight, or glibenclamide, 0.5 mg/kg of body weight were tested. Glucose elicited a small first phase of insulin release in 21 days old fetal islets, while glucose plus glibenclamide evoked a biphasic pattern. The injection of glibenclamide to the mother lowered the blood sugar in the fetus and increased the fetal serum insulin concentration. In one day old newborn rats glibenclamide stimulated the secretion of insulin after an i.p. injection. Glucose was without effect. Both substances increaseded the serum insulin concentration in five day old newborn animals. Dynamic studies at that age revealed a monophasic response to glucose and a biphasic pattern to glucose plus glibenclamide.