Dynamics of glucose-induced plasma insulin increase in the rat fetus at different stages of gestation. Effects of maternal hypothermia and fetal decapitation.

The effect of glucose on the release of insulin from the pancreas of 19.5- to 21.5-day-old rat fetuses has been studied in utero. Fetal hyperglycemia was induced by a square-wave glucose infusion into pregnant rats over a period of 150 min. The infusion of glucose raised the fetal blood glucose concentration to that of the mother and induced a rapid increase of plasma insulin levels on day 19.5 of gestation. There was a progressive rise of the insulin response as the gestation proceeded, with an increase of the two phases of the hormonal secretion. Maternal hypothermia induced by pentobarbital anesthesia decreased markedly the insulin response to hyperglycemia in the mothers and their fetuses. In fetuses decapitated on day 18.5 and studied on day 21.5, the increase of plasma insulin concentration after a 1-hour hyperglycemia was similar to that in the littermate control fetuses.