The effect on plasma insulin of elevating plasma glucose levels was studied in exteriorized sheep fetuses of 68 to 142 days conceptual age and in 2 lambs, 1 and 7 days old. Fetuses of less than 110 days showed, at most, only a very small and delayed rise in plasma insulin following an injection of glucose (1.67–3.45 g/kg body weight) into the umbilical vein. In 5 out of 6 fetuses of 110 days and older intravenous glucose (0.54–1.38 g/kg) was followed by a marked but delayed rise in plasma insulin reaching a peak 25–100 min after glucose administration. In the lambs intravenous glucose (1 g/kg) gave an immediate response in plasma insulin. Intraduodenal glucose was also seen to give a marked rise in plasma insulin in a 123 day fetus and 2 lambs. Intravenous fructose (0.65 and 0.55 g/kg) to two older fetuses caused no rise in plasma insulin although glucose given subsequently evoked a marked response. The onset of appearance of a marked response to glucose in the fetus was preceded by a proliferation of secondary islets in the pancreas. The changes in plasma insulin in the exteriorized fetuses and in 2 isolated fetuses suggest that the placenta must be relatively impermeable to insulin, fetal insulin must largely be derived from the fetal pancreas and fetal tissues must take up insulin.

Keywords:
Fetal, Neonatal, Sheep, Glucose, Insulin
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© 1973 S. Karger AG, Basel
1973
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