Tolbutamide infused into the chronically catheterized sheep fetus produced significant secretion of insulin. An optimal dose range of 100-200 mg/kg estimated fetal weight was demonstrated. Paired tolbutamide and glucose infusions using a square wave technique demonstrated that although early phase insulin secretion is diminished in the fetus, this is not due to an absolute deficiency of stored insulin. Tolbutamide produced peak insulin concentrations of 51.6 ± 9.0 μu/ml by 20 min postinfusion in the fetus. When similar tolbutamide infusions were performed in neonatal lambs, qualitatively similar insulin response curves were demonstrated although peak insulin levels were much greater (260 ± 70 μu/ml at 20 min). A fall in plasma glucose was demonstrated in both fetal and neonatal lambs (to 75 and 39% of control values, respectively) by 60 min after tolbutamide infusion. In the fetus, this fall was not associated with changes in maternal glucose concentration. The maturation of early phase insulin secretion in the neonate may involve a variety of factors beyond storage of insulin. The ability of the neonate to respond briskly to alterations in plasma glucose may be highly significant in an adaptation to 'feast-fast' conditions. The hypoglycemia produced in response to endogenously secreted insulin in the fetus and neonate is consistent with insulin's role in accelerating glucose uptake and utilization.
|Original language||English (US)|
|Number of pages||4|
|State||Published - 1979|
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health