Insulin-glucagon substrate interrelationships in the neonatal sheep

Abstract

The pancreatic alpha and beta cell responses to glucose and deoxyglucose infusion were studied in nine healthy newborn lambs at 24 to 36 hours of age. Steady-state glucose infusion resulted in a significant, though obtunded, increase in plasma insulin concentrations within 45 minutes; glucose/insulin ratios were higher than fetal values observed in similar studies (5.6 vs. 0.88, p < 0.001), indicating a more significant role of insulin in stimulating glucose disposal in the newborn period than in the fetal period. Glucose infusion resulted in a paradoxical rise in plasma glucagon concentrations (360 to 500 pg. per milliliter, p < 0.05). Deoxyglucose infusions did not evoke significant changes in plasma insulin concentrations but there was an increase in plasma glucagon levels (300 to 480 pg. per milliliter, p < 0.05). These data indicate residual immaturity of insulin and glucagon secretion mechanisms in the neonatal period and suggest that such immaturity may be important in the abnormalities of glucose homeostasis in the newborn period.