Insulin, a possible regulator of ketosis in newborn and suckling rats

Abstract

A possible regulatory role of insulin in the development of ketosis in newborn and suckling rats was investigated. The average plasma concentration of total ketone bodies measured at birth was 0.414 ± 0.037 (μmol/ml. Within 24 hr after birth the level of ketones had increased to 4 times its initial value. The 3- to 4-fold increase in plasma ketones was maintained during the first 5 days of life but started to decline thereafter. Plasma insulin of newborn rats at birth (62 ± 8 μU/ml) was comparable to that of fed adult rats (85 ± 10 μU/ml). The levels decreased to 28 μU/ml on the first day of life and stayed low throughout the suckling period despite a tendency to increase at the time close to weaning. The capacities for ketone production in liver homogenates of suckling rats were inversely related to the levels of insulin. Administration of insulin (0.125 mU/g body weight, im) and glucose (1.75 mg/g body weight, ip) both suppressed plasma ketone bodies in suckling rats. Insulin administration increased plasma insulin but failed to decrease plasma glucose. Injection of glucose increased plasma insulin and glucose. Neither insulin nor glucose treatment changed the plasma levels of free fatty acids. These data suggest that a limited availability of insulin permits a high rat of ketogenesis and hence induced ketosis in newborn and suckling rats. Developing rats suckled by their dams derive most of their energy from the high fat and low carbohydrate content of milk. The low concentration of insulin in suckling rats not only minimizes utilization of glucose by insulin-dependent tissues but permits a rapid synthesis of ketone bodies that then serve as energy sources for extrahepatic tissues, particularly the brain. Consequently, the energy requirements of suckling rats can be met with a reduced risk of hypoglycemia. Further studies on the effect of insulin on lipolysis, fatty acid oxidation, and ketone synthesis in vitro could add to our understanding of the action of insulin in reversing ketosis of suckling rats. © 1976 International Pediatric Research Foundation, Inc.