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

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 mumol/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 muU/ml) was comparable to that of fed adult rats (85 +/- 10 muU/ml). The levels decreased to 28 muU/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 was 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 rate of ketogenesis and hence induced ketosis in newborn and suckling rats.