Insulin-stimulated amino acid utilization during glucose and amino acid clamps decreases with development . Wray-Cahen, Diane, Philip R. Beckett, Hanh V. Nguyen, and Teresa A. Davis. United States Department of Agriculture, Agricultural Research Service, Children's Nutrition Research Center, and Endocrinology and Metabolism Section, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030
APStracts 4:0079E, 1997.
Neonatal animals utilize their dietary amino acids for protein accretion with high efficiency, and this efficiency declines during early life. The factors responsible for this developmental change are unknown. Our objectives were to determine whether amino acid (AA) utilization is stimulated by insulin in the neonate, and whether this response changes during the suckling period. Two hyperinsulinemic -euglycemic clamp infusion studies, using 10 to 2000 ng insulin/(kg0.66 x min), were performed in 7- and 26-day-old pigs. In study I, no AA were provided during the infusion, and the resultant decline in plasma AA levels was defined. In study II, plasma AA were clamped at near-fasting levels, and whole body utilization of exogenous AA was determined by measuring the rate of infusion of an AA mixture necessary to maintain basal plasma lysine concentrations. In study I, the ED50 for the fall in AA concentrations with increasing plasma insulin concentration was lower in 7- than in 26 -day-old pigs, and the nadir in AA concentration was achieved by only 20 [mu]U/ml of insulin. In study II, the utilization of exogenous AA during hyperinsulinemic-euglycemic AA clamps exhibited a higher Rmax (49 vs. 26 [mu]mol AAtotal x min-1 x kg-1) and a lower ED50 (18 vs. 45 [mu]U insulin/ml) in 7- than in 26-day-old pigs. Plasma urea nitrogen concentrations did not rise with increasing insulin and AA infusion rates. These results indicate that insulin stimulates the utilization of exogenous AA in neonatal pigs and that both the insulin sensitivity and responsiveness of AA utilization decline over the suckling period. The infused AA were likely utilized for protein accretion. 

Received 4 November 1996; accepted in final form 21 March 1997.
APS Manuscript Number E555-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 15 April 1997