Differential effects of insulin on peripheral and visceral tissue protein synthesis in
neonatal pigs.
Davis, Teresa A., Marta L. Fiorotto, Philip R. Beckett, Douglas G. Burrin, Peter J. Reeds,
Diane Wray-Cahen, and Hanh V. Nguyen.
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, Texas 77030
APStracts 8:0023E, 2001.
We recently demonstrated in neonatal pigs that, with amino acids and glucose maintained
at fasting levels, the stimulation of protein synthesis in longissimus dorsi muscle with
feeding can be reproduced by a physiological rise in insulin alone. In the current report,
we determine whether the response of protein synthesis to insulin in the neonatal pig is 1)
present in muscles of different fiber types, 2) proportional in myofibrillar and
sarcoplasmic proteins, 3) associated with increased translational efficiency and ribosome
number, and 4) present in other peripheral tissues and in viscera. Hyperinsulinemic-
euglycemic-amino acid clamps were performed in 7- and 26-day-old pigs infused with 0,
30, 100, or 1,000 ng•kg«minus»0.66•min«minus»1 of insulin to reproduce insulin levels
present in fasted, fed, refed, and superphysiological conditions, respectively. Tissue
protein synthesis was measured using a flooding dose of l-[4-3H]phenylalanine. Insulin
increased protein synthesis in gastrocnemius muscle and, to a lesser degree, masseter
muscle. The degree of stimulation of protein synthesis by insulin was similar in
myofibrillar and sarcoplasmic proteins. Insulin increased translational efficiency but had
no effect on ribosome number in muscle. All of these insulin-induced changes in muscle
protein synthesis decreased with age. Insulin also stimulated protein synthesis in cardiac
muscle and skin but not in liver, intestine, spleen, pancreas, or kidney. The results
support the hypothesis that insulin mediates the feeding-induced stimulation of
myofibrillar and sarcoplasmic protein synthesis in muscles of different fiber types in the
neonate by increasing the efficiency of translation. However, insulin does not appear to
be involved in the feeding-induced stimulation of protein synthesis in visceral tissues.
Thus different mechanisms regulate the growth of peripheral and visceral tissues in the
neonate.
Received 22 June 2000; accepted in final form 23 January 2001
APS Manuscript Number E280-0.
Article publication pending Am J Physiol Endocrinol Metab
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 27 February 2001