Abstract
The high efficiency of protein deposition during the neonatal period is driven by high rates of protein synthesis, which are maximally stimulated after feeding. In the current study, we examined the individual roles of amino acids and insulin in the regulation of protein synthesis in peripheral and visceral tissues of the neonate by performing pancreatic glucose–amino acid clamps in overnight-fasted 7-day-old pigs. We infused pigs (n = 8–12/group) with insulin at 0, 10, 22, and 110 ng kg−0.66 min−1 to achieve ~0, 2, 6 and 30 μU ml−1 insulin so as to simulate below fasting, fasting, intermediate, and fed insulin levels, respectively. At each insulin dose, amino acids were maintained at the fasting or fed level. In conjunction with the highest insulin dose, amino acids were also allowed to fall below the fasting level. Tissue protein synthesis was measured using a flooding dose of l-[4-3H] phenylalanine. Both insulin and amino acids increased fractional rates of protein synthesis in longissimus dorsi, gastrocnemius, masseter, and diaphragm muscles. Insulin, but not amino acids, increased protein synthesis in the skin. Amino acids, but not insulin, increased protein synthesis in the liver, pancreas, spleen, and lung and tended to increase protein synthesis in the jejunum and kidney. Neither insulin nor amino acids altered protein synthesis in the stomach. The results suggest that the stimulation of protein synthesis by feeding in most tissues of the neonate is regulated by the post-prandial rise in amino acids. However, the feeding-induced stimulation of protein synthesis in skeletal muscles is independently mediated by insulin as well as amino acids.
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Acknowledgments
We thank J. C. Stubblefield for care of animals and L. F. Weiser for secretarial assistance. This work is publication of the United States Department of Agriculture/Agricultural Research Service (USDA/ARS) Children’s Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine. This project has been funded in part by National Institutes of Health (NIH) grant AR-44474 and by the USDA/ARS under Cooperative Agreement no. 6250510000-33.
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Suryawan, A., O’Connor, P.M.J., Bush, J.A. et al. Differential regulation of protein synthesis by amino acids and insulin in peripheral and visceral tissues of neonatal pigs. Amino Acids 37, 97–104 (2009). https://doi.org/10.1007/s00726-008-0149-z
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DOI: https://doi.org/10.1007/s00726-008-0149-z