Differential regulation of protein synthesis by amino acids and insulin in peripheral and visceral tissues of neonatal pigs

Authors: SURYAWAN, AGUS - Children'S Nutrition Research Center (CNRC); O'CONNOR, PAMELA M - Children'S Nutrition Research Center (CNRC); BUSH, JILL - Children'S Nutrition Research Center (CNRC); NGUYEN, HANH - Children'S Nutrition Research Center (CNRC); DAVIS, TERESA - Children'S Nutrition Research Center (CNRC)

Submitted to: Amino Acids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2008
Publication Date: 8/6/2008
Citation: Suryawan, A., O'Connor, P.M.J., Bush, J.A., Nguyen, H.V., Davis, T.A. 2009. Differential regulation of protein synthesis by amino acids and insulin in peripheral and visceral tissues of neonatal pigs. Amino Acids. 37(1):97-104.

Interpretive Summary: The high rate of protein synthesis is needed to support the rapid growth of young children. Protein synthesis is a process using numerous, naturally occurring, and complex combinations of amino acids [an acids that is essential to the diet]; thus, allowing the body to make protein that is vital to the living cells within the body. Feeding is an important factor for stimulation of protein synthesis. In this study, we used very young pigs as model to demonstrate a child’s development. We found feeding can cause a rise in insulin and amino acids (AA), and are factors required to stimulate protein synthesis. Our results show, that insulin and AA are essential to induce protein synthesis in different types of muscles. For skin, we found that insulin alone is enough to support protein synthesis. Likewise, AA alone can also induce protein synthesis in internal organs such as liver and lungs. In summary, the results tell us that after feeding, the increased levels of insulin and AA are responsible for increases in tissue protein synthesis, which ultimately supports muscle growth during early childhood.

Technical 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 approximately 0, 2, 6 and 30 microU ml (-1) insulin to simulate below 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-(3) H] 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.