• Wen Xu, Kaiwen Bai, Jintian He, Weipeng Su, Li Dong, Lili Zhang, and Tian Wang.
• College of Animal Science and Technology, Nanjing Agricultural University, Nanjing, China.
• Nutrition. 2016 Jan 1; 32 (1): 114-21.

ObjectiveLeucine has been reported to alter the gene expression of proteins, the activation of signaling components, and the fractional rates of protein synthesis in multiple organs of piglets. The aim of this study was to investigate the effects of leucine on molecular mechanisms regulating protein synthesis and degradation in skeletal muscle and determine how these adaptations affect body weight gain in intrauterine growth retardation (IUGR) pigs.MethodsThirty-two weaned piglets were randomly assigned to the following four experimental groups (n = 8 per group): normal birth weight, normal birth weight supplemented with leucine, IUGR, and IUGR supplemented with leucine. Piglets were fed from 14 to 35 d of age. Growth performance, major serum biochemical parameters, and enzyme activities were evaluated. The messenger RNA expression of muscle mammalian target of rapamycin (mTOR), muscle atrophy F-box (MAFbx), and muscle-specific ring finger-1 were investigated. Additionally, total and phosphorylated levels of mTOR and ribosomal protein S6 kinase 1 were measured in longissimus muscle.ResultsAverage daily weight gain and average daily feed intake were increased by leucine in IUGR pigs. At the end of the experiment, IUGR pigs had lower liver and kidney weight compared with the normal piglets. However, IUGR supplemented with leucine decreased serum concentration of urea. Leucine supplementation affected the concentrations of isoleucine, valine, lysine, and phenylalanine in serum. There was no significant difference in the expression of mTOR and muscle-specific ring finger-1 in IUGR piglets, whereas muscle atrophy F-box was reduced only by IUGR dependent of leucine. Compared with the IC group, dietary supplementation with 0.35% l-leucine increased the phosphorylated levels of mTOR and ribosomal S6 kinase 1 in IUGR piglets.ConclusionsThe present study identified a major role for leucine in the activation of the mTOR signaling pathway and reducing muscle atrophy in IUGR piglets, which contributed significantly to differences in body weight gain.Copyright © 2016 Elsevier Inc. All rights reserved.

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