Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 4/27/2007
Publication Date: 7/8/2007
Citation: Escobar, J., Nguyen, H.V., Davis, T.A. 2007. Differential effects of leucine on translation initiation factor activation and protein synthesis in skeletal muscle, renal and adipose tissues of neonatal pigs [abstract]. Journal of Animal Science, Proceeding of the 2007 Annual Meeting of the American Society of Animal Science, July 8-12, 2007, San Antonio, Texas. 85(Suppl. 1):618, p. 441. Interpretive Summary:
Technical Abstract: In adult rats, protein synthesis in skeletal muscle and adipose tissue increases in response to pharmacological doses of leucine (Leu) administered orally. In neonatal pigs, a physiological increase in plasma leucine stimulates protein synthesis in skeletal muscle without increasing hepatic protein synthesis. However, the effect of a physiological increase in plasma leucine on renal and adipose tissue on protein synthesis has not been investigated in neonates, an anabolic population highly sensitive to amino acids and insulin. Thus, 11 crossbred pigs were food-deprived for 14 h and intra-arterially infused with Leu (0 or 400 µmol•kg(-1)•h(-1)). Protein synthesis and the activation of translation initiation factors were measured after 60 min in gastrocnemius muscle, kidney, and adipose. We have previously shown that this Leu infusion protocol increases plasma Leu to levels that mimic the physiological postprandial level. The elevation in plasma Leu increased the phosphorylation of eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1) in gastrocnemius muscle and kidney (P < 0.0001) and adipose tissue (P = 0.06). Infusion of Leu increased (P < 0.04) the phosphorylation of ribosomal protein (rp) S6 kinase (S6K1) in gastrocnemius muscle and adipose tissue but not in kidney (P = 0.21). A concomitant increase (P < 0.03) in the phosphorylation of rpS6 was measured in gastrocnemius muscle and adipose tissue but not in kidney (P = 0.12). Fractional rates of protein synthesis were increased in gastrocnemius muscle (P = 0.003) but not in adipose (P = 0.29) or renal (P = 0.64) tissues. The results show that a physiological increase in plasma leucine in neonatal pigs stimulates protein synthesis in skeletal muscle in association with the activation of translation initiation factors. However, leucine does not increase protein synthesis in adipose or renal tissues despite increased activation of translation initiation factors.