Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2005
Publication Date: 7/24/2005
Citation: Escobar, J., Frank, J., Suryawan, A., Nguyen, H., Davis, T. 2005. Cardiac and skeletal muscle protein synthesis and activation of translation initiation factors are stimulated by leucine, but not isoleucine or valine, in neonatal pigs [abstract]. Journal of Animal Science, Proceedings from the 2005 Joint Annual Meeting of the American Dairy Science Association and the American Society of Animal Science. 83(Suppl. 1): abstract 390, p. 239. Interpretive Summary: Not required for an abstract.
Technical Abstract: Protein synthesis in skeletal muscle of neonatal pigs increases in response to a physiological increase in plasma leucine. However, the effect of a physiological increase in plasma isoleucine and valine on skeletal muscle protein synthesis has not been investigated in neonates. In the pig, the left ventricular wall grows about 3 times faster than the right ventricular wall during the first 10 d of postnatal life due to increased hemodynamic workload of the left ventricle. Therefore, the effects of individual branched chain amino acids on protein synthesis in the left and right ventricular walls, as well as individual skeletal muscles, were determined. Fasted pigs (5 d of age) were infused intra-arterially with saline or 400 umol•kg[-1]•h[-1] of leucine, isoleucine or valine and protein synthesis was measured after 60 min. Infusion of leucine, but not isoleucine or valine, increased (P < 0.05) phosphorylation of eukaryotic initiation factor (eIF) 4E binding protein-1, and increased the amount and phosphorylation of eIF4G associated with eIF4E in skeletal muscles composed primarily of white (longissimus dorsi) and red (masseter) muscle fibers, as well as in the left and right ventricular walls. Leucine, but not isoleucine or valine, increased the phosphorylation of ribosomal protein (rp) S6 kinase and rpS6 in longissimus dorsi and masseter but not in the left or right ventricular walls. Phosphorylation of elongation factor 2 was unaffected by treatment. The stimulation (P < 0.05) of protein synthesis by leucine was similar in longissimus dorsi, masseter, and left and right ventricular walls. Isoleucine and valine did not increase protein synthesis in cardiac or skeletal muscles. Thus, leucine, but not isoleucine or valine, stimulates protein synthesis in cardiac and skeletal muscles of neonates by increasing eIF4E availability for eIF4F assembly without affecting elongation factor activation.