Leucine Supplementation of a Low-Protein Meal Increases Skeletal Muscle and Visceral Tissue Protein Synthesis in Neonatal Pigs by Stimulating mTOR-Dependent Translation Initiation

Protein synthesis and eukaryotic initiation factor (elF) activation are increased in skeletal muscle of neonatal pigs parenterally infused with amino acids Leucine appears to be the most effective single amino acid to trigger these effects To examine the response to enteral leucine supplementation overnight food deprived 5-d-old pigs were gavage fed at 0 and 60 min a 1) low-protein diet (LP) 2) LP supplemented with leucine (LP+L) to equal leucine in the high-protein diet (HP) or 3) HP diet Diets were isocaloric and equal in lactose Fractional protein synthesis rates and translation initiation control mechanisms were examined in skeletal muscles and visceral tissues 90 min after feeding Protein synthesis rates in longissimus dorsi gastrocnemius and masseter muscles heart jejunum kidney and pancreas but not liver were greater in the LP+L group compared with the LP group and did not differ from the HP group Feeding LP+L and HP diets compared with the LP diet increased phosphorylation of mammalian target of rapamycin (mTOR) 4E-binding protein 1, ribosomal protein S6 kinase-1 and elF4G and formation of the active elF4E elF4G complex in longissimus dorsi muscle In all tissues except liver activation of mTOR effectors increased in pigs fed LP+L and HP vs LP diets Our results suggest that leucine supplementation of a low-protein meal stimulates protein synthesis in muscle and most visceral tissues to a rate similar to that achieved by feeding a high-protein meal and this stimulation involves activation of mTOR downstream effectors J Nutr 140 2145-2152 2010