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

Abstract

Leucine appears to be the most effective single amino acid to trigger the activation of translation initiation factors that regulate protein synthesis in muscle. The effects of Leu in visceral tissues are not well understood. We hypothesized that enteral Leu supplementation of a low protein diet (LP) in neonatal pigs will acutely increase skeletal muscle and visceral tissue protein synthesis to a rate similar to that achieved by feeding a high protein diet (HP). Fasted 5‐d‐old piglets (n=21) were gavage fed at 0 and 60 min either: 1) LP diet, 2) low protein diet supplemented with Leu (LP+L) to equal HP diet, or 3) HP diet. Diets were isocaloric and lactose was equal. Fractional protein synthesis rates and translational control mechanisms were examined 90 min after feeding. Protein synthesis increased in longissimus dorsi, gastrocnemius, masseter, heart, jejunum, kidney and pancreas, but not liver, of the LP+L group compared to LP group alone and did not differ from HP group. LP+L and HP increased translational efficiency and phosphorylation of S6K1 and 4E‐BP1 in all tissues except liver. Our results suggest that low protein diets supplemented with leucine stimulates protein synthesis in muscle and most visceral tissues to a rate similar to that achieved by high protein diets and this stimulation involves activation of mTOR downstream effectors. (Supported by Ajinomoto Amino Acid Research Program and USDA 58‐6250‐6‐001).Grant Funding Source: Ajinomoto Amino Acid Research Program and USDA 58‐6250‐6‐001