Recent work with young pigs shows that reducing
dietary protein intake can improve gut function after weaning but results in inadequate provision of
essential amino acids for muscle growth. Because acute administration of
L-leucine stimulates
protein synthesis in piglet muscle, the present study tested the hypothesis that supplementing
L-leucine to a
low-protein diet may maintain the activation of translation
initiation factors and adequate
protein synthesis in multiple organs of post-weaning pigs. Eighteen 21-day pigs (Duroc×Landrace×Yorkshire) were fed
low-protein diets (16.9% crude
protein) supplemented with 0, 0.27 or 0.55%
L-leucine (total
leucine contents in the diets being 1.34, 1.61 or 1.88%, respectively). At 35 days of age,
protein synthesis was determined using the [2H]
phenylalanine flooding-dose technique. Additionally, total and phosphorylated levels of
mammalian target of rapamycin (mTOR),
ribosomal protein S6 kinase 1 (S6K1), and eIF4E-binding protein-1 (4E-BP1) were measured in longissimus muscle and liver. Compared with the control group, dietary supplementation with 0.55%
L-leucine for 2 weeks increased (P<0.05): (1) the phosphorylated levels of S6K1 and 4E-BP1; (2)
protein synthesis in skeletal muscle, liver, the heart, kidney, pancreas, spleen, and stomach; and (3) daily
weight gain by 61%. Dietary supplementation with 0.27%
L-leucine enhanced (P<0.05)
protein synthesis in proximal small intestine, kidney and pancreas. These novel findings provide a molecular basis for designing effective nutritional means to increase the efficiency of nutrient utilization for
protein accretion in neonates.