Supplementing L-leucine to a low-protein diet increases tissue protein synthesis in weanling pigs

Amino Acids. 2010 Nov;39(5):1477-86. doi: 10.1007/s00726-010-0612-5. Epub 2010 May 15.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amino Acids / blood
  • Animals
  • Blood Glucose / analysis
  • Dietary Proteins / administration & dosage*
  • Dietary Supplements*
  • Eukaryotic Initiation Factor-4E / metabolism
  • Insulin / blood
  • Leucine / administration & dosage*
  • Muscle Proteins / biosynthesis*
  • Muscle, Skeletal / metabolism
  • Organ Size
  • Phosphorylation
  • Ribosomal Protein S6 Kinases / metabolism
  • Sirolimus / metabolism
  • Swine
  • Weaning


  • Amino Acids
  • Blood Glucose
  • Dietary Proteins
  • Eukaryotic Initiation Factor-4E
  • Insulin
  • Muscle Proteins
  • Ribosomal Protein S6 Kinases
  • Leucine
  • Sirolimus