Effect of different leucine supplementation in low protein diet on Protein Synthesis and Activation of Translation Initiation Factors of Weaned Piglets

Abstract

Acute administration of L‐leucine stimulates protein synthesis in skeletal muscle of young pigs. However, little is known about a role for the chronic enteral feeding of leucine in regulating the activity of translation initiation factors, nutrient utilization, or growth of the neonate. Eighteen 21‐day crossbred pigs with an average live body weight 8 kg were assigned randomly to one of three groups and feed with low protein dietaries (16% crude protein) containing 1.3%, 1.6%, or 1.9% leucine which meets the marginal, adequate and excess leucine requirement of piglets respectively. At 35 d old, protein synthesis was measured and blood samples were obtained at 15, 30, 45min after infusion for metabolite analysis and the abundance and phosphorylation state 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. The results shows that excess leucine could increase (P < 0.05) the fractional synthesis rate (FSR) of heart, posterior small intestine, kidney, liver, spleen, stomach and pancreas compared with pigs adequate and marginal group. Data in the present study also show that excess leucine could increase positive translation initiation factors activity in liver and muscle compared with marginal leucine group. These findings suggest that, despite the activation of positive translation initiation factors, adequate availability of essential amino acids may be necessary for leucine to stimulate muscle protein synthesis in young pigs.