Muscle Protein Metabolism during Compensatory Growth with Changing Dietary Lysine Levels from Deficient to Sufficient in Growing Rats

  • ISHIDA Aiko
    Molecular Nutrition Research Team, National Institute of Livestock and Grassland Science Graduate School of Life and Environmental Sciences, University of Tsukuba
  • KYOYA Takahito
    Molecular Nutrition Research Team, National Institute of Livestock and Grassland Science United Graduate School of Agricultural Science, Tokyo University of Agriculture and Technology
  • NAKASHIMA Kazuki
    Molecular Nutrition Research Team, National Institute of Livestock and Grassland Science
  • KATSUMATA Masaya
    Molecular Nutrition Research Team, National Institute of Livestock and Grassland Science

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Livestock and laboratory animals show compensatory growth when they are fed ad libitum following a period of restriction feeding. Lysine is a major limiting essential amino acid in the diets both for humans and animals. We hypothesized that changing dietary lysine levels from deficient to sufficient induced compensatory growth in young rats. We elucidated the effect of lysine sufficiency on the dynamics of hormones, relevant to muscle protein synthesis and degradation, insulin-like growth factor-I (IGF-I) and corticosterone, and on the expression of proteolytic-related genes in skeletal muscle during compensatory growth. Lysine sufficiency where the dietary lysine level was increased from 0.46% to 1.30% after 2 wk of subjecting the rats to the lower lysine level induced 80% enhancement of growth rate of rats. During compensatory growth with the lysine sufficiency, fractional muscle protein synthesis rates were higher whereas fractional muscle protein degradation rates were lower than those of the control group (p<0.05). After lysine sufficiency, the expression of atrogin-1/MAFbx mRNA was decreased in gastrocnemius muscle (p<0.05). With the lysine sufficiency, serum IGF-I concentration increased (p<0.05) whereas serum corticosterone decreased (p<0.05). These findings suggest that compensatory growth with lysine sufficiency is due to a change of hormone levels before and after changing diets, resulting in incrementation of protein synthesis and suppression of protein degradation of skeletal muscle.

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