Enhancement of Myofibrillar Proteolysis Following Infusion of Amino Acid Mixture Correlates Positively with Elevation of Core Body Temperature in Rats

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  • YAMAOKA Ippei
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.
  • MIKURA Mayumi
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.
  • NISHIMURA Masuhiro
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.
  • DOI Masako
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.
  • KAWANO Yuichi
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.
  • NAKAYAMA Mitsuo
    New Product and Business Development Department, Research and Development Center, Otsuka Pharmaceutical Factory, Inc.

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Abstract

Administration of an amino acid (AA) mixture stimulates muscle protein synthesis and elevates core body temperature (Tb), as characteristically found under anesthetic conditions. We tested the hypothesis that not only AA given, but also AA produced by degradation of endogenous muscular protein are provided for muscle protein synthesis, which is further reflected in Tb modifications. Rats were intravenously administered an AA mixture or saline in combination with the anesthetic propofol or lipid emulsion. We measured plasma 3-methylhistidine (MeHis) concentrations as an index of myofibrillar protein degradation, rectal temperature and mRNA expression of atrogin-1, MuRF-1 and ubiquitin in gastrocnemius and soleus muscles of rats following 3 h infusion of test solutions. Tb did not differ significantly between conscious groups, but was higher in the AA group than in the saline group among anesthetized rats. Plasma MeHis concentrations were higher in the AA group than in the saline group under both conditions. Plasma MeHis levels correlated positively with Tb of rats under both conditions. AA administration decreased mRNA levels of atrogin-1 and ubiquitin in gastrocnemius muscle and all mRNA levels in soleus muscle. These results suggest that AA administration enhances myofibrillar protein degradation and that the change is a determinant of Tb modification by AA administration. However, the mechanisms underlying AA administration-associated enhancement of myofibrillar proteolysis remains yet to be determined.

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