Leucine Oxidation and Protein Turnover in Clofibrate-induced Muscle Protein Degradation in Rats

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Abstract

Treatment of hyperlipidemia with clofibrate may result in development of a muscular syndrome. Our previous investigation (1979. J. Clin. Invest.64: 405.) showed that chronic administration of clofibrate to rats causes myotonia and decreases glucose and fatty acid oxidation and total protein of skeletal muscle. In the present experiments we have investigated amino acid and protein metabolism in these rats. Clofibrate administration decreased the concentration of all three branched-chain amino acids without affecting those of others in muscle. Studies to examine the mechanism of decreases in muscle concentrations of branched-chain amino acids showed the following: (a) Plasma concentration of leucine was decreased, whereas there was no significant change in the concentration of isoleucine and valine. (b) Liver concentrations of all three branched-chain amino acids remained unaltered. (c) The uptake of cycloleucine (a nonmetabolizable analogue of leucine) by both muscle and liver was unaffected. (d) The percentage of a trace amount of injected [1-14C]leucine expired as 14CO2 in 1 h was significantly increased. (e) The capacity of muscle homogenate for α-decarboxylation of leucine was enhanced, whereas that of liver was unaffected. (f) The activity of leucine transaminase was unaffected, whereas that of α-ketoisocaproate dehydrogenase was increased in muscle.

Authors

Harbhajan S. Paul, Siamak A. Adibi