Protein Metabolism in Different Types of Skeletal Muscle During Early and Late Sepsis in Rats

Protein synthesis and degradation rates were measured in incubated soleus (SOL) and extensor digitorum longus (EDL) muscles 4, 8, and 16 hours following cecal ligation and puncture (CLP) in rats. No significant differences in protein synthesis between septic and control rats were found. The proteolytic rate in SOL muscle was increased by 36% eight hours after CLP and by 42% 16 hours after CLP. In EDL muscle, protein breakdown was not significantly increased until 16 hours after CLP, at which time it was 53% above the control value. The plasma amino acid pattern became increasingly deranged during the course of the study, and at 16 hours almost all individual amino acid levels were significantly different in septic rats compared with control rats. There was a significant positive correlation between plasma concentrations of phenylalanine, histidine, and ornithine and the proteolytic rate in EDL and SOL muscles, with the best correlation being found between phenylalanine concentration and proteolytic rate in SOL muscle. These results suggest that muscle wasting during sepsis is caused by increased protein breakdown, not by decreased protein synthesis, and that accelerated muscle proteolysis is an early phenomenon in sepsis.