Effects of temperature on protein turnover in isolated rat skeletal muscle.

To understand the net loss of muscle protein during fever and the possible changes in body protein balance with hyperthermia, we investigated the influence of temperature on protein synthesis and degradation in rat skeletal muscles. In the incubated soleus, extensor digitorum longus, or diaphragm, net protein degradation increased by about 11%/degrees C between 33 and 42 degrees C. This loss of muscle protein resulted from an increase in protein degradation (172% between 33 and 42 degrees C). By contrast, protein synthesis increased by only 25% between 33 and 39 degrees C and fell markedly by 42 degrees C. Unlike muscle, in isolated rat hepatocytes, protein breakdown did not increase significantly between 36 and 39 degrees C. The stimulation of protein degradation between 36 and 39 degrees C was not reduced by leupeptin or Ep-475, which inhibit lysosomal thiol proteases and reduce net protein degradation in the incubated muscles. Prostaglandin E2 (PGE2) has been implicated in the accelerated muscle proteolysis during fever. However, PGE2 release by muscles was unchanged between 33 and 42 degrees C, and inhibition of PGE2 synthesis by indomethacin did not reduce the stimulation of proteolysis at 40 degrees C. This catabolic effect of increased temperature may contribute to the negative nitrogen balance during fever.