Effect of exercise on synthesis and degradation of muscle protein.

Several reports have shown that amino acid utilization via oxidation and gluconeogenesis is increased during exercise. The purpose of this study was to investigate whether these changes are accompanied by alterations in protein synthesis and degradation in the muscle of exercising rats. One group of rats was made in swim for 1h and then protein synthesis and protein degradation were measured in a perfused hemicorpus preparation. Protein synthesis was decreased and protein degradation was increased in exercised rats compared with sedentary control rats. Exercise also decreased amino acid incorporation by isolated polyribosomes from muscle. Measurement of several muscle proteinase activities demonstrated that exercise had no effect on alkaline proteinase or Ca2+-activated proteinase. However, the free (unbound) cathepsin D activity was elevated in muscle of exercised rats, whereas the total activity of catepsin D was unchanged. This increase in the proportion of free cathepsin D activity suggests that lysosomal enzymes may be involved in the increased protein degradation that was observed.