Increased protein degradation and decreased protein synthesis in skeletal muscle during cancer cachexia

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Abstract
The effects of progressive cachexia on protein metabolism in skeletal muscle has been investigated in mice bearing the MAC16 adenocarcinoma which produces cachexia with tumour burdens of < 1% of the host weight. Weight loss was accompanied by loss of whole body nitrogen in proportion to the overall loss of body mass. Using L-[4-3H]phenylalanine to label proteins in gastrocnemius muscle, a significant depression (60%) in protein synthesis occurred in animals with a weight loss between 15 and 30% accompanied by an increase in protein degradation, which increased with increasing weight loss between 15 and 30%. Muscle degradation in vitro could be achieved by serum from cachectic animals, which appeared to contain a proteolysis-inducing factor. These results suggest that the increased degradation of skeletal muscle seen in this model of cachexia may be due to a circulating proteolysis-inducing factor.