Protein metabolism in the tumour-bearing mouse. Rates of protein synthesis in host tissues and in an Ehrlich ascites tumour at different stages in tumour growth

We have investigated the time course of the changes in protein metabolism in skeletal muscle and liver in mice during the progression of growth of an Ehrlich ascites tumour. The rate of protein synthesis in muscle begins to fall very rapidly, and the decrease is clearly established by the time the tumour first becomes visible at 4 days after implantation of the cells. Liver protein synthesis increases substantially, and protein breakdown in muscle increases, but the onset of both these changes occurs later than the fall in muscle protein synthesis. A decrease in food intake in these animals occurs very rapidly after introduction of the cells. The fractional rate of protein synthesis in the tumour cells falls from 73%/day at 5 days to 26%/day at 12 days after injection, but on an absolute basis the rate of protein synthesis in the tumour at 5 days of growth is very small compared with that in muscle and liver. These results are consistent with the notion that the initial effects on muscle protein synthesis and food intake are brought about by humoral factors rather than as direct consequences of the metabolic demands of the growing tumour.