Energy metabolism in nongrowing mice with sarcoma.

The time course of energy metabolism has been studied in weight-stable and nongrowing mice with a transplantable methylcholanthrene-induced sarcoma. Daily oxygen consumption and carbon dioxide production were measured in relation to the tumor growth from the time of tumor implantation. The time course of energy dynamics was related to the end-state changes in body composition. Freely fed sarcoma-bearing mice decreased their whole-body energy expenditure in proportion to the tumor growth. This was due to the accompanying anorexia. The alteration in oxygen consumption and carbon dioxide production was continuously evident 24 hr/day in sarcoma-bearing mice. The tumor-bearing mice lost body fat and had decreased respiratory quotient, while pair-fed controls maintained their body composition, and their respiratory quotients agreed with the food respiratory quotient. Loss of body lipids in freely fed sarcoma-bearing mice reflected a negative energy balance, accompanied with increased fat oxidation, while maintenance of body composition in pair-fed controls reflected a decreased metabolic rate. Sarcoma-bearing mice showed a significantly higher energy expenditure in relation to their food intake compared to that of pair-fed controls. Estimates of partition of oxygen uptake in sarcoma-bearing mice support that both the host and the tumor account for the elevated energy expenditure. This study has confirmed a small but significantly increased energy expenditure in sarcoma-bearing mice, which was continuously present 24 hr/day in spite of unlimited availability of food. This illustrates the fatal outcome of experimental cancer.