Contribution of inert mass to experimental cancer cachexia in rats

An inert artificial tumor (AFT) was inflated in male F344 rats to simulate, experimentally, the growth in mass of large transplantable tumors that produce cachexia. The AFT depressed host weight gain and skeletal muscle mass up to 30% and food intake up to 20% of the depression induced by tumors of comparable size. When the growth rate of the AFT was low, there was no depression of food intake. Work-induced hypertrophy of skeletal muscles, as assessed by a gastrocnemius tenotomy model, was approximately equal to that of normal, tumor-bearing, and AFT-bearing animals. The AFT elevated host total energy expenditure by 12.5% and compartment-of-energy expenditure attributable to motor activity by 10.5%. The elevation of energy expenditure accounted for most of the depression of weight gain of AFT-bearing animals below that of intact animals. The large mass of most transplantable tumors leads to an overestimate of the malignant tissue-depletive effects of tumor and an under-estimate of the asthenic effects.