Components of energy expenditure in tumor-bearing animals

Single snapshot measurements of resting energy expenditure (REE) suggest that hypermetabolism contributes to cancer cachexia, but tumor impact on total 24-hr energy expenditure (TEE) is unknown. Automated multicage indirect calorimetry was employed to measure daily energy expenditure in adult Buffalo rats (n = 16) randomized to tumor inoculation or controls. Measurements included baseline REE, activity EE (AEE), thermic response to food (TEF), and TEE. Rats (n = 16) were randomized. Metabolic measurements, tumor size, and body weight were recorded weekly. Animals were sacrificed at Week 5 for analysis of host and tumor composition. Significant depletion of total lean body mass occurred in TB rats (greater than 15% wt loss, ANOVA P less than 0.001) which inversely correlated with tumor growth (r = -0.81, P less than 0.001). REE, TEF, AEE, and TEE did not change in controls (ANOVA P = n.s.). In TB rats, a 19.5% increase in REE occurred (119.4 +/- 3.3 to 138.7 +/- 1.8 kcal/kg LBM/day, P less than 0.01). TEE remained unchanged (157.3 +/- 5.6 vs 152.9 +/- 3.6 kcal/kg LBM/day, P = n.s.) due to a 66% decrease in AEE (32.9 +/- 3.1 to 10.5 +/- 1.7 kcal/kg LBM/day, P = 0.01). TEF did not change (4.7 +/- 0.8 vs 5.0 +/- 0.3 kcal/kg LBM/day, P = n.s.). Both TB and controls demonstrated a decreased REE in response to a 24-hr fast (7.9% vs 4.8%, P = n.s.). Respiratory quotient decreased in both groups when comparing fed to fasted values: TB (0.86 to 0.76) and controls (0.86 to 0.71), but the decline was greater in controls (P = 0.04).(ABSTRACT TRUNCATED AT 250 WORDS)