Indirect calorimetry of mice.

WT and Ctrp7-KO mice fed an LFD or HFD for 26 wk were used for simultaneous assessments of daily body weight change, food intake (corrected for spillage), physical activity, and whole body metabolic profile in an open-flow indirect calorimeter (CLAMS, Columbus Instruments, Columbus, OH). Data were collected for three consecutive days to confirm that mice were acclimated to calorimetry chambers (indicated by stable body weights, food intakes, and diurnal metabolic patterns), and data from the fourth day were analyzed. Rates of oxygen consumption (V̇o₂) and carbon dioxide production (V̇co₂) in each chamber were measured throughout the studies. Respiratory exchange ratio (RER; V̇co₂/V̇o₂) was calculated by CLAMS software (version 4.02) to estimate relative oxidation of carbohydrates (RER = 1.0) vs. fats (RER = 0.7), not accounting for protein oxidation. Energy expenditure (EE) was calculated as EE = V̇o₂ × [3.815 + (1.232 × RER)]. V̇o₂, V̇co₂, and EE data were normalized to body mass. Physical activity was measured by infrared beam breaks in the metabolic chamber. Average metabolic values were calculated per subject and averaged across subjects for statistical analysis.