Oxygen consumption in mice (I strain) after feeding.

To determine if excess heat production can account for the lower fat accumulation in I strain mice, oxygen consumption, a measure of energy expenditure, was measured in I mice and C57BL mice (a control strain) to determine basal metabolic rate (BMR) and resting metabolic rate (RMR) and response to food consumption and acute cold exposure. Oxygen consumption was higher in the I strain than in the C57BL mice only after the dark cycle (feeding period). No difference between I and C57BL mice in spontaneous activity was found during the dark or light cycle. Body temperature was also not different in I and C57BL mice. Oxygen consumption in response to norepinephrine was similar in the two strains. These results indicate oxygen consumption is greater in I than C57BL mice only in response to feeding. Differences in glucose utilization by I and C57BL mice, including a lower glucose tolerance curve, greater deposition of glucose to muscle glycogen and lactate production in I mice also indicate differences in nutrient processing. Higher oxygen consumption after feeding in I mice than in C57BL mice indicates inefficient food utilization and accounts for their lower ability to store energy as fat.