Effects of ambient temperature on adaptive thermogenesis during maintenance of reduced body weight in mice

Ravussin Y, LeDuc CA, Watanabe K, Leibel RL. Effects of ambient temperature on adaptive thermogenesis during maintenance of reduced body weight in mice. Am J Physiol Regul Integr Comp Physiol 303: R438-R448, 2012. First published July 3, 2012; doi:10.1152/ajpregu.00092.2012.-We showed previously that, at ambient room temperature (22 degrees C), mice maintained at 20% below their initial body weight by calorie restriction expend energy at a rate below that which can be accounted for by the decrease of fat and fat-free mass. Food-restricted rodents may become torpid at subthermoneutral temperatures, a possible confounding factor when using mice as human models in obesity research. We examined the bioenergetic, hormonal, and behavioral responses to maintenance of a 20% body weight reduction in singly housed C57BL/6J +/+ and Lep(ob) mice housed at both 22 degrees C and 30 degrees C. Weight-reduced high-fat-fed diet mice (HFD-WR) showed similar quantitative reductions in energy expenditure-adjusted for body mass and composition-at both 22 C and 30 C: -1.4 kcal/24 h and -1.6 kcal/24 h below predicted, respectively, and neither group entered torpor. In contrast, weight-reduced Lep(ob) mice (OB-WR) housed at 22 degrees C became torpid in the late lights-off period (0200-0500) but did not when housed at 30 C. These studies indicate that mice with an intact leptin axis display similar decreases in absolute energy expenditure in response to weight reduction at both 22 degrees C and 30 degrees C ambient temperature. More importantly, the percent decrease in total energy expenditure observed in the HFD-WR compared with AL mice is much greater at 30 degrees C (-19%) than at 22 degrees C (-10%). Basal energy expenditure demands are similar to 45% lower in mice housed at 30 degrees C vs. 22 degrees C, since the mice housed at thermoneutrality do not allocate extra energy for heat production. The higher total energy expenditure of mice housed at 22 degrees C due to these increased thermogenic demands may mask physiologically relevant changes in energy expenditure showing that ambient temperature must be carefully considered when quantifying energy metabolism in both rodents and humans.