Effects of 2-G exposure on temperature regulation, circadian rhythms, and adiposity in UCP2/3 transgenic mice

Altered ambient force environments affect energy expenditure via changes in thermoregulation, metabolism, and body composition. Uncoupling proteins (UCPs) have been implicated as potential enhancers of energy expenditure and may participate in some of the adaptations to a hyperdynamic environment. To test this hypothesis, this study examined the homeostatic and circadian profiles of body temperature (T(b)) and activity and adiposity in wild-type and UCP2/3 transgenic mice exposed to 1 and 2 G. There were no significant differences between the groups in the means, amplitudes, or phases of T(b) and activity rhythms at either the 1- or 2-G level. Percent body fat was significantly lower in transgenic (5.2 +/- 0. 2%) relative to the wild-type mice (6.2 +/- 0.1%) after 2-G exposure; mass-adjusted mesenteric and epididymal fat pads in transgenic mice were also significantly lower (P < 0.05). The data suggest that 1) the actions of two UCPs (UCP2 and UCP3) do not contribute to an altered energy balance at 2 G, although 2) UCP2 and UCP3 do contribute to the utilization of lipids as a fuel substrate at 2 G.