P1.98 Jan. 4 The contribution of shivering and nonshivering thermogenesis to summit metabolism in deer mice VAN SANT, Matthew J*; HAMMOND, Kimberly A; Univ. of California, Riverside email@example.com
Small mammals acclimated to cold have been shown to have higher cold induced maximum metabolic rates (VO2sum) than animals acclimated in warm environments. Studies have also shown that cold acclimation increases brown adipose tissue. It is often assumed that the increase in VO2max is due to an increase in brown adipose tissue which increases nonshivering thermogenesis (NST). It is possible that the prolonged shivering associated with cold acclimation leads to “training effects” in the muscle that increase the efficiency of shivering thermogenesis (ST). Nonshivering thermogenesis is thought to be a much more efficient way to produce heat than shivering, so increasing brown adipose tissue in response to cold acclimation seems more likely than increasing ST. We used deer mice (Peromyscus maniculatus) to test the hypothesis that VO2sum increases after cold acclimation primarily due to increases in NST. We acclimated 27 deer mice to 5ºC for eight weeks and acclimated 30 deer mice to 22ºC for eight weeks. We then measured VO2sum and BMR. An injection of norepinephrine was administered to all animals to stimulate NST while concurrently measuring oxygen consumption. Cold acclimated animals did have a higher VO2sum than the warm acclimated animals as expected. VO2sum consists of the sum of BMR, NST and ST, allowing us to use our data to estimate ST. We will explain how cold acclimation impacts NST and ST capacity. We will also explain the relative importance of NST and ST with regards to VO2sum in deer mice. These results further explain the effects of cold acclimation and the physiological mechanisms animals use to survive in cold environments.