Heat production in cold and long scotophase acclimated and winter acclimatized rodents

Heat production by means of oxygen consumptionVo₂ (at T_a = 6° C, 25° C, 30° C, and 32° C) and non-shivering thermogenesis (NST) were studied in individuals of a diurnal rodent (Rhabdomys pumilio) and a nocturnal rodent (Praomys natalensis). The studied mice were acclimated to cold at T_a=8°C with a photoperiod of LD 12:12. On the otherhand specimens of these two species were acclimated at T_a=25°C with a long scotophase LD8:16. The results were compared with a control group (T_a=25° C, LD 12:12) and winter acclimatized individuals of both species.Vo₂ in cold acclimated mice of both species was significantly increased when compared to the control group and was even higher than the winter acclimatized group when measured below the lower critical temperature. Long scotophase acclimated mice of both species also increased their oxygen consumption significantly when compared to the control group. NST was significantly increased in long scotophase acclimated mice from both species when compared to the control group. The results of this study indicate that the effects of acclimation to long scotophase are similar to those of cold acclimation. As changes in photoperiod are regular, it may be assumed that heat production mechanisms in acclimatization to winter will respond to changes in photoperiodicity.