Abstract
In most mammalians, the homeostasis of body temperature is maintained within a narrowly defined range by autonomic and behavioral thermoregulatory responses. The same is also true that most mammalians are able to maintain their body temperatures at slightly lower than usual levels when they are constantly exposed to higher or lower than usual thermoneutral environmental temperature. These altered body temperatures are results of adaptation to new thermal environments, and underlying mechanisms of such alterations are well documented. In the present study, we examined a question whether repeated changes of environmental temperature exert any influence on animals. For this purpose, levels of plasma corticosterone, activity of animals, and their deep core temperature were monitored in rats while environmental temperature was changed with differing magnitude that was maintained for differing period of time. The deep core temperature was monitored using telemetry system. It was found that when environmental temperature was repeatedly changed with 1h cycle between 4C and 27C, plasma levels of corticosterone in this animal group were significantly higher than those of animals constantly exposed to 4C for the same period of time. It was also found that the former group exhibited higher levels of locomotion and core temperature than the latter group. The results are discussed in terms of thermal stress. [Jpn J Physiol 54 Suppl:S228 (2004)]
