Abstract
Kei Nagashima, Dept Physiol, Waseda Univ Sch Human Sci
A reduction in body temperature during fasting in rats
Body temperature (Tb) is determined by the balance between heat production and heat loss. In rats, Tb is linked with heat production during free-feeding. Fasting reduces the production of heat throughout a day; however, Tb is maintained during the dark phase and decreases markedly during the early light phase. The reduction in Tb would protect animals from excessive heat loss, minimizing the temperature difference between the body and environment. Temperature of the tail, reflecting active heat loss, also decreases during the fasting. These results indicate that rats suppress heat loss to maintain Tb. However, the suppression is weaker in the light phase than dark phase, which would be a mechanism involved in the reduction in Tb. Although it still remains unclear if rats control the phase-specific change in thermoregulation, a couple of evidences proving the possibility are presented in this symposium. When the suprachiasmatic nucleus (SCN, the master clock for circadian rhythm) are lesioned, the reduction in Tb does not occur, although metabolic heat production decreases in the same manner as the sham-operated rats. Moreover, when rats are exposed to constant darkness, the reduction is attenuated and the phase of the reduction is delayed. These results suggest that the reduction of Tb occurs in response to the stimulus originating the SCN. Moreover, the light is an important factor for this response. In summary, the reduction of Tb during low energy storage would be a regulated phenomenon linked with biological rhythm. [Jpn J Physiol 54 Suppl:S56 (2004)]
