抄録
Introduction Body temperature is finely regulated, although feeding condition is a factor modulating the regulation. Fasting is a strong stimulus reducing metabolism (i.e. heat production). However, body temperature is well maintained in the active phase, indicating change in thermoregulation. I discuss about neural and hormonal mechanisms involved in the change in thermal regulation during fasting and the possible role of clock genes. Experiments and Results 1) Fasting induced greater reduction of metabolism and its circadian amplitude. Although the reduction of heat production, body temperature rhythm was well maintained except for greater decrease of body temperature around the lights onset. During the fasting, body surface temperature was greatly reduced, meaning that heat loss mechanisms were suppressed. 2) During fasting, heat producing response to the cold was attenuated in rats. However, this response is attenuated in the presence of i.c.v. leptin. 3) Feed-fast cycle generated daily oscillation of body temperature in clock mutant and cry knockout mice, both mice could not modulate heat loss responses to the fasting. 4) Fasting affects neural activities in the suprachiasmatic nucleus, estimated by c-Fos expression. Conclusion Fasting is a strong signal modulating thermal regulation. Leptin level in the central may be a factor to change metabolic activity, deactivating the sympathetic nerves to the brown adipose tissue. Moreover, circadian clock receive fasting signals, which may alter heat loss responses and maintain body temperature rhythm. [J Physiol Sci. 2007;57 Suppl:S32]
