Abstract
Introduction We have reported that estrogen has influence on thermoregulation in the heat and cold. In ovariectomized rats, in the heat, an increase in body temperature (Tb) was greater with a reduction in heat dissipation from the skin. In the cold, Tb was smaller with a decrease in metabolic heat production. However, 17β-estradiol (E2) replacement restores these responses to normal levels. The purpose of the present study was to test the hypothesis that the estrogen fluctuation in normal estrus cycle would modulate the thermoregulary response to the cold in rats. Methods Female WKY rats were laparectomized and radiotelemeters for Tb were placed. At least 2 wks after the surgery, rats' vaginal smear was obtained to determine the estrus cycle. At 9 am, rats in proestrus or diestrus period were exposed to 5°C or 25°C environment for 2 h, and Tb was monitored. After the cold exposure, rats were perfused with phosphate buffered saline and the brains were excised. cFos immunoreactive cells in the hypothalamic area were counted. Results Tb increased in the cold in the proestrus period, but decreased in the diestrus period. Plasma E2 was higher in the proestrus period than estrus period with a small difference in progesterone level. cFos immunoreactive cells in the medial preoptic area and dorsomedial hypothalamus were greater in the proestrus period. Conclusion Thermoregulation in the cold differs among the periods of estrus cycle in rats. The fluctuation of plasma E2 level may be involved in the mechanism. [J Physiol Sci. 2008;58 Suppl:S60]
