Abstract
Body temperature (Tb) is different between male and female, e.g. daily change in Tb is fluctuated with menstruation cycle in female rats. We hypothesized that estrogen plays a crucial role in the sex difference in Tb. Methods (1) Daily change of Tb was measured after gonadectomy in male and female rats. After the measurement, silicon tubes containing 17-beta estradiol (E2) crystalline, aimed to maintain blood estrogen constant, were subcutaneously placed in the rats. Then Tb measurement was repeated. (2) Thermoregulation during 2-h heat exposure at 34°C or cold exposure at 5°C was assessed in gonadectomized female rats, and the same protocol was conducted in those with E2 tubes. Results (1) Compared with male rats, Tb rhythm in female gonadectomized rats became unstable, showing 2-4 h irregular oscillations. Tb rhythm remained unchanged in male gonadectomized rats. In female gonadectomized rats with E2 tubes, Tb rhythm returned to the normal level. However, there was no influence of E2 on Tb rhythm in the male rats. (2) Both in the heat and cold, gonadectomized female rats could not maintain their Tb as those with E2 tubes. Histological analysis for the rat brain showed that Fos-immunoreactive cells in the hypothalamus were smaller in the rats without E2 tubes. Conclusion These results show that estrogen is involved in the thermoregulation in female rats. Estrogen may modulate thermal sensitivity to the environment at the level of the hypothalamus [J Physiol Sci. 2006;56 Suppl:S102]
