Interleukin-1b fever in rats: gender difference and estrous cycle influence

Mouihate, A., X. Chen, and Q. J. Pittman. Interleukin-1b fever in rats: gender difference and estrous cycle influence. Am. J. Physiol. 275 (Regulatory Integrative Comp. Physiol. 44): R1450–R1454, 1998.—Evidence exists to support the concept of sex difference in immune system activation by pyrogenic cytokines. In this study, fever development was monitored to analyze the effect of peripheral administration of interleukin (IL)-1b (1 μg/kg) in adult male and cycling or ovariectomized female rats with or without ovarian hormonal replacement. In male and randomly cycling female rats, a similar increase in body temperature occurred after intraperitoneal IL-1b injection. Two representative stages of estrus with higher and lower levels of ovarian hormones (proestrus and diestrus, respectively) were chosen for study of the febrile response induced by IL-1b. The fever induced by IL-1b was found to be significantly higher and more prolonged in females at proestrus than at diestrus. The differential fever response seems to be mainly linked to the ovarian hormonal levels because bilaterally ovariectomized females, supplemented with sequential injections of estradiol 17b and progesterone, showed a significantly higher IL-1b fever than did ovariectomized rats receiving estradiol 17b only. These results indicate that gonadal hormones can influence fever development and raise the possibility of interaction between sex hormones and thermogenesis in females during the estrous cycle.