BODY-TEMPERATURE RESPONSE TO IL-1-BETA IN PREGNANT RATS

Rats have an attenuated or absent febrile response to exogenous pyroge n (e.g., bacterial endotoxin) near term of pregnancy. With the aim of providing insight into possible mechanism(s) of the altered febrile re sponse to exogenous pyrogen, experiments have been carried out on 67 t ime-bred Sprague-Dawley rats to investigate the febrile response to en dogenous pyrogen [i.e., interleukin-1 beta (IL-1 beta)]. On day 23 of gestation, intravenous injection of IL-1 beta produced a significant i ncrease in body temperature with a latency of similar to 30 min and a duration of similar to 120 min. In contrast, on clays 17 and 21 of ges tation as well as on the day of delivery, intravenous injection of IL- 1 beta produced significant decreases in body temperature. Thus rats d o not develop fever in response to endogenous pyrogen near term of pre gnancy but rather become hypothermic. The mechanism of the altered bod y temperature response to exogenous pyrogen as pregnancy proceeds rema ins unknown. We speculate, however, that it most likely lies downstrea m from the formation of endogenous pyrogen.