INFLUENCE OF PREGNANCY ON THE FEBRILE RESPONSE TO INTRACEREBROVENTRICULAR ADMINISTRATION OF PGE(1) IN RATS

Rats have an attenuated or absent febrile response to exogenous pyroge n (e.g., bacterial endotoxin) and endogenous pyrogen (e.g., interleuki n-1 beta) near term of pregnancy. The present experiments have been ca rried out on 19 nonpregnant and 18 time-bred pregnant Long-Evans rats to investigate the febrile response to intracerebroventricular (ICV) a dministration of prostaglandin E(1) (PGE(1)). Each rat was anesthetize d, a biotelemetry device mas placed in the peritoneal cavity for measu rement of body core temperature (T-bc), and guide cannulas were placed above the lateral cerebral ventricles for ICV injection of PGE(1). At least 6 days were allowed to lapse between surgery and the experiment s. ICV injection of 0.2 mu g PGE(1) produced significant increases in T-bc in both nonpregnant and pregnant animals (day 19 of gestation). T he increase in T-bc as well as the fever index, however, were signific antly attenuated in the pregnant compared with the nonpregnant rats. V ehicle had no effect on T-bc or fever index in either group of animals . The attenuated febrile response to PGE(1) in the pregnant rats may h ave resulted from a pregnancy-related activation of endogenous antipyr etics and/or impaired thermoregulatory effector mechanisms.