Arginine vasopressin does not mediate the attenuated febrile response to intravenous IL-1 beta in pregnant rats

Rats have an attenuated febrile response to intravenous endogenous pyrogen [e.g., interleukin-1 beta (IL-1 beta)] near the term of pregnancy. The pres ent experiments were carried out on 25 nonpregnant and 32 pregnant rats to test the hypothesis that arginine vasopressin functioning as an endogenous antipyretic substance in the central nervous system mediates this attenuate d febrile response. An intravenous injection of recombinant rat IL-1 beta ( rrIL-1 beta) after intracerebroventricular vehicle produced a significant i ncrease in core temperature in both nonpregnant and pregnant animals, the m agnitude and duration of which was greater in the nonpregnant rats. In nonp regnant rats, intravenous rrIL-1 beta after intracerebroventricular vasopre ssin V-1-receptor antagonist accentuated the core temperature response comp ared with that observed with intravenous rrIL-1 beta after intracerebrovent ricular vehicle. In pregnant animals, however, intravenous rrIL-1 beta afte r intracerebroventricular vasopressin V-1-receptor antagonist produced a de crease in core temperature rather than an increase in core temperature, whi ch was observed with intravenous rrIL-1 beta after intracerebroventricular vehicle. Thus our data do not support the hypothesis that a pregnancy-relat ed activation of arginine vasopressin as an endogenous antipyretic substanc e in the central nervous system attenuates the febrile response to intraven ous rrIL-1 beta near the term of pregnancy in rats.