AVP MEDIATES THE ATTENUATED FEBRILE RESPONSE TO ADMINISTRATION OF PGE(1) IN RATS NEAR-TERM OF PREGNANCY

Rats have an attenuated febrile response to intracerebroventricular in jection of PGE(1) near the term of pregnancy, the mechanism of which i s unknown. The present experiments were carried out to test the hypoth esis that arginine vasopressin (AVP), functioning as an endogenous ant ipyretic substance in the central nervous system, mediates this attenu ated febrile response. The febrile response to intracerebroventricular injection of 0.2 mu g PGE(1) was determined in pregnant and nonpregna nt rats after an intracerebroventricular injection of either vehicle o r a vasopressin V-1-receptor antagonist. After intracerebroventricular administration of vehicle, intracerebroventricular administration of 0.2 mu g PGE(1) produced significant increases in core temperature in both nonpregnant and pregnant animals. The increase in core temperatur e, however, was attenuated both in magnitude and duration in pregnant compared with nonpregnant animals. After intracerebroventricular admin istration of a vasopressin V-1-receptor antagonist, intracerebroventri cular administration of 0.2 mu g PGE(1) produced significant increases in core temperature that were similar in nonpregnant and pregnant ani mals. Our data support the hypothesis that a pregnancy-related activat ion of AVP as an endogenous antipyretic substance in the central nervo us system attenuates the febrile response to intracerebroventricular a dministration of PGE1 near term of pregnancy in rats.