EFFECT OF INTRACEREBROVENTRICULAR ADMINISTRATION OF VASOPRESSIN ON STRESS-INDUCED HYPERTHERMIA IN RATS

Vasopressin has been reported to be an endogenous antipyretic peptide. The present study assessed whether this peptide has similar effects o n stress-induced hyperthermia. Infusion of 3 ng of vasopressin into th e lateral ventricle prior to a 40-min restraint stress reduced signifi cantly the hyperthermic response of rats to this stress, compared to s aline-injected controls. Half of the vasopressin-injected animals show ed an immediate hypothermic response, with a significant reduction in body temperature of 0.34 degrees C or more within 10 min; however, the effect of vasopressin on stress-induced hyperthermia remained signifi cant after exclusion of these animals from the analysis. Administratio n of a V-1 receptor antagonist prior to the stress did not affect the hyperthermic response, which may suggest that the hyperthermic respons e had reached maximal (ceiling) levels. Administration of vasopressin, or of the V-1 receptor antagonist immediately after the stress, did n ot affect defervescence, suggesting that vasopressinergic systems are not implicated in the defervescence process. Thus, the results show th at ICV admininstration of vasopressin reduces stress-induced hyperther mia. The mechanisms underlying the effects remain to be elucidated.