Hormonally active arginine-vasopressin suppresses endotoxin-induced fever in rats: lack of effect of oxytocin and a behaviorally active vasopressin fragment.

Vasopressin and oxytocin modulate memory processes which effects are dissociated from the typical peripheral endocrine effects of these neuropeptides. Recently, vasopressin has been implicated in the regulation of body temperature. In view of this, experiments were designed to determine whether the antipyretic effect of vasopressin was related to the action of the neuropeptide on memory processes. Fever was induced in rats by intracerebroventricular (i.c.v.) injection of 10 ng bacterial endotoxin (ET), which resulted in a rapid rise in colonic temperature. A second i.c.v. injection 15 min after ET administration of graded amounts (0.01, 0,1, 1 and 100 ng) or arginine-vasopressin (AVP) suppresses ET-induced fever in a dose-dependent manner, 1 ng being the minimally effective amount. Equivalent amounts of des-9-glycinamide-arginine-vasopressin (DG-AVP) or oxytocin (OXT) were ineffective. Large amounts (1,000 ng) of the latter two peptides, however, transiently mimicked the effect of AVP. On one-trial learning passive avoidance behavior, the neurohypophyseal peptides exerted a completely different pattern of effects. AVP and DG-AVP induced a dose-dependent facilitation, while OXT resulted in a dose-dependent attenuation of passive avoidance behavior. These findings suggest that AVP-induced antipyresis is related to the hormonally active AVP and dissociated from the effects of neurohypophyseal hormones and hormone fragments on other CNS processes-like learning and memory.