Central vasopressin pretreatment sensitizes phosphoinositol hydrolysis in the rat septum

Previous in vivo and in vitro studies have demonstrated that exposure of the brain to arginine vasopressin (AVP) can potentiate various responses to a second central challenge with AVP. To determine whether this sensitization is mediated by changes at the receptor level, we investigated the effects of AVP on the phosphoinositide metabolism in septal slices prepared from rats centrally pretreated with saline or AVP. Addition of vasopressin (10(-7) M, 10(-6) M) to septal slices from saline-pretreated rats failed to elicit a significant stimulation of inositol-1-phosphate (IP1). In contrast, AVP (10(-7) M) significantly stimulated IP1 release in septal slices prepared from rats pretreated intracerebroventricularly (i.c.v.) 24 h earlier with 10 or 100 ng AVP. Pretreatment with the same i.c.v. doses of AVP also induced a significant enhancement of the carbachol-induced stimulation of IP1 release, but i.e.v. pretreatment with carbachol did not stimulate the IP1 release in response to AVP. Our results suggest that a novel facilitation of phosphoinositide metabolism can be induced by central AVP pretreatment.