Systemic angiotensin II and volume expansion release norepinephrine in thepreoptic recess

The periventricular tissue surrounding the anteroventral portion of the thi rd cerebral ventricle (AV3V) of the preoptic recess is critical for several responses evoked by central and peripheral angiotensin II (ang II), and th e natriuresis produced by extracellular fluid volume expansion. In addition , several other studies have suggested that the presser and natriuretic res ponses evoked by these stimuli are regulated by activation of noradrenergic systems in AV3V tissue. The purpose of the present experiments was to dire ctly determine if i.v. infusion of ang II and volume expansion increase nor epinephrine release in the AV3V area using in vivo microdialysis. Male, Spr ague-Dawley rats were implanted with microdialysis probes in the AV3V and w ere tested conscious and unrestrained. Dialysate was collected before, duri ng, and following i.v. administration of ang II or phenylephrine which rais ed blood pressure 40-50 mmHg, or volume expansion with isotonic saline. Dia lysate norepinephrine concentrations from these rats were compared to dialy sate norepinephrine content from animals which received no treatment. Both i.v. infusion of ang II and isotonic volume expansion significantly increas ed dialysate norepinephrine concentration, while infusion of phenylephrine did not alter norepinephrine release in AV3V tissue. These data demonstrate that peripheral ang II and volume expansion selectively increase norepinep hrine release in the AV3V region, and are consistent with the conclusion th at activation of noradrenergic systems in the AV3V region contribute to car diovascular and drinking responses evoked by peripheral ang II and to natri uresis following volume expansion. (C) 2000 Elsevier Science B.V. All right s reserved.