Effect of forebrain lesions on response to chronic intraventricular angiotensin II.

We previously reported that chronic (10 days) intracerebroventricular (ivt) infusion of angiotensin II (ANG II) into conscious rabbits produced a significant rise in mean arterial pressure (MAP), water intake (WI), and urinary sodium excretion (UNaV), and a significant fall in plasma sodium (PNa) and potassium (PK) concentrations. Urinary potassium excretion (UKV) and body fluid volume were not changed significantly. In the present experiments, similar chronic infusions were carried out in intact rabbits and in rabbits with an electrolytic lesion placed in the anteroventral third cerebral ventricle (AV3V) region. Integrity of the AV3V area is essential for normal expression of a variety of acute physiological responses to ANG II injected into the brain. In rabbits with AV3V lesions, chronic ivt infusion of ANG II did not significantly alter MAP, but WI and fractional UNaV increased, and PNa decreased in a manner identical to that of sham-lesioned control rabbits. Plasma and extracellular fluid volumes increased, and body weight and food intake decreased in all rabbits during ANG II infusion, but to a slightly greater extent in the AV3V-lesioned rabbits. We conclude that an intact AV3V region is crucial for the hypertensive effect of chronic ivt fusions of ANG II in the rabbit but is not necessary for most of the fluid and electrolyte alterations associated with such infusions.