Centrally Mediated Effects of Sodium and Angiotensin II on Arterial Blood Pressure and Fluid Balance

Four kinds of infusions were made for 1 h periods into the 3rd cerebral ventricle of hydrated, conscious goats: 1) Angiotensin in hypertonic NaCI, 2) angiotensin in slightly hypotonic NaCI, 3) angiotensin in isotonic d‐glucose, and 4) hypertonic NaCI. The influence of these infusions on carotid blood pressure and fluid balance was studied. The infusions of angiotensin in hypertonic NaCl had conspicuous hypertensive, dipsogenic, antidiuretic and natriuretic effects. More moderate responses of the same kinds were obtained during the infusions of hypertonic NaCl and of angiotensin in slightly hypotonic NaCI. In contrast, no or only weak effects were obtained by the infusions of angiotensin in isotonic d‐glucose. The results are taken as support for the idea that a Na + sensitive system in the vicinity of the 3rd ventricle may be of importance in the central contml of fluid balance and arterial blood pressure. Such a system may be influenced by the Na + concentration of the cerebrospinal fluid, and angiotensin may either sensitize it to Na+ or make it more exposed to Na + ions.