Role of the renin-angiotensin system in the control of vasopressin secretion in conscious dogs.

The present studies were designed to evaluate the physiological significance of angiotensin II in the control of vasopressin secretion in conscious dogs. They demonstrated that exogenous angiotensin II (10 ng/kg per min) increased vasopressin secretion more when the pressor effect of angiotensin II was abolished. The fact that endogenous angiotensin II levels are normally increased without an increase in arterial pressure suggests that angiotensin II may play a greater role in the control of vasopressin secretion than was previously thought. The present study also evaluated the role of endogenous angiotensin II in the control of vasopressin secretion during sodium depletion, a state in which angiotensin II levels are elevated. Intracarotid infusion of a low dose of the angiotensin II antagonist, saralasin, decreased plasma vasopressin concentration, suggesting that endogenous angiotensin II acts in an area of the brain perfused by the carotid arteries to stimulate vasopressin secretion in sodium-deprived dogs. Finally, the present experiments evaluated the role of angiotensin II in baroreceptor reflex control of vasopressin secretion. Baroreflex function was assessed by examining the relationship between the change in blood pressure and the log of the change in vasopressin secretion over a range of blood pressure levels. Exogenous angiotensin II (10 ng/kg per min) altered baroreflex function by causing a shift of this relationship to a higher pressure level in sodium-replete dogs. In sodium-depleted dogs, inhibition of the renin-angiotensin system with saralasin or captopril produced an opposite shift. These results suggest that endogenous angiotensin II may be necessary for the maintenance of normal baroreflex control of vasopressin secretion during sodium depletion. Collectively, these results support the hypothesis that endogenous angiotensin II plays a role in the control of vasopressin secretion.