Central effects of angiotensin II and dopamine in sodium-depleted sheep

The effects of intracerebroventricular (IVT) infusion of angiotensin II (ANG II), the converting enzyme inhibitor SQ 20881, and dopamine were studied in 15 conscious Na-depleted sheep. IVT ANG II (25 ng/min) significantly increased plasma aldosterone (163 +/- 24%) and vasopressin (ADH) (533 +/- 100%). Plasma renin activity (PRA) was decreased to 64 +/- 10% of basal. IVT SQ (1 microgram/min) decreased aldosterone to 70 +/- 10% and ADH to 55 +/- 9% of basal. PRA increased to 124 +/- 10%. There were no significant changes in plasma Na, K, or cortisol levels nor in mean arterial or intracranial pressure after either infusion. Increasing the dose of SQ to 10 micrograms/min resulted in an increased magnitude of change in the same variables. IVT SQ (1 microgram/min) significantly decreased aldosterone level in five nephrectomized sheep. The responses to IVT dopamine (20 micrograms/min) were qualitatively similar to those elicited by IVT SQ. These data support the existence of an endogenous brain renin-angiotensin system (RAS) independent of the renal RAS. ANG II acts centrally to regulate plasma ADH, aldosterone, and PRA levels. The similarity of the responses to SQ and dopamine suggests that a dopaminergic pathway may be involved in these responses.