Cerebral sodium/angiotensin interaction studied by RIA-determination of urinary arginine vasopressin in the hydrated goat.

Radioimmunoassay determination of urinary arginine vasopressin (AVP) was employed to study quantitatively cerebral Na+/angiotensin II (A II) interaction in the hydrated goat. The solutions infused for 30 min at 0.02 ml/min into the lateral cerebral ventricle were: a) Hypertonic (0.25 M) NaCl, b) AII (0.3 ng/kg min) in isotonic (0.15 M) NaCl, and c) A II (doses as in b) in 0.25 M NaCl. The mean amounts of AVP detected in the urine in response to the various infusions were: a) 2.8 ng, b) 3.6 ng, and c) 13.3 ng. Thus, the A II/NaCl stimulation induced a detected renal excretion of AVP that was two times as large as the sum of the effects recorded in response to separate stimuli. Infusion c) invariably induced a pronounced, long-lasting inhibition of the water diuresis, intense thirst, and natriuresis. The corresponding effects of infusions a) and b) were much weaker and, as regards thirst and natriuresis, inconsistent. The determinations of renal AVP excretion provide additional, and rather direct evidence for the concept of a synergistic action of elevated cerebrospinal fluid [Na+] and A II as concerns cerebral control of fluid balance. With regard to this kind of interaction, the observed dipsogenic and natriuretic effects mainly confirm earlier observations.