Circulating angiotensin II and drinking behavior in rats.

This study was designed to investigate the effects on water drinking of acute and chronic increases in circulating angiotensin II (ANG II) concentrations in rats. Experiments were conducted in male Sprague-Dawley rats chronically instrumented with femoral arterial and venous catheters and permanently housed in metal metabolism cages. ANG II was infused intravenously either acutely (30 min-2 h) or chronically (3 days) in a dose range of 10-60 ng/min. In no instance did such infusions cause a statistically significant increase in water intake. Other experiments examined the influence of ANG II (10 ng/min iv) on drinking elicited by infusion of hypertonic sodium chloride (1.5 M at 3.5 microliters/min). ANG II administration did not increase drinking to a hypertonic saline stimulus or lower the osmotic threshold for drinking. Nitroprusside (12 micrograms/min) was infused for 30 min to produce hypotension and drinking. Water intake associated with this stimulus was not changed by blocking ANG II formation with enalapril (2 mg/kg iv) or by concomitant infusion of ANG II (10 ng/min iv). Finally, plasma ANG II concentrations were measured before and after 1-h intravenous infusion of saline or ANG II to determine the levels of circulating ANG II produced by the infusion rates used here. It is concluded that the range of circulating ANG II concentrations found under most physiological conditions in rats does not directly stimulate drinking or participate importantly in osmotic or hypotension-induced drinking.