Evidence that brain angiotensin II is involved in both thirst and sodium appetite in baboons

The roles of ANG II in the brain mechanisms subserving thirst and Na appetite in baboons were investigated by chronic intracerebroventricular infusions of ANG II and AT₁-receptor antagonists using subcutaneous miniosmotic pumps and by oral administration of captopril. ANG II at 3 or 5 μg/h for 7 days increased water intake from 2,455 ± 107 to 7,052 ± 562 ml/day by day 6 and 300 mM NaCl intake from 8.3 ± 1.1 to 275 ± 87 mmol/day by day 5. Concurrent intracerebroventricular losartan (300 μg/h) did not substantially reduce these responses, but they were abolished by intracerebroventricular ZD-7155 (50 μg/h). The increase of 300 mM NaCl intake when it was offered after intramuscular injection of furosemide, 2 mg · kg^-1 · day^-1 for 3 days, was unaltered by intracerebroventricular losartan (300 μg/h) but was reduced by intracerebroventricular ZD-7155 (50 μg/h) infused throughout Na depletion/repletion; oral captopril (1 g, 3 and 18 h before access to 300 mM NaCl) also reduced NaCl intake. Restriction of water intake to 25% of daily intake for 3 days caused a high intake of water on day 4, and this was reduced by intracerebroventricular losartan (300 μg/h) infused throughout the period of water restriction/rehydration. These novel results in a primate species suggest that brain ANG II is involved in both thirst and Na appetite, acting via AT₁ receptors.