Water deprivation-induced drinking in rats: role of angiotensin II

The role of angiotensin II in the control of water intake following deprivation of water for varying lengths of time was studied. Male rats were deprived of water for 0, 12, 24, 36, or 48 h. Water intakes were measured with and without pretreatment with the angiotensin I-converting enzyme inhibitor, captopril (50 mg/kg, ip). Captopril had no significant effect on water intake following either 0 or 12 h of water deprivation. However, captopril significantly attenuated water intake following 24-48 h of water deprivation with the magnitude of the attenuation increasing as the length of the period of water deprivation increased. Plasma renin activity was significantly increased over control levels after 24-48 h of water deprivation but not after 12 h of water deprivation. Plasma renin activity tended to increase as the length of the water-deprivation period increased. Serum osmolality and sodium concentration were significantly increased over control levels following 12-48 h of water deprivation. Serum osmolality and sodium concentration failed to show any further increases with increasing length of water deprivation beyond the increases following 12 h of water deprivation. The data indicate that the water intake of water-deprived rats can be divided into an angiotensin II-dependent component and angiotensin II-independent component. The angiotensin II-independent component appears to be more important in the early stages of water deprivation whereas the angiotensin II-dependent component becomes more important as the length of the water-deprivation period increases.