Acute effect of water on blood pressure. What do we know?

Water drinking elicits a large, acute, pressor response in patients with autonomic failure who experience severe orthostatic hypotension. This essentially cost-free intervention has been successfully employed therapeutically in these patients to attenuate orthostatic and postprandial hypotension. In orthostatic intolerance patients, water drinking blunts the orthostatic tachycardia but has only a modest effect on blood pressure. Water drinking also has effects on blood pressure and heart rate in normal subjects, although the actions are more subtle. The cardiovascular effects seem to be in part mediated through sympathetic activation. The exact mechanism that causes the sympathetic activation is not known.