The polyuric syndromes.

The cardinal element of understanding the water repletion reaction includes the following features. First, the system is deliberately redundant. For example, vasopressin release can be driven either by a 2% increase in extracellular fluid osmolality or by a rather larger—approximately 10%—decrease in circulating fluid volume. Second, water acquisition is driven not only by water conservation but also by thirst, the latter being mediated by angiotensin II formed intracerebrally. Finally, stimulation of the oropharyngeal reflex can modulate both vasopressin release and thirst. The negative feedback for the system involves yet another hormone, atrial natriuretic peptide, which suppresses both vasopressin release and angiotensin II release within the central nervous system. ADH release