Thirst and Its Disorders

Fortunately most of us live under conditions where we are not forced to stay without water for so long that thirst becomes unendurable. In reality, our need for water is usually satisfied by anticipated and habitual, not thirst­ motivated, drinking occurring in the absence of any real water deficit. Nevertheless, an efficient thirst mechanism and appropriate regulation of vasopressin (antidiuretic hormone, ADH) secretion are indispensable for optimal water balance, the maintenance of which has very high homeostatic priority. During seVere dehydration the craving for water becomes excruciating and constitutes one of the most urgent needs experienced by man, as evi­ denced by the harrowing introspective descriptions of tormenting thirst quoted in Wolf's admirable monograph (1). Published more than two decades ago, that book remains an inestimable source of knowledge about thirst in man and the regulation of water intake in mammals. A valuable, up-to-date complement is Fitzsimons' recent monograph (2). In addition, the regulation of water intake, and the closely related regulation of ADH secretion, have in the last few years been subjects of extensive reviews (3-6). Therefore, this brief survey of thirst and its disorders may seem superfiuous. However, our aim is to condense the multiplex information presently avail­ able on the physiology and pathophysiology of thirst into a succinct, easily comprehensible view of the subject, and to discuss briefly some controver­ sies in the area.