Fluid deprivation in enuresis--effect on urine output and plasma arginine vasopressin.

Desmopressin responders tend to have a large volume of urine production at night, in contrast to desmopressin refractory patients who often produce normal volumes of urine. Controls and adolescent/adult primary monosymptomatic nocturnal enuretics were included in a study measuring urine volume and plasma vasopressin levels before and during a 24-hour water deprivation test. The results indicate a significantly higher urine production in desmopressin responders when compared with controls and non-responders. Before fluid deprivation, only the nocturnal polyuric patients showed a urine osmolality significantly lower than that of controls and desmopressin non-responders. A significant decrease in the clearance of osmols was evident in the desmopressin refractory group from day to night. All three groups showed a significant increase in plasma vasopressin during fluid deprivation, with polyuric, desmopressin-responding patients showing a lower increase that the non-responders and controls. Plasma vasopressin levels were normal in adolescent and adult enuretics regardless of their response to desmopressin. Moreover, response to fluid deprivation in both polyuric and enuretic patients resulted in a significant decrease in urine output from the first to the second night.