Urinary aquaporin-2 excretion in nocturnal enuresis

Objective: To evaluate the role of the arginine vasopressin (AVP)-aquaporin -2 (AQP-2) axis in the pathogenesis of nocturnal enuresis. Study participants: Twelve children (seven male and five female), aged 11.6 +/-4.3 (6.7-15.6) years, suffering from primary monosymptomatic nocturnal enuresis and 12 healthy children, matched for sex and age. Enuretic childre n were further subdivided into responders and non-responders to treatment w ith 1-desamino-8-D-AVP (DDAVP). Methods: Serum concentrations of AVP, and plasma and urine osmolality were measured at night (0100, 0400 and 0700 h), together with nocturnal urinary excretion of AQP-2 (2000-0800 h). Magnetic resonance imaging (MRI) of the p ituitary gland was carried out to evaluate the amount of AVP stored in the posthypophysis. Results: Mean AVP serum concentrations were similar in patients and control s. Urinary AQP-2 was also similar in patients and controls, but responders had a significantly lower level of AQP-2 than non-responders (P<0.005). Pla sma osmolality was greater in patients than in controls (P<0.001), whereas urinary osmolality was similar in both groups. No difference in the ratio o f the signal intensity of the posterior lobe of the hypophysis to that of t he pons (AVP content) was found between patients and controls or between re sponders and non-responders. Conclusion: A decreased urinary excretion of AQP-2 is associated with, and seems to have a role in, nocturnal enuresis, at least in some children, and this could also explain why only some of them respond to DDAVP treatment.