Journal of the American Society of Nephrology
Clinical Nephrology
Urinary Aquaporin 2 and Calciuria Correlate with the Severity of Enuresis in Children
VALENTI, GIOVANNA*; LAERA, ANTONIA*; PACE, GIUSEPPE†; ACETO, GABRIELLA‡; LOSPALLUTI, MARIA L.‡; PENZA, ROSA‡; SELVAGGI, FRANCESCO P.†; CHIOZZA, MARIA L.§; SVELTO, MARIA*
*Department of General and Environmental Physiology, University of Bari, Italy.
†Department of Emergency and Transplantation (DETO), University of Bari, Italy.
‡Department of Developmental Age Biomedicine, University of Bari, Italy.
§Department of Pediatrics, University of Padova, Italy.
Correspondence to Dr. Giovanna Valenti, Dipartimento di Fisiologia Generale ed Ambientale, Via Amendola 165/A, 70126 Bari, Italy. Phone: 390-805-443-444; Fax: 390-805-443-388; E-mail: [email protected]
Accepted March 10, 2000
Received January 21, 2000
Abstract
This study examined the hypothesis that nocturnal enuresis might be paralleled by aquaporin 2 (AQP2) urinary excretion. Eighty children who experienced nocturnal enuresis were studied and compared with 9 healthy children. The 24-h urine samples were divided into two portions: night collections and day collections. Creatinine equivalents of urine samples from each patient were analyzed by Western blotting. AQP2 levels were semiquantified by densitometric scanning and reported as a ratio between the intensity of the signal in the day urine sample versus the night urine sample (D/N AQP2 ratio). The D/N AQP2 ratio was 0.59 ± 0.11 (n = 9) in healthy children and increased to 1.27 ± 0.24 (n = 10) in a subpopulation of enuretic children who had low nocturnal vasopressin levels. In enuretic children who displayed hypercalciuria and had normal vasopressin levels, the D/N AQP2 ratio was 1.05 ± 0.27 (n = 8). These data indicate that reduced secretion of vasopressin and absorptive hypercalciuria are independently associated with an approximately twofold increase in the urinary D/N AQP2 ratio. When low nocturnal vasopressin levels were associated with hypercalciuria, a nearly threefold increase in the D/N AQP2 ratio was observed (1.67 ± 0.41, n = 11). In addition, in all enuretic patients tested, the urinary D/N AQP2 ratio correlates perfectly with the severity of the disorder (nocturnal polyuria). The findings reported in this article indicate that urinary AQP2 correlates with the severity of enuresis in children.