Suppressed urinary excretion of aquaporin-2 in an infant with primary polydipsia

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.

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Exaggerated Urinary Excretion of Aquaporin-2 in the Pathological State of Impaired Water Excretion Dependent upon Arginine Vasopressin1

The Journal of Clinical Endocrinology & Metabolism ◽

10.1210/jcem.83.11.5218 ◽

1998 ◽

Vol 83 (11) ◽

pp. 4034-4040

Author(s):

Takako Saito ◽

San-e Ishikawa ◽

Fumiko Ando ◽

Nobukazu Okada ◽

Tomoatsu Nakamura ◽

...

Keyword(s):

Urinary Excretion ◽

Pathological State ◽

Water Excretion ◽

Aquaporin 2 ◽

Impaired Water

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Urinary aquaporin-2 excretion in nocturnal enuresis

Acta Endocrinologica ◽

10.1530/eje.0.1450435 ◽

2001 ◽

pp. 435-438 ◽

Cited By ~ 12

Author(s):

G Radetti ◽

C Paganini ◽

F Rigon ◽

L Gentili ◽

U Gebert ◽

...

Keyword(s):

Urinary Excretion ◽

Nocturnal Enuresis ◽

Plasma Osmolality ◽

Urine Osmolality ◽

Posterior Lobe ◽

Healthy Children ◽

Serum Concentrations ◽

Aquaporin 2 ◽

Magnetic Resonance Imaging Mri ◽

Study Participants

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 children were further subdivided into responders and non-responders to treatment with 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 pituitary gland was carried out to evaluate the amount of AVP stored in the posthypophysis. RESULTS: Mean AVP serum concentrations were similar in patients and controls. 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). Plasma osmolality was greater in patients than in controls (P<0.001), whereas urinary osmolality was similar in both groups. No difference in the ratio of the signal intensity of the posterior lobe of the hypophysis to that of the pons (AVP content) was found between patients and controls or between responders 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.

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Decrease in Urinary Excretion of Aquaporin-2 Associated with Impaired Urinary Concentrating Ability in Diabetic Nephropathy

Nephron ◽

10.1159/000063285 ◽

2002 ◽

Vol 92 (2) ◽

pp. 445-448 ◽

Cited By ~ 13

Author(s):

Tomoatsu Nakamura ◽

Takako Saito ◽

Ikuyo Kusaka ◽

Minori Higashiyama ◽

Shoichiro Nagasaka ◽

...

Keyword(s):

Diabetic Nephropathy ◽

Urinary Excretion ◽

Aquaporin 2 ◽

Urinary Concentrating Ability

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Urinary excretion of aquaporin-2 in humans: a potential marker of collecting duct responsiveness to vasopressin.

Journal of the American Society of Nephrology ◽

10.1681/asn.v73403 ◽

1996 ◽

Vol 7 (3) ◽

pp. 403-409 ◽

Cited By ~ 1

Author(s):

S Elliot ◽

P Goldsmith ◽

M Knepper ◽

M Haughey ◽

B Olson

Keyword(s):

Urinary Excretion ◽

Collecting Duct ◽

Water Channel ◽

Apical Plasma Membrane ◽

Hydration Status ◽

Standard Curve ◽

Western Analysis ◽

Aquaporin 2 ◽

Potential Marker ◽

Collecting Ducts

The vasopressin-sensitive water channel (aquaporin 2; AQP-2) mediates water transport across the apical plasma membrane of the renal collecting ducts and is excreted in human urine. This study presents the hypothesis that measurements of the AQP-2 excretion rate might be used as a marker of collecting-duct responsiveness to vasopressin, and therefore could be useful in the clinical evaluation of various water-balance disorders. This study presents information about the development of an antibody to human AQP-2, and measures the urinary excretion of AQP-2 by quantitative Western analysis. A standard curve of band densities was generated by using known quantities of the modified immunizing peptide to derive the amount of AQP-2 contained in aliquots of urine. AQP-2 urinary excretion changed with short-term alterations in hydration status produced either by water loading (76% decrease, P < 0.01) or by 3% sodium chloride (760% increase, P < 0.01). Steady-state 24-h urinary excretion of AQP-2 was 43 +/- 10 nmol/24 h (or 28.5 +/- 6.9 pmol/mg creatinine), and 20 +/- 6 nmol/24 h (or 18.3 +/- 7.9 pmol/mg creatinine) in men and women, respectively. Therefore, urinary AQP-2 excretion can be quantified by using Western analysis, and may serve as a marker of collecting-duct responsiveness to vasopressin in different physiologic settings.

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