Dissociation between urine osmolality and urinary excretion of aquaporin-2in healthy volunteers

Citation
R. Baumgarten et al., Dissociation between urine osmolality and urinary excretion of aquaporin-2in healthy volunteers, NEPH DIAL T, 15(8), 2000, pp. 1155-1161
Citations number
20
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Urology & Nephrology
Journal title
NEPHROLOGY DIALYSIS TRANSPLANTATION
ISSN journal
0931-0509 → ACNP
Volume
15
Issue
8
Year of publication
2000
Pages
1155 - 1161
Database
ISI
SICI code
0931-0509(200008)15:8<1155:DBUOAU>2.0.ZU;2-9
Abstract
Background. It has been suggested that urinary excretion of the vasopressin -dependent water channel of the kidney collecting duct, aquaporin-2 (AQP2), reflects renal vasopressin action and might be used clinically. It is uncl ear, however, what relation exists between urine osmolality and urinary exc retion of AQP2 (UAQP2) and it is unknown whether UAQP2 is influenced by hyp erosmolality of urine or tubular flow rates. Methods. We measured urine osmolality and UAQP2 in healthy volunteers in Va rious conditions: (i) overnight dehydration continued during the day, (ii) after infusion of 700 ml hypertonic saline (NaCl 2.5%), and (iii) after int ranasal administration of 40 mu g 1-desamino-8-D-arginine vasopressin (DDAV P). The last two tests were performed after water loading. In addition, a D DAVP test was performed, after administration of frusemide. Results. After overnight dehydration, the urine osmolality increased from 8 88+/-18 to 1004+/-17 mosmol/kg during additional hours of thirsting, wherea s UAQP2 doubled from 140+/-45 to 285+/-63 fmol AQP2/mu mol creatinine. Infu sion of hypertonic saline increased urine osmolality from 70+/-3 to 451+/-6 8 mosmol/kg, while UAQP2 remained almost zero. Urine osmolality increased f rom 101+/-17 to 860+/-30 mosmol/kg after administration of DDAVP, with a pa rallel increase in UAQP2 from 32+/-14 to 394+/-81 fmol AQP2/mu mol creatini ne. Pre-treatment with frusemide attenuated the increase in urine osmolalit y, but had no effect on UAQP2 after DDAVP. Conclusions. Our data demonstrate that a simple relationship between urine osmolality and UAQP2 does not exist. Therefore, random or once-only measure ments of UAQP2 as an index of renal vasopressin action are not useful. In c ontrast, intranasal application of DDAVP resulted in a parallel rise in uri ne osmolality and UAQP2. Therefore this test might be useful in studying pa tients with urine concentration defects. The DDAVP-frusemide test revealed that the release of AQP2 into urine is not caused by hypertonicity of tubul ar fluid.