Urinary aquaporin-2 excretion in dogs: a marker for collecting duct responsiveness to vasopressin.
In humans, the urinary aquaporin-2 (U-AQP2) excretion closely parallels changes in vasopressin (VP) action and has been proposed as a marker for collecting duct responsiveness to VP. This report describes the development of a radioimmunoassay for the measurement of U-AQP2 excretion in dogs. In addition, the localization of AQP2 in the canine kidney was investigated by immunohistochemistry. Basal U-AQP2 excretion was highly variable among healthy dogs. Two hours after oral water loading, the mean U-AQP2/creatinine ratio decreased significantly from (231 +/- 30) x 10(-9) to (60 +/- 15) x 10(-9) (P = 0.01), while the median plasma VP concentration decreased from 4.2 pmol/l (range 2.2-4.8 pmol/l) to 1.2 pmol/l (range 1.0-1.9 pmol/l). Subsequent intravenous administration of desmopressin led to a significantly increased mean U-AQP2/creatinine ratio of (258 +/- 56) x 10(-9) (P = 0.01). Two hours of intravenous hypertonic saline infusion (20% NaCl, 0.03 ml/kg body weight/min) significantly increased the mean U-AQP2/creatinine ratio from (86 +/- 6) x 10(-9) to (145 +/- 23) x 10(-9) (P = 0.045), while the median plasma VP concentration increased significantly from 2.2 pmol/l (range 1.1-6.3 pmol/l) to 17.1 pmol/l (range 8.4-67 pmol/l) (P < 0.001). Immunohistochemistry revealed extensive labeling for AQP2 in the kidney collecting duct cells, predominantly localized in the apical and subapical region. As in humans, U-AQP2 excretion in dogs closely reflects changes in VP exposure. Urinary AQP2 excretion may become a diagnostic tool in dogs for the differentiation of polyuric conditions such as (partial) central or nephrogenic diabetes insipidus, primary polydipsia, and inappropriate VP release.
van Vonderen
I K
IK
Department of Clinical Sciences of Companion Animals, Utrecht University, P.O. Box 80.154, Yalelaan 8, 3508 TD, The Netherlands.
Wolfswinkel
J
J
van den Ingh
T S G A M
TS
Mol
J A
JA
Rijnberk
A
A
Kooistra
H S
HS
D000818:Animals; D051399:Aquaporin 2; D020346:Aquaporins / Q000652:urine*; D015415:Biomarkers / Q000652:urine*; D003894:Deamino Arginine Vasopressin / Q000008:administration & dosage; D004285:Dogs / Q000652:urine*; D005260:Female; D007150:Immunohistochemistry; D007668:Kidney / Q000737:chemistry; D007685:Kidney Tubules, Collecting / Q000187:drug effects* / Q000502:physiology; D008297:Male; D012462:Saline Solution, Hypertonic; D014667:Vasopressins / Q000097:blood / Q000494:pharmacology*; D014867:Water / Q000008:administration & dosage
D051399:Aquaporin 2; D020346:Aquaporins; D015415:Biomarkers; D012462:Saline Solution, Hypertonic; D014867:Water; D014667:Vasopressins; D003894:Deamino Arginine Vasopressin