title: Water immersion increases urinary excretion of aquaporin-2 in healthy humans.
abstract: Many previous studies have shown that aquaporin-2 (AQP2), the vasopressin-regulated water channel, is excreted in the urine and that the excretion increases in response to vasopressin. Moreover, recently a close correlation between AQP2 excretion in urine and kidney AQP2 expression has been demonstrated, showing that urinary excretion of AQP2 is a reliable indicator for AQP-2 function. As head-out water immersion causes an expansion in the central vascular volume equal to that induced by 2 liters of saline, without modifying plasma composition, we used immersion in water to evaluate if the response to acute expansion of the central vascular volume could involve vasporessin (AVP) and AQP2. In healthy subjects, concentrations of plasma atrial natriuretic factor (ANF) and AVP, and urinary AQP2 were measured during a 2-hour immersion period. In all subjects, immersion caused a prompt and marked increase in immunoreactive ANF (23.0 +/- 2.12 pg/ml at second hour vs. 2.17 +/- 0.42 pg/ml at baseline) and in urinary excretion of AQP2 (23.9 +/- 2. 69 pmol/mg creatinine at second hour vs. 4.42 +/- 0.14 pmol/mg creatinine at baseline), while a significant decrease was found in plasma AVP. Recovery was associated with a prompt return to pre-study levels. These findings demonstrate that heat-out water immersion stimulates urinary excretion of AQP2 in absence of an increase in plasma AVP.
authors.affiliation: Department of Internal Medicine, University of Messina, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Buemi
authors.forename: F
authors.initials: F
authors.lastname: Corica
authors.forename: G
authors.initials: G
authors.lastname: Di Pasquale
authors.forename: C
authors.initials: C
authors.lastname: Aloisi
authors.forename: M
authors.initials: M
authors.lastname: Sofi
authors.forename: T
authors.initials: T
authors.lastname: Casuscelli
authors.forename: F
authors.initials: F
authors.lastname: Floccari
authors.forename: M
authors.initials: M
authors.lastname: Senatore
authors.forename: A
authors.initials: A
authors.lastname: Corsonello
authors.forename: N
authors.initials: N
authors.lastname: Frisina
mesh_terms: D000328:Adult; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins / Q000652:urine*; D009320:Atrial Natriuretic Factor / Q000097:blood; D001794:Blood Pressure; D004231:Diuresis / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D012016:Reference Values; D014667:Vasopressins / Q000097:blood; D014867:Water; D014882:Water-Electrolyte Balance / Q000502:physiology*; D015431:Weight Loss
chemical_list: C496023:AQP2 protein, human; D051399:Aquaporin 2; D051403:Aquaporin 6; D020346:Aquaporins; D014867:Water; D014667:Vasopressins; D009320:Atrial Natriuretic Factor