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The aquaporin-2 (AQP2) plays a key role in AVP-induced absorption of water, and its urinary excretion is related to its function. We aimed to test if the assumption of water with different mineral content can modify the expression of AQP2, leading to a change in AQP2 urinary concentration, in 20 healthy young subjects. Each subject received an oral water load (LM or HM) of 250 mL/hour for four hours, and several variables were measured. Plasmatic osmolality after water assumption was significantly reduced with no differences after the low (LM) or the high mineral (HM) water load. Urinary osmolality and plasmatic vasopressin concentration were significantly reduced after an assumption of both kinds of water. However, serum vasopressin was lower after HM water assumption than after LM. AQP2 urinary excretion was significantly reduced after water assumption with respect to the basal level and it was lower after LM than after HM water assumption. The different mineral content of water was investigated as a factor contributing to the development of hypertension. Considering that AQP2 can play a role in pathogenesis of hypertension, our demonstration that AVP-mediated AQP2 urinary excretion is strictly influenced by the consumption of water with different mineral content suggests a new, interesting field of investigation related to the link between blood pressure alterations and nutritional habits. [ABSTRACT FROM AUTHOR]

Background: Healthy subjects and patients after successful kidney transplantation show a circadian rhythm for glomerular filtration rate and for the glomerular transport of macromolecules. We aimed to evaluate by bioelectrical impedance analysis (BIA) whether body hydration status also follows a circadian rhythm in patients with impaired renal function. Methods: The study was conducted on 28 subjects divided into 3 groups: 8 healthy volunteers, 8 patients affected by chronic kidney disease and 12 end-stage renal disease (ESRD) patients on hemodialysis. During 24 h, 9 BIA measurements were taken in every subject every 180 min. Results: BIA findings demonstrate that normal subjects have a circadian rhythm in hydration status that reaches maximum body water content at night, between 21.00 and 23.00 h. In patients with chronic kidney disease, this rhythm, with maximum at night, is maintained. The rhythm is also present in ESRD patients, if the residual diuresis is at least 500 ml/day, while there is no rhythm when residual diuresis is <300 ml/day. Conclusions: In normal subjects, body hydration status shows a circadian rhythm, which is weakened or lost in oligoanuric patients on dialysis, but partially maintained in subjects with preterminal uremia and in hemodialyzed patients with residual diuresis >500 ml/day. Copyright © 2007 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]