Hypovolemic state: involment of nitric oxide in the age-related alterations of aquaporin-2 in rat kidneys.

ARRECHE N, LOPEZ M, LOPEZ J, ARRANZ C, FELLET A, BALASZCZUK

Miami, USA

Congreso; Sessions of the Inter-American Society of Hypertension and the Consortium for Southeastern Hypertension Control; 2007

Background: Nitric oxide (NO) system would be one of the factors involved in control of water homeostasis which would be affected by ageing. Previous results in our laboratory showed that inhibition of renal nitric oxide synthase (NOS) increased AQP-2 abundance during hypovolemic state induced by acute hemorrhage in young rats. Objective: To evaluate the effects of the NOS inhibition on regulation of collecting duct water permeability during severe hemorrhage (arterial bleeding of 20% of the total blood volume) in rats at ages 3 mo (young) and 12 mo (adult). Methods: Groups of animals (n=8 per group): C: control; H: hemorrhage (20% of the total blood volume); L: L-NAME infusion (1 mg/kg iv followed by 0.5 mg/kg.h iv=100 µl/h); HL: hemorrhage + L-NAME infusion. AQP-2  channel was evaluated by indirect immunofluorescence and confocal microscopy in renal medulla and papilla after 120 min of bleeding in young and adult rats. Results: Studies showed that in control rats, AQP-2 labeling was mainly associated with apical and basolateral membrane domains in collecting duct principal cells of 3- and 12-mo old rats. L-NAME infusion increased the immunoreactive area and the number of subapical vesicles in adult rats. In young rats, NOS inhibition increased AQP-2 localization in the apical side of collecting duct cells. In H group the majority of AQP-2 water channels are shown in vesicles distributed throughout the cytoplasm but not in the apical membrane in both, young and adult rats. In HL group, AQP2 staining is more intense compared to the other groups. Staining of apical membrane and cytoplasm is increased in both, the 3- and 12-mo old rats. Conclusion: Changes in distribution of AQP-2 water channels may be an adaptive process of renal function in response to acute hemorrhage. NO plays a modulatory role in AQP-2 membrane translocation and immunoreactivity in young and adult rats.