Hypovolemic state: Involvement of nitric oxide in the aged related alterations of aquaporins-2 abundance in rat kidney

Abstract Aim To examine the effect of nitric oxide (NO) on the expression and/or localization of inner medulla collecting duct aquaporin-2 water channel (AQP2) in young and adult hemorrhaged anesthetized rats. Methods Rats of 2 (young) and 12 mo (adult) old ( n  = 15) were divided into: Sham animals with and without N G -nitro-l-arginine methyl ester (L-NAME) treatment (S L-NAME and S); hemorrhaged animals (20% blood loss) with and without L-NAME (H L-NAME and H). Mean arterial pressure (MAP) was continuously monitored and AQP2 expression and inmunolocalization were evaluated at 120 min after bleeding. Results L-NAME blunted the hypotension induced by hemorrhage at 120 min in young (106 ± 2 mm Hg) and adult (103 ± 4 mm Hg) rats. AQP2 expression increased after bleeding in young (from 22 to 50 densitometric units) and adult rats (from 15 to 30 densitometric units). Pretreatment with L-NAME enhanced this effect, being this rise lower in adult than young animals (young: 318%, adult: 233%). Electron microscopy showed that AQP2 labeling increased after withdrawal, being the number of gold particles smaller in adult than young animals in the inner medulla. L-NAME enhanced this effect. Conclusion NOS activity decreases AQP2 expression/traffick in the inner collecting duct principal cells in response to hemorrhage and this effect is lower with aging.