Urinary excretion of the water channel aquaporin 2 correlated with the pharmacological effect of tolvaptan in cirrhotic patients with ascites.

Background The water channel aquaporin 2 (AQP2) at the apical membrane of renal collecting duct cells mediates water reabsorption. The expression of AQP2 at the apical membrane is tightly regulated by vasopressin and was quantitated by measurement of the urinary form by a recently developed ELISA. Tolvaptan, an antagonist of vasopressin type 2 receptor, inhibits water reabsorption in cirrhosis. The aim of this study was to determine the correlation between the pharmacological effect of tolvaptan and the dynamics of urinary AQP2 levels.