Al Therwani S, et al. – This study gauged the effect of tolvaptan on renal handling of water and sodium, GFR and central hemodynamics in autosomal dominant polycystic kidney disease. Partly via an AVP–dependent mechanism, tolvaptan antagonized both the antidiuretic and the antinatriuretic effect of L–NMMA (L–NG–monomethyl–arginine), during nitric oxide (NO) inhibition. Possibly, due to a counteracting effect of elevated plasma concentrations of vasopressin (p-AVP), urinary excretion of aquaporin–2 channels (u–AQP2) was not changed by tolvaptan.