Glomerular filtration reate ( GFR ) , fractional excretions of sodium ( FENa ) , urinary excretion of aquaporin-2 ( u-AQP2 ) and epithelial sodium channels ( u-ENaC ) , vasoactive hormones ( renin , angiotensin II , aldosterone , arginine vasopressin , endothelin-1 and brain natriuretic peptide ) and central blood pressure ( BP ) estimated by applanation tonometry were measured before and after systemic administration of the NO inhibitor L-NMMA .