Amiloride end-point experiment Until amiloride infusion the procedures will be similar. At time point 0, venous infusion of a loading dose of amiloride will be started (150 μg/kg in 60 minutes) followed by maintenance infusion (0.20 μg/kg/min) for 4 hours. Amiloride will be obtained as a sterile powder in the form of amiloride HCl/2H2O . Directly before use, the powder will be dissolved in NaCl 0,9% up to a concentration of 1 mg/ml and the solution was filtered through a 0.22 μm Millipore filter. Venous blood for measurement of the amiloride concentration will be sampled at 60, 180, 300 and 420 minutes. All the other procedures will be similar to the furosemide experiment.