Visit 3 (day 9) after the overnight fast again oral sodium load is going to be given in a form of a standardized meal (soup) in a same amount as previous day and again consumed in 30 minutes, they are going to drink afterwards 1/2 L of water during next 1 h like pervious day. Synthetic GLP-1 (1.5 pmol/kg/min) dissolved in 500 ml 0.9% saline is going to be infused during 3 hours from beginning of oral sodium load. During 6 hours (from oral sodium load) urine is gong to be collected, blood samples are going to be drawn after 3 and 6 hours for the same analysis as in Visit 2, just like urine collection after 6 hours.