Visits 3 and 4 will also occur over two consecutive days, at least one week after visit 2. Subjects will attend at 07.30 and be given a light breakfast. An intravenous sampling cannula will be inserted into the antecubital vein of one arm. Blood samples (5 mL) will be taken immediately prior to an intravenous bolus infusion (t=0; 08.00) of 5 mg (Pyr1)apelin-13 over 15 min and at 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 180, 240, 300, 360, 480 and 600 min after injection. Subjects will then be discharged from the facility and reattend the following day at 08.00 for a single venous sample.