Treatment of Vascular Stiffness in ADPKD

Objective of the study: The investigators aim to investigate if arterial stiffness is exacerbated due to a high-salt diet in patients with ADPKD. The investigators also aim to explore whether treatment with amiloride prevents the arterial stiffness caused by a high-salt diet. Study design: Randomized, double blinded and placebo-controlled clinical trial with open-label treatment with amiloride Study population: Adults with ADPKD with an estimated glomerular filtration rate (CKD-EPI) of ≥ 60 ml/min/1.73m2 Intervention: All participants will be subjected to a low-salt diet (3,5 grams/day) throughout the study for a total of 6 weeks. After a run-in period of 2 weeks, participants will be randomized into two treatment groups: Group 1: Sodium chloride capsules (6 grams/day) for 2 weeks, combined with amiloride (20 mg/day) in last 2 weeks Group 2: Placebo capsules for 2 weeks, combined with amiloride (20 mg/day) in last 2 weeks. Primary study parameters/outcome of the study: The three primary outcomes of this study are a difference in central arterial stiffness (pulse wave velocity, PWV) between: 1. The high-salt group versus low-salt group; 2. The high-salt group: before versus after amiloride treatment; 3. The low-salt group: before versus after amiloride treatment. The burden of participation includes: * A dietary salt restriction of 3.5 grams/day for a total period of 6 weeks * Salt supplementation or placebo for a total period of 4 weeks * Drug intervention with amiloride during the last 2 weeks * Hospital visits