Effect of the Aquaretic Tolvaptan on Nitric Oxide System

Inclusion Criteria: 1. Caucasian men and women 2. Age between 18-65 years 3. ADPKD, diagnosed by genetic testing of PKD1 (\>85%) or PKD2 mutations, or by ultrasonography: 1. patients with negative family history for ADKPD and more than 10 cysts in each kidney and no extrarenal or renal findings that suggest causes to cyst formation. 2. patients with positive family history for ADPKD: * 15-39 yr of age and at least 3 or more unilateral or bilateral. * 40-59 yr of age and 2 or more cysts in each kidney. * 60 yr of age and at least 4 cysts in each kidney. 4. Kidney function corresponding to CKD stages 1-3(eGFR\> 30 mL/min/1,73 m2), 5. BMI between 18.5 and 35.5 kg/m2. Exclusion Criteria: 1. Clinical signs of diseases in the heart, lungs, endocrine organs, brain or neoplastic disease, 2. clinically significant abnormalities in blood or urine sample at the inclusion 3. previous cerebrovascular insults, 4. previous clinical evidence for aneurysm 5. Alcohol or drug abuse, 6. smoking, 7. pregnancy or breastfeeding, 8. clinically significant changes in the electrocardiogram, 9. medication except antihypertensive agents and oral contraceptives, 10. blood pressure\>170/105 mmHg despite treatment with metoprolol and/or amlodipine.