Wishing to Decrease Aquaresis in ADPKD Patients Treated With a V2Ra; the Effect of Regulating Protein and Salt

Autosomal Dominant Polycystic Kidney Disease (ADPKD) is characterized by the formation of numerous cysts in both kidneys and progressive renal function decline leading to renal replacement therapy (RRT) at a median age of 58 years. The first (and at the moment only) drug to slow down renal function decline, is a vasopressin V2 receptor antagonist (V2RA). This medicament slows renal function decline by 26 to 34%. V2RA also causes aquaresis associated side-effects such as polyuria of \>6 liter per day in the majority of patients. These side-effects limit wide spread use among ADPKD-patients. Therefore, there is a need to improve its tolerability. While using a V2RA, urine concentrating ability is strongly diminished. Therefore, urine volume is largely determined by total osmolar excretion. This is a well-known fact in nephrogenic diabetes insipidus, a disease with clear pathophysiological similarities to treatment with a vasopressin V2 receptor antagonist (a defect receptor versus pharmacological blockade). A recent study found osmolar excretion to be associated with urinary volume during V2RA treatment. Whether a change in osmolar load changes polyuria during V2RA has not yet been investigated. The investigators hypothesize that changing sodium and protein intake will reduce polyuria.