Hyponatremia and cyst growth in neonatal polycystic kidney disease: a case for aquaretics?

Hyponatremia is a common complication in neonatal polycystic kidney disease and is thought to be due to water retention. Aquaretics are drugs that promote free water excretion by blocking the arginine vasopressin receptor type 2 (AVPR2) in the collecting duct and thus impair urinary concentration. AVPR2 is also a key stimulant for cyclic AMP production in the collecting duct and in this way promotes cyst proliferation and pathologic kidney growth in autosomal dominant polycystic kidney disease (ADPKD). Consequently, the aquaretic tolvaptan is now used to slow down progression of ADPKD in adult patients. Whether this beneficial effect on retarding cystic disease progression also extends to recessive forms of polycystic kidney disease (PKD) is currently not known. A recent case report in Pediatric Nephrology touches on the intersecting indications for tolvaptan for both hyponatremia and cyst retardation in neonatal PKD and suggests that use for one indication may have beneficial effects on the other.