AVPR2 and cyst: Based on the observation of increased intracellular cAMP in cyst epithelium, increased vasopressin levels in the serum of ADPKD patients and increased levels of V2 receptor expression as well as the knowledge that vasopressin via the V2 receptor increases intracellular cAMP, a second approach suggested that inhibition of the vasopressin-V2R-cAMP axis may reduce cystogenesis an cyst growth (48).