AVPR2 and cyst: Inhibition of vasopressin action by the V2R antagonist tolvaptan exerts opposite effects, resulting in decreases in Uosm (hypotonic urine) and slowing of cyst volume expansion.3,4 Because the effects of vasopressin or tolvaptan in both collecting ducts and kidney cysts are mediated by the same V2R, their physiologic effects in each system are mirrored by those in the other.