AVP and cystic kidney disease: For several years, it has been suggested that the suppression of AVP by increasing fluid intake could also slow renal cyst growth in ADPKD.7 11 In support of the hypothesis, preclinical experiments in the pck rat model of PKD showed that increased water intake reduced kidney enlargement,12 13 and comparison with separate studies imply that the efficacy might be similar (but with physiological differences) to vasopressin receptor antagonists.14 However, whether this hypothesis is also true in humans with ADPKD remains unknown.