AVPR2 and autosomal dominant polycystic kidney disease: This post hoc analysis of data from TEMPO 3:4 supports reduction in Uosm as an indicator of longer-term effects on TKV during tolvaptan V2R antagonist therapy, a relationship with a mechanistic basis in the dual role of vasopressin in increasing urinary concentration and driving cystic proliferation and expansion in ADPKD.2 The observation that tolvaptan was associated with greater inhibition of TKV growth in TEMPO 3:4 at month 12 than placebo for similar spot Uosm values at week 3 suggests the limitations of spot Uosm as a means of measuring the suppression of vasopressin activity.