Desmopressin (dDAVP) induces a decrease in immunolabelling of aquaporin (AQP) 4 protein in the terminal inner medulla (IM) of the Brattleboro (BB) rat kidney. It is disputed, however, whether the decreased labelling reflects real down-regulation of protein abundance, or whether it is a result of epitope shielding in the AQP4 protein, preventing binding of the antibody as previously suggested. Furthermore, it is unknown if vasopressin regulates AQP4 in the connecting tubule (CNT) and in the cortical collecting duct (CCD). Using BB rats, we aimed to determine (i) whether the dDAVP-induced decrease in AQP4 labelling in the terminal IM reflects down-regulation in protein abundance and (ii) whether dDAVP increases the AQP4 protein abundance in the CNT and the CCD.