AQP2 and chronic kidney disease: The novelty of this study is two-fold: 1) This is the first study that documents the changes in u-NKCC2 in healthy subjects as well in patients with CKD in response to a hypertonic saline load, 2) Measurements of the urinary excretion of NKCC2, AQP2 and ENaCγ in the same study has never been performed previously.