High salt intake increases copeptin but salt sensitivity is associated with fluid induced reduction of copeptin in women.

This study investigated if copeptin is affected by high salt intake and whether any salt-induced changes in copeptin are related to the degree of salt sensitivity. The study was performed on 20 men and 19 women. In addition to meals containing 50 mmol NaCl daily, capsules containing 100 mmol NaCl and corresponding placebo capsules were administered during 4 weeks each, in random order. Measurements of 24 h blood pressure, body weight, 24 h urinary volume, and fasting plasma copeptin were performed at high and low salt consumption. Copeptin increased after a high compared to low dietary salt consumption in all subjects 3,59 ± 2,28 versus 3,12 ± 1,95 (P = 0,02). Copeptin correlated inversely with urinary volume, at both low (r = -0,42; P = 0,001) and high (r = -0,60; P < 0,001) salt consumption, as well as with the change in body weight (r = -0,53; P < 0,001). Systolic salt sensitivity was inversely correlated with salt-induced changes of copeptin, only in females (r = -0,58; P = 0,017). As suppression of copeptin on high versus low salt intake was associated with systolic salt sensitivity in women, our data suggest that high fluid intake and fluid retention may contribute to salt sensitivity.