Proposition of a feasible protocol to evaluate salt sensitivity in a population-based setting

Although a variety of techniques have been devised to assess salt sensitivity, most have proven cumbersome from a methodological perspective. We therefore attempted to develop a 2-week method by which participants could be tested in an outpatient setting without requirement of a strict dietary regimen. In this method, subjects take 140 mEq of an NaCl supplement per day for 1 week and 25 mg of hydrochlorothiazide daily for another week while maintaining their customary diet. In our first trial, 8 healthy volunteers submitted to this method, as well as to a widely-used rapid volume expansion and contraction protocol. Blood pressure measurements, blood sampling and 24-h urine collection were performed before, in the middle of, and after each intervention. There was a fair correlation (r = 0.69) between the two protocols with respect to the changes in mean blood pressure (deltaMBP), a measure of salt sensitivity. In our second trial, we tested the method on 82 Japanese subjects who had never been treated with antihypertensive drugs. DeltaMBP was significantly correlated with plasma renin activity (PRA) during salt loading (r = 0.52, p < 0.0001) and with the changes in atrial natriuretic peptide (deltaANP) (r = -0.34, p = 0.0018). When total subjects were divided into two subgroups by age, a similar tendency of correlation was observed. Age, PRA during salt loading, deltaANP, and delta norepinephrine were proven to be significant predictors of salt sensitivity and accounted for 46% of the deltaMBP variances. Based on these results, the dietary method presented here seems to be applicable for a population-based survey. Our preliminary data also suggest that PRA and ANP would be of predictive value in the salt sensitivity test.