Normalization of increased sodium sensitivity by maintenance hemodialysis. Blood pressure (BP) becomes more sodium and body fluid sensitive as renal function deteriorates. Thus, hypertension in chronic renal failure is mostly of the sodium sensitive type. We studied whether the increased sodium sensitivity (SS) can be restored to normal on the maintenance phase of hemodialysis (HD) therapy. Body weight (BW) and BP (specifically, mean arterial pressure [MAP]) were measured after HD and before the next HD, and the body fluid sensitivity (BFS) was calculated as the ratio of changes in these factors on both introduction and maintenance phases in HD patients (n = 56) who were not taking any antihypertensive drugs (BFS = delta MAP/delta BW). In a preliminary study, the amount of interdialytic sodium intake (QNa+) was measured (n = 30), and SS was calculated as the ratio of the change in MAP to QNa+ (SS = delta MAP/QNa+). Interdialytic BW gain (3.1 +/- 0.1 kg) was correlated with the amount of sodium intake (136 +/- 17 mEq), resulting in a positive relationship between BFS and SS (r = 0.79, P less than .0001). Therefore, BFS was used as an index of SS. As a whole, BFS decreased from the introduction to the maintenance phase (6.5 +/- 1.0 to 3.5 +/- 0.6 mm Hg/L, P less than .01). This decrease was marked (6.2 +/- 1.1 to 2.9 +/- 0.6 mm Hg/L, P less than .01) in patients (n = 46) whose BP was normalized in the maintenance phase, while not significant (7.9 +/- 1.9 to 6.3 +/- 1.3 mm Hg/L) in patients (n = 10) whose BP was still high. 