Influence of progressive salt restriction on urinary bicarbonate wasting in uremic acidosis

In steady state, the acidosis in the majority of 17 uremic patients was characterized by a persistent bicarbonaturia (FEHCO3 ranging between 0% and 17.65%). An NH4Cl loading test in 17 patients revealed two distinct groups: group A (n = 11) with complete disappearance of the urinary bicarbonate loss and a mean UpH of 5.39 +/- 0.10 at a PHCO3 level of 13.3 +/- 0.5 mEq/L; and group B (n = 6) with urinary acidification disturbances with a persistent FEHCO3 ranging between 1.06% and 3.15% and a mean UpH of 6.53 +/- 0.06 at a PHCO3 level of 13.5 +/- 0.7 mEq/L. Between the two groups, there were no differences in CCr, plasma Na, K, Cl, Ca, PO4, PCO2, and aldosterone levels. Calculation of the THCO3/TNa reabsorption ratio over a wide range of PHCO3 levels revealed no differences between the two groups. The mean levels of circulating PTH were significantly higher in group B compared with group A (40.1 +/- 10.8 mU/dL v 19.3 +/- 4.4 mU/dL; P less than .05), and the spontaneous steady-state FENa was more pronounced in group B than in group A (12.1% +/- 1.5% v 4.9% +/- 0.7%; P less than .05). Four patients from group B with a well-documented salt-losing nephropathy (FENa ranging from 10.20% to 15.10%) were submitted to a progressive dietary salt restriction over several weeks. At this stage, the four patients no longer had bicarbonaturia, and the urinary pH decreased to levels between 5.15 and 5.65 during NH4Cl-induced acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)