Dietary acid increases blood and renal cortical acid content in rats

We examined whether dietary acid that increases net acid excretion (NAE) without measurably decreasing plasma pH or total CO(2) (tCO(2)) causes net acid retention. Control rats drinking distilled H(2)O were compared with those drinking 40 mM (NH(4))(2)SO(4), 40 mM Na(2)SO(4), or drinking Na(2)SO(4) and given aldosterone (Na(2)SO(4) + Aldo) to increase NAE without dietary acid. Systemic plasma tCO(2) increased in Na(2)SO(4) + Aldo animals, but systemic and stellate vessel plasma tCO(2) and pH were not different from control among remaining groups. NAE increased in (NH(4))(2)SO(4) and Na(2)SO(4) + Aldo but not in Na(2)SO(4) animals. Blood base excess (BBE) decreased compared with its respective baseline in (NH(4))(2)SO(4) (-0.44 +/- 0.06 vs. 0.66 +/- 0.04 mu mol/ml; P < 0.01, paired t-test), increased in Na(2)SO(4); Aldo (0.79 +/- 0.05 vs. 0.61 +/- 0.03 mu mol/l; P < 0.04, paired t-test), but was unchanged in Na(2)SO(4) animals. Renal cortical H(+) content assessed by microdialysis of the renal cortex in situ increased in (NH(4))(2)SO(4), decreased in Na(2)SO(4) + Aldo, but was unchanged in Na(2)SO(4) animals. The data show that dietary acid sufficient to increase NAE without decreasing plasma tCO(2) or pH nevertheless decreases BBE and increases renal cortical acid content, consistent with net acid retention.