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 CO2 (tCO2) causes net acid retention. Control rats drinking distilled H2O were compared with those drinking 40 mM (NH4)2SO4, 40 mM Na2SO4, or drinking Na2SO4 and given aldosterone (Na2SO4 + Aldo) to increase NAE without dietary acid. Systemic plasma tCO2 increased in Na2SO4 + Aldo animals, but systemic and stellate vessel plasma tCO2 and pH were not different from control among remaining groups. NAE increased in (NH4)2SO4 and Na2SO4 + Aldo but not in Na2SO4 animals. Blood base excess (BBE) decreased compared with its respective baseline in (NH4)2SO4 (-0.44 +/- 0.06 vs. 0.66 +/- 0.04 mumol/ml; P < 0.01, paired t-test), increased in Na2SO4 + Aldo (0.79 +/- 0.05 vs. 0.61 +/- 0.03 mumol/ml; P < 0.04, paired t-test), but was unchanged in Na2SO4 animals. Renal cortical H+ content assessed by microdialysis of the renal cortex in situ increased in (NH4)2SO4, decreased in Na2SO4 + Aldo, but was unchanged in Na2SO4 animals. The data show that dietary acid sufficient to increase NAE without decreasing plasma tCO2 or pH nevertheless decreases BBE and increases renal cortical acid content, consistent with net acid retention.