HCO3- and H+ secretion in rat ileum in vivo.

Replacing Cl- in the perfusion fluids decreased the luminal pH of rat ileum perfused in vivo. Varying the initial pH in Cl- depletion studies indicated an equilibrium pH near 6.6. Na+ depletion in Cl- deleted fluids partially inhibited luminal acidification. Addition of HCO3- accelerated Na+ absorption and decreased Cl- absorption. Luminal PCO2 was increased using fluids buffered to initial pH 6.6, suggesting secretion of HCO3- rather than OH-. The decreased HCO3- secretion using Cl- depleted fluids was not due to an acclerated rate of H+ secretion. Reaffirmed and expanded in this study is an ileal H+ secretory process that is partially related to Na+ absorption and direct HCO3- secretion that is related to Cl- and Na+ absorption.