Intestinal Drug Absorption and Metabolism III: Glycine Conjugation and Accumulation of Benzoic Acid in Rat Intestinal Tissue

Abstract

Glycine conjugation of 14C-benzoic acid to 14C-hippuric acid was demonstrated in in vitro rat intestinal slices and everted intestinal preparations. Hippuric acid was detected and quantified by two independent analytical techniques, a quantitative TLC method, and a reverse isotope dilution method. Comparison of hippuric acid concentration after 2 hr. in mucosal and serosal fluids when hippuric acid was formed endogenously from benzoic acid, and with mucosal and serosal concentrations when hippuric acid was added exogenously to the mucosal fluid, indicated that hippuric acid is formed in the tissue compartment rather than by bacterial or intestinal enzymes in the mucosal fluid. Hippuric acid is apparently formed enzymatically in the mucosal cell according to a previously proposed cell compartment model and subsequently diffuses to both mucosal and serosal fluids. The net amount of hippuric acid formed under the conditions of the study was small (about 1%) and was found to be due to limited synthesis rather than to extensive hydrolysis. Both exogenously added benzoic acid and hippuric acid accumulated in the intestinal tissue compartment (11.2 and 6.4%, respectively) during transfer from the mucosal fluid.