[Influence of pH on the transfer of volatile fatty acids in the isolated cecal wall of the rat].

The influence of pH on the transfer of acetic, propionic and butyric acids was studied in vitro using everted sacs of the rat caecum. The sacs were filled with 2 ml of saline medium and then shaken 1 hr at 38 degrees C in flasks containing the same medium. A Krebs-Ringer phosphate incubation medium was used with O2 as gas phase. Incubation mediums containing 15 mM acetic, propionic and butyric acids were adjusted to give three different pH values: 7.91, 7.00 and 6.03. After incubation the mucosal and serosal fluids were collected and samples were taken to determine the pH and the volatile fatty acid concentrations. The pH values of mucosal and serosal fluids changed slightly during the course of the experiments. There was net volatile fatty acid influx into caecal tissue from the serosal medium and into the mucosal medium from the caecal tissue. Lowering the pH from 7.00 to 6.03 resulted in a significant decrease of serosal volatile fatty acid influxes. Caecal tissue retained more volatile fatty acids by lowering the pH from 7.91 to 7.00 and 6.03. Acetic acid accumulated in the caecal tissue against its electro-chemical gradient at pH 6.03. Two different mechanisms appeared to favor the transport of ionized and non-ionized forms of volatile fatty acids through the caecal membranes.