Transport of acetate and butyrate in the hind-gut of rabbits.

1. Everted sacs of colonic mucosa from the wild rabbit did not transport acetate against a concentration gradient, but permeation down a concentration gradient did occur. 2. Butyrate was shown to permeate sheets of caecal mucosa with some conversion into ketone bodies during the passage. More ketone bodies were released from the serosal surface of the sheet than from the epithelial surface, regardless of the side to which the butyrate was added. 3. During absorption in vivo of [1-(14)C]butyrate from the caecum the ratio of [(14)C]butyrate to (14)C-labelled ketone bodies in the blood collected from the appropriate caecal vein was 13. The extent of conversion of butyrate into ketone bodies during absorption in vivo was less than that observed during transport in vitro. Possible explanations of these differences are discussed. 4. The relative concentrations of the individual volatile fatty acids in blood collected from the caecal vein during absorption in vivo were similar to those present in contents from the caecum. 5. The results are compared with similar transport and absorption studies on the ruminant fore-stomach.