TRANSEPITHELIAL TRANSPORT OF SHORT-CHAIN FATTY-ACIDS AND THEIR METABOLISM IN PIG HINDGUT

In vitro experiments in Ussing chambers were performed in order to stu dy the transport as well as the intraepithelial metabolism of short ch ain fatty acids in the caecum, proximal and distal colon. Stripped epi thelial tissues were incubated in isotonic buffer solutions. SCFA were only present in the mucosal solutions at a concentration of 60 mmol/l consisting of 60 % acetate, 25 % propionate and 15 % butyrate at the beginning of each flux rate measurement. For osmotic reasons SGFA were completely replaced by gluconate in serosal buffer solutions. The tis sues were incubated under short-circuit current conditions for 1 h. In addition, with epithelia from the proximal colon flux rate measuremen ts were also performed after setting the transepithelial potential dif ference (PD) to 25 mV with the serosa being positive. At the end of ea ch Ih flux period samples were taken from the mucosal and serosal solu tions for HPLC analysis of SCFA concentrations. SCFA transport and rat e of intraepithelial metabolism were calculated from mucosal uptake an d serosal release during the experimental periods. In the presence of 2 cm(2) serosal area of the tissues, mucosal SCFA uptake ranged betwee n 53 and 15 mu mol with no change of molar SCFA proportions irrespecti ve of hindgut segment. Voltage clamp condition did not influence mucos al SCFA uptake indicating the presence of electroneutral transport mec hanisms. Serosal SCFA release ranged between 105 and 126 mu mol thus e xceeding mucosal loss. In serosal solutions molar butyrate proportions were significantly lower in comparison with mucosal solutions. This w as accompanied by slight increases of molar acetate proportions indica ting intraepithelial butyrate cleavage. The net SCFA gain might have b een due to an additional SCFA release from the epithelial tissues with in the experimental period which had still been present from the in vi vo situation.