Transepithelial transport of short chain fatty acids and their metabolism in pig hindgut.

In vitro experiments in Ussing chambers were performed in order to study the transport as well as the intraepithelial metabolism of short chain fatty acids in the caecum, proximal and distal colon. Stripped epithelial 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 SCFA were completely replaced by gluconate in serosal buffer solutions. The tissues were incubated under short-circuit current conditions for 1 h. In addition, with epithelia from the proximal colon flux rate measurements were also performed after setting the transepithelial potential difference (PD) to 25 mV with the serosa being positive. At the end of each 1h flux period samples were taken from the mucosal and serosal solutions for HPLC analysis of SCFA concentrations. SCFA transport and rate of intraepithelial metabolism were calculated from mucosal uptake and serosal release during the experimental periods. In the presence of 2 cm2 serosal area of the tissues, mucosal SCFA uptake ranged between 53 and 75 mumol with no change of molar SCFA proportions irrespective of hindgut segment. Voltage clamp condition did not influence mucosal SCFA uptake indicating the presence of electroneutral transport mechanisms. Serosal SCFA release ranged between 105 and 126 mumol thus exceeding mucosal loss. In serosal solutions molar butyrate proportions were significantly lower in comparison with mucosal solutions. This was accompanied by slight increases of molar acetate proportions indicating intraepithelial butyrate cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)