Modulation of distal colonic epithelial barrier function by dietary fibre in normal rats

Background-Dietary fibre influences the turnover and differentiation of the colonic epithelium, but its effects on barrier function are unknown. Aims-To determine whether altering the type and amount of fibre in the diet affects paracellular permeability of intestinal epithelium, and to identif y the mechanisms of action. Methods-Rats were fed isoenergetic low fibre diets with or without suppleme nts of wheat bran (10%) or methylcellulose (10%), for four weeks. Paracellu lar permeability was determined by measurement of conductance and Cr-51-EDT A flux across tissue mounted in Ussing chambers. Faecal short chain fatty a cid (SCFA) concentrations were assessed by gas chromatography, epithelial k inetics stathmokinetically, and mucosal brush border hydrolase activities s pectrophotometrically. Results-Body weight was similar across the dietary groups. Conductance and Cr-51-EDTA Aux were approximately 25% higher in animals fed no fibre, compa red with those fed wheat bran or methylcellulose in the distal colon, but n ot in the caecum or jejunum. Histologically, there was no evidence of epith elial injury or erosion associated with any diet. The fibres exerted differ ent spectra of effects on luminal SCFA concentrations and pH, and on mucosa l indexes, but both bulked the faeces, were trophic to the epithelium, and stimulated expression of a marker of epithelial differentiation. Conclusions-Both a fermentable and a non-fermentable fibre reduce paracellu lar permeability specifically in the distal colon, possibly by promoting ep ithelial cell differentiation. The mechanisms by which the two fibres exert their effects are likely to be different.