The colonic mucus barrier lines the entire colon and acts as the first line of innate protection of the body against the myriad factors within the colonic lumen. Vital to this protective role are the maximal attainable thickness of the mucus barrier, as well as the rate of mucus replenishment. This study aimed to test whether certain colonic luminal factors, namely dietary fibre type, butyrate and reactive oxygen species (ROS), could alter these measures of colonic mucus barrier functionality.

Male Wistar rats were terminally anaesthetised by intraperitoneal administration of 0.26 ml (g body weight)^-1 Inactin. Colonic mucus layer dynamics were measured in vivo using the methods of Atuma et al. (2001). For dietary fibre studies, rats (n = 10 for each diet) were fed diets containing approximately 14 % w/w fibre, except the fibre-deficient diet. Various saline-based ROS-generating solutions (0.5 mM EDTA/Fe²⁺ and 5-50 mM H₂O₂) and 7 mM butyrate were applied to the colonic lumen of separate animals (n = 5). The effects of these luminal agents on colonic mucus barrier thickness and mucus replenishment rate were then assessed. One-way analysis of variance was used for statistical analyses (significant difference taken as P < 0.05). Butyrate at 7 mM trebled the rate of mucus replenishment (compared to saline controls).

ROS-generating solutions containing 17.5 mM H₂O₂ or higher significantly reduced maximal mucus thickness linearly over time, by as much as 50 % of the initial thickness (in the case of 50 mM peroxide). The mean effects of dietary fibre types on colonic mucus dynamics are summarized in Table 1. High levels of ROS in the colon reduce the protective capacity of the mucus layer. Low ROS (5 mM) and 7 mM butyrate increase mucus barrier functionality. Feeding rats on diets containing wheat bran and ispaghula husk increased mucus barrier function compared to cellulose and pectin. The latter two diets showed similar trends on mucus barrier dynamics to a fibre-deficient diet.

This study suggests that the protective action of the colonic mucus barrier, and therefore the potential for mucosal damage, is altered by colonic luminal factors of dietary and bacterial origin.