Caecal and colonic tissue structure and proliferation as influenced by adaptation period and indigestible polysaccharides

Growing rats were fed experimental diets differing in the type of polysaccharide, for adaptation periods of either 9, 19, 33, 47, or 61 days. The experimental diets contained 8% of either cellulose (GEL), guar gum (GG), pectin (PEG), or resistant starch (RS). A fibre-free diet (FF), containing normal corn starch only, acted as a control diet, Caecal and colonic proliferation activities, in terms of labelling indexes, were significantly higher at the initiation of the experiment (day 0) than observed after the respective adaptation periods, Differences between the adaptation periods were small and inconsistent, Epithelial structure and cellular proliferation depended on the diet and diet effects appeared to be most pronounced in the caecum and least in the distal colon. Epithelial cell migration rates were increased by diet RS and to some extent by diet GG as compared to diet GEL. The more fermentable diets (diets GG and PEG) increased the labelling indexes in the caecum, proximal colon and, to some extent, the distal colon compared to the diet with microbially inert fibre (diet GEL), In the caecum, the increased labelling index was associated with an expansion of the proliferation zones, The expansion of the proliferation zone appeared to take place towards the crypt base rather than towards the crypt mouth, Only small changes in epithelial structure and proliferation were observed after day 9, indicating that adaptation to the experimental diets persisted for as long as the rats received the diets.