CECAL AND COLONIC TISSUE STRUCTURE AND PROLIFERATION AS INFLUENCED BYADAPTATION PERIOD AND INDIGESTIBLE POLYSACCHARIDES

Growing rats were fed experimental diets differing in the type of poly saccharide, 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 (F F), containing normal corn starch only, acted as a control diet, Caeca l 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 be tween the adaptation periods were small and inconsistent, Epithelial s tructure and cellular proliferation depended on the diet and diet effe cts appeared to be most pronounced in the caecum and least in the dist al colon. Epithelial cell migration rates were increased by diet RS an d to some extent by diet GG as compared to diet GEL. The more fermenta ble diets (diets GG and PEG) increased the labelling indexes in the ca ecum, 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 prol iferation zones, The expansion of the proliferation zone appeared to t ake place towards the crypt base rather than towards the crypt mouth, Only small changes in epithelial structure and proliferation were obse rved after day 9, indicating that adaptation to the experimental diets persisted for as long as the rats received the diets.