Relationship of hydrolase activities to epithelial cell turnover in distalcolonic mucosa of normal rats

Background: The relationships between changes induced by diet in colonic ep ithelial kinetics and in the activities of brush border hydrolases are poor ly defined. The aims of this study are to define these relationships, as ch anges in kinetics would be expected to influence differentiation, and to de termine whether the type of ingested dietary indigestible carbohydrates inf luences hydrolase activities. Methods: Groups of eight rats were fed a low fibre diet +/- supplements of different types of indigestible carbohydrates for 4 weeks. Alkaline phospha tase (ALP) and dipeptidyl peptidase IV (DPPIV) activities and epithelial ki netics were measured in distal colonic mucosa. Results: Median ALP activities correlated positively and DPPIV activity neg atively with the median proportion of cells entering metaphase (r=0.58 and -0.58, respectively; P<0.05) and number of metaphase arrests per crypt colu mn across the diets (r=0.59 and -0.58, respectively; P<0.05). Step-wise reg ression analysis showed that both hydrolases independently predicted these kinetic indices (R-2 > 63% for each). Mucosal ALP activities were markedly elevated during consumption of raw potato starch, guar gum and methylcellul ose, while only potato starch caused a significant elevation of DPPIV activ ities. Conclusions: The type of indigestible carbohydrate in the diet influences c olonic mucosal hydrolase activities. The opposite relationship between kine tics and each of the two hydrolases indicates that these hydrolases do not reflect the same event; dipeptidyl peptidase IV might relate to differentia tion status while ALP could also be influenced by epithelial irritation due to changes in luminal conditions. (C) 1999 Blackwell Science Asia Pty Ltd.