EFFECT OF DIETARY FIBER ON CYTOCHROME-P450IA1 INDUCTION IN RAT COLONIC MUCOSA

The effect of dietary fiber on the induction of cytochrome P450IA1 in rat colonic mucosa after a single intragastric injection of 3-methylcholanthrene (3MC, 20 mg/kg) was investigated by examining the drug-metabolizing enzyme activity, immunoblotting for cytochrome P4501A1 and immunohistochemistry. 7-Ethoxycoumarin-O-deethylase activities were approximately 20-fold higher in microsomes from both proximal and distal portions of the colonic mucosa of control diet-fed 3MC-treated rats compared with those of control diet-fed untreated rats. Strong immunofluorescence for cytochrome P4501A1 was localized in the cytoplasm of the colonic mucosa surface epithelium from the control diet-fed 3MC-treated rats. 7-Ethoxycoumarin-0-deethylase activity and cytochrome P450IA1 content determined by immunoblotting were significantly lower in wheat bran-fed 3MC-treated rats than in control diet-fed 3MC-treated rats. Immunohistochemical analysis showed much weaker immunofluoresence for cytochrome P4501A1 in the surface epithelium of the colonic mucosa of the wheat bran-fed 3MC-treated rats. These observations suggested that dietary fiber can affect the induction of cytochrome P4501A1 in colonic mucosa by dietary inducers or carcinogens.