Phenobarbital and 3-methylcholanthrene treatment alters phase I and II enzymes and the sensitivity of the rat colon to the carcinogenic activity of azoxymethane.

It has been hypothesized that cancer risk may be influenced by phase I and II drug-metabolizing enzyme systems. This study attempted to determine the relationship between colon phase I and II enzyme activity and the subsequent induction of aberrant crypt foci (ACF), preneoplastic lesions by azoxymethane (AOM), a colon-specific carcinogen. Phenobarbital (PB) and 3-methylcholanthrene (MC) treatment (prototype hepatic inducers of phase I and II enzymes) provided the framework to study the induction of phase I and II enzymes in the rat colonic mucosa. Following induction for five consecutive days, the animals were given a single injection of AOM. Phase I and II enzymes were determined fluorometrically and spectrophotometrically and ACF were identified microscopically. Phase I and II xenobiotic metabolizing enzymes were induced in the rat colonic mucosa by prototype hepatic inducers. A lower number of ACF and crypt multiplicity was observed in animals induced with MC than in those in the non-induced and PB groups. Altered levels of phase I and II enzymes in the colon during preinitiation stages were associated with modulation in the growth of ACF, putative preneoplastic lesions.