The intestinal monoxygenase enzyme system in DMH-induced rat colonic carcinogenesis

Four enzymes of the microsomal mixed function oxidase system were studied in two different segments of each the small and large intestine and in the liver of untreated female Wistar rats. In order to test a possible induction of this enzyme system, due to the application of the colonic carcinogen N,N-dimethyl hydrazine, three of these enzymes were determined in the same intestinal segments, in the liver and, in addition, in the kidney after 4 and 8 weeks of DMH-treatment (weekly s.c. injections of 20 mg DMH/kg b.w.). In the untreated rats, the four enzymes under investigation revealed significantly higher specific activities in the liver and in the jejunum than in the ileum and colon. In the DMH-treated animals, liver AHH-activity was decreased after 4 and 8 weeks when compared with the EDTA-treated controls; so was the AHH in the jejunum and in the ileum after 8 weeks. Liver EOD was only decreased after 4 weeks and had normalized after 8 weeks, being diminished, however, in the jejunum at that time. UDP-GT-activity was not altered at all. No alterations of the investigated enzyme activities could be demonstrated either in the colonic segments or in the kidney. These findings indicate that a local induction of the mixed function oxidase system is not likely to be responsible for the organotropism of the DMH-induced colonic carcinogenesis.