Abstract

The effects of indole and l-tryptophan feeding on the activities of two liver microsomal enzymes, dimethylnitrosamine demethylase (DMN-d) and arylhydrocarbon hydroxylase (AHH), were studied in rats and hamsters. Both indole and tryptophan increased cytochrome P-450 concentration and DMN-d activity in rats, but only indole was effective in hamsters. AHH activity in both species was induced by indole. Both indole and tryptophan increased the ratio A 392–500nm/ A 410–500nm obtained by n-octylamine difference spectroscopy of rat liver microsomes but not of hamster liver microsomes. Indole increased the absorbance difference ratio A 455–500nm/ A 430–500nm of rat liver cytochrome P-450 obtained by ethyl isocyanide. The opposite was true for hamsters, which showed a low band at 455 nm. Indole gave a type II binding spectrum with rat liver microsomes, but the values for absorption minimum and maximum for tryptophan were somewhat outside the reported values for type II binders. Indole which induced liver AHH activity, protected against 7,12-dimethylbenz[a]anthracene (DMBA)-produced mammary gland carcinogenicity, whereas tryptophan was without effect.

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