Carcinogenic Azo Dyes. XI. Analysis of Biliary and Urinary Metabolites of 3'-Methyl-4-(methylamino) azobenzene in Rat

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Metabolites of 3'-methyl-4-(methylamino) azobenzene (3'-Me-MAB) in the rat bile and urine were investigated by use of a tracer technique. ³H-3'-Me-MAB in cottonseed oil was administered orally by a stomach tube. The dye metabolites in the bile and urine collected during 24 hr after the administration were hydrolyzed with β-glucuronidase/arylsulfatase. The hydrolyzed metabolites were then extracted with chloroform or separated by chromatography on an Amberlite XAD-2 using methanol as solvent. The metabolites in the chloroform extract or methanol eluate were identified by the reverse isotope dilution analysis, after or before separation by thin-layer chromatography. The N-demethylated, aryl hydroxylated, and their azo-reduced products were detected in the bile, in addition to the products oxidized at the ring methyl group as the new metabolites of 3'-Me-MAB. On the other hand, the metabolites retaining the azo-linkage were hardly excreted in urine. Instead, 3-aminobenzoic acid, 3-amino-6-hydroxytoluene, and their N-acetylated products were major metabolites in urine. The present results indicate that the metabolism for 3'-Me-MAB in the rat involves oxidation at the ring methyl group. Effect of the ring methyl group on the carcinogenic action of aminoazo dyes is also discussed.