Analysis of biliary and urinary metabolites of 3'-methyl-4-(dimethylamino)azobenzene in rats.

Metabolites of 3'-methyl-4-(dimethylamino)azobenzene (3'-Me-DAB) in the rat bile and urine were investigated by the use of a tracer technique. 3H-3'-Me-DAB 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 beta-glucuronidase/arylsulfatase. The hydrolyzed metabolites were then extracted with chloroform or separated by chromatography on Amberlite XAD-2 using methanol as a solvent. The metabolites in the chloroform or methanol eluates were identified by the reverse isotope dilution analysis, before or after 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. On the other hand, the metabolites retaining the azo-linkage were scarcely detected in urine and instead 3-aminobenzoic acid, 3-amino-6-hydroxytoluene, and their N-acetylated products were major metabolites in urine. These results indicate that the metabolism of 3'-Me-DAB in the rat involves oxidation of the ring methyl group. Significance of the ring methyl group in the carcinogenic action of aminoazo dyes is also discussed.