Mutagenicity of the urine extracts of the rats to which either
o-tolidine or Evans Blue, an
o-tolidine-based azo dye, had been orally given was assayed in the Salmonella/mammalian-microsome test. The urine extracts obtained from the rats treated with
o-tolidine showed stronger mutagenicity than
o-tolidine itself. While Evans Blue did not show mutagenicity at all, the urine extracts derived from the substance were found mutagenic. Both 3, 3'-dimethyl-
N-acetylbenzidine and 3, 3'-dimethyl-
N,
N'-diacetylbenzidine were identified as urinary metabolites of
o-tolidine. They were found not only in the urine of the rats treated with
o-tolidine but also in the urine of the rats to which Evans Blue had been orally administered. The experimental results suggest that the accidental intake of biphenyl-based dyestuffs through the mouth should be cautiously avoided. Some aspects of the metabolism of
o-tolidine and Evans Blue are discussed along with the problem associated with the mutagenic activities of the
o-tolidine metabolites.
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