2,4-diaminoanisole-induced thyroid pigmentation in rats inhibited by m-phenylenediamine

The effect of the carcinogenic hair dye component 2,4-diaminoanisole (2,4-DAA) on thyroid and pituitary morphology was studied. Heavy pigmentation of the hypertrophied thyroid epithelium was present when the animals were fed with 2,4-DAA for 6 weeks. Another hair dye component m-phenylenediamine (m-PDA), which lacks the methoxy group, and which is not carcinogenic, prevented the dark pigmentation of the thyroid epithelium caused by 2,4-DAA, but had only a slight effect on the hypertrophy of the gland. In the pituitary gland of 2,4-DAA-fed animals only a few aldehyde fuchsin positive thyrotrope cells were present. When 2,4-DAA and m-PDA were fed simultaneously, the number of hypertrophied chromophobic cells was greatly increased and the aldehyde fuchsin-positive cells were practically absent.