Possible relationship between black pigmentation and tumor development in the inguinal mammary tissues of tumor-prone male Millardia meltada.

点击翻译按钮获取中文摘要

Adult males of Asian soft-furred rat,Millardia meltada,had pigmented mammary tissues in the inguinal region, corresponding to the 3rd mammary gland of the female. The degree of black pigmentation was closely related to tumor development in tumor-prone lines. Female mammary glands were macroscopically free of pigment and tumor. Black mammary tissues consisted of pigment-laden hyperplastic acinar cells. Electron microscopically,hyperplastic acinar cells had various-sized secondary lysosomes. As a heavy metal,only iron was detected in the pigment granules. In addition,a battery of stains for lipofuscin were all positive and fitted best with the tone and intracytoplasmic distribution of the pigment.A few males of the specific-pathogen-free line developed mammary tumors at an old age. These tumors,as well as those of tumor-prone lines,took in male nude mice. Androgen treatments induced black pigmentation in all mammary glands of females,but no macroscopic tumor developed. All these data suggest that the pigments of the black mammary tissues of Millardia males are most likely lipofuscin and hemosiderin. Since there is so far no evidence for retrovirus involvement in Millardia mammary tumorigenesis,a possible relationship between the deposits of the pigments and tumorigenesis merits further studies,for example,from the point of view of free radical formation.