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

亚洲软毛大鼠（milardia meltada）成年雄性在腹股沟区有色素乳腺组织，与雌性的第三乳腺相对应。在肿瘤易发系中，黑色色素沉着的程度与肿瘤的发展密切相关。女性乳腺镜下无色素及肿瘤。黑色乳腺组织由富含色素的增生性腺泡细胞组成。电镜下，增生性腺泡细胞有大小不一的次级溶酶体。作为重金属，在颜料颗粒中只检测到铁。此外，一系列脂褐素染色均为阳性，与色素的色调和胞浆内分布最吻合。少数无特定病原体系的雄性在老年时发生乳腺肿瘤。这些肿瘤，以及那些易患肿瘤的细胞系，在雄性裸鼠身上发生。雄激素治疗导致所有女性乳腺黑色色素沉着，但没有发生肉眼可见的肿瘤。所有这些数据表明，雄性米拉迪亚黑乳组织的色素最有可能是脂褐素和含铁血黄素。由于到目前为止还没有证据表明逆转录病毒参与乳腺米拉迪亚病毒的肿瘤发生，色素沉积与肿瘤发生之间的可能关系值得进一步研究，例如，从自由基形成的角度来看。

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.