Author(s): Russo J, Tait L, Russo IH
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Abstract The rat mammary gland epithelium is composed of three cell types: dark cells (DCs), intermediate cells (ICs), and a layer of myoepithelial cells (MCs), which are evenly distributed along the mammary gland tree in rather constant proportions. The present study was carried out for a determination of the effect of the carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) on the distribution and proliferative activity of these cell populations. The proportion and the DNA labeling index (DNA-LI) of each cell type were determined in terminal end buds (TEBs), terminal ducts (TDs), alveolar buds (ABs), and alveoli of the normal Sprague-Dawley rat mammary gland and in intraductal proliferations (IDPs) and carcinomas removed at selected intervals after DMBA administration. DMBA-induced changes in cell distribution were limited to TEBs and TDs, whereas ABs and alveoli were unaffected. The alterations consisted in an increment in ICs from 11\% in TEBs and TDs to 90\% in tumors and a decrease in DCs from 77\% in TEBs and TDs to 7\% in tumors. MCs were relatively unaffected. The DNA-LI of DCs, which in the normal gland TEB was 14\%, was depressed by DMBA to 6\%, whereas the DNA-LI of ICs remained unchanged from the basal level of 40\% during the process of carcinogenesis. The progressive increment in number of ICs with a steady DNA-LI suggested that the IC is the target cell of the carcinogen and the cell of origin of mammary carcinomas.
This article was published in Am J Pathol
and referenced in Journal of Steroids & Hormonal Science