Pattern of distribution of cells positive for estrogen receptor alpha and progesterone receptor in relation to proliferating cells in the mammary gland

Since cell proliferation is indispensable for the growth and development of the breast, and estrogens are considered to play a major role in promoting cell proliferation, while progesterone influences its differentiation, the present work was designed with the purpose of verifying the relationship b etween cells containing steroid hormone receptors and proliferating cells i n the normal human breast. Twelve breast samples were analyzed for their co ntent of lobules type 1 (Lob1), Lob2, Lob3, and Lob4, and the number of cel ls containing estrogen receptor alpha (ER-alpha), progesterone receptor (Pg R), or expressing Ki67 antibody was determined by double immunocytochemical technique with specific antibodies. The highest percentage of ER-alpha, Pg R, and Ki67 positive cells was found in Lob1, with a progressive reduction in the more differentiated Lob2 and Lob3. ER-alpha and PgR positive cells w ere found exclusively in the breast epithelium and were negative for Ki67, while cells positive for Ki67 did not express receptors. These findings wer e compared with the distribution of ER-alpha and PgR in the autoradiographs of mammary gland of young virgin rats inoculated with H-3-thymidine for de termination of the DNA labeling index (DNA-LI). Both the DNA-LI and the per centage of ER-alpha and PgR positive cells were maximal in the epithelium o f terminal end buds, and these values were reduced in alveolar buds and lob ules. ER-alpha and PgR positive cells did not proliferate, and those cells that had incorporated H-3-thymidine were negative for both receptors. Our r esults led us to conclude that the content of ER-alpha and PgR in the norma l mammary tissue varies with the degree of lobular development, in parallel with cell proliferation. However, the expression of receptors occurs in ce lls other than the proliferating cells, indicating that they represent at l east two separate cell populations. These findings open new avenues towards the understanding of the mechanisms through which estrogens and progestero ne affect the proliferative activity of breast epithelial cells, and their role in the initiation of the cascade of events that leads a normal cell to cancer.