Early
exposure of the rat mammary gland to estrogen and progesterone blocks
colocalization of ER expression and proliferation
Journal of Endocrinology v.171, i.1, Oct01
L Sivaraman, S G Hilsenbeck1, L Zhong, J Gay, O M Conneely, D Medina and B W O’Malley
Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA 1Breast Center, Baylor College of Medicine, Houston, Texas 77030, USA(Requests for offprints should be addressed to B O’Malley, Department of Molecular and Cellular Biology, Baylor College of Medicine, 1 Baylor Plaza, Houston, Texas 77030, USA)
Abstract
An early single full-term pregnancy induces a long-lasting protective effect against mammary tumor development in humans and rodents. This protective effect can be mimicked in rats by short-term administration of estrogen (E) and progesterone (P) hormones prior to carcinogen administration. Hormones of pregnancy are able to induce a proliferative block upon carcinogen challenge that is not observed in the age-matched virgin. We wished to determine whether carcinogen is needed to induce a paracrine-to-autocrine shift of proliferation in steroid receptor positive cells or if such a cell population already exists in the age-matched virgin mammary gland. Here we show that ER+ proliferating cells are rare in the developing mammary gland of the virgin rat but represent the majority of the proliferating cells in the mature (96 day old) mammary gland of the virgin rat. As the majority of the proliferating cells before carcinogen challenge were ER positive, the estrogen receptor positive proliferating cells in the mature mammary gland may represent the target cells for carcinogen-induced transformation. Importantly, prior exposure of the mammary gland to pregnancy levels of E/P blocked this positive association. This ability to block the proliferation of the ER+ cells may be one factor by which pregnancy induces protection against breast cancer.
source: http://journals.endocrinology.org/joe/171/joe1710075.htm 3oct01
|
If you have come to this page from an outside location click here to get back to mindfully.org |
