Short-term exposure to estrogen and progesterone induces partial protection against N-nitroso-N-methylurea-induced mammary tumorigenesis in Wistar--Furth rats.
The lifetime protective effect of a full term pregnancy for breast cancer is a reproducible and consistent finding in human beings and in rodent models. The duration of pregnancy necessary to confer protection has yielded contradictory results. As the administration of estrogen and progesterone mimics the full-term pregnancy effect on conferring protection, we examined whether short-term exposure to estrogen and progesterone confers protection against N-nitroso-N-methylurea-induced mammary carcinogenesis in Wistar--Furth rats. The results reported herein show that treatment of rats with estrogen or progesterone alone for 21 days does not confer protection, but a 10-day exposure to the same concentrations of estrogen and progesterone induced a partial protective effect. The significance of these results are discussed in terms of the contradictory results in the literature and the role of morphological differentiation in conferring the protective effect.
Medina
D
D
Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Peterson
L E
LE
Moraes
R
R
Gay
J
J
D000230:Adenocarcinoma / Q000139:chemically induced / Q000517:prevention & control*; D000818:Animals; D016588:Anticarcinogenic Agents / Q000494:pharmacology*; D002273:Carcinogens; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000254:growth & development; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced / Q000517:prevention & control*; D008770:Methylnitrosourea; D011374:Progesterone / Q000494:pharmacology*; D051381:Rats; D011920:Rats, Inbred WF
D016588:Anticarcinogenic Agents; D002273:Carcinogens; D004967:Estrogens; D011374:Progesterone; D008770:Methylnitrosourea