Date of Defense

Fall 11-11-1977


Biological Sciences


The dependence of experimental mammary tumors on hormonal status is well established. Ovarian steroids and pituitary hormones have been demonstrated to be critical importance in the initiation, promotion and maintenance of mammary tumors. This study investigates mammary tumorigenesis in pregnant and non-pregnant female rats by two carcinogens, Dimethylbenz(a)anthracene (DMBA) and N-Mthyl-N-nitrosourea (MNU). A procedure for detecting single strand breaks in H3-labelled DNA in mammary tissue from pregnant rats was developed. This method, per se, was not applicable to virgin tissue, due to a smaller and less proliferative epithelial cell population. Extensive and dose dependent damage was detected in mammary cell preparations from MNU treated pregnant rats, while no damage was detected in DMBA treated pregnant rats. The observed DNA damage correlated with tumor incidence of carcinogen treated rats (i.e. DMBA treated rats had no DNA damage to mammary tissue and control tumor incidence, while MNU treated rats had extensive damage and high incidence of mammary tumors). Tumor incidence, latent period and number of tumors per animal were significantly different between virgin females and those which were pregnant when treated with either DMBA or MNU.

Access Setting

Honors Thesis-Campus Only