NTP evaluates differences in mammary gland development in rats
Researchers at the National Toxicology Program (NTP) designed a study to evaluate mammary gland development in different strains of rats commonly used in carcinogenicity studies. When scientists evaluate an endocrine disrupting chemical, they can assess the ability of that chemical to affect susceptibility to mammary tumor development when combined with a carcinogen challenge. However, the rate at which the mammary gland develops may differ between rat strains, and this information should be taken into consideration when designing the timing of carcinogen exposure. In this study, the rate of mammary gland development was evaluated in three different strains of rats based on a variety of growth and developmental parameters.
Mammary glands of two of the rat strains, Charles River Sprague Dawley and Charles River Long Evans, developed terminal end buds significantly earlier than the third strain, Harlan Sprague Dawley. These differences in the rate of development differed across the rat strains independently of other factors, such as body weight and timing of vaginal opening, which commonly play a role in development. These results indicate that when designing studies to evaluate susceptibility to mammary carcinogens, appropriate timing must be considered, to properly evaluate the cancer-causing potential of a chemical. (KS)
Citation: Stanko JP, Kissling GE, Chappell VA, Fenton SE. 2016. Differences in the rate of in situ mammary gland development and other developmental endpoints in three strains of female rat commonly used in mammary carcinogenesis studies: implications for timing of carcinogen exposure. Toxicol Pathol 44(7):1021−1033.