Influence of age and parity on the susceptibility of rat mammary gland epithelial cells in primary cultures to 7,12-dimethylbenz(a)anthracene.

Mammary gland epithelial cells from rats of different ages or with different reproductive histories vary in their proliferative properties and susceptibility to dimethylbenz(a)anthracene (DMBA) carcinogenesis in vivo. The present study was carried out to determine whether these differences are maintained under in vitro conditions. Primary cultures of mammary gland epithelial cells of young virgin, old virgin, and parous rats were treated with various doses of DMBA. Growth rates, DNA synthesis, and dose-response curves were determined; the toxicity of DMBA was measured by its effect on cell growth. Cell morphology was studied by transmission and scanning electron microscopy. Epithelial cells from the mammary gland of young virgin rats adapted rapidly to the culture conditions, behaving as if the cells were in the logarithmic phase of growth prior to plating. Mammary gland epithelial cells from old virgin and parous rats required a lag period prior to cell growth during which the proliferating cells adapted to the culture conditions. Cells from each group had comparable doubling times, and DNA synthesis peaked approximately 1 d after initiation of growth in culture. The numbers of proliferating cells decreased with increasing age and parity of the donor. Mammary gland epithelial cells of young virgin rats were more susceptible to both low and high doses of DMBA than those of old virgin and parous rats when the carcinogen was added either 24 h after plating or at the peak of DNA synthesis. These results indicate that age and parity influence the proliferative status of the cells and their susceptibility to DMBA in vitro, simulating in that way the in vivo situation.