C.J. Fong, M.R. Fielden, S.Z. Haslam, T.R. Zacharewski.
Department of Biochemistry & Molecular Biology, Institute of Environmental Toxicology, National Food Safety & Toxicology Center, Michigan State University, East Lansing, MI, USA, 48824.

There exists paradoxical results demonstrating opposite effects of prenatal and postnatal exposure to estrogens on mammary gland development, however, the effects of gestational and lactational exposure to estrogens has not been described. The objective of the study was to assess the effects on mammary gland morphology following gestational and lactational exposure to maternal doses of 0, 0.1, 1, and 10 µg/kg diethylstilbestrol (DES) or 0, 0.1, 0.5, 2.5 and 10 mg/kg genistein (GEN) from gestational day 12 to postnatal (PND) 21. The doses of genistein approximated human exposure levels. Body weight and anogenital distance (AGD) of female B6D2F1 offspring were measured on PND 7, 21 and 49. Mammary gland whole mounts were examined on PND 49 for epithelial growth (% of fat pad occupied by epithelium), length of mammary epithelial tree, number of terminal end buds (TEBs, undifferentiated proliferating structures) and density of alveolar buds (ABs, differentiated milk secreting lobules). Prior to analyzing female offspring, an initial study was performed to determine the time course (3, 4, 5, 7 and 10 weeks) of mammary gland development in naïve female B6D2F1 mice. Seven weeks of age was chosen as a suitable time point to examine treatment-related changes in mammary development. There were no significant changes in body weight or AGD in female offspring of DES or GEN treated dams. Although there was a trend towards an increase in mammary gland growth and an increase in alveolar bud formation in DES-exposed offspring, the results were not significant due to large interlitter variability. We also did not detect any significant changes in mammary growth, TEBs, or ABs in GEN-exposed offspring. These results suggest that combined gestational and lactational exposure to genistein has little effect on mammary gland morphology at human exposure levels.