A stable isotope/GC-MS method for measuring mammary epithelial cell turnover in vivo

We developed a stable isotope gas chromatographic/mass spectrometric (GC/MS) method for measuring MEC proliferation in vivo. Using this method, the effects of genistein, a soy derived phytoestrogen, on rat mammary epithelial cell (MEC) proliferation were investigated in vivo . Interactions with timing of exposure and hormonal status were studied. Once developed in rodent models, the method was further developed for use in humans.; The first study, "Measurement of mammary epithelial cell proliferation with 2H2O in Rodents", demonstrated sensitivity of the stable isotope GC/MS method for measuring changes in MEC proliferation due to pregnancy or hormone treatment in ovariectomized rats. Labeling and delabeling experiments were also completed to characterize the kinetics of MEC proliferation in rats and mice. We conclude that extensive proliferation occurs in the pregnant mouse model, there is a dose-dependent increase in MEC proliferation through the physiological range of estrogen in the ovariectomized rat, and that there appears to be both fast and slow turnover epithelial cell populations within the mammary glands of rodents.; In the second study "Effects of genistein on mammary epithelial cell proliferation: interactions with timing of exposure and hormonal status" we applied this method to determine the effects of a promising chemopreventive agent, genistein, on rat MEC proliferation in vivo. This study was designed to measure the effects of pre-pubertal and adult genistein exposure in the adult rats, the interaction of genistein and estrogen in ovariectomized rats, and the effects of long-term dietary exposure in ovariectomized rats. We conclude that exposure during both pre-pubertal and adult stages significantly suppressed proliferation, but that exposure during either period by itself did not significantly alter proliferation. We also conclude that genistein did not have significant direct agonist effects in ovariectomized adult rats treated with estrogen compared to controls, nor in adult ovariectomized rats fed a genistein diet for 13 weeks.; Finally, the method was further developed for use in humans. The final study "A method for measuring breast epithelial cell proliferation in vivo in humans" describes the methods development process and presents normative breast epithelial proliferation data for women across a wide range of ages and with varying reproductive histories and hormonal status. We conclude that the stable isotope GC/MS method was successful in measuring in vivo breast epithelial cell proliferation in women, that there is significant inter-individual and intra-individual variability in proliferation rates and that both age and hormonal status significantly influence proliferation rates in women.