Abstract. The effects of bisphenol A (BPA) on placentation have not been fully determined. The aim of this study was to clarify the structural changes of the placenta, abortion rate, and survival of neonates after BPA administration in mice. BPA (10 mg/kg/day) was administered to pregnant mice (BPA mice) subcutaneously from the first day of pregnancy (Day 0) to Day 7 (8 days total). The number of embryos and weights of whole uteri were measured on Days 10 and 12. Morphological changes in the placentae were examined by light microscopy on the corresponding days of pregnancy. The number of neonates was also counted. Survival rates were periodically calculated for neonates from the first day after parturition (P-Day 0) to P-Day 56. The number of embryos and weight of the uterus on Days 10 and 12 were significantly decreased by BPA injection. No notable differences were recognized between the left and right uteri. The proportion of the labyrinthine zone per whole placenta in the BPA mice became lower than that in the controls, and that of the metrial gland was higher in the BPA mice. The intervillous spaces of the placenta were narrower in the BPA mice. Degenerative changes were found in the trophoblastic giant cells and spongiotrophoblast layers of the BPA mice. The number of BPA mouse neonates was drastically decreased within 3 days after birth, and no mice survived after P-Day 56. The results suggest that BPA not only disrupts placental functions and leads to abortion through chronic stimulation of gene expression by binding to DNA but that it also affects the mortality of neonates through indirect exposure of embryos.

ABSTRACT. To understand effects of Bisphenol-A (BPA) exposure on the reproductive organ across generations, we analyzed morphology of the uterus and ovary, and the methylation pattern of HOXA10 gene of the 2 nd generation. Pregnant mice (F0) were treated with sc injection of BPA in sesame oil at various doses of 0-1,000 mg/kg Bwt on days 12-16 of gestation. Their offspring (F1) were bred by foster mice, and the offspring (F2) from F1 mice were prepared. That is, F1 mice experienced in utero BPA exposure during the developmental period of reproductive organs, while F2 mice did not at all. Using these F2 mice, the present study was carried out. Comparing to the control, the body weights in BPA exposure groups were significantly increased. Correlating with the increase of body weight, the relative weights of the ovary and uterus in each group were decreased. The histological analysis revealed expansion or emphraxis of the uterine lumen and partial loss of the uterine epithelium. Unmethylation of HOXA10 gene in the uterus was observed in the intron region. The present study suggested that BPA exposure to F0 mice could affect reproductive organ of F2 mice who were not exposed to BPA. Bisphenol-A (BPA) is a nonsteroidal estrogen that is ubiquitous in the environment. There are a lot of reports about effects of BPA on formation and function of female reproductive organs. Among these reports, well known are (i) that BPA exposure advanced puberty [6], (ii) that BPA exposure changed patterns of estrous cycle [11], (iii) that BPA exposure brought about the loss of uterine decidualization [13], and (iv) that BPA exposure decreased the endometrial weight and increased expressions of estrogen receptor  and progesterone receptor [7]. We previously reported that BPA exposure during implantation and placentation periods decreased the number of fetus and pups, and the survival rate before weaning [14]. These suggest that in utero BPA exposure altered reproductive performance and formation of reproductive organs. DNA methylation is supposed to be one of the ways that BPA induces the endocrine disruption. DNA methylation regulates gene expression that is involved with growth and development [3,8]. There are many reports that unmethylation by BPA occurred in the promoter region of phosphodiesterase type 4 [5], that BPA induced unmethylation of agouti gene, using the viable yellow agouti (Avy) mouse [4], and that in utero BPA exposure brought about unmethylation of HOXA10 gene [2,12]. These suggest that BPA exposure can also affect molecular biologically next generation. The present study is designed to understand effects of BPA exposure on the reproductive organ across generations. We analyzed the morphology of uterus and ovary, and the methylation pattern of HOXA10 gene using the next generation of the offspring that was born from mother exposed to BPA. ICR mice obtained from Kyudo Company (Saga, Japan) were used in this study. Mice were housed in standard polypropylene cages in a temperature-controlled room (22°C) with a 12 hr li...