Bisphenol A (BPA), a monomer used for the production of polycarbonate, is known to have estrogen activity. In this study, pregnant mice were fed chow diet containing 1% BPA, and we examined the influence of dietary BPA on delivery and growth of newborn pups in mice. When pregnant mice were fed BPA diet, the mice normally delivered pups on day 21 of gestation. The number of offspring pups in maternal mice fed BPA diet was same to those fed normal diet. Therefore, the growth of fetuses and the process of delivery were not influenced by dietary BPA. However, the growth of newborn pups was markedly suppressed when maternal mice were fed BPA diet. The growth of neonatal mice depends on breast milk, and stomach was filled with milk in pups. In newborn pups from maternal mice supplemented with BPA diet, the weight of stomach was lower than that from maternal mice with normal diet. Since the serum level of prolactin was limited in maternal mice supplemented with BPA diet, the suppressed growth of newborn pups by dietary BPA may be due to the insufficient supply of breast milk. These results suggest that the influence of BPA on the growth of newborn pups is related to hormonal condition in maternal mice.Key words ---bisphenol A, breast milk, growth of pups, prolactin
INTRODUCTIONBisphenol A (BPA) is a class of monomer widely used in the production of polycarbonate plastic products. The level of human exposure to BPA is not insignificant, as microgram amounts of BPA were reported to be detectable in liquid from canned vegetables.1) Since children are thought to be more sensitive to endocrine disrupters including BPA than adults, the influence of the exposure of BPA may depend on age and hormonal condition. BPA binds to estrogen receptor with approximately 10000 times less affinity than 17β-estradiol and it exhibits estrogenic activity both in vitro and in vivo assay systems.2) In vivo assay, BPA enhances the uterine weight in immature animals, and accelerate the onset of puberty.3) It is known that BPA exhibits estrogenic properties in sexual organs, but the effects of BPA in vivo are still not clear.Estrogens are synthesized from androgens by aromatase (CYP19). 4) We have reported that aromatase-deficient (ArKO) mice show underdeveloped uteri and mammary gland, bone loss by increased bone resorption and abnormal lipid metabolism.5-7) All of these phenotypes in ArKO mice are due to estrogen deficiency caused by loss of aromatase, and the replacement of estrogen restore these phenotypes to normal. When ArKO were fed chow diet supplemented with 0.1% or 1% BPA, they were protected from ovarian degeneration, uterine diminution and bone loss in a dose-dependent manner.8) Therefore, estrogenic effects of BPA on the reproductive tract as well as skeletal tissue were evident in adult female ArKO mice. Since ArKO mice completely lose estrogen synthesis, ArKO is a useful animal model for characterization of estrogenic compounds. However, the influence of estrogenic compounds in normal animal may be related to the hormonal condition...