Modification of transplacental distribution of salicylate in rats by acidosis and alkalosis

Mechanisms regulating toxicant disposition to the embryo during early pregnancy: An interspecies comparison

The dose of toxicant reaching the embryo is a critical determinant of developmental toxicity, and is likely to be a key factor responsible for interspecies variability in response to many test agents. This review compares the mechanisms regulating disposition of toxicants from the maternal circulation to the embryo during organogenesis in humans and the two species used predominantly in regulatory developmental toxicity testing, rats and rabbits. These three species utilize fundamentally different strategies for maternal-embryonic exchange during early pregnancy. Early postimplantation rat embryos rely on the inverted visceral yolk sac placenta, which is in intimate contact with the uterine epithelium and is equipped with an extensive repertoire of transport mechanisms, such as pinocytosis, endocytosis, and specific transporter proteins. Also, the rat yolk sac completely surrounds the embryo, such that the fluid-filled exocoelom survives through most of the period of organogenesis, and can concentrate compounds such as certain weak acids due to pH differences between maternal blood and exocelomic fluid. The early postimplantation rabbit conceptus differs from the rat in that the yolk sac is not closely apposed to the uterus during early organogenesis and does not completely enclose the embryo until relatively later in development (approximately GD13). This suggests that the early rabbit yolk sac might be a relatively inefficient transporter, a conclusion supported by limited data with ethylene glycol and one of its predominant metabolites, glycolic acid, given to GD9 rabbits. In humans, maternal-embryo exchange is thought to occur via the chorioallantoic placenta, although it has recently been conjectured that a supplemental route of transfer could occur via absorption into the yolk sac. Knowledge of the mechanisms underlying species-specific embryonic disposition, factored together with other pharmacokinetic characteristics of the test compound and knowledge of critical periods of susceptibility, can be used on a case-by-case basis to make more accurate extrapolations of test animal data to the human.

Maternal Exposure to Bisphenol A during Late Pregnancy Resulted in an Increase of Calbindin-D9k mRNA and Protein in Maternal and Postnatal Rat Uteri

It has been reported that Calbindin-D9k (CaBP-9k) is rapidly and strongly induced by environmental estrogenic compounds, possibly through estrogen receptors (ERalpha) in the uterus of mammals. CaBP-9k can be evaluated as an early gene marker for assaying estrogenic effects of putative environmental chemicals in the rat uterus. This study was undertaken to investigate CaBP-9k mRNA and protein expression in the postnatal rat uterus following maternal exposure to 17beta-estradiol (E2) and bisphenol A (BPA) during the neonatal period. Treatment with a high dose of BPA (600 mg/kg body weight (BW) per day) resulted in a 3-fold increase in CaBP-9k mRNA expression for 3 days, while a single dose of E2 (40 microg/kg BW per day) induced 2-fold increase of this gene in the maternal uterus. In an agreement with maternal CaBP-9k mRNA, postnatal CaBP-9k mRNA in the uterus increased 4-fold when treated with BPA (600 mg/kg BW per day). In addition, treatment with increasing concentrations of BPA resulted in significant increases in CaBP-9k protein in the maternal rat uterus. It is of interest that increasing doses of BPA induced a significant ERalpha mRNA increase in the postnatal uterus. Furthermore, immunohistochemistry revealed that treatment with BPA induced CaBP-9k protein in the maternal uterus. We demonstrated that maternal exposure to BPA during late pregnancy induced CaBP-9k mRNA and protein in maternal and postnatal rat uteri. These results suggest that rapid absorption and distribution of environmental estrogenic compounds occurs in maternal and neonatal rat uteri and these chemicals can easily pass though the placenta during pregnancy to affect postnatal reproductive functions.

Induction of Calbindin-D9k Messenger RNA and Protein by Maternal Exposure to Alkylphenols During Late Pregnancy in Maternal and Neonatal Uteri of Rats1

Environmental chemicals are proposed to possess hormone-like properties, such as mimicking natural hormones, inhibiting the action of hormones, and inducing abnormal gene expression. Among environmental chemicals, the alkylphenol products (APs), octylphenol (OP) and nonylphenol (NP), are derived from alkylphenol ethoxylates and have been reported to be environmentally persistent. Thus, in the present study, we examined the effect of two APs, OP and NP, on the expression of Calbindin-D(9k) (CaBP-9k) following maternal exposure during late pregnancy in maternal and fetal uteri. Treatment with a high dose (600 mg/kg body weight [BW]) of OP and NP resulted in an induction of CaBP-9k mRNA at Day 5 of lactation, as did a single treatment with diethylstilbestrol (DES) and 17beta-estradiol (E2) in maternal uteri. The expression of CaBP-9k mRNA was also induced following treatment with a high dose (600 mg/kg BW) of OP, transferred from the mother, exposed to fetuses during late pregnancy, and persisted through Day 5 of lactation. It is of interest that treatments with high doses of OP (400 and 600 mg/kg BW) reduced the expression of maternal estrogen receptor alpha (ERalpha) mRNA, as E2 did. However, all doses of NP resulted in an inhibition of neonatal ERalpha, while only the high does of OP (600 mg/kg BW) induced the reduction of neonatal ERalpha mRNA expression, as E2 did. Parallel to mRNA, the expression of CaBP-9k protein was significantly induced by treatment with a high dose of OP and NP. In conclusion, maternal exposure to APs, OP and NP, during late pregnancy increased the expressions of CaBP-9k mRNA and protein in maternal and neonatal uteri. These results suggest that the absorption and distribution of environmental estrogenic compounds in maternal and neonatal uteri are extremely rapid, and these chemicals can easily pass though the placenta during pregnancy to affect functions of neonatal reproductive tissues.

Maternal-fetal transfer of endocrine disruptors in the induction of Calbindin-D9k mRNA and protein during pregnancy in rat model

Estrogenic compounds may influence the growth, differentiation and function in many target tissues, especially in the female reproductive tract during pregnancy. The present study was designed to investigate whether CaBP-9k expression in the maternal tissues and fetal uterus is altered following maternal treatment with diethylstilbestrol (DES), 17beta-estradiol (E2), 4-tert-octylphenol (OP), nonylphenol (NP) and bisphenol A (BPA) during late pregnancy. The expression level of CaBP-9k mRNA in maternal uterus significantly increased when treated with a high dose (600 mg/kg BW per day) of OP and NP. Interestingly, the expression level of CaBP-9k mRNA in extra-embryonic membrane decreased in a dose-dependent manner, suggesting that the expression level of CaBP-9k mRNA in the fetal membrane may be differentially regulated when compared to the expression of CaBP-9k in maternal uterus. In parallel with CaBP-9k mRNA level, a high dose (600 mg/kg) of OP and BPA resulted in an increase of CaBP-9k protein in maternal uterus and low dose of OP and NP increased the expression level of CaBP-9k protein in the placenta. High doses of BPA (400 and 600 mg/kg) resulted in an increase of CaBP-9k protein in maternal uterus and placenta, indicating that these estrogenic compounds may affect both maternal uterus and placenta in the induction of CaBP-9k mRNA and/or protein. In parallel with the expression level of CaBP-9k, mRNA decreased in extra-embryonic membrane, treatment with OP (400 and 600 mg/kg) resulted in a significant decrease of CaBP-9k protein in this tissue, suggesting that both CaBP-9k mRNA and protein may be conversely regulated by OP in extra-embryonic membrane when compared to other tissues. Treatment with OP, NP, and BPA induced a significant increase of CaBP-9k mRNA in fetal uterus, indicating that maternally injected estrogenic compounds may transfer directly from placenta to fetus in the induction of fetal uterus CaBP-9k gene. Taken together, we demonstrated for the first time that maternally injected estrogenic compounds resulted in an increase of CaBP-9k mRNA and/or protein in the maternal tissues (uterus and placenta) and fetal uterus during late pregnancy, suggesting that placenta may not be a reliable barrier against these estrogenic compounds for fetal health.

Disposition of orally administered 2,2-Bis(4-hydroxyphenyl)propane (Bisphenol A) in pregnant rats and the placental transfer to fetuses

We studied the disposition of bisphenol A (BPA) in pregnant female F344/DuCrj(Fischer) rats and its placental transfer to fetuses after a single oral administration of 1 g/kg BPA dissolved in propylene glycol. BPA in maternal blood, liver, and kidney reached maximal concentrations (14.7, 171, and 36 microg/g) 20 min after the administration and gradually decreased. The levels were 2-5% of the maximum 6 hr after the administration. The maximal concentration of BPA in fetuses (9 microg/g) was also attained 20 min after the administration. BPA levels then gradually reduced in a similar manner to maternal blood. These results suggest that the absorption and distribution of BPA in maternal organs and fetuses are extremely rapid and that the placenta does not act as a barrier to BPA.