[The effect of maternal exposure to dioxin on fetal steroidogenesis in the steroidogenic organs]

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exposed to pregnant or lactational mother impairs the reproduction and development of the pups. The defect is a serious problem, because it is caused by TCDD at much lower doses than that needed for acute toxicity in the mother. However, the toxic mechanism underlying the defect remains to be obscure. We have previously revealed that maternal exposure to TCDD (1 microg/kg) causes a reduction in luteinizing hormone in the fetal pituitary, leading to the reduced expression of testicular steroidogenic proteins such as steroidogenic acute-regulatory protein (StAR) and cytochrome P450 (CYP) 17. In addition, we have provided evidence that such a reduction imprints defects in sexual behaviors at adulthood. In this study, we investigated TCDD effect on fetal steroidogenesis in the extra-gonadal tissues. Even when pregnant Wistar rats at gestational day (GD) 15 were orally treated with TCDD (0.25, 1 or 3 microg/kg), neither expression of StAR nor CYP17 mRNA was affected in the adrenal gland, placenta and hypothalamus of male fetuses (GD20). However, TCDD induced placental StAR (3 microg/kg) and adrenal CYP17 mRNAs (0.25 microg/kg) in female fetuses. Therefore, our study suggests that while TCDD gives damage to male fetal steroidogenesis in a testis-specific manner, the dioxin enhances the steroidogenesis of the fetal adrenal gland and placenta in females. Thus, the mechanism whereby TCDD exerts its endocrine-disrupting properties is considered to differ, at least partially, between male and female fetuses.