Effect of lactational exposure to 1,2,3,4- tetrachlorodibenzo-p-dioxin on cytochrome P-450 1A1 mRNA in the neonatal rat liver: quantitative analysis by the competitive RT-PCR method.

BACKGROUND AND METHODS

The aim of this study was to assess the effect of lactational exposure to dioxins in neonates on the cytochrome P450 1A1 (CYP1A1) induction in the level of gene expression. Maternal rats were treated with a single dose of 50 or 100 micromol/kg 1,2,3,4-tetrachlorodibenzo-p-dioxin (1,2,3,4-TCDD), a low potent congener of dioxins, on the first day post-partum (day 1). Induction of CYP1A1 mRNA expression was quantitatively analyzed by the competitive reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS

The CYP1A1 mRNA was detectable at extremely low amounts in the liver of control neonates and mothers. The mRNA ratios of CYP1A1 to beta-actin in neonates were dose-dependently increased by the treatment of 1,2,3,4-TCDD of their mothers. Its peak occurred on day 6 and was sustained at the same level on day 10. Increases of the ratio with 100 micromol/kg 1,2,3,4-TCDD on day 2, 6 and 10 were 26-, 40- and 40-fold of the appropriate controls, respectively. These levels paralleled the activity of ethoxyresorufin-o-deethylase, representing CYP1A mediated monooxygenase. In the mother, the mRNA ratio was increased only to threefold of the control, 10 days after treatment.

CONCLUSION

Current RT-PCR procedure enabled to assess both constitutive and induced levels of CYP1A1 mRNA in the neonatal rat livers. Although the dose of 1,2,3,4-TCDD selected in this study was about 5000 times higher than the daily intake of dioxins in breast-fed infants, CYP1A1 mRNA was highly induced for a longer period of time in neonatal rats receiving 1,2,3,4-TCDD via lactation than the treated maternal rats.