EFFECTS OF 3,3',4,4',5,5'-HEXACHLOROBIPHENY ON CYTOCHROME P450lA AND ESTROGEN-INDUCED VITELLOGENESIS IN RAINBOW TROUT (ONCORHYNCHUS MYKISS)

摘要

Estrogen-regulated synthesis of vitellogenin (Vg), a yolk-protein precursor required for reproduction, was monitored to explore the potential antiestrogenic effects of the coplanar polychlorinated biphenyl (PCB), 3,3',4,4',5,5 '-hexachlorobiphenyl (3,4,5- HCB), in juvenile rainbow trout (Oncorhynchus mykiss). The effects of l7β -estradiol on 3,4,5-HCB induction of cytochrome P450lA (CYPlA) were also examined. Trout were injected with 3,4,5-HCB (0.25, 2.5, 25, 50, or l00 mg/kg) or a vehicle control, and after l0 weeks, they were sampled or injected with l7β-estradiol (0.l mg/kg). Markers of vitellogenesis, such as liver somatic index, hepatic estrogen-binding sites, and plasma Vg concentrations, in l7β-estradiol-treated fish were not affected by 3,4,5-HCB. Maximal induction of CYPlA protein and mRNA occurred at doses above 2.5 mg/kg, and l7β-estradiol reduced CYPlA protein content at a single dose (0.25 mg 3,4,5-HCB/kg). Ethoxyresorufin-O-deethylase (EROD) activity was induced by 3,4,5-HCB doses of between 0.25 and 2.5 mg/kg, but induction was reduced at higher doses, indicating that 3,4,5-HCB suppressed CYPlA catalytic activity. In 3,4,5-HCB/l7β -estradiol--treated fish, plasma estradiol was significantly reduced at l00 mg 3,4,5-HCB/kg, but the depression was not associated with CYPlA induction or with other antiestrogenic effects. Although CYPlA was induced, 3,4,5- HCB did not interfere with vitellogenesis, which suggests that the PCB congener is not a potent antiestrogen in rainbow trout.