Effects of 3,3 ',4,4 ',5,5 '-hexachlorobiphenyl on cytochrome P4501A and estrogen-induced vitellogenesis in rainbow trout (Oncorhynchus mykiss)

Estrogen-regulated synthesis of vitellopenin (Vg), a yolk-protein precursor required for reproduction, was monitored to explore the potential antiestr ogenic 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 17 beta-estradiol on 3,4,5-HCB induction of cytochr ome P4501A (CYPIA) were also examined. Trout were injected with 3,4,5-HCB ( 0.25, 2.5, 25, 50, or 100 mg/kg) or a vehicle control, and after 10 weeks, they were sampled or injected with 17 beta-estradiol (0.1 mg/kg). Markers o f vitellogenesis. such as Liver somatic index, hepatic estrogen-binding sit es, and plasma Vg concentrations, in 17 beta-estradiol-treated fish were no t affected by 3,4,5-HCB. Maximal induction of CYPIA protein and mRNA occurr ed at doses above 2.5 mg/kg, and 17 beta-estradiol reduced CYPIA protein co ntent 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 su ppressed CYPIA catalytic activity. In 3,4,5-HCB/17 beta-estradiol-treated f ish, plasma estradiol was significantly reduced at 100 mg 3,4,5-HCB/kg, but the depression was not associated with CYPIA induction or with other antie strogenic effects. Although CYPIA was induced, 3,3,5-HCB did not interfere with vitellogenesis, which suggests that the PCB congener is not a potent a ntiestrogen in rainbow trout.