2,2{prime},4,4{prime},5,5{prime}-hexachlorobiphenyl (2HCB) and 3,3{prime},4,4{prime},5,5{prime}-hexachlorobiphenyl alter plasma thyroxine (T4) levels in rainbow trout (Oncorhynchus mykiss)

Di-ortho polychlorinated biphenyls (PCBs) are prominent environmental contaminants and their interaction with the thyroidal axis may be more significant in fish than previously thought. Four weeks after ip injection with 50 or 250 mg 2HCB/kg or 5 or 25 mg 3HCB/kg, rainbow trout plasma and liver microsomes were prepared. Plasma T4 levels were increased in 50 but not 250 mg 2HCB/kg treated fish. Plasma T4 levels were unchanged in 3HCB treated fish. Liver microsome ethoxyresorufin deethylase (EROD) activity increased with 2HCB dose. EROD increased after the low but not the high 3HCB dose. Western immunoblotting us 1A trout-anti-rabbit primary antibody showed a 2HCB and 3HCB dose related increase. In another experiment, twelve weeks after ip injection was 25 or 100 mg 3HCB/kg, rainbow trout plasma, thyroidal tissue, and liver microsomes were prepared. Plasma T4 levels were increased in 25 not 100 mg 3HCB/kg treated fish. Thyroid follicle cell height was increased in 25 but not 100 mg 3HCB/kg treated fish. Interaction with the receptor, as measured by cytochrome P450 1A induction, does not correlate with altered T4 plasma levels.