The effects of polychlorinated biphenyls 77 and 126 on the thyroidal status of a marine flatfish, the American plaice (Hippoglossoides platessoides)

Abstract

The effects of polychlorinated (PCB) congeners 77 (a tetrachlorobiphenyl) and 126 (a pentachlorobiphenyl) on the thyroid physiology of American plaice (Hippoglossoides platessoides) were investigated. The thyroid criteria examined were the activities of tissue thyroid hormone (TH) deiodinating enzymes, the plasma TH levels and the properties of the plasma TH-binding proteins. Deiodination pathways were examined in 7 major tissues. Two in vivo experiments were performed. Injection of plaice with PCB 77, and a second experiment with PCB 77 or PCB126. In vitro studies involved incubation of plaice or rainbow trout liver microsomes with PCB 77, PCB 126 or three hydroxylated PCBs (OH-PCBs). In an attempt to clone plaice deiodinase enzymes, ribonucleic acid (RNA) was isolated from liver and brain tissue of American plaice and Atlantic cod (Gadus morhua) and used in the reverse transcription polymerase chain reaction (RT-PCR). A 306-bp cDNA was isolated using cod liver RNA as a template. The plaice is not highly responsive to injected PCBs, but does show some changes that parallel those in other poikilothermic vertebrates. PCBs have no demonstrated potential to directly impact TH deiodination or plasma binding of THs in plaice. (Abstract shortened by UMI.)