Effects of perinatal exposure to specific PCB congeners on thyroid hormone concentrations and thyroid histology in the rat.

Time-mated Sprague-Dawley rats were exposed to PCB 28 (2,4,4'-trichlorobiphenyl), 8 or 32 mg/kg/day; PCB 118 (2,3',4,4',5-pentachlorobiphenyl), 4 or 16 mg/kg/day; or PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl), 16 or 64 mg/kg/day. At weaning, serum thyroxine (T4) was markedly depressed in pups, but not dams, exposed to PCB 118 or 153. Triiodothyronine (T3) was unchanged in pups and dams. In a histological evaluation of thyroids, the PCB 118 pups revealed changes suggestive of sustained TSH stimulation, including increased follicular cell vacuolization and height, increased nuclear vesiculation, and decreased colloid area. Decreases in body and brain weights and increases in liver weights were observed in some groups, with the high dose PCB 118 pups showing the greatest effect.