As the active metabolites of
polychlorinated biphenyl (
PCBs), hydroxylated
polychlorinated biphenyls (
OH-
PCBs) are found in wildlife and human tissues. They have been proposed as main contributors for endocrine disruption of
PCBs in living organisms. In this study, mono-ortho
PCB 156 and its hydroxylated metabolites 4'-OH-PCB 159, 4'-OH-PCB 121, and 4'-OH-PCB 72 were selected to investigate the toxic effects on rat
hepatoma H4IIE cell line and rat thyroid follicle FRTL-5 cell line at concentrations of 1, 10(2), 10(4) nM. 7-Ethoxyresorufin-O-deethylase (
EROD) and 7-pentoxyresorufin-O-dealkylase (
PROD) activities were determined with micro-
EROD/
PROD to indicate
cytochrome P4501A1 (
CYP1A1) and
cytochrome P4502B (CYP2B) induction in the H4IIE cell after exposure for 72 h. To assess thyroid disruption of these compounds,
thyroglobulin concentrations also were detected inside FRTL-5 cell with immunocellularchemistry and in its medium with radioimmunoassay after exposure for 24 h. Significant inductions of
EROD activity by PCB156
at 10(2) and 10(4) nM (p < 0.05) were observed, but no effects by the three
OH-
PCBs in H4IIE cell line. 7-Pentoxyresorufin-O-dealkylase activities were induced only by 10(4) nM of PCB156 and the three
OH-
PCBs (p < 0.05). Meanwhile, significant increases of
thyroglobulin concentrations were observed in the medium of FRTL-5 cell exposed to 4'-OH-PCB 121 and 4'-OH-PCB 72 at all of the test concentrations (p < 0.05), but not to the other compounds. The results demonstrated that mono-ortho
PCBs mainly could be metabolized to hydroxylated metabolites through
CYP1A1 instead of CYP2B. Moreover, after being metabolized,
OH-
PCBs still sustained the ability to induce
PROD activity and did exhibit the disruption on
thyroglobulin synthesis/excretion in rat cells.