Effects of gestational and lactational exposure to coplanar polychlorinated biphenyl (PCB) congeners or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on thyroid hormone concentrations in weanling rats |
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| Affiliation: | 1. Neuroscience Program, University of Illinois at Urbana-Champaign, 1101 W. Peabody Drive, Urbana, IL 61801, USA;2. Institute for Environmental Studies, University of Illinois at Urbana-Champaign, 1101 W. Peabody Drive, Urbana, IL 61801, USA;3. Department of Veterinary Biosciences, University of Illinois at Urbana-Champaign, 2001 S. Lincoln, Urbana, IL 61801, USA;4. School of Pharmacy and Environmental Toxicology Center, University of Wisconsin, Madison, WI 53706, USA;1. Department of Gynecology and Obstetrics, Nanfang Hospital, Southern Medical University, Guangzhou, 510515, China;2. Department of Disease Surveillance, Center for Disease Control and Prevention of Southern Theatre Command, Guangzhou, 510507, China;3. College of Pharmacy, Guangdong Pharmaceutical University, Guangzhou, 510006, China;4. Department of Pharmacy, Guangzhou Brain Hospital, Guangzhou, 510510, China;1. Department of Neurology, Klinikum Bayreuth, Bayreuth, Germany;2. Department of Physiological Psychology, Otto-Friedrich-University of Bamberg, Bamberg, Germany;1. Division of Rheumatology, Immunology and Allergy, Brigham and Women’s Hospital, Boston, MA 02115, USA;2. Department of Medicine, Harvard Medical School, Boston, MA 02115, USA |
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| Abstract: | Perinatal exposure to polychlorinated biphenyl (PCB) mixtures or to certain ortho-substituted PCB congeners dramatically reduces circulating thyroxine (T4) concentrations. It is not clear whether perinatal exposure to coplanar PCBs or2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has a similar effect. In this study, time-mated Sprague-Dawley rats were dosed with 2 or 8 mg/kg/day PCB 77 (3,3′,4,4′-tetrachlorobiphenyl), 0.25 or 1.00 μ/kg/day PCB 126 (3,3′,4,4′,5-pentachlorobiphenyl), 0.025 or 0.10 μg/kg/day TCDD, or corn oil vehicle orally on gestation days 10–16. At weaning, plasma total T4 concentrations in PCB 77 and TCDD high-dose female pups were significantly depressed, but the changes were modest (84.4 and 79.6% of control, respectively). T4 concentrations in PCB 126 high-dose females and all high-dose males were also depressed slightly, but the changes were not statistically significant. UDP-Glucuronosyl transferase (UDP-GT) activity towards 4-nitrophenol was increased in all high-dose groups. Thus, the modest decreases in T4 could be due in part to increased T4 glucuronidation by UDP-GT. Triiodothyronine (T3) and thyroid stimulating hormone (TSH) concentrations were unchanged in all groups. In contrast to the minor changes in thyroid hormone status, liver microsomal ethoxyresorufin-O-deethylase (EROD) was markedly induced in all exposure groups and thymus weights were depressed in the high-dose groups. Because doses of coplanar PCBs or TCDD that caused marked induction of EROD activity had only minor effects on T4, we conclude that changes in thyroid hormone status at weaning are not among the more sensitive effects of perinatal exposure to these compounds. |
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