Title page for ETD etd-07072006-011649


Type of Document Master's Thesis
Author Webb, Catherine Marie
Author's Email Address cmwebb@vt.edu
URN etd-07072006-011649
Title Polychlorinated biphenyl effects on avian hepatic enzyme induction and thyroid function
Degree Master of Science
Department Biological Sciences
Advisory Committee
Advisor Name Title
McNabb, F. M. Anne Committee Chair
Ehrich, Marion F. Committee Member
Moore, Ignacio T. Committee Member
Keywords
  • mice
  • uridine diphosphate-glucuronosyltransferase
  • thyroid hormones
  • PCBs
  • Aroclor
  • Japanese quail
Date of Defense 2006-06-09
Availability unrestricted
Abstract
Polychlorinated biphenyls (PCBs) decrease thyroid function in rats and mice by inducing activity of a liver enzyme, uridine diphosphate-glucuronosyltransferase (UDP-GT), thereby increasing thyroxine (T4) clearance. This loss of T4 can lead to hypothyroidism. In this study, an assay was validated for measuring UDP-GT activity toward T4 in Japanese quail (Coturnix japonica). Then UDP-GT induction by Aroclor 1254 was evaluated in quail, and quail and mice were compared in their responses to Aroclor 1254. In Experiment 1, Japanese quail and Balb/c mice were dosed orally with vehicle or Aroclor 1254 (250 or 500 mg/kg) and sacrificed five days later. In Experiment 2, Japanese quail were dosed orally with vehicle or Aroclor 1254 (500 mg/kg) and sacrificed either five or 21 days later. Total liver UDP-GT capacity increased with Aroclor 1254 exposure in all treatment groups of both species. Enzyme induction led to a trend to decreased plasma T4 concentrations at both doses and exposure times in quail and significantly decreased plasma T4 concentrations at both doses in mice. PCBs altered thyroid function in quail, but they did not become hypothyroid. This was in contrast to mice, which did become hypothyroid. It is unclear how PCBs affect the hypothalamic-pituitary-thyroid (HPT) axis in quail, and activation of the HPT axis appears to be inhibited in mice. Overall, quail showed a lesser response than mice to equivalent doses of Aroclor 1254, so it appears that birds may be less vulnerable to PCBs than mammals.
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