Polychlorinated biphenyl effects on avian hepatic enzyme induction and thyroid function.

Area of Science:

• Environmental Toxicology
• Comparative Endocrinology

Background:

• Polychlorinated biphenyls (PCBs) disrupt thyroid function in mammals by inducing liver uridine diphosphate-glucuronosyltransferase (UDP-GT), increasing thyroxine (T4) clearance and potentially causing hypothyroidism.
• Understanding avian thyroid responses to PCBs is crucial for assessing ecological risks.

Purpose of the Study:

• To validate an assay for measuring T4-specific UDP-GT activity in Japanese quail.
• To compare the thyroid-disrupting effects of PCBs (Aroclor 1254) in Japanese quail and Balb/c mice.

Main Methods:

• Validated a T4-specific UDP-GT assay in Japanese quail.
• Administered Aroclor 1254 orally to quail and mice at doses of 250 or 500 mg/kg.
• Measured UDP-GT activity and plasma T4 levels at 5, and 21 days post-exposure.

Main Results:

• PCB exposure significantly increased UDP-GT activity in both quail and mice.
• Plasma T4 levels decreased significantly in mice but only tended to decrease in quail.
• Mice exhibited hypothyroidism, while quail did not, suggesting differential vulnerability.

Conclusions:

• This study demonstrates the first T4-specific avian UDP-GT response to PCBs.
• Avian thyroid function appears less vulnerable to PCB exposure than mammalian thyroid function.
• PCB effects on the hypothalamic-pituitary-thyroid (HPT) axis differ between quail and mice.