Effects of Aroclor 1254 on the Thyroid Gland, Immune Function, and Hepatic Cytochrome P450 Activity in Mallards

• Published in: Environmental research 1997-11, Vol.75 (2), p.119-129
• Main Authors: Fowles, Jefferson R, Fairbrother, Anne, Trust, Kimberly A, Kerkvliet, Nancy I
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Antibody Formation - drug effects; Applied ecology; Aroclors - administration & dosage; Aroclors - toxicity; Aves; Biological and medical sciences; Chlorodiphenyl (54% Chlorine); Corticosterone - blood; Cytochrome P-450 Enzyme System - metabolism; cytochrome-P450; Dose-Response Relationship, Drug; Ducks; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on vertebrates; Environmental Monitoring; Environmental Pollutants - administration & dosage; Environmental Pollutants - toxicity; Fundamental and applied biological sciences. Psychology; Immunity - drug effects; immunotoxicity; Killer Cells, Natural - drug effects; Liver - drug effects; Liver - metabolism; Lymphocyte Activation - drug effects; Male; mallards; polychlorinated biphenyls; thyroid; Thyroid Gland - drug effects; Thyroid Gland - pathology; Thyroid Gland - physiology; Triiodothyronine - blood
• ISSN: 0013-9351; 1096-0953
• DOI: 10.1006/enrs.1997.3776

Adult male mallards were exposed to 0, 4, 20, 100, 250, and 500 mg/kg Aroclor 1254 by gavage twice per week for 5 weeks. Immunotoxic effects, as measured by antibody titers to sheep erythrocytes, natural killer cell activity and lymphocyte mitogenesis to phytohemagglutinin, were not detected as a consequence of polychlorinated biphenyl (PCB) exposure. Hepatic cytochrome P450 activities were measured as microsomal dealkylations of ethoxy-resorufin (EROD) and pentoxyresorufin (PROD). Significant elevations in EROD and PROD were noted at 20 mg/kg and peaked in birds treated with 100 mg/kg. Total P450 was induced beginning at 100 mg/kg and peaked at 250 mg/kg. Relative liver weights were dose-dependently increased following treatment with 100 mg/kg or more. Thyroid weights were significantly increased in PCB-treated birds treated with 100 mg/kg or greater, but no significant histological abnormalities were observed, except at the highest dose. Plasma total triiodothyronine (T3) was decreased in a dose-dependent manner, with a significant lowest-observed-adverse-effect level (LOAEL) of 20 mg/kg. T3 was decreased following 7 days treatment with 100 mg/kg. The no-observed-adverse-effect level (NOAEL) was 4 mg/kg for decreased T3. Plasma glucose levels were decreased on days 28 and 35 in mallards treated with 500 mg/kg, while other clinical plasma biochemistry parameters were unaltered by PCB treatment. Plasma corticosterone levels were unchanged by PCB treatment. These results indicate that thyroid hormone levels and P450 activity in mallards are sensitive to subchronic PCB exposure in the absence of gross toxic effects and immunotoxicity.