Effect of Polybrominated Biphenyls (PBB) on the Pituitary-Thyroid Axis of the Rat 1 2

Abstract

Abstract

The effects of polybrominated biphenyls (PBB) on the pituitary-thyroid axis were investigated in male rats. PBB was administered by gavage for 20 days at 1, 3, or 6 mg/kg/day; controls were gavaged with vehicle alone. PBB treatment had no effect on body weight. There was a definite time- and dose-dependent reduction in plasma thyroxine (T₄) levels after 10 and 20 days of PBB administration. Reduced plasma T₄ levels were correlated with increased plasma TSH levels at 20 days. In rats treated with 6 mg/kg PBB, an increase in 5-hr thyroidal ¹³¹I uptake was seen, with a decrease in ¹³¹I incorporation into monoiodotyrosine and an increase in intrathyroidal iodine. In contrast to propylthiouracil, acute administration of PBB had little effect on intrathyroidal radioiodine accumulation and incorporation into iodoamino acids. Liver and thyroid weights remained elevated at 2 and 5 months after the last 1 and 3 mg/kg PBB administration, respectively, and plasma T₄ levels were significantly lower than controls in both groups. PBB was detected in thyroid tissue after 20 days of 3 mg/kg treatment and was retained in thyroid and liver for 5 months post-treatment. Exposure to PBB resulted in a disruption of the normal homeostasis of the pituitary-thyroid axis and was associated with accumulation and retention of PBB in thyroid and liver.