Effect of thyroidectomy and thyroxine on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induced toxicity

Chemical thyroidectomy effectively protected athyroid rats from mortality during 45 days after dosing with 100 μg 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)/kg, whereas 70 to 80% of nonthyroidectomized-euthyroid and thyroidectomized-T₄ (thyroxine)-maintained-euthyroid rats died within the same period of time. There was a significant decrease in body weight of all TCDD-treated groups compared to vehicle controls. However, body weight loss was much slower in thyroidectomized-athyroid (≅1 g/day) than in nonthyroidectomized-euthyroid or in thyroidectomized-T₄-euthyroid (≅8 g/day) rats. TCDD significantly reduced feed intake in nonthyroidectomized-euthyroid and thyroidectomized-T₄-euthyroid rats, but no altered feed consumption was observable in thyroidectomized-athyroid animals. These data indicate that thyroid hormone(s) play(s) an important role in mediating the toxicity of TCDD.