Effects of Chronic Treatment of Intact and Hypophysectomized Rats with Thyroid-Stimulating Hormone on the Metabolism of [35S]Methimazole and [36S]Propylthiouracil

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Abstract
Chronic treatment of intact rats with various doses of TSH [thyroid stimulating hormone] increased the thyroidal 35S accumulation after single doses of [35S]methimazole (MMI) and [35S]propylthiouracil (PTU). No effect on the intrathyroidal breakdown of the drugs was observed. Absolute thyroidal levels of unmetabolized MMI and PTU were increased by factors of up to 2 and 3, respectively, compared to the control groups. Simultaneous decreases in the levels of thyroidal total I were observed. Hypophysectomized rats showed a marked inhibition of both thyroidal accumulation and oxidation of [35S]-MMI but TSH treatment of hypophysectomized rats restored the accumulation and oxidation to sham-operated and control group levels. In rats TSH has an important role in the control of thyroidal levels of antithyroid drugs currently used in the treatment of hyperthyroidism.