A 24-year-old woman was found to have mild hyperthyroidism due to Graves’ disease. She appears to be in good health otherwise.
The decision is made to begin treatment with methimazole. Methimazole reduces serum concentration of T3 primarily by which of the following mechanisms?
Accelerating the peripheral metabolism of T3
Inhibiting the proteolysis of thyroid-binding globulin
Inhibiting the secretion of TSH
Inhibiting the uptake of iodide by cells in the thyroid
Preventing the addition of iodine to tyrosine residues on thyroglobulin
The thioamides (methimazole and propylthiouracil) act in thyroid cells to prevent conversion of tyrosine residues in thyroglobulin to MIT or DIT. The answer is E.