Question 2 of 18

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.