Reverse T3 is most commonly produced by deiodination of T4 in peripheral tissues. Which molecule is the precursor?

Reverse T3 is most commonly produced by deiodination of T4 in peripheral tissues. Which molecule is the precursor?

• A. T4
• B. T3
• C. Thyroglobulin
• D. TSH

Answer: (A)

Reverse T3 is formed in peripheral tissues by inner-ring deiodination of thyroxine (T4). This means the molecule that serves as the starting substrate is T4, the circulating prohormone that the body converts through deiodinase enzymes. Outer-ring deiodination of T4 yields T3, the active thyroid hormone, while inner-ring deiodination produces reverse T3, which is inactive. Thyroglobulin is simply the protein scaffold inside the thyroid gland used to make thyroid hormones, not a direct precursor for circulating deiodination products, and TSH is a pituitary hormone that stimulates thyroid hormone synthesis rather than being a substrate for deiodination.

Reverse T3 is formed in peripheral tissues by inner-ring deiodination of thyroxine (T4). This means the molecule that serves as the starting substrate is T4, the circulating prohormone that the body converts through deiodinase enzymes. Outer-ring deiodination of T4 yields T3, the active thyroid hormone, while inner-ring deiodination produces reverse T3, which is inactive. Thyroglobulin is simply the protein scaffold inside the thyroid gland used to make thyroid hormones, not a direct precursor for circulating deiodination products, and TSH is a pituitary hormone that stimulates thyroid hormone synthesis rather than being a substrate for deiodination.