Local production of T3 inside neurons of the cerebral cortex and in thyrotrophs of the anterior pituitary depends chiefly on which enzyme?

• A Type 1 deiodinase (D1)
• B Type 2 deiodinase (D2) ✓
• C Type 3 deiodinase (D3)
• D Thyroid peroxidase (TPO)

Explanation

Type 2 deiodinase is the activating outer-ring deiodinase expressed in the brain, pituitary, brown adipose tissue, and placenta. It converts circulating T4 to T3 locally, and in the pituitary it generates the intracellular T3 signal that mediates negative feedback on TRH and TSH. Type 1 deiodinase contributes mainly to plasma T3 production and is blocked by propylthiouracil. Type 3 deiodinase inactivates hormone by inner-ring deiodination, producing reverse T3, so it cannot supply cellular T3.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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