Wolff-Chaikoff effect describes a transient inhibition of thyroid hormone synthesis that occurs with large iodine loads. The molecular mechanism underlying iodine-mediated inhibition of organification involves:
- A Excess iodide activates TSH receptor downregulation, reducing cAMP signaling and thyroid peroxidase gene transcription
- B Iodide activates a chloride channel (pendrin) that diverts iodide away from the follicular lumen back into the bloodstream
- C High intracellular inorganic iodide inhibits thyroid peroxidase (TPO)-mediated iodination of tyrosine residues on thyroglobulin via an allosteric or oxidative inhibitory mechanism ✓
- D High iodide concentrations activate the sodium-iodide symporter in reverse, pumping iodide out of thyrocytes
Explanation
The Wolff-Chaikoff effect is the acute inhibition of thyroid organification (iodination of thyroglobulin tyrosines) when intracellular iodide exceeds a threshold concentration. Excess iodide generates iodolactones and possibly other oxidized iodine species that directly inhibit thyroid peroxidase (TPO) activity. This is transient because the thyroid escapes the Wolff-Chaikoff effect within 1–2 weeks by downregulating the sodium-iodide symporter (NIS), reducing iodide uptake and restoring organification. This escape mechanism explains why chronic iodine supplementation does not cause permanent hypothyroidism in most people; it also forms the basis for using potassium iodide preoperatively (to reduce vascularity via Plummer effect) before thyroid surgery.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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