Wolff-Chaikoff effect

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Wolff-Chaikoff effect is used to describe hypothyroidism caused by ingestion of a large amount of iodine.^[1]

It is an autoregulatory phenomenon which inhibits formation of thyroid hormones inside of the thyroid follicle. This becomes evident secondary to elevated levels of circulating iodide. Wolff-Chaikoff effect lasts several days, after which it is followed by an "escape phenomenon",^[2] which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" used to be believed to occur because of decreased inorganic iodine concentration secondary to down-regulation of sodium-iodide symporter on the basolateral membrane of the Thyroid Follicular cell. This is no longer the case. High levels of intracellular Iodide suppress transcription of thyroid peroxidase (TPO) enzyme, as long with NADPH oxidase. The downregulation of transcription of colloid enzymes that attach iodide to thyroglobulin causes a reduction in the synthesis of the downstream product, Thyroxin. Older texts suggested that the Na-I-Cotransporter was implicated in Iodide abundance, newer texts suggest it is the transcription of intra-colloid enzymes.

Wolff-Chaikoff effect can be used as a treatment principle against thyroid storm by infusion a large amount of iodine to shut down the hyperfunctioning thyroid gland, or an unpleasant iatrogenic effect of several iodine containing drugs, of which the most famous is amiodarone.

Jodbasedow effect is iodine-induced hyperthyroidism.

[edit] References

1. ^ Physiology at MCG 5/5ch5/s5ch5_6
2. ^ Eng P, Cardona G, Fang S, Previti M, Alex S, Carrasco N, Chin W, Braverman L (1999). "Escape from the acute Wolff-Chaikoff effect is associated with a decrease in thyroid sodium/iodide symporter messenger ribonucleic acid and protein". Endocrinology 140 (8): 3404-10. PMID 10433193.