Wolff—Chaikoff effect

Wohl-Aue synthesis Wohlwill process Wolff-Chaikoff effect... 

Iodide and Other Inorganic Anions. When large doses of iodide ion are administered, a transient inhibition of synthesis and release of the thyroid hormones is brought about by the so-called Wolff-Chaikoff effect. 

Wittig reaction, 2 64-65, 19 65 Wobbe Number, 12 378-379 Wohl-Aue synthesis, 2 787 Wohlwill refining process, 22 647 Wolff-Chaikoff effect, 14 373 Wolff-Kichner reduction, 13 569-570,... 

Two neonates who had been given intravenous amiodarone as fetuses at 26 and 29 weeks and whose mothers had also taken it orally developed hypothyroidism (83). The authors suggested that low dietary iodine intake by the mothers may have contributed, by enhancing the Wolff-Chaikoff effect. 

Growth of mammary breast cancer cells, which also express the same NIS as thyroid cells, is inhibited by iodine and also 6-iodolactone. Thus, a sufficient iodine supply has an important role, not only for thyroid function and growth, but also for the mammary gland. 2-IHDA, inhibits nicotinamide adenine dinucleotide hydride (NADH)-dependent H2O2 generation in vitro, as well as in vivo. It also inhibits adenylate-cyclase activity, and therefore is supposed to mediate the well-known Wolff—Chaikoff effect. 

The Wolff-Chaikoff effect is evidenced by the perchlorate discharge test, i.e., the release of radioiodide by the thyroid in response to perchlorate after administration of high levels of iodide. The fraction of the trapped iodide that is not organified is released by perchlorate. 

I2 itself, which may inhibit TPO and thus iodination however, such a specific mechanism would only explain in part the inhibition of iodination, but not of H2O2 production (Nunez and Pommier, 1982), i.e., part of the Wolff—Chaikoff effect. 

Two iodolipids have been identified as candidates for XI iodolactones which act on the thyroid but may not be synthesized in the gland, and 2-IHDA which is found in the thyroid and may account for some iodide effects including the Wolff-Chaikoff effect. 

A low or even a moderate single dose of iodide causes no or only a minor, reduction of hormone production in a normal thyroid. An excessive single dose of iodide leads, via inhibition of the thyroid peroxidase (TPO) mediated iodination (the Wolff-ChaikofF effect), to a transient decrease of intrathyroidal hormone concentration. This was first demonstrated by Wolff and Chaikoff (1949). When high plasma levels of iodide are sustained by repeated iodine administration, the inhibiting effect disappears and normal organic iodine levels in the thyroid are restored, with a decrease in thyroid sodium symporter, as demonstrated by Eng et al. (1999). This effect was demonstrated by Haydl and Waldhausl (1975) in the course of health resort treatments administering iodine-containing mineral waters. 

Hypothyroidism can also occur with amiodarone use. Although possible, the condition is likely to be related to the inability to avoid the Wolff-Chaikoff effect. Amiodarone itself can induce Hashimotos thyroiditis, which can result in permanent hypothyroidism. Otherwise, hypothyroidism is reversible once amiodarone wears off This warrants a review of the condition and a trial of replacement therapy approximately 6-12 months after the cessation of amiodarone due to its particularly long half life (Basaria and Cooper, 2005). 

Acute excess iodine ingestion has long been known to result in a transient decrease in iodine organification, termed the Wolff—Chaikoff effect (Wolff and Chaikoff, 1948). With sustained excess iodine exposure, however, most individuals thyroid glands escape from acute Wolff— Chaikoff effect, despite continued excess iodine exposure, and resume synthesis of normal amounts of T4 and T3. The mechanism responsible for this escape or adaptation to the iodine load probably involves a decrease in the Na /H symporter protein, resulting in a decrease in thyroid iodide content (Eng et ai, 1999). In some individuals... 

High doses of iodide can also transiently block thyroid hormone synthesis through inhibition of the organification process. This is known as the Wolff-Chaikoff effect. In certain susceptible individuals the thyroid cannot escape from the transient inhibitory effect of iodide on the organification mechanism. As a result, hypothyroidism may develop after prolonged excess iodide administration. The hypothyroidism is usually transient and thyroid function returns to normal after iodide withdrawal. 

Amiodarone is mostly given in a daily dose of 200 mg. This dose contains about 7 mg iodine which amounts to 35-times the daily recommended dietary iodine supply. A healthy thyroid gland compensates this overdose of iodine (Wolff—Chaikoff effect). However, patients with (subclinical) thyroid autonomy (in a euthyroid goiter in an iodine-deficient region) or subclinical thyroid autoimmune disease are very susceptible to IIH because this autoregula-tory mechanism is disturbed. 

According to Pitsiavas et al. (1999), the inhibitory effect of amiodarone occurs at a lower iodide concentration than that for sodium iodide, and the effect of amiodarone is irreversible, indicating possible persistence of the Wolff—Chaikoff effect due to a persistently high intracellular iodide level. 

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