Wolff-Chaikoff effect
Encyclopedia
The Wolff–Chaikoff effect is a reduction in thyroid hormone
levels caused by ingestion of a large amount of iodine
.
It is an autoregulatory phenomenon that inhibits organification
(oxidation
of iodide) in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. This becomes evident secondary to elevated levels of circulating iodide
. The Wolff–Chaikoff effect lasts several days (around 10 days), after which it is followed by an "escape phenomenon", which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" is 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.
The Wolff–Chaikoff effect can be used as a treatment principle against hyperthyroidism
(especially thyroid storm) by infusion of a large amount of iodine to suppress the thyroid gland. Iodide was used to treat hyperthyroidism before antithyroid drugs
such as propylthiouracil
and methimazole
were developed. Hyperthyroid subjects given iodide may experience a decrease in basal metabolic rate
within 24 hours that is comparable to that seen after thyroidectomy
. The Wolff–Chaikoff effect also explains the hypothyroidism
produced in some patients by several iodine-containing drugs, including amiodarone
.
Thyroid hormone
The thyroid hormones, thyroxine and triiodothyronine , are tyrosine-based hormones produced by the thyroid gland primarily responsible for regulation of metabolism. An important component in the synthesis of thyroid hormones is iodine. The major form of thyroid hormone in the blood is thyroxine ,...
levels caused by ingestion of a large amount of iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
.
It is an autoregulatory phenomenon that inhibits organification
Organification
Organification is a biochemical process that takes place in thyroid glands. It is the oxidation of iodide by peroxide, and then its binding to tyrosyl residues within the thyroglobulin molecule....
(oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of iodide) in the thyroid gland, the formation of thyroid hormones inside the thyroid follicle, and the release of thyroid hormones into the bloodstream. This becomes evident secondary to elevated levels of circulating iodide
Iodide
An iodide ion is the ion I−. Compounds with iodine in formal oxidation state −1 are called iodides. This page is for the iodide ion and its salts. For information on organoiodides, see organohalides. In everyday life, iodide is most commonly encountered as a component of iodized salt,...
. The Wolff–Chaikoff effect lasts several days (around 10 days), after which it is followed by an "escape phenomenon", which is described by resumption of normal organification of iodine and normal thyroid peroxidase function. "Escape phenomenon" is believed to occur because of decreased inorganic iodine concentration secondary to down-regulation of sodium-iodide symporter
Sodium-iodide symporter
The sodium/iodide symporter , also known as solute carrier family 5, member 5 is a protein that in humans is encoded by the SLC5A5 gene. The sodium/iodide symporter is a transmembrane glycoprotein with a molecular weight of 87 kDa and 13 transmembrane domains, which transports two sodium cations ...
on the basolateral membrane of the thyroid follicular cell.
The Wolff–Chaikoff effect can be used as a treatment principle against hyperthyroidism
Hyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
(especially thyroid storm) by infusion of a large amount of iodine to suppress the thyroid gland. Iodide was used to treat hyperthyroidism before antithyroid drugs
Antithyroid agent
An antithyroid agent is a hormone antagonist acting upon thyroid hormones.The main antithyroid drugs are carbimazole , methimazole , and propylthiouracil/PTU...
such as propylthiouracil
Propylthiouracil
Propylthiouracil or 6-n-Propylthiouracil is a thioamide drug used to treat hyperthyroidism by decreasing the amount of thyroid hormone produced by the thyroid gland...
and methimazole
Methimazole
Methimazole is an antithyroid drug, and part of the thioamide group.-Indications:...
were developed. Hyperthyroid subjects given iodide may experience a decrease in basal metabolic rate
Basal metabolic rate
Basal Metabolic Rate , and the closely related resting metabolic rate , is the amount of daily energy expended by humans and other animals at rest. Rest is defined as existing in a neutrally temperate environment while in the post-absorptive state...
within 24 hours that is comparable to that seen after thyroidectomy
Thyroidectomy
A thyroidectomy is an operation that involves the surgical removal of all or part of the thyroid gland. Surgeons often perform a thyroidectomy when a patient has thyroid cancer or some other condition of the thyroid gland...
. The Wolff–Chaikoff effect also explains the hypothyroidism
Hypothyroidism
Hypothyroidism is a condition in which the thyroid gland does not make enough thyroid hormone.Iodine deficiency is the most common cause of hypothyroidism worldwide but it can be caused by other causes such as several conditions of the thyroid gland or, less commonly, the pituitary gland or...
produced in some patients by several iodine-containing drugs, including amiodarone
Amiodarone
Amiodarone is an antiarrhythmic agent used for various types of tachyarrhythmias , both ventricular and supraventricular arrhythmias. Discovered in 1961, it was not approved for use in the United States until 1985...
.