organification

Maternal fetal transfer of thyroxine in congenital hypothyroidism due to a total organification defect or thyroid agenesis.

The American Thyroid Association (ATA) guideline [1] recommends that iodine be administered at least 1 hour after thionamide therapy to avoid further iodide organification [3].

Administration of high doses of iodine causes a rapid inhibition of the iodine organification and synthesis of ThOx and T4, followed by an inhibition of hormones secretion.

This enzyme is responsible for the oxidation of iodide and binding of iodine to tyrosyl residue of thyroglobulin (organification).

As a result of organification, hormonally active iodothyronine, T4 and T3 precursor monoidotyrosines and diiodotyrosines occurs.

NIS mediates iodide accumulation and organification in the thyroid gland and thus allows the use of radioisotopes for the treatment of thyroid cancer.

Organification (oxidation) of iodide is accomplished by [H.sub.2][O.sub.2] (hydrogen peroxide) catalyzed by the enzyme thyroid peroxidase, and leads to the formation of T3 and T4.

Thyroid hormone biosynthesis is impaired because of the persistent block in intrathyroidal iodine organification as evident by the positive perchlorate discharge test in patients with AIH.14 This may arise from an underlying thyroid abnormality like autoimmune thyroiditis and suggests that iodide excess could unmask some pre-existent subclinical thyroid disease to produce overt thyroid failure.9

(10) Most patients with Pendred syndrome remain euthyroid, as dietary iodine intake is usually sufficient to compensate for the iodide organification defect.

It blocks organification in thyroid cells, thus inhibiting the production of the thyroid hormones (thyroxine and triiodothyronine).

Schmutzler et al (8) demonstrated inhibition of iodide uptake and irreversible inactivation of thyroid peroxidase (TPO) in an in vitro study employing rodent tissue thereby indicating interference with thyroid hormone biosynthesis at the level of iodide uptake and organification by genistein, a soy isoflavone.

Thiocyanate, a major component of smoke, derived from hydrogen cyanide leads to increased excretion of iodine, inhibits iodide uptake by the thyroid, competes with iodide in the organification process (Ermans et al., 1980) and inhibits thyroid hormone synthesis (Fukayama et al., 1992).

(5) Therefore, drugs that inhibit the organification process are not as successful in type II AIT, and glucocorticoids are more often used.

Methimazole works by blocking the organification of iodide, which decreases thyroid hormone production.