Iodine-induced thyroid gland

The concentration of Li+ in the thyroid is three to four times that in serum [179]. It is thought that Li+ may be concentrated in the thyroid gland by a mechanism similar to the incorporation of iodide, I-, resulting in competition between Li+ and I the levels of intracellular 1 decrease when those of Li+ increase, and vice versa [182]. Li+ inhibits both the ability of the gland to accumulate 1 and the release of iodine from the gland. In vitro, Li+ has no effect on thyroid peroxidase, the enzyme that catalyzes the incorporation of I" into tyrosyl residues leading to thyroidal hormone synthesis, but does increase the activity of iodotyrosine-deio-dinase, which catalyzes the reductive deiodination of iodotyrosyls, thus maintaining the levels of intracellular I [182]. The increase in iodoty-rosine-deiodinase activity is probably a response to the Li+-induced decrease in the concentration of thyroidal I". Li+ has no effect on the conversion of thyroxine to triiodothyronine. The overall effect of this competition between Li+ and 1 is, therefore, reduced levels of thyroid hormone in the presence of Li+. 

Walker and Levy (1989) used implantable pellets of propylthiouracil to induce thyroid dysfunction in rats. In the modification based on uptake of labelled iodine, as standard dose of radio-iodine 131-1 is injected in each animal, and the amount of radioactivity in the thyroid gland is determined in a gamma counter. 

Goiter is the human pathology of hyperplasia of the thyroid gland induced by the deficiency of dietary iodine. The disease is localized in those regions where soils are low in iodine or where seafood is not consumed. Fortification of fable salt with sodium iodide, where applied, has practically eradicated this disease. Unfortunately, many regions of the world do not practice this public health policy. 

Broussolle C, Ducottet X, Martin C, Barbier Y, Bornet H, Noel G, Orgiazzi J. Rapid effectiveness of prednisone and thionamides combined therapy in severe amiodarone iodine-induced thyrotoxicosis. Comparison of two groups of patients with apparently normal thyroid glands. J Endocrinol Invest 1989 12(1) 37 2. 

As parent metal alters sodium balance and lipid metabolism it induces metallothionein synthesis. Nickel chloride affects the T-cell system and suppresses the activity of natural killer cells. If given orally or by inhalation, nickel chloride has been reported to decrease iodine uptake by the thyroid gland. 

Iodine is are primarily used to induce a euthyroid state before surgery. It increases vascularity and increase the density of the thyroid gland, which decreases postoperative complications. 

It has been known that excessive iodine intake results in goiter, hypothyroidism, or hyperthyroidism in humans (Institute of Medicine, 2001). The biological basis for iodine-induced hyperthyroidism (IIH) appears most often to be mutational events in thyroid cells that lead to autonomy of function. When the mass of cells with such an event becomes sufficient, and the iodine supply is increased, the subject may become thyrotoxic. These changes may occur in localized foci within the gland or... 

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