Antithyroid substances

P. 1. anger and M. A. Greer, Antithyroid Substances and Naturally Occurring Goitrogens, S. Karger, Basel, Switzerland, 1977. 

Toxicology. Ethylene thiourea (ETU) is an antithyroid substance and animal carcinogen. 

In Langer P, Greer MA, editors. Antithyroid Substances and Naturally Occurring Goitrogens. Basel-Munchen-Paris-London-New York-Sidney Karger, 1977 54. 

Similar effects to those for hormones are seen in antithyroid substances (strumigens), which inhibit the synthesis of thyroxine in the thyroid gland. Heterocyclic compounds containing thiourea residues in their molecules, for example thiouracils and mercaptoimidazoles, are very potent strumigens. Examples of the main antithyroid drugs include propylthiouracil (6-propyl-... 

Antithyroid Substances. Various substances are able to interfere with the normal process of thyroxine synthesis. First of all, several univalent anions (e.g. thio-... 

Fig. 53. Diagram of thyroid activity. Iodine ions are taken up from blood (left), oxidized in the gland by removal of electrons and bound organically. From the iodinated tyrosine residues in the thyroglobulin molecule arise tri- and tetraiodothyronine, which are freed by proteolysis and released to the blood stream. At right is the addition compound with a-globulins. At the bottom, the sites of action of the inhibitors (antithyroid substances) are indicated.

The main role of the human thyroid gland is production of thyroid hormones (iodinated amino acids), essential for adequate growth, development, and energy metaboHsm (1 6). Thyroid underfunction is an occurrence that can be treated successfully with thyroid preparations. In addition, the thyroid secretes calcitonin (also known as thyrocalcitonin), a polypeptide that lowers excessively high calcium blood levels. Thyroid hyperfunction, another important clinical entity, can be corrected by treatment with a variety of substances known as antithyroid dmgs. 

In addition to drugs used for their antithyroid effects, the following substances can cause hypo-th3rroidism lithium (for mania/depression), amio-darone (cardiac antiarrhythmic), PAS (for tuberculosis), phenylbutazone (antirheumatic), iodide (see above), cobalt salts (for anaemia), resorcinol (for leg ulcers). Effects are generally reversible on withdrawal. 

Perchlorates (see Section 6.3.2.2) and some degradation products of glucosinolates, such as goitrin, isothiocyanates, nitriles and thiocyanate (rhodanide) ions (SCN ), have goitrogenic (antithyroid) activities. Thiocyanate ions also arise in the body as detoxification products of cyanides. The other compounds that show antithyroid activity are some congeners of polychlorinated biphenyls (PCBs), some pesticides and a number of veterinary drugs containing thiourea residues (such as thiouracils, aminothiazoles and mercaptoimidazoles) that inhibit the enzyme thyroid peroxidase. These substances may be present in foods as contaminants (see Section 12.8.3.1). 

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