Triiodothyronine production

Hyperthyroidism is treated by administering antithyroid medication, which inhibits thyroxine and triiodothyronine production. These are ... 

Panda, S., and A. Kar. 1999. Gugulu (Commiphora mukul) induces triiodothyronine production Possible involvement of lipid peroxidation. Life Sci. 65(12) PL137-141. 

Amino acid-derived hormones include the catecholamines, epinephrine and norepinephrine (qv), and the thyroid hormones, thyroxine and triiodothyronine (see Thyroid AND ANTITHYROID PREPARATIONS). Catecholamines are synthesized from the amino acid tyrosine by a series of enzymatic reactions that include hydroxylations, decarboxylations, and methylations. Thyroid hormones also are derived from tyrosine iodination of the tyrosine residues on a large protein backbone results in the production of active hormone. 

The thyroid gland, located in the base of the neck, exerts i key role on growth and metabolism. In contrast with that of some of the other endocrine glands, this control is effected Ihrough a pair of relatively simple molecules, thyroxine, and its close congener, triiodothyronine. Cases of thyroid deficien-cy (hypothyroidism) are common enough to warrant the production... 

Estrogen may increase hepatic production of thyroxine-binding globulin (TBG) and decrease TBG clearance, thus increasing serum total thyroxine (tT4) and, to a lesser extent, total triiodothyronine (tT3). As a result, increased tT4 and tT3 are seen in states of excessive estrogen and/or progestin, such as... 

Thyroxine (57) was rapidly photodeiodinated by light filtered to give wavelengths above 300 nm. In the first few minutes the main product was 3,3, 5-triiodothyronine, but by 15 min, 3,5-diiodothyronine and 3-iodothyronine were present in major amounts. There were also traces of 3,3, 5-triiodothyronine and 3,3 -diiodothyronine. In some runs traces of 3,3, 5 -triiodothyronine and 3, 5 -diiodothyronine were detected. Over 30 min the main product was 3-iodothyronine. Further deiodination to thyronine was very slow, presumably because the UV spectra had lower-wavelength maxima as iodine was removed. Similar photolysis of 3,3, 5-triiodothyronine for 10 min also gave 3,5-diiodo-... 

The gland is situated in the neck across the front of the trachea. It secretes thyroxine (T4), which is converted to the active form of the hormone, triiodothyronine (T3), in peripheral tissues. It stimulates metabolic activity in tissues so that it increases heat production (for example, by stimulating protein turnover and substrate cycles). 

Hypothyroidism (myxedema) results when there is a breakdown of thyroid hormone production in the thyroid gland. Treatment consists of replacing this hormone with aforementioned drugs. Treatment with levothyroxine, 3,5,3, 5 -tetraiodothyronine, is preferred. Lyothyronin, L-3,5,5 -triiodothyronine, is also used, as is lotrix, a mixture of levothyroxine and levothyronine in a 4 1 ratio. Of the drugs of animal origin, thyroidin and thy-roglobulin (proloid) are used. 

The thyroid gland produces thyroxine (T4) and triiodothyronine (T3) and this production is under control of the hypothalamus and the pituitary gland. 

An important product of tyrosine metabolism in vetebrates is the thyroid hormone101 of which the principal and most active forms are thyroxine (T4) and triiodothyronine (T3).102 The thyroid gland is rich in iodide ion, which is actively concentrated from the plasma to 1 pM free I. 103 This iodide reacts under the influence of a peroxidase (see Fig. 16-14 and accompanying discussion)104 to iodinate tyrosyl residues of the very large 660-kDa dimeric thyroglobulin, which is stored in large amounts in the lumen of the... 

An advantage of T-3/L-triiodothyronine administration over T-4/L-thyroxine was the lack of dependence upon the liver enzyme responsible for T-4/T-3 conversion. During diet restricted periods the liver naturally decreases the liver enzyme levels as a control measure to prevent metabolic rate induced starvation. Just as the liver increases production of this enzyme in response to elevated calorie intake it also reduces levels in response to decreased calorie intake. Remember that T-4 /L-thyroxine is only 20% as active as T-3/L-triiodothyronine. 

The abuse of synthetic T-3/L-triiodothyronine will result in severe suppression of natural (endogenous) thyroid function. This is especially true of this drug because it actually circumvents the normal thyroid hormone manufacturing process the body utilizes to produce endogenous forms as required. Simplified this is because T-3/L-triiodothyronine is the most potent thyroid hormone so the body shuts down each level required for production to try to reduce circulatory T-3/L-triiodothyronine levels. Of course this does not reduce the level if the hormone is being administered exogenously (from outside the body). 

Triacana is a trade or brand name for the thyroid drug Tiratricol. The body naturally (endogenously) produces T-4/L-thyroxine, T-3/L-triiodothyronine, and T-2 /L-diiodothyronine. Triacana is simply a synthetic form of these three thyroid hormones natural metabolite product, Triiodothyroacetic acid, or tiratricol for short. This means the body naturally produces Triacana as a metabolic by-product of other thyroid hormones. 

Thyroid hormone production is controlled by the hypothalamic-pituitary system (see Chapter 28). Thyrotropin-releasing hormone (TRH) from the hypothalamus stimulates the release of thyroid-stimulating hormone (TSH) from the anterior pituitary.17,63 TSH then travels via the systemic circulation to the thyroid gland to stimulate the production of thyroxine and triiodothyronine. 

Hyperthyroidism (excessive production of thyroid hormones) asually requires surgery, but before. surgery the patient mu.st be prepared by preliminary abolition of the hyper-thyroidi.sm through the use of antithyroid drugs. Thiourea and related eompounds. show an antithyroid activity, but they arc too toxic for clinical use. The more useful drugs are 2-thiouracil derivatives and a closely related 2-thioimidazolc derivative. All of these appear to have a similar mechanism of action (i.c.. prevention of the iodination of the precursors of thyroxine and triiodothyronine). The main difference in the compounds lies in their relative toxieities. 

A deficiency in production of thyroxine and triiodothyronine is called hypothyroidism. There are two types of hypothyroidism ... 

An excess production of thyroxine and triiodothyronine is called hyperthyroidism. 

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