Iodide thyroid function

The only commonly used radioisotope in this class is used in small (- IS.S MBq (500 -lCi) injected dose) quantities as a diagnostic for the evaluation of thyroid function. The compound is adininistered as Nal and these procedures are only possible owing to the favorable biological distribution of iodide. Up to 25% of the entire injected dose of iodide is accumulated in the thyroid with a very slow washout the rest is rapidly excreted in the urine. No other compound exhibits so high a ratio of concentration in a target tissue to that of other tissues. 

Potassium Iodide. When potassium iodide [7681-11-0] is adrninistered orally for several (6—8) weeks, a therapeutic effect may be obtained ia the subcutaneous form of sporotrichosis. Amphotericin B is used iatravenously to treat systemic sporotrichosis. The KI dosage is usually a saturated solution ia water (1 g/mL). The usual oral dose is 30 mg/kg/d. Children should receive five droplets, three times a day (after meals) the dose may be iacreased to 15—20 droplets. Side effects iaclude digestive disorders, swelling of the saUvary glands, and lacrimation. Thyroid function tests may be disturbed. 

At a level of 1000 ppm in the diet of rats, significant enlargement of the thyroid could be detected as early as 3 days. At a dietary level of 60 or 120 ppm, there was enlargement of the thyroid within 2 weeks. Morphologic changes were noted in the thyroid of rats fed 10 or 50 mg/kg amitrole for 11-13 weeks. Amitrole is thought to interfere with the formation of thyroxine by inhibiting the peroxidase-dependent iodide oxidation in the thyroid. Suppression of thyroid function leads to further stimulation by the pituitary, with resultant hyperplasia and tumor formation. 

Sodium iodide is an iodine supplement in food, an expectorant, cloud seed to cause rain, and solubilizes iodine in aqueous solution for analytical work. The radioactive iodide salt of sodium, Na(I-131) is used to diagnose thyroid function. 

Potassium salts (as iodide) act by both direct action and reflexly to increase the respiratory secretions and decrease its viscosity thus they are easy to expel out. Potassium iodide is generally used for cough associated with chronic bronchitis and asthma but it interferes with thyroid function tests, so it is dangerous in patients... 

A small group of cyclic thioureas have been used in the treatment of excessive thyroid function. They include 6-n-propylthiouracil (176 R1 = H, R2 = Prn), 5-iodo-2-thiouracil (176 R1 = I, R2 = H), l-methyl-2-mercaptoimidazole (methimazole) and its ethoxycarbonyl derivative carbimazole (177), which lacks the bitter taste of the unacylated compound. These compounds block the synthesis of thyroxin by inhibiting the oxidation of iodide to iodine and the oxidative coupling of iodotyrosine residues. 

The effects of iopromide on thyroid function have been investigated in 20 pre-term infants with very low birth weights and 26 matched premature infants who did not receive contrast medium (571). The dose of iopromide (iodine 300 mg/ml) was 0.3-1.0 ml. Iopromide did not affect the concentrations of free thyroxine and thyroid stimulating hormone. This was attributed to the small amount of free iodide that iopromide contains... 

Iodide. Relatively large dosages of iodide (exceeding 6 mg/d) cause a rapid and dramatic decrease in thyroid function.35 In sufficient amounts, iodide inhibits virtually all the steps involved in thyroid hormone biosynthesis. For instance, high iodide levels limit the uptake of iodide into thyroid follicle cells, inhibit the formation of T4 and T3, and decrease the secretion of the completed hormones from the thyroid cell. 

By virtue of its iodine content, isopropamide iodide can interfere with thyroid function tests. 

Low iodine levels can be easily corrected. In most developed countries today, companies that make table salt add a small amount of potassium iodide (Kl) to their salt. The salt is labeled "iodized salt." People who use iodized salt get all the iodine they need for normal thyroid function. 

Nondietary sources of cyanide include sodium nitro-prusside (a hypotensive agent), succinonitrile (an antidepressant agent), acrylonitrile (used in the plastic industry and as a fumigant to kill dry-wood termites), and tobacco smoke. Chronic exposure to cyanogenic compounds leads to toxic manifestations such as demyelination, lesions of the optic nerves, ataxia (failure of muscle coordination), and depressed thyroid functions. This last effect arises from accumulation of thiocyanate, the detoxified product of cyanide in the body (see below). Thiocyanate inhibits the active uptake of iodide by the thyroid gland and, therefore, the formation of thyroid hormones (Chapter 33). 

Vagenakis AG Braverman LE (1975) Adverse effects of iodides on thyroid function. Med Clin North Am, 59 1075-1088. 

Three- to four-day old northern bobwhite were used to evaluate the influence of ammonium perchlorate (AP) on thyroid function, as well as thyroidal hormone level systemic effects on the hypothalamic-pituitary-thyroid axis [46], The perchlorate ion competitively inhibits iodide uptake, thus with time AP has the potential to reduce... 

Radioactive iodine finds its widest use in the treatment of hyperthyroidism and in the diagnosis of disorders of thyroid function. Sodium iodide (lodotope Therapeutic) is available as a solution or in capsules containing essentially carrier-free suitable for oral administration. Sodium iodide is available for scanning procedures. Discussion here is limited to the uses of... 

RELATION OF IODINE TO THYROID FUNCTION Normal thyroid function requires an adequate intake of iodine without this, thyroid hormone cannot be made, TSH is secreted in excess, and the thyroid becomes hyperplastic and hypertrophic. The enlarged and stimulated thyroid becomes remarkably efficient at extracting the residual traces of iodide from the blood, developing an iodide gradient that may be 10 times normal. In mild-to-moderate iodine deficiency, the thyroid usually succeeds in producing sufficient hormone, in part by preferentially secreting T. In more severe deficiency, as is common in some parts of the world, adult hypothyroidism or cretinism may occur. 

The mechanisms of disruption of thyroid function have not been established. Direct interaction of CMs with thyroid hormone receptors or serum thyroid binding proteins seems unlikely but has not been investigated. The adverse histophysiological alterations in the thyroid and change.s in serum thyroid homione levels may be a result of CMs directly interfering with the iodide transporter or... 

On the other hand, excess iodine intake may also inhibit thyroid function, by either inhibition of iodide organification (Wolff-Charkoff effect) or inhibition of Tg proteolysis with reduction in hormone secretion, and may manifest itself either as a goiter, as hypothyroidism with/without goiter, or as hyperthyroidism (0.01-0.6% in populations on iodine prophylaxis), the outcome depending on the initial and current iodine status and current thyroid dysfunction (European Commission, 2002). The comparison of iodine intake and concentrations of serum Tg at various physiological or pathophysiological conditions is shown in Table 6.1. 

The expression of the sodium iodide symporter is perhaps nowhere more important than in the thyroid gland. A complete review of the physiological importance of the thyroid is beyond the scope of this chapter. It is sufficient to say that the symporter provides the iodine needed for normal thyroid function. Once the symporter has been trafficked to the basolateral surface of the thyrocyte, it can transport iodine from the blood into the cell. Once inside the cells, iodine is transported to the apical membrane where it is organified through attachment to a tyrosine residue and incorporated into the thyroid hormone thyroglobulin. The thyroglobu-lin is then stored inside thyroid follicles as colloid, to be released into the bloodstream as thyroid hormones (thyroxine and triiodothyronine) via TSH stimulation. 

Perchlorate is a competitive inhibitor of the sodium-iodide symporter (NIS) and has been used in pharmacological doses to treat hyperthyroidism, especially iodine-induced hyperthyroidism. Perchlorate appears to be ubiquitous in the environment, and has been detected in trace amounts in the urine in almost all subjects evaluated both in the United States and Europe. In prospective clinical studies and environmental studies, there is no convincing evidence that environmental perchlorate adversely affects thyroid function. 

Iodate is generally considered to be an important component of the human diet, as it is rapidly reduced to iodide in the body and iodide is essential for thyroid function (Burgi et ai, 2001). However, high levels of iodate (>600 mg/day) have been shown to cause damage to the retina, resulting in ocular toxicity (Burgi et ai, 2001). 

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