Iodine-123: thyroid function

Iodine. Of the 10—20 mg of iodine in the adult body, 70—80 wt % is in the thyroid gland (see Thyroid and antithyroid preparations). The essentiahty of iodine, present in all tissues, depends solely on utilisation by the thyroid gland to produce thyroxine [51-48-9] and related compounds. Well-known consequences of faulty thyroid function are hypothyroidism, hyperthyroidism, and goiter. Dietary iodine is obtained from eating seafoods and kelp and from using iodized salt. 

Body fluids are analyzed for T and T by a variety of radioimmunoassay procedures (31) (see Immunoassays). The important clinical parameter for estimating thyroid function, the protein-bound iodine (PBI), is measured as described in treatises of clinical chemistry. High performance Hquid chromatographic (hplc) methods have replaced dc (32,33). 

No significant interactions have been reported when tiie expectorants are used as directed. The exception is iodine products. Lithium and other antithyroid drug may potentiate the hypotliyroid effects of these drug if used concurrently with iodine products. When potassium-containing medications and potassium-sparing diuretics are administered with iodine products, the patient may experience hypokalemia, cardiac arrhythmias, or cardiac arrest. Thyroid function tests may also be altered by iodine... 

Altered blood chemistry, diminished food intake, and reduced growth within a few days Thyroid function affected decreased iodine uptake at 1 mg/kg BW, increased at 25 mg/kg BW, and decreased at 100 mg/kg BW Decreased liver weight... 

Evidence of a different sort also indicates wide variability with respect to thyroid function. In endemic areas not all of the individuals exhibit endemic goiters, only certain individuals. These, it would be assumed, are individuals who for some reason connected with the production of thyroid hormone need more iodine than their fellows. Similarly, it may be noted that in areas where sea food is abundantly used and iodine is therefore relatively plentiful, there are still some individuals who develop simple goiter. 

Studies of low-dose perchlorate exposure in healthy human subjects A small number of studies have been published investigating the effects of low doses of perchlorate in thyroid function in healthy adults (without thyroid disease). One study was conducted in healthy male volunteers, involving the administration of 10 mg of perchlorate in drinking water for 14 days. A significant decrease in the uptake of iodine by the thyroid was observed at this dose, but there was no evidence of adverse effects on thyroid hormones or TSH concentrations [262]. Another recent study was conducted in healthy adults to determine the highest dose of perchlorate at which there is no effect on the uptake of iodine by the thyroid gland [263]. 

Administered in the drinking water of rats for 100 days, 1, 3, 10, or lOOmg/1 of iodine caused no signs of overt toxicity but some modifications of thyroid function occurred. Specifically, there was a dose-related trend in increased plasma thyroxine levels and a statistically significant increase in the thyroxine-to-triiodothyronine ratio. 

Oral contraceptives have their most significant effect on endocrine parameters. Blood cortisol, thyroxine, protein-bound iodine, T3 uptake, and urinary free cortisol are elevated. Urinary 17,21-dihydroxy steroids, 17-ketosteroids, and estrogens are decreased. There is no effect on urinary catecholamines or VMA (Table 10) (LIO). The effect of thyroid functions tests is due to the administered hormone stimulating an increase in the production of thyroid-binding globulin which in turn binds 1-thyroxine. The lowering of free thyroxine stimulates the anterior pituitary to produce thyrotropin, which in turn stimulates the thyroid to produce more thyroxine. Since the additional thyroxine is bound to the extra protein, there is an equilibrium and the patient remains clinically euthyroid, but the protein-bound iodine and the thyroxine are elevated. 

Recent restrictions in the use of hexachlorophene preparations for antisepsis and the recommendation that povidone-iodine (Betadine) be used in its place will undoubtedly lead to increased thyroid function assay... 

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. 

Countries affected by iodine deficiency require to develop national programmes to assess the extent and severity of the problem. Once an IDD control programme is initiated monitoring and evaluation are required. There are three major components needed to meet this goal, namely determination of thyroid size and goitre prevalence, the determination of urinary iodine excretion, and the measurement of thyroid function, including serum TSH levels. 

Adverse reactions are related to the iodine content of the drug the toxicity is often expressed as skin reactions, thyroid enlargement, and interference with thyroid function studies. Headache and diarrhea also occur. Chronic use of clioquinol, a closely related agent, has been linked to a myelitislike illness and to optic atrophy with permanent loss of vision. 

Although toxicity from isoflavones may arise from their action as alternative substrates for the enzyme thyroid peroxidase and people in southeast Asia would be protected by the dietary inclusion of iodine-rich seaweed products, a recent study has shown that isoflavone supplements do not affect thyroid function in iodine-replete postmenopausal women. Considerations of the safety of soy isoflavones is an area of great interest in relation to their potential benefits to human health and has recently been comprehensively reviewed. ... 

Bruce B, Messina M, Spiller GA. Isoflavone supplements do not affect thyroid function in iodine replete postmenopausal women. J. Med. Food 6, 309-316, 2003. 

It is a long acting antiarrhythmic drug. It contains iodine and may cause disorders of thyroid function. 

Metabolically, radionuclides are handled in the same way as stable elements of the same atomic numher. Thus radioactive iodine simulates stable iodine, being concentrated in the thyroid gland so predictably that its rate of uptake provides an accurate measure of thyroid function. The metabolism of other radionuclides also is sufficiently characteristic so that their patterns of uptake, distribution, translocation, and excretion are similarly predictable. 

Amiodarone blocks the peripheral conversion of thyroxine (T4 ) to triiodothyronine (T3). It is also a potential source of large amounts of inorganic iodine. Amiodarone may result in hypothyroidism or hyperthyroidism. Thyroid function should be evaluated before initiating treatment and should be monitored periodically. Because effects have been described in virtually every organ system, amiodarone treatment should be reevaluated whenever new symptoms develop in a patient, including arrhythmia aggravation. 

Laminaria angusta Kjellim. L. cichorioides Miyabe. L. japonica Aresch. L. longipedalis Okam. L. religiosa Miyabe. Kun Bu or Hai Dai (thallus) Iodine, potasium, calcium, amino acids, laminarin, laminine, algin.33 Improve thyroid function, correct the malignant vicious cycle effect of iodine deficiency, lower blood pressure. 

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. 

Physiologic Function Testing, An example of this application is the assay of thyroid hormone levels in (lie blood winch, in turn, can aid in the assessment of thyroid function. The radioactive iodine uptake test, which involves the administration of a dose of l31l (iodine-131) to the patient, is also a valuable procedure in assessing thyroid function. At present, the technique is best reserved for problem cases rather than used as a primary screening test. The main disadvantage of this test is the effect of the dietary intake of iodine, which reacts in various ways in different individuals. 

Even a single dose of corticotropin briefly inhibits the secretion of thyrotrophic hormone. The uptake of radioactive iodine is also suppressed by corticotropin and by glucocorticoids, but this has no clinical relevance. Pathological changes in thyroid function induced by glucocorticoid treatment are reportedly rare. 

IODINE AND DRUGS THAT AFFECT THYROID FUNCTION... 

Neonatal goiter caused by the use of potassium iodine as an expectorant during pregnancy has been reported (67). The neonate, a girl, had acute hypothyroidism, with myxedema and respiratory distress. She was given levothyroxine for 6 months, with complete normalization of thyroid function. 

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