Thyroid hormone radioactive iodine

Strong iodide solutions act by decreasing the vascularity of the thyroid gland by rapidly inhibiting the release of the thyroid hormones. Radioactive iodine is distributed within the cellular fluid and excreted. The radioactive isotope accumulates in the cells of the tiiyroid gland, where destruction of tiiyroid cells occurs without damaging other cells throughout the body. 

Radioactive iodine, although not a hormone itself, is taken up by the thyroid gland and incorporated into thyroid hormones. During this process, it emits radiation that causes destruction of the thyroid gland. It is used specifically to treat thyroid tumours. Radioactive iodine is also used to treat thyrotoxicosis (Chapter 6). 

Excess production of thyroid hormone can be reduced in four ways iodides, antithyroid drugs, radioactive iodine, and... 

In patients with excess thyroid hormone production, reduce hormone production with an antithyroid drug and/or radioactive iodine. Choose therapy based on patient-specific factors and preference. 

An elevated 24-hour radioactive iodine uptake (RAIU) indicates true hyperthyroidism the patient s thyroid gland is overproducing T4, T3, or both (normal RAIU 10% to 30%). Conversely, a low RAIU indicates that the excess thyroid hormone is not a consequence of thyroid gland hyperfunction but is likely caused by thyroiditis or hormone ingestion. 

Trace amounts of iodine are required for a healthy body. Iodine is part of the hormone thyroxin produced by the thyroid gland. Thyroid secretions control the physical and mental development of the human body. A goiter, a swelling of the thyroid gland, is caused by the lack of iodine. Adding thyroid medication and iodized salt to the diet helps prevent this disease. Radioactive iodine (1-131), with a half-life of eight days, is used to treat some diseases of the thyroid gland. 

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaT ). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak 8-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion. 

Thyroid cancer Exogenous thyroid hormone may produce regression of metastases from follicular and papillary carcinoma of the thyroid and is used as ancillary therapy of these conditions with radioactive iodine. Larger doses than those used for replacement therapy are required. 

RAIU = radioactive iodine uptake TSH = thyroid-stimulating hormone h"4 uptake method TT4 X RT3LI method ... 

Thyroid suppression therapy- 75 to 100 mcg/day for 7 days radioactive iodine uptake is determined before and after administration of the hormone. 

In the adult population, the prevalence of overt hypothyroidism is 19 per 1000 women and 1 per 1000 men with annual incidence of overt hypothyroidism is 4 per 1000 women and 0.6 per 1000 men. Subclinical hypothyroidism is also more common in women, the incidence increases with age, with up to 10% of women older than 60 years having an increased thyroid-stimulating hormone concentration. Subclinical hypothyroidism is more common in people who have been treated for hyperthyroidism with radioactive iodine or surgery, and in those with organ-specific autoimmune diseases, such as pernicious anaemia, type 1 diabetes mellitus, or Addison s disease. 

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. 

Radioactive isotopes of iodine are handled by the thyroid in the same way as stable iodine and are therefore actively concentrated, incorporated into thyroglobulin, stored, metabolized, and secreted as thyroid hormones. Small amounts of radioactive iodine are therefore ideal probes to analyse the uptake of iodine, the distribution of iodine in the gland, and possibly even its turnover and incorporation into thyroid hormones. Larger amounts of radioactive iodine selectively radiate the thyroid gland and therefore selectively impair the function of the follicular thyroid cells and eventually destroy them. 

Male Sprague-Dawley rats weighing 180-240 g are fed a commercial laboratory with low concentrations of thyroid hormones, containing constant amount of unlabelled iodine. The animals are treated for at least seven days with the test compound to be evaluated, at a pharmacologically active dose determined by a previous biological studies. On the morning of the test day, rats are injected with a test dose of 131-1 (intravenously or intraperitoneally), and the concentration of radioactivity in the thyroid glands is measured after 1 1 hours. The blood concentration of 131-1 at these time points is measured, and the tissue to blood ratios are calculated for individual animals. 

Hypothyroidism is a relative deficiency in thyroid hormones. It manifests as a slowing down of all body functions or a decrease in metabolic rate. There are many causes for hypothyroidism, including Hashimoto s thyroiditis, drug-induced, radiation and radioactive iodine, dyshormono-genesis, congenital, and secondary causes (pituitary or... 

The most common iodine isotope used is iodine-131. When iodine (of any kind) enters the body, it tends to go directly to the thyroid. The iodine is then used to make thyroid hormones. If radioactive iodine is used, a doctor can tell how well the thyroid gland is working. If a high... 

The study of the thyroid hormones was greatly facilitated when radioactive isotopes of iodine became available. Using I it was soon con6rmed (576, 612, 665, 666) that activity administered as iodide was converted in the thyroid to diiodotyrosine and then thyroxine. 

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