Iodine physiology

Thyronine—receptor complexes stimulate or inhibit gene expression in almost every tissue in the human body, and therefore necessarily command our focus. The result is a thyroid hormone (TH)-centric perspective of iodine physiology that persuades us to avoid consideration of nonthyronine pharmacologic activity associated with iodine. The role for so-called extrathyroidal iodine has been discussed in the hterature as iodide uptake in the majority of breast cancers has aroused the interest of several researchers (Venturi et at. 

DNLM 1. Iodine—physiology—congresses. 2. lod 1 ne—defic1ency--congresses. 3. Nutritional Requirements—congresses. QV 283 1633 1992]... 

See also Coronary Heart Disease Prevention. Fatty Acids Omega-3 Polyunsaturated. Iodine Physiology, Dietary Sources and Requirements. Supplementation Dietary Supplements. 

See also Iodine Physiology, Dietary Sources and Requirements. Selenium. 

In other applications of CT, orally administered barium sulfate or a water-soluble iodinated CM is used to opacify the GI tract. Xenon, atomic number 54, exhibits similar x-ray absorption properties to those of iodine. It rapidly diffuses across the blood brain barrier after inhalation to saturate different tissues of brain as a function of its lipid solubility. In preliminary investigations (99), xenon gas inhalation prior to brain CT has provided useful information for evaluations of local cerebral blood flow and cerebral tissue abnormalities. Xenon exhibits an anesthetic effect at high concentrations but otherwise is free of physiological effects because of its nonreactive nature. 

Labeling of iodinated aromatics with radioactive or has proved to be a valuable approach to measure GFR in nuclear medicine. Prominent among these is sodium iothalamate, which is specifically marketed in the US for GFR measurement by the name Glofil . Studies have shown that the clearance of this marker by the glomeruli is reproducible, simple, reliable and accurate, especially in children and those with advanced renal diseases [234]. This marker can also be administered by subcutaneous infusion to obtain GFR values without the need for urine collection [235]. Since very low doses (nanomolar scale) of radioactive aromatics are administered, monitoring of renal function may be achieved without disruption of normal physiologic functions. Concerns over radioactivity and associated handling costs may prevent the use of these compounds for routine GFR measurements. 

Luckhardt AB, Koch FC, Schroeder WF, Weiland AH The physiological action of the fumes of iodine. J Pharmacol Exp Ther 15 1-21, 1920... 

A second dietary trace element, selenium, is also essential for normal thyroid hormone metabohsm. Selenium in the form of selenocysteine is a required component for three enzymes that remove iodide from thyroid hormones. Deiodination is the major metabohc pathway by which T4 and T3 are cleared from the system. After secretion by the thyroid gland, T4 may be deiodinated to yield either T3 or the physiologically inactive reverse Tj (3,3, 5 -triiodothyronine, or rX3). T3 and rTj are further deiodinated to form less active metabolites. Selenium, like iodine, is deficient in many areas of the world. 

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. 

Susceptibility factors genetic (unoperated or palliated cyanotic congenital heart disease beta-thalassemia major) sex (conflicting results) altered physiology (iodine intake, conflicting results)... 

Because thyroxine contains four iodine residues, this compound is also referred to by the abbreviation T4. Likewise, triiodothyronine contains three iodine residues, hence the abbreviation T3. There has been considerable discussion about which hormone exerts the primary physiologic effects. Plasma levels of T4 are much higher than T3 levels, but T3 may exert most of the physiologic effects on various tissues, which suggests that T4 is a precursor to T3 and that the conversion of T4 to T3 occurs in peripheral tissues.23 Regardless of which hormone ultimately affects cellular metabolism, both T4 and T3 are needed for normal thyroid function. 

The anthropogenic radionuclides of most concern are those produced as fission products from nuclear weapons and nuclear reactors. The most devastating release from the latter source to date resulted from the April 26, 1986, explosion, partial meltdown of the reactor core, and breach of confinement structures by a power reactor at Chernobyl in the Ukraine. This disaster released 5 x 107 Ci of radionuclides from the site, which contaminated large areas of Soviet Ukraine and Byelorussia, as well as areas of Scandinavia, Italy, France, Poland, Turkey, and Greece. Radioactive fission products that are the same or similar to elements involved in life processes can be particularly hazardous. One of these is radioactive iodine, which tends to accumulate in the thyroid gland, which may develop cancer or otherwise be damaged as a result. Radioactive cesium exists as the Cs+ ion and is similar to sodium and potassium in its physiological behavior. Radioactive strontium forms the Sr2+ ion and substitutes for Ca2+, especially in bone. 

The toxicological hazard of perchlorate salts may depend on the cation in the compound. In general, the salts should be considered as skin irritants and treated as such. Perchlorate ion, C104, may compete physiologically with iodide ion, U. This can occur in the uptake of iodide by the thyroid, leading to the biosynthesis of thyroid hormones. As a consequence, perchlorate can cause symptoms of iodine deficiency. 

Tfcble 1 Physiologic and chemical characteristics of water-soluble, iodinated contrast media ... 

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