IODIC EXCHANGE

From Big Medical Encyclopedia

IODIC EXCHANGE — biochemical transformations of compounds of iodine in an organism. Y. the island is closely connected with activity of a thyroid gland, and also liver, kidneys and some other bodies. Research Y. the lake — an important diagnostic method of diseases of a thyroid gland.

Iodine (see) treats microelements, total quantity it in a human body makes 20 — 30 mg; apprx. 1/3 these quantities contains in to a thyroid gland (see). At a human body and animals iodine is present both at an inorganic form in the form of iodides, and at integrally connected form: in structure thyreoglobulin (see) a thyroid gland, in molecules of the iodated amino acids — iodtyrosines (see) and yodtironin (see) blood, in bodies and biol, liquids.

Daily need of the person for iodine averages 3 mkg on 1 kg of body weight.

Iodine comes to an organism in the form of iodides which are soaked up from intestines in blood; other forms of iodine are recovered in intestines to iodides. From intestines also organic iodinated matters are soaked up: iodated fat to - you, diiodotyrosine, thyroxine, etc. From the circulating blood iodide is taken generally thyroid gland and kidneys, it is less — other bodies.

In a thyroid gland iodide is oxidized to atomic iodine which joins in a molecule of thyreoglobulin with formation of integrally connected iodine. Apprx. 2% of iodine remains in the form of iodides and can be returned to plasma; this iodine is called «labilno connected» and is easily forced out from gland by such monovalent anions as thiocyanates, perchlorates and nitrates. The main iodated components of thyreoglobulin are derivative amino acids of tyrosine — Yodtirozina [mochoyodtirozin (MEATH), diiodotyrosine (DIT), not having hormonal activity] and yodtironina [thyroxine, or tetrayodtironin (T4), and 3,5,3' - triiodothyronine (T3) — the main hormones of a thyroid gland]. These components contain 80 — 90% of all iodine of a thyroid gland; from them 50 — 70% and 25 — 30% — on a share of yodtironin fall to the share of iodtyrosines.

In a hydrolyzate of tissue of thyroid gland and thyreoglobulin also other iodated components are found in insignificant quantities: 2-or 4 monoiodhistidine, 3,3 '-diyodtironin and 3,3', 5' - triiodothyronine, and also tiroksamin and 4-oxy-3,5-diiodine-phenyl-pyruvic to - that.

As a result of splitting of thyreoglobulin proteases and peptidases allocate yodtironina — thyroxine (see) and triiodothyronine (see) and Yodtirozina — monoiodtyrosine and diiodotyrosine. Thyroxine and triiodothyronine come to blood, Yodtirozina are deiodinated in follicles, and their iodine is used in biosynthesis of thyroid hormones again. The main circulating hormone of a thyroid gland is the thyroxine containing 3/4 all iodine of blood. In circulation there are also small amounts 3,5,3 '-triiodothyronine. Besides, at blood constantly there is an iodide making 21 — 30% of all iodine of blood, and, perhaps, minute quantities 3,3', 5 '-triiodothyronine and 3,3 '-diyodtironina which do not change hormonal balance of an organism.

In normal conditions of Yodtirozina in blood, as a rule, are absent, they appear in significant amounts at some morbid conditions (e.g., a thyrotoxicosis, a thyroiditis). Total quantity of extra thyroid iodine at the healthy adult on condition of concentration of the proteinaceous and connected iodine in plasma of 5 mkg of % makes apprx. 1150 mkg; from them 150 mkg there are in plasma, 1000 mkg — in fabrics.

In the circulating blood concentration of iodine makes 8,5 ± 3,5 mkg of %. 0,5 — 1,0 mkg of % make iodides, the rest — the proteinaceous and connected iodine of plasma, more than 90% to-rogo fall to the share of the thyroxine connected with tiroksinsvyazyvayushchy proteins of plasma: tiroksinsvyazyvayushchy alpha globulin, prealbumin and albumine.

As a result of interaction of the connecting proteins with thyroid hormones of 99,9% of thyroxine there is in reversible physical. bonds with baby seals and only 0,1% — in a stand-at-ease. Triiodothyronine is also connected with blood proteins, but this communication less strong. Free forms of hormones come to fabrics, have the effect and are exposed to metabolic transformations.

Iodinated thyroid hormones are exposed in fabrics to a number of chemical transformations: to deiodinating, deamination, decarboxylation), conjugation of phenolic group, etc. Half-life of thyroxine is wounded to 6 — 7 days, triiodothyronine — to 2 — 3 days. An important role in exchange of iodinated hormones is played by a liver, and also kidneys, a brain, muscles and a digestive tract. During the deiodinating of yodtironin the chipped-off iodine partially is used again by an organism for biosynthesis of thyroid hormones, partially excreted. Due to the reutilization loss of iodine with a stake and urine does not exceed 10%. Deamination leads to formation of ketoacid analogs of thyroxine and triiodothyronine — tetrayodtiropirovinogradny, tetrayodtirouksusny, triyodtiropirovinogradny and triyodtirouksusny to - t; fiziol, value of this process is disputable. At decarboxylation of yodtironin it is formed tiroksamin. In a liver there is Konjyugirovaniye of phenolic group of yodtironin with glucuronic and sulfuric to-tami to formation of the corresponding ethers. Conjugates with bile are excreted in intestines. The mucous membrane of intestines contains enzyme the beta glucuronidase which is quickly splitting glyunuronovy ether with release of thyroxine. Thus, the iodine emitted with a stake represents iodine of free thyroxine. In kidneys there is a formation of the sulfoconjugates which are allocated with urine.

Thus, in regulation Y. the lake and maintenance of iodic balance of an organism the thyroid gland, a liver, kidneys and a digestive tract most actively participate.

Methods of a research of iodic exchange use at diagnosis of diseases of a thyroid gland and disturbances Y. the lake at other pathology. In a wedge, laboratories widely apply methods of definition in blood of content of integrally connected iodine and tracer techniques of a research Y. lake.

Allow to judge indicators the content in blood of integrally connected iodine proteinaceous and connected iodine (see) plasmas and butanolekstragiruyemy iodine (see) plasmas. Normal the content of the proteinaceous and connected iodine in plasma makes 3,5 — 8,5 mkg of % — on 0,5 — 1 mkg of % is lower than butanolekstragirovanny iodine.

The radio isotope research allows to estimate versatily a condition Y. lake. The principle of a research consists that dynamics stable 127 I can be tracked by means of its radioisotope entered in the quantity which is not changing iodic balance of an organism.

For a research Y. the lake is most widely used 131 I. The radioactive drug is administered through a mouth, intravenously, or researches are conducted by in vitro with marked hormones. By preparation for a research it is necessary to exclude treatment by iodinated drugs, use of iodinated contrast agents, anti-thyroid drugs, hormones of a thyroid gland and adrenal gland. There are practically no contraindications to use of a radioiodine.

For registration of radioactivity use the domestic V-2, DSU-61, DSU-68 installations, to UR, scanners of various brands, and also well counters.

Fig. 1. Measurement of percent of absorption of iodine-131 a thyroid gland on the remote scintillation DSU-61 installation.
Fig. 2. Skanogramma of a thyroid gland: 1 — norm (it is given for comparison); 2 — at a diffusion toxic craw.

The scheme of radio indication consists that to the patient enter a certain dose of isotope and watch kinetics of the Deputy according to a certain temporary program. Radioactivity measurement is conducted by the external account over body (fig. 1), registration of activity in blood samples and urine or by receiving a picture of distribution of the radioactivity (fig. 2) in a thyroid gland — scanning (see).

Tracer techniques of a research Y. lakes are divided into the methods defining a condition of iodaccumulative function of a thyroid gland (an inorganic phase Y. lake), methods determining the content of integrally connected iodine in blood (an organic phase Y. the lake), and the methods allowing to define a state peripheral Y. lake and exchange of thyroid hormones.

A number of techniques from which practical application was found by two is developed for studying of an inorganic phase of the Deputy: definition of accumulation 131 I in a thyroid gland and its removal with urine. The first of them consists that at the patient who on an empty stomach without pre-treatment accepts 2 — 5 mkkyur of Na 131 I, in 2 and 24 hours measure radioactivity over a thyroid gland, edges is expressed as a percentage to the entered dose. At healthy faces in a thyroid gland in 2 hours about 20% of isotope, in 24 hours — to 50% collect. For studying of removal of isotope with urine to the patient enter 25 — 50 mkkyur 131 I; in the urine collected for two days perform radioactivity measurement in the well counter, edges it is expressed as a percentage to the entered dose. At healthy faces removal 131 I for two days makes 57,7 ±6,9%.

The following techniques are developed for studying of an organic phase of exchange of iodine: definition of proteinaceous and connected 131 I blood plasma and indicator of conversion of inorganic 131 I in organic, a research of inclusion of thyroxine in blood proteins and 131 I-triiodothyronine in erythrocytes, calculation of the relation of radioactivity of erythrocytes to the radioactivity of plasma. The first four techniques are practically used. Proteinaceous and connected 131 I determine by the radioactivity of the besieged blood proteins in 72 hours after introduction 25 — 50 mkkyur 131 I, indicators express as a percentage to the entered dose of isotope per 1 l of plasma. At healthy faces proteinaceous and connected 131 I makes 0,15 ± 0,08%. About conversion of inorganic 131 I in organic judge by the relation of the radioactivity connected with blood proteins to the radioactivity of whole blood in 24 hours after introduction of the same dose 131 I. This indicator at healthy faces makes 36,8 ± 2, 1%.

Definition of thyroxine is carried out to blood with the help 131 I-thyroxine which at electrophoretic division contacts proteins. Results of researches showed that at an euthyroid state the average value of tiroksinsvyazyvayushchy ability of blood proteins makes 2,6*10 - 7 M. A method of definition of hormonal function of a thyroid gland with the help 131 I-triiodothyronine it is based on ability of exogenous triiodothyronine to join in erythrocytes, degree the cut is in direct dependence on a functional condition of a thyroid gland. Normal extent of inclusion of triiodothyronine makes 13 — 14%. Along with the connected thyroxine in blood there is nek-paradise a part free, normal making 0,046%, increasing at a thyrotoxicosis to 0,106%, decreasing at a hypothyroidism to 0,028%.

For assessment of a state Y. the lake and metabolism of hormones of a thyroid gland study exchange of thyroxine with the help 131 I-thyroxine, the content of radio iodine in fabrics, investigate dynamics of removal of hormones, marked on 131 I, to loudspeaker of radioactivity of all body and separate bodies.

Disturbances of iodic exchange are observed at pathology of a thyroid gland and can accompany diseases of a liver, kidneys, a digestive tract.

Disturbances Y. lakes can serve both as the reason, and a consequence of the diseases of a thyroid gland which are followed by development craw (see). Insufficiency of iodine in the environment leads to emergence of endemiya of a craw (see. Craw local ); disturbance of utilization of iodine a thyroid gland — the leading mechanism of development of a sporadic craw (see. Craw sporadic ); profound changes Y. lakes owing to disturbance of a thyroid hormonogenesis, humoral transport and metabolism of iodinated hormones are observed at a diffusion toxic craw (see. Craw diffusion toxic ). Nature of disturbances Y. the lake considerably varies and depends from a wedge, forms of a craw and a functional condition of a thyroid gland. At a hyperthyroidism with development thyrotoxicosis (see) the kontsetration of yodtironin and, therefore, the proteinaceous and connected iodine sharply increases in blood (to 12 — 20 MSC of % and more); at hypothyroidism (see) this indicator does not reach 3,5 mkg of %. At thyroiditis (see) total quantity of intra thyroid iodine can not change, but synthesis of organic iodine is broken, decrease in level of accumulation is often observed 131 The I thyroid gland and contents in a blood plasma belkovo the connected iodine.

A number of inborn disturbances Y is described. the lakes connected with euzymatic defects of a thyroid parenchyma (insolvency of the iodfascinating mechanism, lack of organic binding of iodide or condensation of molecules of iodtyrosines in yodtironina, etc.) or the insufficiency of the dehalogenating fermental systems in fabrics causing disturbance of peripheral exchange of iodinated substances.

Disturbances Y. lakes at diseases of a liver, kidneys and a digestive tract are defined by a role of these bodies in processes of assimilation, metabolic transformations and a reutilization of compounds of iodine. Persistent long dysfunction of intestines can cause a condition of relative insufficiency of iodine in an organism with development of a sporadic craw. At nefroza and some types of pathology of a liver binding of yodtironin is broken by blood proteins and the content of the proteinaceous and connected iodine in plasma decreases; decrease in level of hormonal iodine in blood at cirrhosis is connected with disturbance of synthesis of proteinaceous carriers hepatocytes, and at nefroza — with removal with urine of a significant amount of plasma proteins. There are some forms of inborn family pathology with insufficiency of synthesis of tiroksinsvyazyvayushchy protein (TSB) that is followed by decrease in blood of content of the proteinaceous and connected iodine without the phenomena of a hypothyroidism. Increase in maintenance of TSB and the proteinaceous and connected iodine in blood in the absence of a hyperthyroidism can be noted at pregnancy, administration of estrogen, infectious hepatitis.


Bibliography: Grollman A. Clinical endocrinology and its physiological bases, the lane with English, M., 1969; 3edgenidze G. A. and Zubovsky G. A. Clinical radio isotope diagnosis, page 70, M., 1968; Tracer techniques of a research in endocrinology, under the editorship of A. F. Malenchenko, Minsk, 1976; The Guide to endocrinology, under the editorship of B. V. Alyoshin, etc., M., 1973, bibliogr.; Thyroid hormones, under the editorship of. I. X. Tu-rakulova, Tashkent, 1972; D yo about * t M. et Gcury-Laffont M. Les maladies de la nutrition, P., 1970; L a b h and of t A. Klinik der inneren Sekretion,

B. u. a., 1971.

I. X. Turakulov; E. G. Matveenko (is glad).

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