Morphofunctional characteristics of the thyroid gland in intact and partially sympathectomized rats of different age groups

The morphological and functional age-dependent changes have been studied in the thyroid gland of infantile (1-month-old), immature (2- and 3-month-old) and sexually mature (6-month-old) male rats. The decrease in thyroid functional activity with ageing was proved. Chemical sympathectomy (guanethidine at a dose of 15 mg/kg intramuscularly for 14 days after birth) was accompanied not only by morphological reconstruction of the thyroid tissue, but also (especially in 1-month-old rats) by a delay in transport-organic phase of iodine metabolism and a decline in thyroid hormone serum level. Later on, the compensatory hormonogenesis reinforcement occurs as a result of partial adrenergic innervation recovery.     

Morphological changes in the thyroid gland of rats during various phases of the estral cycle]

The functional state of the thyroid gland and the concentration of thyroid hormones in the peripheral blood were studied in 20 mature female albino rats during their estral cycle. Evaluation of the thyroid functional state was made according to data of histological, morphological (the diameter of folliculi, the height of the thyroid epithelium) and histochemical analysis (determination of NAD and NADP-dehydrogenase, succinatedehydrogenase, lactate dehydrogenase, peroxydase, acid and alkaline phosphatase) as well as biochemical determination of iodine bound with protein (IBP) in the blood plasma and investigation of the ratio of the parameters in question under conditions of the sex cycle. The cyclic changes of the morphological state of the thyroid gland attended by the phases of the estral cycle were revealed. The activation of the organ was observed in proestrus and estrus which was evidenced by high levels of activity of the enzymes under study, high concentration of IBP in the blood and increased height of thyreocytes. A decreased function of the thyroid parenchyma was observed at the period of metaestrus-diestrus.     

Effect of lithium chloride on thyroid structural elements in the rat and on the balance of calcitropic hormones

Chronic experiments were performed to study the effect of lithium chloride on morphological and functional characteristics of rat thyroid and on the endocrine regulation of calcium metabolism. As a result of a prolonged exposure to low doses of lithium the thyroid manifests the signs of activation of tissue structures. As the lithium dose is raised, the thyrostatic effect of lithium occurs according to the mechanism similar to the Wolff-Chaikoff effect (colloid accumulation by follicles and suppression of hormones secretion into blood). Lithium chloride stimulates calcitonin production by C cells of the thyroid. However, the increase of the basal level of calcitonin has no substantial effect on calcium metabolism in the animals, since such an increase is accompanied by increment of the production of the physiological antagonist parathyroid hormone by the secretory cells of the parathyroid glands.     

Recent advances in understanding the molecular basis of primary congenital hypothyroidism

Primary congenital hypothyroidism is characterized by low levels of circulating thyroid hormones and raised levels of thyrotropin at birth. It can be either permanent or transitory. Most permanent cases (80-85%) result from alterations in the formation of the thyroid gland during embryogenesis (thyroid dysgenesis), and several were shown recently to be produced by mutations in genes responsible for the development of thyroid follicular cells (TITF1, TITF2, PAX8 and TSHR). Less frequently, congenital hypothyroidism is determined by defects in thyroid hormone synthesis (hormonogenesis defects). The latter are usually associated with goiter. Recently, the molecular mechanisms of two forms of hormonogenesis defects (iodine transport defects and Pendred syndrome) were elucidated.     

Effect of lithium on the melatonin production in the pineal gland of viscacha

Melatonin is synthesized primarily in the pineal gland. Lithium affects the circadian rhythms that may explain its therapeutic effectiveness in the treatment of bipolar disorder. The objective of this study was to investigate the effect of lithium on the biochemical parameters involved in melatonin synthesis in the pineal gland of viscacha. Viscachas were daily intraperitoneally injected with lithium chloride or saline solution for one month. Pineal mRNAs encoding β₁-adrenoceptor and arylalkylamine-N-acetyltransferase enzyme (AA-NAT) were studied by in situ hybridization. Pineal melatonin concentrations were determined by radioimmunoassay, and AA-NAT and hydroxyindol-O-methyltransferase (HIOMT) activities were investigated by radiometric assays. The only parameters that decreased significantly were the expression of AA-NAT mRNA and pineal melatonin levels. Our data suggest that lithium treatment may decrease melatonin synthesis in the viscacha pineal gland by a complex mechanism that involves currently unknown events that are beyond a decrease in the expression of AA-NAT enzyme.     

The effect of cryopreservation and transplantation factors on the morphofunctional state of the thyroid in dogs

Influence of transplantation of non-specific factors (denervation, delymphatization, surgical trauma, ischemia, changes in blood supply conditions) as well as the effect of cryopreservation (-196 degrees C) on morphological structure and ability for secretion of thyroid hormones and response to TS stimulation were studied using the model of extracorporal biological perfusion in isolated thyroid of dogs. The results of biochemical and morphological investigations of thyroid in different conditions of perfusion showed, that it had preserved its main functional and morphological characteristics under the action of transplantation of nonspecific factors and extremely low temperatures.     

The value of plasma TSH estimation and TRH stimulation test in the course of treatment of differentiated thyroid cancers.

Plasma TSH levels were measured on 114 occasions in 96 patients treated for differentiated thyroid cancer. Prior to thyroid surgery, plasma TSH levels were within the range of normal. Plasma TSH levels increased slightly following partial thyroid resection and definitely after total thyroid ablation. In patients where the removal of normal thyroid induced hormonogenesis in thyroid tumours, plasma TSH levels were dependent on the hormonal secretion of the tumour as shown by inverse relationship between TSH and both PBI and 131I uptake. The increase of radioiodide uptake following stimulation by exogenous bovine TSH was inversely related to the plasma thyrotropin levels. The suppressibility of enhanced thyrotropin levels was complete with individually adjusted doses of synthetic thyroid hormones. With the exception of patients on suppressive treatment, TRH administration induced increase in plasma TSH levels. The findings are discussed with regard to the role played by TSH in the induction of hormonogenesis in thyroid tumours. The practical values of TSH estimation and TRH stimulation seem to be low; the measurements of thyrotropin levels may be important for the estimation of the suppressive effect in the course of and following withdrawal of treatment with thyroid hormones.     

Effect of chronic administration of lithium chloride on the development of dopamine receptor sensitivity during morphine withdrawal in rats

The morphine withdrawal syndrome was studied in male Wistar rats. Spontaneous aggressiveness, enhanced apomorphine aggressiveness, lowered pain threshold and decreased dopamine turnover were observed after withdrawal of 10-day treatment with the increasing doses of morphine (30-300 mg/kg). These changes attested to the increased sensitivity of dopamine receptors. Administration of morphine in conjunction with lithium chloride in a dose of 2 mekv/kg prevented the development of dopamine receptor hypersensitivity. Also, this method did not produce the increased spontaneous and apomorphine aggressiveness or the decreased dopamine turnover. Meanwhile the pain threshold remained lowered.     

Dynamics of postnatal histogenesis of the thyroid in normal rats and after sympathectomy

The changes of the thyroid gland and neurocytes of the cranial sympathetic ganglia were followed in rats of different ages after guanethidine injections with the use of radioimmunological assay, electron microscopy and morphometry. The injection of 15 mg of the drug per kg of body weight within the first two weeks after birth caused the death of over 80% of the cells in the sympathetic ganglion. In the sympathectomized 15-day- and 1-month-old rats the functional activity of the thyroid gland was markedly reduced. Later on, intrathyroid hormonogenesis somewhat increases due, apparently, to partial recovery of the organ adrenergic innervation and increase in the production of thyrotropic hypophysial hormone and calcitonin.     

Thyroid gland hypofunction during separate and combined radiation-thermal injury

A study was made of the dynamics of structural, morphological and histological changes in the thyroid gland of Wistar rats subjected to gamma-irradiation (7.5 Gy) and thermal burn (15% of a body surface) and a combined effect of these two factors. Concurrently, an estimation was made of the iodine content of the gland, using the roentgen-fluorescent method, and of the thyroxin concentration in blood. The results obtained were considered in relation to the clinical course and the outcome of the affection caused by the combined and individual effects of radiation and heat. It is conluded that the cell-tissue substrate providing the thyroid hormones synthesis does not undergo substantial variations from normal values which could be considered as a cause of the decrease in the hormone content of blood after burn, irradiation and the combined radiation and thermal injury. Other possible causes of hyperthyroxynemia are discussed.     

<Emphasis Type="Italic">In Vivo</Emphasis> Evaluation of Transdermal Iodide Microemulsion for Treating Iodine Deficiency Using Sprague Dawley Rats

The objective of this study was to evaluate the transdermal efficiency of iodide microemulsion in treating iodine deficiency using rats as an animal model. Animals were fed either iodine-deficient diet (20 μg/kg iodide) or control diet (200 μg/kg iodide) over a 17-month period. At month 14, iodide microemulsion was applied topically in iodine-deficient group and physiological evaluations of thyroid gland functions were characterized by monitoring the thyroid hormones (T₃, T₄), thyroid-stimulating hormone (TSH), iodide ion excretion in urine, and the overall rat body weights in both groups. Moreover, morphological evaluations of thyroid gland before and after treatment were performed by ultrasound imaging and through histological assessment. Prior to microemulsion treatment, the levels of T₃, T₄, and TSH in iodine-deficient group were statistically significant as compared to that in the control group. The levels of T₃ and T₄ increased while TSH level decreased significantly in iodine-deficient group within the first 4 weeks of treatment. After treatment, iodide concentration in urine increased significantly. There was no statistical difference in weight between the two groups. Ultrasound imaging and histological evaluations showed evidence of hyperplasia in iodine-deficient group. Topical iodide microemulsion has shown a promising potential as a novel delivery system to treat iodine deficiency.     

The functional state of the thyroid gland following partial pancreatectomy]

In Wistar rats a study was made of a functional condition of the thyroid gland 1, 6 and 24 hours after partial pancreatectomy. The following signs-served as criteria of a functional condition of the gland: the amount of neutrone-activated iodine in iron, iodine-absorptive capacity of the gland by I131, the amount of protein-bound stable and radioactive iodine in the blood, a morphological condition of the gland structures. It was demonstrated that, despite the initial intensification of the process of synthesis and secretion in the thyroid gland, its secretory activity fell by the end of the experiment. This reduction is regarded as an adaptive response to partial insulin deficiency.     

The effect of mildronate and related substances on levels of thyroid hormones and some intermediates of lipid and carbohydrate metabolism in hyperthyroid and hypothyroid rats

The effects of mildronate [3(2,2,2-trimethylhydrazinium) propionate dihydrate], γ-butyrobetaine (GBB) and their combination (neomildronate) on the level of thyroid hormones and some intermediates of basal metabolism (free fatty acids, triglycerides, glucose) in serum of laboratory rats with various dysfunctions of thyroid glands including idiopathic hyperfunction and also hypofunction induced by administration of 6-propyl-2-thiouracil (PTU) or L-carnitine administration. Intraperitoneal injections of mildronate (150 mg/kg) during 20 days to male Wistar rats with elevated level of thyroid hormones and basal metabolism normalized thyroxin level and parameters of lipid metabolism in serum. Administration of the compounds studied to rats with hypothyroidism induced by administration of PTU or L-carnitine did not influence natural recovery of the hormonal level. Possible biochemical role of these pharmacological treatments is discussed in terms of in regulation of thyroid gland function.     

Effect of arginine-vasopressin on the rat thyroid gland in vitro

The response of the rat thyroid gland to arginine-vasopressin in vitro was studied to clear a possibility of a direct regulation of this gland by hypothalamic nonapeptide neurohormones. The function of the thyroid gland was estimated by thyrocyte height and quantity of the autoradiographs on a thyrocyte. AVP makes more active hormone synthesis in thyrocytes after 30 min of incubation and it stimulates both synthesis and secretion of the thyroid hormones in 2 hours of incubation. The higher concentrations of AVP activate the thyroid hormone synthesis but not the secretion.     

Structural-functional state of the thyroid gland after thymectomy]

The dynamics of morphologic and biochemical indices of the thyroid gland in puberal rats has been considered. The data obtained suggest that the thymus hormones deficiency in blood circulation after thymectomy affect thyroid-stimulating functions of adenopituitary and thyroliberin production in hypothalamus that results in significant depression of thyroid function, whereas the enhancement of thyroid function to 20-month follow-up has no central genesis but is rather a result of autoimmune processes activation when thymus is removed.     

Relationship of biochemical and morphological changes in rat thyroid and proton spin-relaxation of the tissue water.

The effect was studied of biochemical and morphological changes induced by antithyroid substances (PTU, C10(-4)) on proton spin-relaxation properties of rat thyroid gland. It was found that thyroid stimulated by PTU (0.05%) or C10(-4) (1.0%) exhibit marked morphological changes (hyperplasia and epithelial hypertrophy) with alteration of the soluble iodoprotein pattern (content and composition.). Both relaxation times spin-lattice (T1) and spin-spin (T2) were increasing with the lenght of treatment with antithyroid drugs. Reversibility of the process was noted in accordance with biochemical and morphological data. The relaxation rate (formula: see text) for thyroid tissue water was in positive correlation with the suluble protein concentration and particularly with the TG content in the gland. There was no difference in relaxation times between normal thyroid and gland of rats treated chronically with excess iodide. The observed difference in T1 between normal glands and glands of PTU,-C10(-4)--treated rats was comparable with that found in cases of human thyroid cancer. This finding is of importance when the diagnostic potential of NMR in the detection of malignancy is considered. In conclusion, a strong correlation was found between microstructural and biochemical changes of the thyroid gland and proton magnetic relaxation of tissue water. The striking difference between the proton spin-relaxation times in normal and in goiter thyroid glands of rats suggests that pulsed NMR spectroscopy could be a method for evaluation of some disturbances in thyroid gland.     

A review of chemically-induced alterations in thyroid and vitamin A status from field studies of wildlife and fish

This paper reviews 22 published field studies that have found an association between exposure to environmental contaminants and alterations in thyroid gland structure, circulating thyroid hormones and vitamin A (retinoid) status in free-ranging populations of wildlife and fish. Vitamin A and thyroid hormones play critical roles during development, growth and function 'throughout life. Studies of captive wildlife and laboratory studies support a relationship between alterations in thyroid hormones and vitamin A status and exposure to dioxins, furans, and planar polychlorinated biphenyls, which bind to the aryl hydrocarbon receptor. Some studies have found adverse health effects in wildlife associated with exposure to polyhalogenated aromatic hydrocarbons and altered thyroid and retinoid status including: decreased reproductive success, immune system changes, dermatologic abnormalities and developmental deformities. A direct causal relationship between these effects and thyroid and retinoid changes has not been demonstrated. Field researchers studying the responses to these synthetic chemicals in wildlife and fish should include measurement of thyroid hormones and retinoids and histological examination of the thyroid gland in their study design as biomarkers of exposure to these chemicals in the environment.     

Molecular and cellular mechanisms of transepithelial iodide transport in the thyroid

Thyroid hormone is an essential regulator of developmental growth and metabolism in vertebrates. Iodine is a necessary constituent of thyroid hormone. Due to the scarcity and uneven distribution of iodine on the Earth's crust, the structure of the thyroid gland is adjusted to collect and store this element in order to secure a continuous supply of thyroid hormone throughout life. Still, disease resulting from hypothyroidism due to iodine deficiency is a global health problem, illustrating the great biological significance that iodine saving mechanisms have evolved. Iodide is accumulated together with prohormone (thyroglobulin) in the lumen of the thyroid follicles. The rate-limiting step of this transport is the sodium/iodide symporter located in the basolateral plasma membrane of the thyroid follicular cells. Iodide is also transferred across the apical plasma membrane into the lumen where hormonogenesis takes place. In this review, recent progress in the understanding of transepithelial iodide transport in the thyroid is summarized.     

黑斑蛙变态过程中甲状腺发育及甲状腺激素分泌

系统研究了我国本土两栖动物种黑斑蛙（Rana nigromaculata）变态发育过程中甲状腺组织学和甲状腺激素水平的变化,为甲状腺生物学和甲状腺干扰研究提供基础数据。黑斑蛙蝌蚪发育的形态变化: 第26-40阶段,后腿芽生长并逐渐分化出五趾结构;42阶段,开始进入变态高峰期,前肢展开,尾吸收,蝌蚪身体发生巨大形变;46阶段,蝌蚪完全变态成小蛙。随着形态学的变化,甲状腺的组织结构也发生明显的变化: 26-37阶段,甲状腺体积较小,增长缓慢;38阶段甲状腺体积迅速膨大,进入高峰期,甲状腺的发育达到顶峰;随着变态完成,甲状腺又逐渐缩小。甲状腺组织学变化的同时,甲状腺激素水平也相应发生变化: 在变态前期,下颌中3,3',5-三碘代-L-甲腺原氨酸（T3）水平增长缓慢,进入变态期后,T3含量迅速升高,在变态高峰期达到峰值,随后下降。以上结果表明,黑斑蛙发育过程中甲状腺组织学的变化与甲状腺激素水平的波动相吻合。对黑斑蛙甲状腺系统的研究,可为日后使用黑斑蛙开展甲状腺干扰作用的研究提供基础。       

Thyroglobulin biosynthesis in a larval (ammocoete) and adult freshwater lamprey (Lampetra planeri Bl.).

1. The biosynthesis of 18-19S thyroglobulin has been studied in a larval and adult freshwater lamprey (Lampetra planeri Bl.). 2. In vivo and in vitro experiments have been performed by injecting into the coelomic cavity or by incubating branchial region labeled constituents of Tg of higher vertebrates (125I, [3H]leucine and various [3H]carbohydrates). 3. Larvae (ammocoetes) and adults incorporate all labels into thyroglobulin (18-19S Tg), containing a small proportion of labeled T3 and T4, as identified by paper chromatography, and very minute amounts of stable iodine. 4. In adults, the biosynthesis of 18-19S Tg proceeds much more rapidly and the labels are incorporated in higher percentage than in larvae. 5. The demonstration of the biosynthesis of the specific thyroid protein, 18-19S Tg, in larvae indicates that the biochemical mechanism of hormonogenesis is present in larval endostyle before the morphological differentiation of thyroid cells and follicles occurring during metamorphosis. 6. Some 18-19S Tg is apparently stored in the endostyle.