Effects of thyroidectomy and administration of propylthiouracil (PTU) or thyrotropin (TSH) to pregnant rats on the functional development of the fetal thyroid gland an immunohistochemical study

In order to elucidate the maternal factors influencing the functional development of the fetal rat thyroid gland, pregnant rats were subjected to either thyroidectomy or administration of PTU or TSH and the thyroid glands of the fetuses were examined chronologically by immunohistochemistry to detect thyroglobulin (Tg), T4 and T3. In the group undergoing thyroidectomy, the occurrence of immunoreactive Tg, T4 and T3 was the same as in the control group in spite of slight retardation of the development of the thyroid gland. On the other hand, PTU administration caused remarkable degeneration of the hyperplastic epithelium of the follicles, where immunoreactivity of T4 and T3 was barely detectable, suggesting a transplacental effect of PTU on the fetal thyroid gland. However, Tg remained unaffected and was stained as well as in the controls. Injection of TSH led to a delay in the occurrence of T4 and T3 by one day, probably due to increased levels of thyroid hormone from the stimulated thyroid gland of the mother rats.     

Effect of maternal alcohol consumption on the fetal thyroid in the rat

To investigate the effect of maternal alcohol consumption on the development of the fetal thyroid gland, Sprague-Dawley rats were given 20% ethanol for 4 weeks prior to mating and 30% ethanol throughout gestation. Pair-fed controls received an isocaloric amount of corn starch and chow, with water ad libitum, and ad libitum controls received rat chow and water. On Days 17, 18, 19, and 20 of gestation, the fetuses were weighed and the fetal thyroids were removed for histometric observation. On Days 19 and 20, the fetal thyroids of alcohol-exposed fetuses weighed significantly less than those of the two control groups, but more than the control thyroids 1 day earlier. Maternal alcohol consumption caused a significant decrease in both the follicular cell height and the follicle diameter of the fetal thyroid on all days examined. In the alcohol group on Days 19 and 20 of gestation, the cell height was less than, and the follicle diameter was approximately equal to those in the two controls 2 days earlier. These results indicate that, as a consequence of maternal alcohol consumption, growth of the fetal thyroid gland is retarded, and there are indications of fetal hypothyroidism, as seen from the histometric data. This latter is suggestive of a retarded thyrotropic activity of the fetal pituitary gland.     

The effect of acute external gamma-irradiation and thyroid glands dysfunction on rat reproductive system and frequency of structural mutations in somatic cells of pregnant females and their offspring

Experimental hypofunction of thyroid gland, caused by mercazolil administration, and acute external exposure to 0.5 and 1.0 Gy of gamma-irradiation were shown to result in disturbance of reproductive function in puberal females and of estrogenreceptor interaction, in reduction of pregnancy probability, increase in pre- and postimplantation lethality of fetuses as well as in rise in the frequency of structural mutations in somatic cells of pregnant rats and their offspring.     

Sex dimorphism in the thyroid gland. IV. Cytologic aspects of sex dimorphism in the rat thyroid gland

This study was designed to explain whether the sex-dependent differences in the structure of the thyroid gland of adult male and female rats depend on quantitative or qualitative changes in the thyroid follicular cells. Absolute thyroid gland weight was similar in male and female rats, but its relative weight was markedly higher in females however. Volume fractions of epithelium and stroma were higher and that of colloid lower in male than in female rats and the epithelium/colloid ratio was higher in the males. Also absolute the volumes (in mm3) of epithelium and stroma were higher in the males; the thyroid gland of females contained more colloid. The average volume of a thyroid follicular cell, estimated by stereology, was higher in males than in females, although the thyroid gland contained similar numbers of follicular cells in both sexes. Also, thyroid glands from both male and female rats contained a similar DNA quantity. Results of the present study show that the sex dimorphism in the rat thyroid depends upon a difference in the mean volume of thyroid follicular cells, with males having larger cells than females. However, in both sexes the thyroid gland contains a similar quantity of these cells.     

Failure to prevent degeneration of insect muscles with pepstatin.

Minimal O₂ consumption (MOC), was elevated during pregnancy, lactation and after cold-acclimation. Since the MOC remained elevated in pregnant rats after removal of the gravid reproductive organs and fetuses, it was concluded that maternal tissues were hypermetabolic. Results of experiments using endocrine ablation (thyroidectomy) or replacement (thyroid hormones) techniques could not resolved the question of whether the thyroid was required to sustain this hypermetabolism.In order to determine whether the increased MOC during lactation was secondary to the calorigenic requirements of milk biosynthesis, the MOC was measured after removal of mammary tissue of the lactating rat. Despite the absence of lactating mammary tissue, the MOC remained elevated.Thyroidectomized rats were successfully acclimated to cold but their MOC did not change. In contrast, intact rats acclimated to cold in the same manner became better cold-acclimated, as judged by survival at colder temperatures, and their MOC was elevated. Cold-acclimation appears to consist of two components, only one of which depends on the presence of an intact thyroid gland. The presence of both components confers maximal tolerance to cold.     

Morphofunctional features of the development of the thyroid gland of Dicrostonyx torquatus during the drop in population stage

By means of the histostereometrical method, peculiarities of the thyroid gland formation have been studied in the lemming (Dicrostonyx torquatus) fetuses and newborns at the stage of the population quantity drop, as well specificity of the organ's morphofunctional state during the postnatal period. On the 14th prenatal day the thyroid gland already has the follicular structure. Up to the 19th day progressive follicular growth, accumulation of colloid and increase of its density occur. On the 19th-20th days, as well as in newborn animals, there are certain signs, demonstrating as essential activation of the thyroid gland function. In the newborn animals cavities of the completely formed follicles are devastated. During the postnatal period again growth of follicles, accumulation of colloid are observed, signs of hypersecretion of the hypophysis appear.     

Morphometric studies on the development of human thyroid gland in early fetal life.

Histological and morphometric studies were performed on 30 thyroid glands obtained from normal human fetuses. Their crown-rump length (CRL) ranged from 57 to 190 mm, corresponding to the gestational age of 10-20 weeks. The weight of the thyroid gland increased proportionally in relation to CRL, foot length and fetus weight. The first follicles containing PAS-positive colloid were observed in the peripheral part of the thyroid gland of 57 mm CRL fetus. The number of follicles per 1 mm2 of thyroid surface section increased up to 85 mm CRL and thereafter gradually declined for the end of studied period of fetal life. The volumes (in mm3) of thyroid epithelium, colloid and stroma, beginning from 85 mm increased proportionally to the CRL while the height of epithelial cells did not change. The epithelium/colloid ratio decreased notably to 165 mm CRL and thereafter remained constant. Results of the present study suggest that the thyroid gland of human fetus approaches structural maturity in 17.5 week of gestation.     

Thyroid gland responses to intermale aggression in an inherently aggressive wild rat

The aim of the present investigation was to ascertain whether intermale aggression (by fighting) affects thyroid gland activity in wild rat. Following intermale aggression for three hours, thyro-follicular epithelial height was significantly decreased and colloidal content in follicular lumen increased only in the subordinate rats whereas the thyroid gland of the dominant rats was not perceptibly changed. Thus, aggression inhibits thyroid gland activity only in the subordinate rats. It is suggested that this effect may be due to psychosomatic rather than physical stress during aggression.     

Characteristics of the recovery processes in the resected thyroid of adult rats after sympathectomy

The investigation was carried out on 65 adult white male rats (12-month-old) after normal development or chemical sympathectomy by guanethidine and subtotal thyroidectomy. By means of electronic microscopic, autoradiographic and radioimmunological methods the increased functional activity in thyroid gland of chemically sympathectomized rats was found. This is mainly due to thyrotropin hyperproduction and intensification of proliferative potential of the organ. Partial resection of sympathectomized rats thyroid gland leads to exhaustion of adenohypophysis compensatory potential manifested in disjunction of integrative connections in hypothalamus-hypophysis-thyroid gland system and delay of thyroid status normalization.     

Body, heart, thyroid gland and skeletal muscle weight changes in rats with altered thyroid status

In the present paper we describe changes of anatomical parameters in inbred Lewis strain rats, namely their body weight, body weight gain per week, absolute and relative heart, thyroid gland and skeletal muscle weights, that are assumed to reflect experimentally altered thyroid status. The hyperthyroid state was induced by DL-thyroxine or Na 3,3',5-triiodo-L-thyronine, while methimazole was employed for inducing hypothyroidism. We have found that when compared to euthyroid rats, hypothyroidism resulted in a significantly lower body weight gain, absolute and relative heart weight and, in contrast, in a significant increase of absolute and relative thyroid gland weight. On the other hand, hyperthyroidism led to a significant increase of absolute and relative heart weight and to a significant reduction of absolute and relative thyroid gland weight. However, the body mass was not significantly altered in hyperthyroidism as compared with euthyroid rats. We conclude that our protocol leads to chronic hyper- or hypothyroidism as demonstrated by body, heart and thyroid gland weight changes. These anatomical data can thus be utilized as supplemental criteria for the assessment of the thyroid state of experimental rats.     

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.     

Fine structural aspects of the black thyroid induced by minocycline, and the effects of a low iodine diet, propylthiouracil, thyroxine tablet and TSH, on the black discoloration of the rat thyroid

Fine structural aspects of the effect of minocycline, an antibiotic of the tetracycline group, on the rat thyroid were studied. In all the rats administered minocycline (100 mg/kg/day) for 21 days, diffuse black discoloration of the thyroid gland occurred. However, when the rats were fed on a low iodine diet, given propylthiouracil (PTU) or thyroxine tablet with minocycline the black pigmentation of the thyroid gland did not take place. On the other hand, black discoloration of the thyroid was accelerated in the rats administered TSH and minocycline simultaneously. Ultrastructurally, numerous dense bodies containing highly electron-dense deposits were seen in the supranuclear region of the follicular epithelial cells of the black thyroid. These dense bodies, which showed positive acid phosphatase activity, are considered to be lysosomes containing minocycline or its derivatives. It is speculated that minocycline is taken up into follicular epithelial cells with iodine, and that the black discoloration of the thyroid gland is intimately related to iodine metabolism.     

Compensatory-restorative processes of the thyroid gland in 1- and 3-month-old rats in health and in desympathization

In 172 white male rats 1- and 3-month-old, using electron microscopical, autoradiographical, morphometrical and radioimmunological methods, analysis of structural-functional changes of the thyroid gland has been carried out both under normal conditions and at guanethidine desympathization (15 mg/kg for 14 days after birth). Resection of 2/3 of the organ has been performed on the 3d, 5th, 7th and 15th days before sacrifice. In the 1-month-old desympathized rats hypofunctional state of the gland is observed. By the 3d month at the expense of an increased production of thyrotropin and calcitonin the thyroid status becomes normal. The dynamics of the restorative processes in the thyroid gland after resection of 1/3 of the organ in the control and test rats occurs with a similar intensity. Proliferative potency of the desympathized thyroid tissue is much higher.     

Characteristics of the compensatory repair processes in the thyroid of 1-month-old rats as affected by sympathectomy

A considerable decrease in the amount of sympathetic nervous cells in neonatal rats injected guanethidine resulted in the depression of thyroid gland functional activity in 1-month-old animals, there was an apparent parallel increase in the proliferative activity of the gland. A 2/3 thyroidectomy led to the functional tension of the remaining part of the organ. A comparison of compensatory-reparative processes after thyroidectomy has shown similarity of reparative changes in experimental and control rats, however, the degree of repair potential was much higher in the sympathectomized thyroid gland.     

Morphological study of the neurosecretory hypothalamo-hypophyseal system and thyroid gland in intestinal carcinogenesis]

Pathomorphology of the neurosecretory hypothalamo-hypophyseal system and the thyroid gland of 150 rats of both sexes was investigated in intestinal carcinogenesis induced by 1.2-dimethyl hydrazine. Inhibition of the neurosecretory activity of paraventricular and supraoptical nuclei as well as atrophic changes in th: thyroid gland were found to be associated with the latent period of carcinogenesis. The arising of the intestinal tumor is accompanied by hypertrophy of neurons and their nuclei, by a decrease in the neurosecretory substance content and the thyroid gland tendency to return to normal. The tumor spreading provoked neuron hypertrophy and the reduction of the neurosecretory substance as well and pronounced atrophic changes in the thyroid gland.     

Influence of experimentally induced endotoxemias on the thyroid function of rats

The general membrane-damaging effect of endotoxins (LPS) may be also demonstrated on the follicular cells of thyroid gland. Serum T4 level significantly decreased and the response of thyroid gland to exogenous THS was markedly inhibited in experimental endotoxin and other so-called enteroendotoxemic shocks (e.g. intestinal ischemia, tourniquet shock, intestinal syndrome of radiation disease). A single subtoxic dose of LPS given to newborn rats decreased the T4 level, the response of thyroid to TSH in adulthood and caused a somatic retardation. The radio-detoxified endotoxin (TOLERIN) did not inhibit the thyroid response to TSH. TOLERIN pretreatment protected the rats against LPS and other enteroendotoxemic shocks.     

Response of the developing thyroid gland of rats to a single gamma-irradiation in the period of intrauterine development

A single external exposure of pregnant rats to 2 Gy gamma-radiation caused changes in the functional status of the thyroid gland in offsprings at varying times of the postnatal development. The disturbance of the thyroid hormones balance in the blood, destruction of the thyroid gland combined with high functional tension of secretory elements, and activation of the thyrotropic function of hypophysis were revealed at remote times after irradiation.     

The sexual system of fetal and adult male rats of 2 strains after prenatal exposure to glucocorticoids

Testosterone level in male fetuses and adults after glucocorticoid injection to their mothers on 16-th and 18-th days of pregnancy as well as morphometric characteristics of male adult reproductive system of two outbred strains (aggressive and domesticated) were investigated. Prenatal hormonal treatment resulted in genotype-dependent changes in testosterone level in 21-day-old male fetuses; it was decreased in fetuses of domesticated rats and increased in fetuses of aggressive rats. The direction of these changes coincided completely with the subsequent changes in relative weight of preputial gland and seminal vesicles in adults. Thus, the level of glucocorticoids during prenatal period plays an important role in reproductive system development and the character of the action depends on the genotype.     

Iodine metabolism in the thyroid gland in chronic uranium poisoning]

The exchange of radioactive and stable iodine was studied for 21 days after the I131 injection in the thyroid gland and the blood of rats against the background of chronic uranium intoxication. The latter was accompanied by a decrease in the number of iodine-transport loci of the gland, as well as of the value of the intrathyroid iodine pool and of the stable iodine concentration in the thyroid tissue. The compensatory reaction of the thyroid gland was expressed in the increase of its mass and the rate of the thyroid metabolism as well.     

Effect of radish (Raphanus sativus Linn.) on thyroid status under conditions of varying iodine intake in rats

Cruciferous plants viz. cabbage, cauliflower, turnip, radish, mustard etc. that contain goitrogenic/antithyroid substances, constitute a portion of regular human diet. The effect of chronic feeding of fresh and cooked radish, R. sativus under varying state of iodine intake on morphological and functional status of thyroid in albino rats was evaluated by thyroid gland morphology and histology, thyroid peroxidase activity, serum triiodothyronine, thyroxine and thyrotropin levels. The consumption pattern of iodine and goitrogens of cyanogenic origin was evaluated by measuring urinary iodine and thiocyanate levels respectively. After chronic radish feeding, increased weight of thyroid gland, decreased thyroid peroxidase activity, reduced thyroid hormone profiles and elevated level of thyrotropin were observed resembling a relative state of hypoactive thyroid gland in comparison to control even after supplementation of adequate iodine.