Tejido tiroideo y láser infrarrojo: un estudio morfométrico / Thyroid tissue and infrared laser: a morphometric study

La glándula tiroides posee gran importancia debido a la síntesis y secreción de hormonas, las cuales desempeñan funciones fundamentales para la mantención de la fisiología animal. En este contexto, el objetivo del presente trabajo consistió en determinar parámetros morfométricos de estructuras tiroideas sometidas a estimulaciones con láser infrarrojo (LIR). Para ello, 10 ratas Sprague Dawley de 3 meses de vida y peso aproximado de 200 g, fueron divididas en dos grupos de 5 animales cada uno: grupo control y grupo experimental. Estos últimos recibieron estimulaciones infrarrojas en la tiroides con dosis de 16 J/cm2 durante 15 días seguidos. Una vez sacrificadas las ratas, se extrajeron las glándulas tiroides las que fueron procesadas para microscopía óptica obteniéndose placas histológicas y micrografías con aumentos finales de hasta 1000 X. Se efectuaron estudios morfométricos para determinar en 40 placas, variaciones tisulares generadas por las inducciones infrarrojas, con especial énfasis en la disposición coloidal y dimensiones de folículos y células tiroideas. El análisis de las 40 placas histológicas generados por las inducciones del láser infrarrojo comparados con los controles, reveló que existen marcadas diferencias en todos los componentes del tejido tiroideo analizado, lo cual podría otorgar antecedentes de diferentes funcionalidades en el metabolismo de las glándulas.

The thyroid gland is of great importance because of the synthesis and secretion of hormones which play key roles in the maintenance of animal physiology. In this context, the aim of the present study was to determine morphometric parameters of thyroid structures subjected to infrared laser stimulation (ILS) and for this purpose, 10 Sprague Dawley rats, 3 months of age and weighing approximately 200 grams, were divided into two groups of 5 animals each: the control group and the remaining 5 animals constituting the experimental group received infrared stimulation in the thyroid with doses of 16 J/cm2 for 15 consecutive days. After the rats were sacrificed, the respective thyroids were removed and processed for optical microscopy. Histological plates and micrographs were obtained with final increases of up to 1000 X. Morphometric studies were carried out to determine the tissue variations generated by infrared inductions, with special emphasis on the colloidal arrangement and dimensions of follicles and thyroid cells. Our results revealed that there are marked differences in all the components of the analyzed thyroid tissue which could give antecedents of different functionalities in the metabolism of thyroid glands.

Efecto del láser infrarrojo sobre células tiroideas / Infrared laser effect on thyroid cells

Diez ratas Sprague Dawley de 4 meses de vida y peso aproximado de 250 g fueron divididas en dos grupos de 5 animales cada uno, el grupo A se mantuvo como control y los animales del grupo B recibieron estimulaciones con láser infrarrojo en la tiroides con dosis de 16 J/cm2 durante 15 días consecutivos. Posteriormente las ratas fueron sacrificadas, se extrajeron las respectivas tiroides siendo procesadas para microscopía óptica y se obtuvieron placas histológicas y micrografías de tiroides con aumentos finales de hasta 1000X, las cuales fueron sometidas a estudios morfométricos para determinar en 100 células foliculares: número, áreas y perímetro tanto celular como nuclear, además de disposición coloidal y presencia de vasos sanguíneos. El análisis de los resultados entre las 100 células foliculares pertenecientes a tiroides normal y estimulada revela que existen marcadas diferencias en todos los componentes analizados los que se podría traducir en distintas funcionalidades en el metabolismo de las respectivas glándulas.

Ten 4-month-old Sprague Dawley rats weighing approximately 250 g were divided into two groups of 5 animals each. Group A was the control and the animals in group B received thyroid stimulation with infrared laser in a dose of 16 J/cm2 for 15 consecutive days. Subsequently, rats were euthanized and thyroids were removed and processed for optical microscopy. From both cell types thyroid histological slides and micrographs were obtained with final increases of 400 and 1000X. Morphometric analysis determined the number, areas and cell perimeter as well as colloidal dispersion and presence of blood vessels in 100 follicular cells. Analysis of the results among the 100 follicular cells belonging to normal and stimulated thyroids revealed marked differences in all the analyzed components, which could translate into different functionalities in the metabolism of the respective glands.

Ultrastructure of the thyroid gland in adult West African dwarf goat (Capra hircus) / Ultraestructura de la glándula tiroides en la cabra enana africana occidental (Capra hircus)

The present study examined ultrastructure of the thyroid gland of adult West African Dwarf (WAD) goat in order to further understand the ultrastructural morphology and some of the changes in the components of the thyroid gland in goat with age. Thyroids glands obtained from fifteen adult WAD goats of different ages and sexes slaughtered at the local abattoirs were used in this study. Electron microscopic techniques were used to study the fixed tissue with emphasis on the follicular and parafollicular cells. The results showed that the ultrastructure is generally similar to that of some domestic animals. Follicular cells were cuboidal in young adult goats thyroids but were flattened in older goat thyroids of 5­7 years. These cells remarkably showed highly dilated cisternae of rough endoplasmic reticulum which decreased in frequency the older goats. Microvilli were short and sparse on the follicular cells and the number decreased in the older goats. Different sizes of apical vesicles of varying electron density were encountered that included colloid droplets, secretory vesicles and lysosome-like bodies and the appearance of these vesicles changed with age. Parafollicular cells were encountered in the basal position between follicular cells in all thyroids examined. Numerous dense cytoplasmic granules were observed and they were not apparently different from that described in several mammals.

El presente estudio examinó la ultraestructura de la glándula tiroides en cabra enana de África occidental adulta con el objetivo de tener un mejor conocimiento de la morfología y algunos de los cambios en los componentes de esta glándula en cabras de mayor edad. Se estudiaron glándulas tiroides obtenidas de quince cabras adultas de diferentes edades y sexos, sacrificadas en los mataderos locales. Se utilizaron técnicas de microscopía electrónica para estudiar el tejido con énfasis en las células foliculares y para foliculares. Los resultados mostraron que la ultraestructura generalmente era similar a la de algunos animales domésticos. Las células foliculares en la tiroides de cabras adultas jóvenes eran cúbicas, no obstante en cabras adultas de mayor edad (5 a 7 años) se observaron células aplanadas en las tiroides. Estas células mostraron cisternas de retículo endoplasmático rugoso muy dilatadas que disminuyeron en frecuencia en las cabras de más edad. Las microvellosidades eran cortas y escasas en las células foliculares, y el número disminuyó en las cabras de más edad. Se encontraron diferentes tamaños de vesículas apicales y se observaron gotitas coloidales, vesículas secretoras y organismos similares a los lisosomas; la aparición de estas vesículas fue cambiando en cabras de mayor edad. Se encontraron células parafoliculares en posición basal en todas las células foliculares examinadas. Se observaron numerosos gránulos citoplasmáticos densos sin aparente diferencia de aquellos descritos en otros mamíferos.

Histogenesis of Developing Human Thyroid.

In human beings the thyroid gland is one of the largest of the endocrine organs. It is one of the earliest endocrine organs to be differentiated and has an important hormonal role in embryonic development. The importance of thyroid gland is to promote growth and development of the brain during fetal life and for the first few years of post-natal life[1, 2]. The purposes of present study are 1)to study the microscopic structure of the human thyroid in different gestational age groups of normal stillborn foetuses; 2) to correlate the size of thyroid follicles; the nature and amount of colloid content of thyroid follicles at different stages of development. The study was carried out on 50 stillborn normal human foetuses. The microscopic structure of thyroid was studied under light microscope. The study concluded the developmental staging of thyroid as: the precolloid stage; the colloid formation stage; the folliculogenesis stage; secretory activity stage.

Light and electron microscopic study on the effect of lithium carbonate on the thyroid gland of adult male albino rat

Lithium carbonate is the treatment of choice for acute manic episodes. It is often referred to as an anti-manic drug as it prevents mood swings in patients with manic-depressive disorder. Thyroid disturbances during lithium treatment had been reported. This research was performed to study the effect of lithium carbonate on the thyroid gland of albino rat and the possibility of recovery after drug withdrawal. Thirty adult male albino rats were divided into three equal groups; Group I [Control Group], group II received lithium carbonate at a daily dose of 14.4 rug for each rat for 6 weeks orallyand group III received the same dose of lithium carbonate as group II and then left untreated for another 6 weeks to study the possibility of recovery after the drug withdrawal. The specimens were prepared for light and electron microscopic examination. Sections of lithium carbonate treated rats showed enlarged irregular shaped thyroid follicles with papillary infoldings projecting into the follicular lumena. Detached and desquamated follicular cells were seen in the follicular colloid. The follicular cells showed apparent hyperplasia and bizarre-appearing nuclei. The interstitial tissue showed cellular infiltration, presence of deeply eosinophilic large cells and fibrosis in some specimens. Ultrastructurally, there was cellular debris in the follicular lumena. Some follicles showed dark follicular cells containing electron dense cytoplasm and indistinct organelles. The above structural changes were much less pronounced in group III [Recovery Group]. Lithium carbonate induced histological changes in the thyroid gland of albino rat and most of these changes were seen to be improved after withdrawal of the drug, So, the use of this drug should be justified in clinical situation under direct medical supervision

Effects of chronic estradiol treatment on the thyroid gland structure and function of ovariectomized rats

Estrogen therapy is widely used nowadays in women to treat many postmenopausal symptoms but it may have some undesirable effects due to multiple organs affection. The aim of this study was to determine the effects of chronic estradiol treatment oh the structure and function of the thyroid gland in ovarictomized rats as a model simulating menopause. Thirty adult female albino rats divided into three groups were used in this study, the first group was sham-operated, while the second and third groups were ovariectomized. The first and second groups were injected with olive oil while the third group was injected with estradiol diproprionate daily for three months, after that hormonal assay for T3, T4, TSH and histological specimens of the thyroid were taken and examined by light and electron microscopy. Serum levels of T3 and T4 were significantly decreased in ovariectomized animals and increased with estradiol treatment, while TSH increased in ovariectomized animals and decreased with estradiol. Histological and morphometric study in ovariectomized group revealed marked accumulation of colloid in follicular lumens with decreased epithelial height in addition to increased connective tissue amount while with estradiol treatment the follicles were smaller with small amount of colloid with increased epithelial height in addition to decreased connective tissue content. Ultrastructural study supported these results in addition to the presence of large amount of intracytoplasmic colloid vesicles after estradiol treatment. Decreased amount of estrogen may lead to thyroid hypofunction while estradiol treatment may lead to hyperactivity so it should be used very cautiously in the treatment of postmenopausal symptoms to avoid its undesirable stimulatory effect on the thyroid

Histological study of the effect of amiodarone on the follicular cells of the thyroid gland of male albino rats

Amiodarone is a potent antiarrhythmic drug used for treatment of many types of cardiac arrhythmias. Its structural formula contains a high dose of iodine with a considerable potential to cause thyroid gland dysfunction. The aim of the present work was to study the possible histological changes in the follicular cells of the thyroid gland in male albino rats after long-term administration of amiodarone. Reversibility of these changes was also investigated. The study was confirmed by hormonal assay, to evaluate the thyroid gland endocrine function. The present study was carried out on 40 adult male albino rats, which were divided into 3 study groups; group I, considered as control, group II [the amiodarone- treated group] received amiodarone orally in a daily dose of 30 mg/kg for 12weeks and group III [the withdrawal group] that received the same dose of amiodarone for 12 weeks and were sacrificed 6 weeks after withdrawal of the drug. Rats were sacrificed after ether anesthesia and blood samples were subjected to hormonal assay of TSH, T[4] and T[3] levels. The thyroid gland tissue samples were removed and prepared for light microscopic examination of H and E stain and toluidine blue- stained semithin sections. Electron microscopic examination was also done. Histological examination of thyroid gland in amiodarone treated- rats [group II] revealed different light microscopic and ultrastructural changes. Some follicular cells showed signs of degeneration in the form of irregular dilation of the rough endoplasmic reticulum, vacuolation of the cytoplasm and increased number of lysosomes with irregular nuclei. These changes might be due to direct cytotoxic effect of the high iodine-containing amiodarone on the follicular cells. Other follicles showed signs of hyperactivity manifested by vacuolated colloid with scalloped appearance of its edges and papillary projections of the follicular cells with epithelial stratification. The manifestations of hyperactivity appeared to be compensatory to the direct effect of the drug. Alterations of thyroid function in group II, was further confirmed by results of hormonal assay, which revealed significant increase in serum levels of both TSH and T[3] with significant decrease in the level of T[3]. In group HI, after withdrawal of the drug, many follicles exhibited histological reversibility to almost normal pattern. Manifestations of sustained activity were still depicted in few follicles with focal areas of stratification and dilation of the rough endoplasmic reticulum. Hormonal assay showed that TSH and T[3] returned to nearly normal values while T[4] remained higher than the control level. From the present study, it could be concluded that prolonged amiodarone administration caused manifest histological and biochemical changes in the follicular cells of the thyroid gland. The obtained structural and hormonal changes were almost reversible after stoppage of the drug administration. Baseline and repeated levels of thyroid hormones should be monitored in every patient on amiodarone therapy

Histological and toxicological study on the effect of kojuc acid on the thyroid follicular cells of albino rats

Kojic acid is a natural substance, widely used as a food additive and preservative, in cosmetic preparations as a skin whitening agent, a plant growth factor as well as a chemical intermediate in pharmaceuticals. The goal of the present study was to clarify the impact of kojic acid on the thyroid follicular cells of male albino rats as well as the reversibility of its effect after withdrawal, both histologically and biochemically. A total of 30 adult male albino rats [120-150 g] were randomly divided among 3 equal groups. Group I [control group]: received isotonic saline orally for 4 weeks. Group II [treated group]: received kojic acid in a dose of 0.8g/kg b.w./day orally for 4 weeks. Group III [withdrawal group]: received kojic acid daily in the same dose and duration as in group II followed by its withdrawal for the next 4 weeks. By the end of the experimental periods, blood samples were collected for estimation of plasma triiodothyronine [T3], thyroxine [T4] and thyroid stimulating hormone [TSH] levels. Histological examination of toluidine blue-stained semithin sections, and ultrathin sections of the thyroid gland was also carried out. Statistical assessment of the biochemical parameters of group II rats showed significant reduction in T3 and T4 levels along with evident increase in TSH levels as compared to the control animals. Histologically, overt signs of hyperactivity affecting many thyroid follicles were encountered. It was represented by follicular cell hypertrophy and focal hyperplasia. Stratjfication of the lining follicular cells was also observed in some follicles. Many follicular cells exhibited dilatation of the rough endoplasmic reticulum [rER], cytoplasmic vacuolation, accumulation of numerous lysosomes and mitochondrial affection. Some follicular cells revealed signs of severe degeneration in the form of dense cytoplasm and small irregular dense nuclei. Withdrawal of kojic acid in group III rats resulted in return of the biochemical parameters as well as histological picture of the follicular cells to nearly normal control patterns. However, some follicular cells still revealed evident dilatation of the rER and many lysosomes. As well, few follicles were lined by more than one layer of follicular cells. Kojic acid exerted an evident toxic effect on the thyroid follicular cells. Although such effect was nearly completely reversible after kojic acid withdrawal, yet, it is recommended to restrict its use in food and cosmetic agents

Histological study of the possible toxic effect of selenium on the thyroid follicular cells of albino rats

Selenium is a trace element, essential in small amounts, but it can be toxic in larger amounts. Selenium compounds are widely used as a dietary supplement and as a prophylaxis for the prevention of cancer, cardiovascular diseases and viral mutations. However, there is a narrow margin between safe therapeutic and toxic doses of selenium. The goal of the present study was to study the histological effect of the adequate and toxic doses of selenium on the follicular cells of thyroid gland of albino rats. The study was carried out on 30 adult male albino rats weighing 120-150 gm. Animals were divided into 3 equal groups: Control group; which received adequate diet but without the addition of selenium. Group I [supplemented group]: received sodium selenite in a dose of 75 microgram / kg b.w., and group II [Intoxicated group]: received sodium selenite in a dose of 300 microgram /kg bw. Histological examination of the semithin and ultrathin sections of the supplemented group [group I] revealed nearly normal control image in most of the examined thyroid follicles. Few follicles showed some follicular cells with vacuolated cytoplasm and many dense bodies and others showed irregular nuclei. Ultrastructural examination revealed some cells with dilated cisternae of rough endoplasmic reticulum, widened intercellular spaces and the infiltration of the interstitial spaces with some inflammatory cells and excessive collagen deposition. Histological examination of the intoxicated group [group II] revealed hypertrophy and hyperplasia of the thyroid follicles which appeared crowded with minimal interfollicular spaces. Some follicles showed stratification of their lining cells while others showed dome shaped cells with vacuolated cytoplasm and many dense bodies. Numerous basal and lateral cytoplasmic processes, interrupted epithelial lining and exfoliated cells in the lumina were frequently encountered. The present work recommend the intake of natural diet enriched with high content of selenium and warn about daily intake of exceeding doses of selenium supplementations

Histological study of the effect of potassium bromate on the thyroid gland of adult male albino rats and the protective role of vitamin C supplementation

Thirty adult male albino rats were used in this study aiming to study the effect of chronic oral administration of potassium bromate on the structure of the thyroid gland and to study the possible protective role of the concomitant supplementation of vitamin C. The animals were divided equally into three groups [10 animals each]; a control group and two experimental ones. The animals of the first experimental group were subdivided equally into 2 halves. The animals of the first half were given a daily oral dose of potassium bromate 30 mg/kg body weight for successive 2 months. While the animals of the other half were given the same daily oral dose of potassium bromate for successive 6 months. The animals of the second experimental group were also subdivided equally into 2 halves. These animals were given a daily intraperitoneal injection of 20 mg/kg body weight of vitamin C for 2 and 6 months respectively simultaneous with a daily oral dose of potassium bromate as in the first experimental group. At the time of sacrifice, all the animals of each group were anaesthetized with ether inhalation and their thyroid glands were dissected out carefully and processed for light and electron microscope examinations. Light microscope observations of the thyroid glands of the potassium bromate treated rats for 2 months revealed alterations of many thyroid follicles. Their follicular cells became squamous with deeply stained nuclei. Ultrastructurally, the follicular cells contained irregular heterochromatic nuclei. Their cytoplasm contained dilated rough endoplasmic reticulum and swollen mitochondria. Mast cells were seen in the connective tissue between the affected follicles. Light microscope examination of the thyroid glands of the rats treated with potassium bromate for 6 months showed loss of the architectures of the glands. The follicular cells appeared with deeply stained nuclei and marked cytoplasmic vacuolations. Ultrastructrually, the follicular cells contained dilated and fragmented rough endoplasmic reticulum. Their nuclei showed irregular outlines and much clumps of heterochromatin. While light and electron microscope examinations of the thyroid glands of the animals treated with vitamin C concomitant with potassium bromate revealed preservation of the architectures of the glands. Most of their follicles appeared with few colloid. The follicular cells contained well developed rough endoplasmic reticulum with some dilated cisternae, numerous mitochondria with few swollen ones and cytoplasmic vacuolations. In conclusion, the results of this study revealed that chronic oral administration of potassium bromate led to structural changes in the thyroid gland which were duration dependant. Vitamin C supplementation with potassium bromate showed a moderate protection against these alterations

study of effects of the Infrared laser on the adult albino rat thyroid gland

The thyroid gland and its hormones are so essential for normal growth and develodopment. The thyroid gland is unique in having a histological organization that provides for extracellular storage of its products in lumen of the follicles. Nowadays, laser is widely used in medical therapy. Laser beams are most effective as biological stimulants. Low energy laser irradiation produces various effects at the biochemical, cellular, histological and functional levels. So, this study aimed at studying the histological and ultrastructural effects of laser irradiation on the thyroid gland. In the present work 20 adult male albino rat were used. These animals were divided into two groups, control and experimental, each of them was formed of 10 animals. Each experimental animal was exposed to spot laser irradiation over the right lobe of the thyroid gland. The laser beam was applied for 5 minutes once daily for one month in a dose of 1.92 J/cm 2. The thyroid gland was fixed in either 10% formaldehyde solution for paraffin sections or in 5% gluteralehyde for semithin and ultrathin sections and routinely processed. The paraffin sections were stained with Hematoxeline and Eosin and Van Gisson stains. Whowever, semithin sections were stained with toluidine blue. Ultrathin sections were stained with uranyl acetate and lead citrate. The results showed that: The thyroid follicles were larger in size in experimental group than that of control group, more widely separated by thickened interacinar reticular septa. Heights of their follicular cells were variable from cuboidal in engorged thyroid acini, to columnar in less distended acini. Their colloid secretion was not homogeneously distributed among different follicles and even inside the same acinus. There was an increased vascularily in the form of perifollicular distended and tortuous blood vessels. Also, interacinar capillaries appeared more winded, engorged by blood cells and had thicker walls. By electron microscopy: apical surface of follicular cells was devoid of indentations and microvilli, in reverse to the control group. The cytoplasm was paler and contained lesser amounts of cytoplasmic organelles specially rough endoplasmic reticulum and its cisternae, mitochondria, lysosomes and large secretory granules but not free ribosomes. In conclusion, laser irradiation increases blood supply and does some cellular changes

Light and electron microscopic study of the thyroid gland of female albino rats after collagen-induced arthritis

Adult female albino rats were subjected to experimental arthritis by the injection of arthritic material formed of bovine collagen II dissolved in acetic acid and mixed with Incomplete Freund's Adjuvant [IFA]. Thyroid glands were processed for light and electron microscopic examination. Two groups of control rats were used. The first control group comprised healthy non-treated rats. The second control group comprised IFA -treated rats. Compared with the control rats, light microscopic examination of the thyroid gland of the arthritic rats revealed a marked distortion of the thyroid architecture. The thyroid follicles appeared either degenerated, homogenized or lost. The follicular cells appeared low cubical or flattened with scanty cytoplasm and darkly stained nuclei. The parafollicular C-cells were ill-defined. The colloidal material was either highly vacuolated or depleted. Intraluminal and interfollicular mononuclear cell infiltration was observed. Compared with the control rats, electron microscopic examination of the thyroid gland of the arthritic rats revealed a distorted ultrastructure of the follicular cells. The rough endoplasmic reticulum appeared dilated, distorted, vesiculated and partially degranulated. Secretory granules were rarely seen. Lysosomes and apical cytoplasmic granules were absent. Large cytoplasmic vacuoles and secretory crystalline deposits were seen in some follicular cells. The luminal border lost its apical microvilli and the follicular lumen of some cells contained crystalline colloidal deposits. The nucleus appeared folded and contained more electron-dense clumped chromatin. Pyknotic and karyolytic nuclei were observed. The C-cells showed irregular plasma membrane, disintegrated nucleus and grouping of the secretory granules at one pole of the cell. The present observations may reflect a reduction in the functional activity of the thyroid gland [hypothyroidism] in the female rats subjected to collagen-induced arthritis. Therefore, it is recommended to monitor the thyroid hormones in patients with rheumatoid arthritis and to check the presence of thyroid auto-antibodies in these patients

Histological and biochemical study on the toxic effects of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin [TCDD] on the follicular cells of thyroid gland of rats

2,3,7,8, TCDD and related substances are ubiquitous environmental pollutants causing a wide variety of pathological alterations. They are capable of altering endocrine homeostasis. This work was carried out to study the histological and biochemical changes of acute and chronic administration of TCDD on the follicular cells of thyroid gland of rats. Thirty six male Sprague-Dawley rats were used in this study. They were divided into three groups. Group I was given corn oil and served as a control group. Group II was given 10 micro g/Kg TCDD as an acute single oral dose. Group III was further subdivided into subgroup IIIa and subgroup IIIb that were given 0.125 micro g /Kg/ day TCDD for 4 weeks and 16 weeks respectively. At the end of the experiment, animals were sacrificed and thyroid glands were removed and examined by light and electron microscope [EM]. Biochemical estimation of serum thyroxin [T[4]], triiodothyronine [T[3]] and thyroid stimulating hormone [TSH] were also done to all animals. Histologically, Thyroid gland of group II showed beginning of follicular hypertrophy and hyperplasia in some follicles. These follicles were lined by high cuboidal epithelium with appearance of follicles lined by more than one layer of cells. Dilated rough endoplasmic reticulum [rER], well developed Golgi apparatus and numerous lysosomes were evident. Microvilli of some follicular cells were short and blunted. Subgroup IIIa and IIIb showed signs of hyperactivity affecting most of the follicles. These changes were more pronounced in animals of subgroup IIIb that received TCDD for 16 weeks. Most of the follicles were small and irregular. Many of them were lined by tall columnar epithelium with appearance of papillary projections in their lumens that appeared empty or with sparse scalloped colloid. EM examination revealed marked dilatation of rough endoplasmic reticulum and prominent well developed Golgi complexes with accumulation of numerous lysosomes and membrane bound colloid droplets. Some follicles of this group revealed degenerative changes due to direct toxic effect of TCDD. These histological changes were accompanied by a significant decrease in serum level of T[4] and a significant increase in TSH level. These biochemical changes were more pronounced in animals that received TCDD for 16 weeks. TCDD had deleterious effect on thyroid gland which is time and dose dependent

Ultrastructural study on thyroid glands of Bufo arenarum larvae kept in potassium perchlorate solution

The ultrastructure of thyroid glands in Bufo arenarum tadpoles was studied with inhibited thyroid function. After hatching, larvae were kept in potassium perchlorate solution, a goitrogenic substance known to prevent absorption of iodine from water or food, resulting in impaired thyroid hormone synthesis. Increased thyroid gland volume and follicular cell height were observed in treated larvae. The changes in size and volume of follicular cells in experimental tadpoles appeared to be mainly a function of the overstimulation of proteinpoietic apparatus. The cell shows a conspicuous development of endoplasmic reticulum and Golgi complex, as well as an increase in number of mitochondria and colloid droplets. These observations in follicular thyroid cells from Bufo arenarum, obtained under such experimental conditions, were interpreted in terms of interruption of negative feedback mechanisms involving the decrease in the thyroxine circulatory level, and therefore the increase in hypothalamo-hypophyseal endocrine secretory stimulation.

Alterations of the rat thyroid gland under experimental conditions

The thiyroid gland of rats, was studied under experimental conditions porvided by administration of several doses of lithium carbonate. It was noted a drug a cumulative effcct on the serum; and the decrease of T3 and T4 hormones in the blood, as well as, the red blood cells, hemoglobin, hematocrit platelets and leukocytes; the diameter of the thy roid follicles, the size of the follicular cells and colloid droplets. On the othcr hand the stroma was invaded by of collagen fibers and blood capillaries.