Histologic changes in tissue components of the hyperplastic thyroid gland during its involution in the rat

Regeneration of thyroid follicles from primordial cells in a murine thyroidectomized model

The functional unit of the thyroid gland, the thyroid follicle, dynamically responds to various stimuli to maintain thyroid hormone homeostasis. However, thyroid follicles in the adult human thyroid gland have a very limited regenerative capacity following partial resection of the thyroid gland. To gain insight into follicle regeneration in the adult thyroid gland, we observed the regeneration processes of murine thyroid follicles after partial resection of the lower third of the thyroid gland in 10-week-old male C57BL/6 mice. Based on sequential observation of the partially resected thyroid lobe, we found primitive follicles forming in the area corresponding to the central zone of the intact lateral thyroid lobe. The primitive thyroid follicles were multiciliated and had coarsely vacuolated cytoplasm and large vesicular nuclei. Consistently, these primitive follicular cells did not express the differentiation markers paired box gene-8 and thyroid transcription factor-1 (clone SPT24), but were positive for forkhead box protein A2 and leucine-rich repeat-containing G-protein-coupled receptor 4/GPR48. Follicles newly generated from the primitive follicles had clear or vacuolar cytoplasm with dense, darkly stained nuclei. At day 21 after partial thyroidectomy, the tall cuboidal follicular epithelial cells had clear or vacuolar cytoplasm, and the intraluminal colloid displayed pale staining. Smaller activated follicles were found in the central zone of the lateral lobe, whereas larger mature follicles were located in the peripheral zone. Based on these observations, we propose that the follicle regeneration process in the partially resected adult murine thyroid gland associated with the appearance of primitive follicular cells may be a platform for the budding of differentiated follicles in mice.

Morphological and Functional Changes in the Thyroid Follicles of the Aged Murine and Humans

BACKGROUND

Although both thyroid histology and serum concentrations of hormones are known to change with age, only a few reports exist on the relationship between the age-related structural and functional changes of the thyroid follicles in both mice and humans. Our objectives were to investigate age-related histological changes of the thyroid follicles and to determine whether these morphological changes were associated with the functional activity of the follicles.

METHODS

The thyroid glands of mice at 18 weeks and at 6, 15, and 30 months of age were histologically examined, and the serum levels of thyroid hormones were measured in 11-week-old and 20-month-old mice. Samples of human thyroid tissue from 10 women over 70 years old and 10 women between 30 and 50 years of age were analyzed in conjunction with serum thyroid hormone level.

RESULTS

The histological and functional changes observed in the thyroid follicles of aged mice and women were as follows: variable sizing and enlargement of the follicles; increased irregularity of follicles; Sanderson's polsters in the wall of large follicles; a large thyroglobulin (Tg) globule or numerous small fragmented Tg globules in follicular lumens; oncocytic change in follicular cells; and markedly dilated follicles empty of colloid. Serum T3 levels in 20-month-old mice and humans were unremarkable.

CONCLUSIONS

Thyroid follicles of aged mice and women show characteristic morphological changes, such as cystic atrophy, empty colloid, and Tg globules.

Recent insights into the cell biology of thyroid angiofollicular units

In thyrocytes, cell polarity is of crucial importance for proper thyroid function. Many intrinsic mechanisms of self-regulation control how the key players involved in thyroid hormone (TH) biosynthesis interact in apical microvilli, so that hazardous biochemical processes may occur without detriment to the cell. In some pathological conditions, this enzymatic complex is disrupted, with some components abnormally activated into the cytoplasm, which can lead to further morphological and functional breakdown. When iodine intake is altered, autoregulatory mechanisms outside the thyrocytes are activated. They involve adjacent capillaries that, together with thyrocytes, form the angiofollicular units (AFUs) that can be considered as the functional and morphological units of the thyroid. In response to iodine shortage, a rapid expansion of the microvasculature occurs, which, in addition to nutrients and oxygen, optimizes iodide supply. These changes are triggered by angiogenic signals released from thyrocytes via a reactive oxygen species/hypoxia-inducible factor/vascular endothelial growth factor pathway. When intra- and extrathyrocyte autoregulation fails, other forms of adaptation arise, such as euthyroid goiters. From onset, goiters are morphologically and functionally heterogeneous due to the polyclonal nature of the cells, with nodules distributed around areas of quiescent AFUs containing globules of compact thyroglobulin (Tg) and surrounded by a hypotrophic microvasculature. Upon TSH stimulation, quiescent AFUs are activated with Tg globules undergoing fragmentation into soluble Tg, proteins involved in TH biosynthesis being expressed and the local microvascular network extending. Over time and depending on physiological needs, AFUs may undergo repetitive phases of high, moderate, or low cell and tissue activity, which may ultimately culminate in multinodular goiters.

Pulse modulated 900 MHz radiation induces hypothyroidism and apoptosis in thyroid cells: a light, electron microscopy and immunohistochemical study

PURPOSE

In the present study we investigated the possible histopathological effects of pulse modulated Radiofrequency (RF) fields on the thyroid gland using light microscopy, electron microscopy and immunohistochemical methods.

MATERIALS AND METHODS

Two months old male Wistar rats were exposed to a 900 MHz pulse-modulated RF radiation at a specific absorption rate (SAR) of 1.35 Watt/kg for 20 min/day for three weeks. The RF signals were pulse modulated by rectangular pulses with a repetition frequency of 217 Hz and a duty cycle of 1:8 (pulse width 0.576 ms). To assess thyroid endocrine disruption and estimate the degree of the pathology of the gland, we analysed structural alterations in follicular and colloidal diameters and areas, colloid content of the follicles, and height of the follicular epithelium. Apoptosis was confirmed by Transmission Electron Microscopy and assessing the activites of an initiator (caspase-9) and an effector (caspase-3) caspases that are important markers of cells undergoing apoptosis.

RESULTS

Morphological analyses revealed hypothyrophy of the gland in the 900 MHz RF exposure group. The results indicated that thyroid hormone secretion was inhibited by the RF radiation. In addition, we also observed formation of apoptotic bodies and increased caspase-3 and caspase-9 activities in thyroid cells of the rats that were exposed to modulated RF fields.

CONCLUSION

The overall findings indicated that whole body exposure to pulse-modulated RF radiation that is similar to that emitted by global system for mobile communications (GSM) mobile phones can cause pathological changes in the thyroid gland by altering the gland structure and enhancing caspase-dependent pathways of apoptosis.

Clinical, biochemical and therapeutical aspects of amiodarone-induced hypothyroidism (AIH) in geriatric patients with cardiac arrhythmias

The clinical features and the laboratory aspects of the amiodarone-induced hypothyroidism (AIH) in the elderly as well as the effects of amiodarone treatment in aged AIH people have not yet been well clarified. In the present paper, we evaluated 18 subjects of both sexes (7 females, 11 males), aged 65-83 years, affected by AIH, recruited in Central Tuscany, Italy. The patients were divided in two subsets on the basis of thyroid stimulating hormone (TSH) values: mild (TSH < 20 mU/l; Group A, n=11) and severe (TSH > 20 mU/l; Group B, n=7) hypothyroid patients. On the basis of clinical features, hypothyroidism was diagnosed only in two patients (out of Group B). Concerning the hormonal pattern, we found that free tetraiodothyronine (fT4) levels were significantly lower than the normal range only in Group B subjects; TSH and thyroglobulin were higher than normal in both groups; free triiodothyronine (fT3) were always in the normal range. Thyroid autoantibodies were found positive only in one patient out of Group A and in two patients out of Group B. In 5/18 patients T4 substitutive therapy was rapidly assigned, because of severe degree of hypothyroidism. In the remaining 13/18 patients, we evaluated the clinical behavior of AIH. After additional cardiac evaluation, amiodarone was withdrawn in 5/13 patients: during follow-up period (4-10 months) four patients became quickly euthyroid while one worsened. In 8/13 patients, amiodarone treatment had to be carried on; during follow-up (2-48 months), four patients remained mildly hypothyroid, while other four patients became severely hypothyroid. In conclusion, in amiodarone treated elderly people, diagnosis of hypothyroidism is reliable only on the basis of high values of TSH; clinical features and fT3 serum levels never enable diagnosis.

Descriptive epidemiology of thyroid carcinoma in Carinthia, Austria: 1984-2001. Histopathologic features and tumor classification of 734 cases under elevated general iodination of table salt since 1990: population-based age-stratified analysis on thyroid carcinoma incidence

INTRODUCTION

The aim of the study was to investigate the current thyroid carcinoma (TC) incidence in Carinthia, a former iodine-deficient, goiter-endemic region in Austria with approximately 550,000 inhabitants from 1984 to 2001. Using age-cohort analysis we analyzed the TC incidence under the impact of two regional risk factors: the contamination of Austrian soils by the radioactive fallout in from Chernobyl 1986 and the increased iodination of table salt in a general program of goiter prophylaxis begun in 1991. To evaluate the characteristics of TC incidence, we compared the results of the periods 1984-1989, 1990-1995, and 1996-2001.

RESULTS

A total of 734 TC cases were diagnosed. Papillary, follicular, medullary, oxyphilic, and anaplastic TC accounted for 76%, 18%, 3%, 1%, and 2%, respectively. The female to male ratio was 3:1. The annual incidence rate increased by 8.05% in females and 11.6% in males. TC cases younger than 40 years of age accounted for 22.6%, with a rate increase of 18% per year in young males, the female-to-male ratio decreased from 8.3, 6.1, 2.7 younger than 40 in the compared periods. Along with a further increase in papillary TC incidence and papillary thyroid carcinoma (PTC) follicular thyroid carcinoma (FTC) ratio in the adult population, the ratio tended to decrease in the younger than 40-year-old population. T4 class TC and loco-regional lymph node involvement increased significantly.

INTERPRETATION

The observed changes in TC incidence, particularly in the young population, as in adults, could be linked to the abovementioned risk factors involved in the initiation and early growth of TC, and iodine may play a role in stimulating overall thyroid activity.

Effects of Propyithiouracil (PTU) Administration on the Synthesis and Secretion of Thyroglobulin in the Rat Thyroid Gland: A Quantitative Immuno-electron Microscopic Study Using Immunogold Technique

To clarify the effects of an antithyroid drug on the kinetics of thyroglobulin synthesis, secretion, and reabsorption in the thyroid follicles, propylthiouracil (PTU) was administered to rats and the thyroid glands were examined by a refined post-embedding immunogold technique during and after withdrawal of PTU. Seven-wk-old male Wistar rats were administered with S mg of PTU/d through a gastric tube, and sacrificed at 1 and 2 wk of administration and at 1, 2, and 3 d, and 1, 2, 3, and 4 wk, after discontinuation. The administration of PTU caused a remarkable dilatation of the rER and Golgi apparatus, but these areas gradually recovered after withdrawal of PTU. During the experiment, no significant change in the density of thyroglobulin (Tg) was observed except for a transient increase immediately after withdrawal of PTU. The expression of Tg on subapical vesicles (SV) and follicular colloid took a relatively parallel course; increasing during administration of PTU and decreasing with a transient peak immediately after treatment was discontinued. In contrast to the remarkable changes in the morphology of compartments involved in Tg synthesis, the development of colloid droplets and formation of secondary lysosomes were suppressed during and after discontinuing administration of PTU. However, the basic pattern of the gradient of Tg density among the cellular compartments was essentially retained in the experimental group. Thus the present immunoelectron-microscopic study provided evidence that administration of PTU stimulates the synthesis and secretion of Tg in the follicular epithelium in vivo, and, also, suppresses reabsorption and degradation of Tg. Further, it was speculated that the density gradient of Tg among the compartments involved in Tg synthesis, secretion and storage is regulated by an unknown constitutive mechanism and not by the thyroid-stimulating hormone (TSH)-TSH receptor-mediated system.

The pituitary-muscle axis in mdx dystrophic mice

As myogenesis, muscle growth and differentiation and growth factor expression are influenced by thyroid and growth hormone (GH) levels, it is important to investigate the possibility that altered activity of the pituitary-muscle axis prevents the lethal progression of mdx dystrophy and/or contributes to the muscle fiber hypertrophy of limb muscles. The ultrastructure of pituitary and thyroid tissues in age-matched control and mdx mice at 2 and 12 months of age was examined. Pituitary GH, and serum thyroid stimulating hormone (TSH), thyroid hormone (T4), and creatine kinase (CK) levels were measured. Mdx thyroid gland structure was similar to age-matched control glands. Mdx thyroid gland weighed significantly more than in age-matched controls, but was unchanged relative to body weight. TSH and T4 levels were not different from levels in control mice. High CK levels reflected the active dystrophy in mdx muscles. Somatotrophs in mdx pituitaries were hypertrophied in comparison to controls, indicating increased secretory activity, and pituitary GH was slightly but significantly greater in old mdx female mice compared to age-matched female controls. These observations rule out hypopituitary or hypothyroid function as a reason for the low impact of dystrophin deficiency in mdx muscles. Results suggest a contribution by raised GH to the fiber hypertrophy in mdx limb and heart muscle, which might also assist the large capacity for limb muscle regeneration in mdx mice.

Involvement of T cell immunity in the transient thyroid inflammation induced by iodide in goitrous BALB/C and nude mice

To evaluate the involvement of T cell immunity in the thyroiditis induced in goitrous mice by iodide administration, we analyzed the immunological changes happening in the thyroid glands and lymph nodes during goiter involution in balb/c and athymic nude mice of similar background. In both balb/c and nude mice, goiter involution was characterized by thyroid cell necrosis and inflammation. In balb/c mice, the inflammatory infiltrate was made of numerous Ia+ cells. Their number was unchanged during goiter development, but was significantly increased after 2 days of involution and remained high after 8 days. CD4+ and CD8+ T cells were also observed, some of which were clearly activated since they expressed the receptor for Interleukin-2 (IL-2R). The numbers of CD4+, CD8+ and IL-2R+ T cells were increased during goiter as compared to control mice, and they reached a maximum at day 1 of involution. In nude mice, unexpectedly, CD4+ and CD8+ T cells were also found in the thyroid. Their numbers, as well as the number of Ia+ cells, were significantly increased at the onset of involution, but they remained systematically lower than in the corresponding groups of balb/c mice. Iodide treatment of goitrous mice also induced modifications of the lymph nodes draining the thyroid: enlargement of the paracortical T zone, presence of germinal centers in cortical follicles, and increase of the density of IL-2R+ cells. Mesenteric lymph nodes taken as controls were unchanged. Thus, three observations suggest the involvement of T cell immunity in iodine-induced thyroid inflammation: 1. Infiltration of Ia+, CD4+, CD8+ and IL-2R+ cells. 2. Signs of stimulation in thyroid lymph nodes, 3. Significant differences between balb/c and nude mice, in which the inflammatory reaction is weaker.