Calcitonin cell population and distribution in the thyroid gland of the rat

The Association of Myo-Inositol and Selenium Contrasts Cadmium-Induced Thyroid C Cell Hyperplasia and Hypertrophy in Mice

Previous studies have demonstrated that, in addition to inducing structural changes in thyroid follicles, cadmium (Cd) increased the number of C cells. We examined the effects of myo-inositol (MI), seleno-L-methionine (Se), MI + Se, and resveratrol on C cells of mice exposed to cadmium chloride (Cd Cl2), as no data are currently available on the possible protective effects of these molecules. In contrast, we have previously shown this protective effect against CdCl2 on the thyroid follicles of mice. Ninety-eight C57 BL/6J adult male mice were divided into 14 groups of seven mice each: (i) 0.9% NaCl (vehicle; 1 ml/kg/day i.p.); (ii) Se (0.2 mg/kg/day per os); (iii) Se (0.4 mg/kg/day per os); (iv) MI (360 mg/kg/day per os); (v) Se (0.2 mg/kg/day) + MI; (vi) Se (0.4 mg/kg/day) + MI; (vii) resveratrol (20 mg/kg); (viii) CdCl2 (2 mg/kg/day i.p.) + vehicle; (ix) CdCl2 + Se (0.2 mg/kg/day); (x) CdCl2 + Se (0.4 mg/kg/day); (xi) CdCl2 + MI; (xii) CdCl2 + Se (0.2 mg/kg/day) + MI; (xiii) CdCl2 + Se (0.4 mg/kg/day) + MI; (xiv) CdCl2 + resveratrol (20 mg/kg). After 14 days, thyroids were processed for histological, immunohistochemical, and morphometric evaluation. Compared to vehicle, Cd significantly decreased follicle mean diameter, increased CT-positive cells number, area and cytoplasmic density, and caused the disappearance of TUNEL-positive C cells, namely, the disappearance of C cells undergoing apoptosis. Se at either 0.2 or 0.4 mg/kg/day failed to significantly increase follicular mean diameter, mildly decreased CT-positive cells number, area and cytoplasmic density, and was ineffective on TUNEL-positive C cells. Instead, MI alone increased significantly follicular mean diameter and TUNEL-positive cells number, and decreased significantly CT-positive cells number, area and cytoplasmic density. MI + Se 0.2 mg/kg/day or MI + Se 0.4 mg/kg/day administration improved all five indices more markedly. Indeed, follicular mean diameter and TUNEL-positive cells number increased significantly, while CT-positive cells number, area and cytoplasmic density decreased significantly. Thus, all five indices overlapped those observed in vehicle-treated mice. Resveratrol improved significantly all the considered parameters, with a magnitude comparable to that of MI alone. In conclusion, the association Myo + Se is effective in protecting the mouse thyroid from the Cd-induced hyperplasia and hypertrophy of C cells. This benefit adds to that exerted by Myo + Se on thyrocytes and testis.

Crinophagy in Thyroid Follicular and Parafollicular Cells of Male Obese Zucker Rat

Comparison between lean (Fa/?) and obese (fa/fa) young adult male Zucker rat thyroids reveals that obese rats display larger clusters of parafollicular cells than the lean ones with a lesser blood supply. Fa/? thyroid typically shows single or "twin" C cells in follicles; fa/fa parafollicular cells appear with three functional aspects. Crinophagy is found in the fa/fa C cells amassing numerous aberrant calcitonin-containing vesicles among which lysosomes build these autophagic bodies by capturing vesicle contents, other organelles and, fusing with each other, increase their size. Other C cells contain many secretory vesicles but show few or no crinophagic structures. Another parafollicular cell type is revealed with scant organelles and highly contrasted secretory vesicles, different from calcitonin. Hypercalcemia of fa/fa rats corresponds to increased C cells population with accrued calcitonin production but a low calcitonin plasma level - verified by others - is likely caused by crinophagy of the altered vesicles. In addition, the T thyrocytes of fa/fa rats exhibit crinophagy bodies; this can confirm their hypothyroidism. Possibly, the known leptin mutation along with other unknown paracrine secretions alter both T and C thyrocytes' functions of the fa/fa rats, allowing high intracellular calcium and lower pH favoring autophagocytosis. Other longitudinal, interdisciplinary studies should further clarify the complex paracrine interactions existing between these endocrine structures because this animal model could be useful to understand human defects, such as the metabolic syndrome that involves obesity, cardiovascular, renal, hepatic, non-insulin dependent diabetes mellitus (NIDDM), hypothyroidism defects, as well as the etiology of thyroid medullary tumors.

Decrease of parafollicular thyroid C-cells in experimental esophageal atresia: further evidence of a neural crest pathogenic pathway

Adriamycin-induced experimental esophageal atresia (EA) is often associated with malformations of neural crest (NC) origin, such as abnormal pharyngeal pouch derivatives like the thymus and the parathyroids. The aim of the present study was to examine whether NC-derived thyroid C-cells were abnormal in a rat model. Pregnant rats received intraperitoneally either 2 mg/kg Adriamycin (EA) or vehicle (controls) on days 8 and 9 of gestation. Fetuses were recovered on day 21, and blocks including the trachea and thyroid were fixed in formalin, coronally sectioned at 3-mum widths, and stained with standard hematoxylin and eosin until the largest area of thyroid was reached. From this point on, the 1st, 10th, and 20th slices were immunohistochemically stained with anti-calcitonin antibody. Positively-stained cells in each section of the gland were counted using a computer-assisted image analysis method, and the results were averaged. The distribution of the cells within the gland was assessed as well. Comparisons between EA and control rats were made by nonparametric tests with a significance threshold of p<0.05. The number of C-cells was dramatically reduced in EA animals compared with controls (32.4+/-36 vs. 92.3+/-60.5, p<0.001). Histology of the thyroid was similar in both groups, but the distribution of positive C-cells within the gland followed an abnormal pattern in EA rats. Adriamycin causes a pattern of NC-derived malformations, including a severe decrease in thyroid C-cells accompanied by abnormal distribution or migration patterns. These results represent further evidence of the involvement of NC organogenic control dysregulation in the pathogenesis of EA and its associated malformations. The similarities between the rat model and the clinical picture strongly support investigating other subclinical NC-derived anomalies in patients with EA.

C-cell distribution in ovine thyroid gland

The number and percentage of C-cells per unit area were investigated in 2-3-year-old sheep by an immunoperoxidase technique, using a digital-image analysis. C-cells were distributed throughout the thyroid lobes but were not present in either the isthmus or the superior and inferior poles of the thyroid. C-cells were more concentrated in the deep central region of the lobes and decreased gradually toward the periphery. There was a high correlation between the number and the percentage of C-cells per unit area of thyroid gland in sheep. Significant differences were not present between male and female sheep of 2-3 years of age.

Postnatal variations in the number and size of C-cells in the rat thyroid gland

The heterogeneous distribution of thyroid C-cells has until now hindered an objective evaluation of changes caused by age or experimental stimuli. To overcome this, a rigorous methodology has been designed to detect variations in shape, size, and number of C-cells throughout development. Using this methodology, we have demonstrated that C-cells do not significantly alter their shape with age. However, their volume increases gradually from 472 microns3 in newborn rats to 1653 microns3 in 120-day-old animals. Over the same time period, the mean number of C-cells within the thyroid gland increased 9-fold (from 1.6 x 10(4) to 1.5 x 10(5), and the number of C-cells per unit area decreased (from 6.15 x 10(4)/mm3 to 2.6 x 10(4)/mm3). We conclude that there are marked variations in size, total number, and number of C-cells per unit area in the rat thyroid gland after birth.

Quantitative changes in the frequency and distribution of the C-cell population in the rat thyroid gland with age

The development of calcitonin cells (C-cells) was investigated in rat thyroid glands from birth to 120 days, using an immunoperoxidase technique and a point-counting method. The proportion of C-cells to follicular cells was 4.5% on the day of birth and increased progressively to 10.4% by 120 days. The highest density of C-cells was noted in the mid-region of the lobes along a longitudinal axis. The caudal and cephalic regions of the lobes contained smaller numbers of C-cells. The C-cells tended to be more numerous in the posterior aspects of the lobes. Although the numbers of C-cells in 120-day-old animal were markedly increased as compared to animals at the time of birth, the cell distributions within the glands were similar at all ages.

Changes in parafollicular cells of rats neonatally treated with estradiol

The parafollicular cells of male and female rats neonatally (3rd day) treated with a single dose (1 mg) of estradiol dipropionate, and sacrificed in peripubertal (38th day) or adult (80th day) period of life, were investigated. These studies included examinations of silver-stained properties of parafollicular cells, morphometric analyses of both the cells and nuclear area and ultrastructural characteristics. Estradiol treatment led to a significant increase of the cellular and nuclear area (micron 2) in both females and males. Different from intact animals remarkable degranulation and hyperplasia of parafollicular cells were evident in estradiol-treated rats. It may be concluded that this sexual hormone applied in neonatal period has an effect on parafollicular cells expressed up to adult period of life.

Early calcitonin hypersecretion and C cell hyperplasia in rats with high incidence of C cell tumors (Wag/Rij)

Wag/Rij rats, a Wistar-derived strain, develop on aging a spontaneous medullary thyroid carcinoma which shows many morphological similarities to the human neoplasm. Using biochemical and histological methods, we studied calcitonin secretion and C cell distribution in young and adult Wag/Rij rats, to characterize possible modifications in calcitonin synthesis and secretion as compared to the original Wistar strain. During the period investigated, the mean basal circulating levels of calcitonin of both sexes were not significantly different between the two strains, although the Wag/Rij rats tended to have higher values. After a calcium challenge, the circulating calcitonin levels increased normally in the Wag/Rij strain as compared to Wistar rats of the same ages. Histological observations of their thyroids revealed a significant C cell hyperplasia, along with a weak immunostaining in some of the cells, due to a lack of secretory granules. Thus, in addition to the ability of developing C cell tumours on aging, the Wag/Rij strain is characterized by an early C cell hyperplasia leading to an increase of calcitonin secretion after a provocative secretion test.