Genesis of C-cells of the thyroid gland in Wistar rats]

Proliferation of the C cells of the rat thyroid gland under conditions of prolonged hypercalcemia induced with vit. D3 leading sometimes to a formation of adenoma-like nodules was observed. Metaplasia of the follicular epithelium into the C cells observed in the process of nodules formation seems to point out that the C cells and the follicular cells of the thyroid gland arise from a common maternal cell.     

Desmosomes of follicular cells and C-cells in the thyroid gland of rats]

Well developed desmosomes can be seen between the C-cells and follicular cells in the rat thyroid gland. They are structurally similar to the desmosomes at the boundaries of homotypic cells. This observation speaks in favour of the development of C-cells from the initial cells of thyroid embryonic analage.     

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 m³ in newborn rats to 1653 m³ in 120-day-old animals. Over the same time period, the mean number of C-cells within the thyroid gland increased 9-fold (from 1.6x10⁴ to 1.5x10⁵), and the number of C-cells per unit area decreased (from 6.15x10⁴/mm³ to 2.6x10⁴/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.     

Cholecystokinins but not gastrin-17 release calcitonin from thyroid C-cells in the rat

Subcutaneous injections of gastrin-17, cholecystokinin-39, cholecystokinin-8 (sulfated and non-sulfated forms), cholecystokinin-4 or pentagastrin induced hypocalcemia in rats. The hypocalcemia was associated with calcitonin release for pentagastrin and the cholecystokinins but not for gastrin-17, even at very high doses. Permanent hypergastrinemia, induced by surgical removal of the acid-producing part of the stomach (fundectomy) or by treatment with high doses of omeprazole, a blocker of acid secretion, was not accompanied by elevated plasma calcitonin. Long-lasting hypergastrinemia is known to cause hyperplasia of gastrin-sensitive endocrine cells in the rat stomach while hypogastrinemia does the reverse. In antrectomized rats, having low serum gastrin, and in fundectomized rats, having high serum gastrin, the serum calcitonin concentration, the thyroid calcitonin content and the number of C-cells remained as in sham-operated controls two months after the operations. We conclude that neither exogenous nor endogenous gastrin stimulates calcitonin secretion in the rat and that long-standing hypo- or hypergastrinemia is without effect on the number of thyroid C-cells. Our results, however, do not exclude the possibility that the cholecystokinins might act as calcitonin secretagogues in the rat although such a role remains to be established.     

S-100 protein and neuron-specific enolase in parathyroid glands and C-cells of the thyroid

Summary Normal parathyroid glands and parafollicular cells (C-cells) of man, rat and rabbit, and also human parathyroid adenomas and medullary carcinomas were investigated for the presence of S-100 protein and neuron-specific enolase (NSE). For determination of the proteins immuno-peroxidase methods were applied, i.e., the PAP method and the avidin-biotin system. The antisera, of polyclonal origin, were specifically directed against cow S-100 protein and rat or bovine NSE. The respective antisera are known to crossreact with S-100 protein from man, rat, and rabbit, as well as with NSE from man and rat. Surprisingly, the test for S-100 protein was found to be strongly positive in the parathyroid glands of rat and rabbit and was focally positive in normal and adenomatous human parathyroid glands, but completely negative in C-cells and medullary carcinoma cells. NSE was present in C-cells of rat and man, and in medullary carcinoma cells, but was absent in normal and adenomatous parathyroid cells. The results support data that indicate that both parathyroid cells and C-cells are derived from elements of the neural crest, but undergo different maturation processes during embryological development.     

S-100 protein and neuron-specific enolase in parathyroid glands and C-cells of the thyroid

Normal parathyroid glands and parafollicular cells (C-cells) of man, rat and rabbit, and also human parathyroid adenomas and medullary carcinomas were investigated for the presence of S-100 protein and neuron-specific enolase (NSE). For determination of the proteins immunoperoxidase methods were applied, i.e., the PAP method and the avidin-biotin system. The antisera, of polyclonal origin, were specifically directed against cow S-100 protein and rat or bovine NSE. The respective antisera are known to crossreact with S-100 protein from man, rat, and rabbit, as well as with NSE from man and rat. Surprisingly, the test for S-100 protein was found to be strongly positive in the parathyroid glands of rat and rabbit and was focally positive in normal and adenomatous human parathyroid glands, but completely negative in C-cells and medullary carcinoma cells. NSE was present in C-cells of rat and man, and in medullary carcinoma cells, but was absent in normal and adenomatous parathyroid cells. The results support data that indicate that both parathyroid cells and C-cells are derived from elements of the neural crest, but undergo different maturation processes during embryological development.     

Ultrastructural localization of calcitonin in C-cells of dog thyroid; an immunocytochemical study

Summary Light microscopic observations of normal rat peritoneal mast cells and ultrastructural observations of human mast cells from lesions of nodular mastocytosis indicated that structural damage results in a pronounced increase in percentage of cells with a positive dopa reaction. Recent studies have indicated that the dopa reaction in mast cells is peroxidase-dependent. Enhancement of the dopa reaction by structural damage (latency) is probably related to increased substrate-enzyme interaction. Ultrastructural localization of dopa melanin to mast cell granules and the high percentage of mast cells showing a positive dopa reaction after structural damage is evidence against the possibility that dopa melanin is formed in mast cells by phagocytized enzyme.Supported by USPHS Grant Tl Am 5220, and by The General Research Support Fund, Boston City Hospital.     

Reactivity of monoclonal islet cell antibodies on normal hyperplastic and neoplastic thyroid C-cells

Summary Thyroid C-cell reactivity to 15 monoclonal antibodies raised against a series of pancreatic islet cells (H[human]ISL, B[bovine]ISL and R[rat]ISL) was evaluated using an indirect immunoperoxidase technique on frozen thyroid sections. Of the monoclonal anti-islet cell antibodies, five reacted specifically with bovine C-cells or human hyperplastic and neoplastic C-cells but not with follicular cells. Two monoclonal antibodies of the bovine series showed strong immunoreactivity with C-cells and only a weakly positive immunostaining of follicular cells. Five monoclonal antibodies reacted with both thyroid C-cells and follicular cells, whereas 3 monoclonal anti-islet cell antibodies did not stain any cell type of the thyroid. In human medullary carcinomas, calcitonin- and somatostatin-producing neoplastic cells were immunoreactive with the same monoclonal antibodies as were normal human C-cells. The protein bands identified by the monoclonal antibodies in human medullary carcinomas had the same molecular weight as those from pancreatic islet extracts. Our study demonstrates the presence of similar differentiation antigens on thyroid C-cells and pancreatic islet cells; this further illustrates common modes of differentiation and specialisation of these embryologically different members of the dispersed neuroendocrine system. The crossreactivity of seven of the monoclonal antibodies investigated with follicular epithelium of the thyroid suggests the existence of common antigenic determinants in different endocrine organs and may partly explain the multiple organ autoimmune response found in patients with polyendocrine diseases.     

Reciprocal epithelial:endothelial paracrine interactions during thyroid development govern follicular organization and C-cells differentiation

The thyroid is a highly vascularized endocrine gland, displaying a characteristic epithelial organization in closed spheres, called follicles. Here we investigate how endothelial cells are recruited into the developing thyroid and if they control glandular organization as well as thyrocytes and C-cells differentiation. We show that endothelial cells closely surround, and then invade the expanding thyroid epithelial cell mass to become closely associated with nascent polarized follicles. This close and sustained endothelial:epithelial interaction depends on epithelial production of the angiogenic factor, Vascular Endothelial Growth Factor-A (VEGF-A), as its thyroid-specific genetic inactivation reduced the endothelial cell pool of the thyroid by >90%. Vegfa KO also displayed decreased C-cells differentiation and impaired organization of the epithelial cell mass into follicles. We developed an ex vivo model of thyroid explants that faithfully mimicks bilobation of the thyroid anlagen, endothelial and C-cells invasion, folliculogenesis and differentiation. Treatment of thyroid explants at e12.5 with a VEGFR2 inhibitor ablated the endothelial pool and reproduced ex vivo folliculogenesis defects observed in conditional Vegfa KO. In the absence of any blood supply, rescue by embryonic endothelial progenitor cells restored folliculogenesis, accelerated lumen expansion and stimulated calcitonin expression by C-cells. In conclusion, our data demonstrate that, in developing mouse thyroid, epithelial production of VEGF-A is necessary for endothelial cells recruitment and expansion. In turn, endothelial cells control epithelial reorganization in follicles and C-cells differentiation.     

Production of monoclonal antibodies against a novel glycoprotein synthesized and secreted by dog thyroid C-cells.

A monoclonal antibody (MAb) that reacted only with thyroid C-cells was raised against cell suspensions from dog thyroid glands, to examine a glycoprotein secreted by C-cells. After chronically-induced hypercalcemia and administration of an anti-thyroid drug, reaction products for the antibody markedly decreased in C-cells, coinciding with alterations in calcitonin immunoreactivity. The antigen recognized by the MAb appears to be a secretory protein. The MAb reacted with C-cells from a wide variety of mammalian species, including rats, mice, hamsters, cattle, cats, rabbits, and monkeys. Furthermore, tumor cells of human medullary thyroid carcinoma, which is derived from C-cells, were immunoreactive to the MAb. Exceptionally, C-cells from guinea pigs and pigs were not stained with the MAb. No crossreactivity was observed in any of the dog tissues examined. Immunoblot analysis demonstrated that the MAb recognized a single prominent band at a molecular weight of approximately 79,000. The 79 KD band reacted with various digoxigenin-labeled lectins, including GNA, DSA, SNA, and MAA; it is a glycoprotein containing mannose, N-acetylglucosamine, and sialic acid. Dog thyroid C-cells were also densely stained with these lectins. The results indicate that thyroid C-cells synthesize and secrete a specific glycoprotein in addition to peptide hormones.