Unimpaired membrane dynamics in parathyroid cells in insulin deficient rats

The responsiveness of parathyroid cells in insulin deficient and short-term diabetic rats was investigated by morphometric analysis. Insulin deficiency was produced by intravenous injection of D-mannoheptulose and short-term (7 days) diabetes mellitus by intraperitoneal application of streptozotocin. Parathyroid glands were stimulated for parathyroid hormone secretion by decreasing the serum calcium concentration through intravenous infusion of EGTA. Parathyroid cells of controls, insulin deficient, and short-term diabetic rats responded to reduced serum calcium by a 45% increase of the cell surface area. This increase is assumed to be the result of the membrane-bound transport of parathyroid hormone from the Golgi complex and secretory granules to the plasma membrane and subsequent exocytic release of parathyroid hormone induced by the low serum calcium concentration. Therefore, the unimpaired increase in the cell surface area of parathyroid cells in insulin deficient and short-term diabetic rats indicates that insulin does not modulate the release of parathyroid hormone. It is also considered likely that synthesis of parathyroid hormone is not suppressed in short-term diabetes but that fat metabolism is disturbed leading to accumulation of lipid vacuoles.     

Regeneration of the parathyroid glands in experimental hyperthyroidism

By means of morphological, morphometric and radioautographic methods, regeneration of mechanically traumatized parathyroid glands has been studied in 22 euthyroid and 22 hyperthyroid rats on the 1st-20th days after the operation. The thyroid gland is stimulated by daily injection of thyrotropin (1 ME/100 g of body mass). Twelve non-operated animals (6 hyperthyroid and 6 euthyroid rats) serve as control. In the regenerating parathyroid glands of the hyperthyroid animals in comparison with the euthyroid ones, certain increase of proliferative activity is noted in parathyrocytes and in cells of the granular tissue on the 2d-6th days, a more pronounced hypertrophy of epitheliocytes on the 2d-20th days, hyperplasia of their nucleolar apparatus on the 2d-5th days. The experimental hyperthyroidism stimulates manifestation of restorative processes in the regenerating parathyroid glands during development of active inflammatory reaction in them; however, it does not influence the parameters of the organ's structure studied in the nonoperated animals.     

Ultrastructural morphometry of parathyroid cells in rats of different ages

Summary Parathyroid glands of newborn to 1-year-old male Sprague-Dawley rats were fixed by perfusion or by immersion, and prepared for electron microscopy. Parathyroid glands fixed by immersion exhibited parenchymal cells with variable ultrastructure, indicating that these cells were in different stages of the proposed secretory cycle in parathyroid cells. In contrast, parathyroid cells of glands fixed by perfusion were uniform in ultrastructure, suggesting that all cells were in the same stage of secretory activity. Parathyroid glands of 3-, 4-, 6-, 8- and 10-week-old rats also were fixed by perfusion and analysed by electron-microscopic morphometry. These data demonstrated an increase in cell volume and in surface area of the membrane compartments concerned with parathyroid hormone secretion: these changes were not related to variations in serum calcium concentration. Both the qualitative observations and the quantitative data do not favour the idea of a secretory cycle in rat parathyroid cells.     

Participation of tissue basophils of the parathyroid glands in the regulation of the morphofunctional state of the organ

By means of cytometry estimation of mitotic index and nucleo-cytoplasmic relation of parathyrocytes, parathyroid glands have been studied in 52 white rats and 28 white mice under conditions of intal inhibition (30 mg/kg of body mass twice a day intraperitoneally) of tissue basophils (TB) secretory activity. For stimulation of the glands, repeated injections of trilon B and hemiparathyroidectomy are used. The experiment lasts for 3.5 days. In the rat parathyroid glands, containing a considerable amount of TB, intal does not produce any important effect of quantitative parameters of the organ's structure in intact animals, nevertheless it prevents development of hypertrophy of the parathyrocytes in the stimulated glands, as well as makes weaker the proliferative response of the cells to hemiparathyroidectomy. In mice, their parathyroid glands containing single TB, under conditions of stimulation of the parathyroid function, intal does not produce any inhibitory effect to growth of middle size parathyrocytes. The results obtained demonstrate that the parathyroid TB actively participate in regulation of the organ's morphofunctional state, intensifying the stimulating effect of hypocalcaemia to the parathyroid parenchyma.     

Cryosurgery of parathyroid glands

The effectiveness of cryosurgery in destruction of parathyroid glands in rats was studied by comparison of 4 experimental groups: 1. cryosurgery utilizing 3 patterns of repetitive freezing, 2. excision, 3. sham operation, or 4. no treatment. Evaluation included clinical observation of respirations and voice, serum calcium concentration, and histologic examination of parathyroid tissue. The results indicate that the extent of destruction of parathyroid glands in rats can be controlled by specific cryosurgical techniques without thyroidectomy or risk of permanent injury to the recurrent laryngeal nerves.     

Biosynthetic activity of parathyroid cells during different function of the parathyroid glands

By means of autoradiograph c and morphometric methods parathyroid glands of 31 rats after single injection of 3H-leucin (2,5 mc Cu/g of body mass 25 min. before killing) were investigated. Parathyroid glands were inhibited by multiple injections of calcium gluconate solution or by a diet with increased content of calcium and vitamin D2. Parathyroids were stimulated by multiple injections of Trilon B solution, by a diet with increased content of phosphates or by subtotal parathyroid resection. Straight correlation between parathyroid function, average section area of parathyrocytes and average number of silver granules per one parathyrocyte was revealed. Hence, average section area of parathyrocytes is objective morphometric criterion of parathyroid function.     

Integrated transcriptomic and proteomic analyses for the characterization of parathyroid oxyphil cells in uremic patients

Amino Acids - Chief cells are the predominant cells in parathyroid glands of healthy adults; however, parathyroid oxyphil cells, whose function is unknown, increase dramatically in patients with...     

Ultrastructural observations on the mechanism of secretion in the rat parathyroid after fluoride ingestion

Summary The secretory mechanism of the parathyroid glands of fluoride treated rats is evaluated ultrastructurally and compared to that of control rats. The principal difference between the two groups of rats concerns the rate of activity of the chief cells of the gland. In the control animals, these cells are predominantly inactive. In the fluoride-treated rats, they exhibit a more active stage of the secretory cycle. The active chief cells in rats treated with fluoride contain increased numbers of secretory granules. These granules are released into the perivascular spaces within cytoplasmic projections suggesting an apocrine-like mechanism for the secretion of parathyroid hormone. Secretory granules are observed free in the perivascular spaces and within the cytoplasm of capillary endothelial cells in the parathyroid glands.     

Activation of calcium-sensing receptor accelerates apoptosis in hyperplastic parathyroid cells

Calcimimetic compounds inhibit not only parathyroid hormone (PTH) synthesis and secretion, but also parathyroid cell proliferation. The aim of this investigation is to examine the effect of the calcimimetic compound NPS R-568 (R-568) on parathyroid cell death in uremic rats. Hyperplastic parathyroid glands were obtained from uremic rats (subtotal nephrectomy and high-phosphorus diet), and incubated in the media only or the media which contained high concentration of R-568 (10(-4)M), or 10% cyclodextrin, for 6h. R-568 treatment significantly suppressed medium PTH concentration compared with that of the other two groups. R-568 treatment not only increased the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling assay-positive cells, but also induced the morphologic changes of cell death determined by light or electron microscopy. These results suggest that CaR activation by R-568 accelerates parathyroid cell death, probably through an apoptotic mechanism in uremic rats in vitro.     

Abnormal calcium distribution in human parathyroid adenomas as possible cause of primary hyperparathyroidism

Current knowledge suggests that normal parathyroid glands and parathyroid adenomas have different sensitivities to environmental calcium. In search for morphological equivalents, 5 normal human and 10 porcine parathyroid glands, as well as 10 human parathyroid adenomas were investigated with regard to intracellular and extracellular calcium distribution. The glands were incubated for 2, 4, 6 and 20 h in tissue cultures using HAM's F10 medium with various calcium concentrations. For visualization of the calcium distribution in the tissue the method of pyroantimonate precipitation was applied. Specificity of the reaction was controlled by X-ray microanalysis. Shifts of the calcium pyroantimonate precipitates were quantitated by morphometry using an area-counting system. The results demonstrate that in normal parathyroid glands calcium precipitates are distributed randomly. Incubation of normal glands in medium with low calcium concentration (0.6 mM) provoked reduced amounts of intracellular and extracellular calcium complexes. When the incubations were performed in medium with high calcium content (2.6 mM), calcium accumulated inside parathyroid and stroma cells. In contrast to normal parathyroid glands, parathyroid adenomas fixed immediately after surgery showed an atypical calcium distribution with low amounts of intracellular and high amounts of extracellular calcium grains. The data suggest that in normal parathyroid glands the intracellular calcium concentration follows the extracellular environmental calcium concentration. Thus, calcium modulates parathyroid hormone (PTH) secretion via intracellular regulatory mechanisms. In parathyroid adenomas the calcium transport via the tumor cell membrane appears to be disturbed resulting in lowered intracellular calcium levels. This is remarkable since the environmental calcium concentration is elevated due to the hypercalcemia of primary hyperparathyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Fine structure of the fetal rat thyroid and parathyroid glands at term and during prolonged gestation

Summary The fine structure of the fetal rat thyroid and parathyroid glands was studied at term and during prolonged gestation, which was induced by subcutaneous injections of progesterone to the mothers from gestational days 20 through 24. At term, the follicular and parafollicular cells of the thyroid as well as cells of the parathyroid exhibited well developed cytoplasmic organelles. Morphological changes were not detected in either of the endocrine glands during prolonged gestation. The results are discussed in relationship to 1) thyroid follicular cell activity during stress and 2) the function of thyroid parafollicular and parathyroid cells in calcium homeostasis.Supported by the Medical Research Council of Canada Grant No. MA4740.     

Effects of pinealectomy on the ultrastructure of the golden hamster parathyroid gland

Ultrastructural changes of the parathyroid glands of pinealectomized golden hamsters were investigated. The main changes in the parathyroid glands 1 hour and 1 day after pinealectomy compared with the control and sham-operated groups were an increase of the Golgi complexes, cisternae of the granular endoplasmic reticulum and large vacuolar bodies. In addition, many chief cells contained numerous prosecretory granules in the Golgi areas and many secretory granules in the peripheral cytoplasm. The morphology of the parathyroid glands 7 and 30 days after pinealectomy resembled that of the control parathyroid glands. These results suggest that pinealectomy affects the secretory activity of the parathyroid gland.     

Humoral factors of the spleen in the regulation of the calcium content in blood plasma of rats]

Introduction of protein-free peptides-enriched spleen extract increases the calcium content in blood plasma of rats. After the effect of stress factor (long swimming) it falls. The value of the index under study increases in the splenectomized rats and remains unchanged after stress and introduction of the spleen factors. The most pronounced increase of the calcium concentration is observed in the case of experimental hypersplenism induced by methylcellulose introduction. The calcium-regulating effects of introduction of the enriched protein-free spleen extract and pharmacopoeial splenin preparation are compared. It is supposed that spleen contains two humoral factors of different chemical nature which are able to influence somewhat differently the calcium content in blood plasma.     

An in vitro study on the effects of melatonin on the ultrastructure of the hamster parathyroid gland.

Isolated parathyroid glands from adult female golden hamsters were incubated on a black Millipore filter in an incubation vessel containing Ham's F-12 medium, with or without melatonin at final concentration of 10(-5) M for 1 hour. In the parathyroid glands used for in vitro treatments with melatonin, the Golgi complexes associated with a few prosecretory granules and cisternae of the rough endoplasmic reticulum showed a significant decrease, and lipid droplets and lysosomes appeared to be increased compared with those of the control parathyroid glands. These changes are considered to be induced by suppression of the synthesis of parathyroid hormone in parathyroid glands incubated in a vessel containing medium with melatonin.     

Quantitative aspects of membrane shifts in rat parathyroid cells initiated by decrease in serum calcium

The secretory activity of parathyroid glands in rats was stimulated by decreasing the serum Ca++ concentration through constant intravenous infusion of EGTA. The morphometric analysis of the nuclear and cytoplasmic volume and of the surface area of the rough endoplasmic reticulum, Golgi complex, secretory granules and plasma membrane revealed a membrane shift from secretory granules and Golgi complex to the plasma membrane within 1 hr of calcium depression. Subsequently, between 1 and 3 hr of calcium depression, the membrane shift was from the plasma membrane to the Golgi complex. It is considered likely that these membrane shifts are related to a rise in release of parathyroid hormone by exocytosis and a subsequent increase in retrieval of plasma membrane by endocytosis—probably through the compartment of coated pits and coated and uncoated vesicles.     

Inclusion of the calcium-regulating hormones,cortisol, and blood electrolytes into early adaptive responses of the body

Comparative study of calcium-regulating hormones, cortisol and electrolytes content in blood as well as of the cardiac contractions and respiration rate before and in early terms (the 5th min., the 45th min., the 5th hour) of the motor activity maximal limitation (immobilisation) was performed in rats. It as ascertained that the maximal, limitation of motor activity even at the earliest stages are accompanied with activation of the adaptive accessory responses as well as with a significant increase in content of calcium, sodium and potassium in the blood, along with a relatively minor decrease in content of parathyroid hormone, thereocalcitonine and phosphorus. Possible mechanisms of the revealed changes as well as the role of the above endogenic factors in the organism's early adaptive responses, were discussed.     

Spatial organization of proliferative processes in the parathyroid glands upon acute stimulation of parathyroid function

A quantitative analysis on homogeneity degree in distribution of proliferating parathyrocytes in the parathyroid glands under conditions of an acute stimulation of their function, produced by bilateral nephrectomy (12 rats, 50-70 h after the operation) and by hemiparathyroidectomy (12 rats, 2-3 days after the operation) have been performed. Six intact animals serve as the control. In order to reveal proliferating cells, 1 h before sacrifice 3H-thymidine (1 mc Ci/g) is injected intraperitoneally, and to some animals--colchicine (1 mg/kg) is injected 6 h before the sacrifice. By means of successive investigation of the glands serial sections along their whole area the amount of the microscope field of vision, having various content of proliferating cells are calculated; using the criterion chi 2, the correspondence of the empiric distributions obtained to the Poisson distribution are estimated. In the hyperfunctioning parathyroid glands the proliferating cells form foci of clusters and rarifaction. A similar clustering appears when a definite level of mitotic activity of the parathyrocytes is reached (1-1.2%), probably reflecting certain regional peculiarities of their functional state.     

A vasopressor factor partially purified from human parathyroid glands.

Recently, a parathyroid hypertensive factor was postulated to play a role in the pathogenesis of hypertension in genetically hypertensive rats. Therefore it was examined, whether in human parathyroid glands a vasopressor substance can be detected. For this purpose, homogenates of hyperplastic parathyroid glands from 20 patients with tertiary hyperparathyroidism were deproteinized and fractionated by gel chromatography. The fractions obtained were tested for vasopressor activity in isolated perfused rat kidneys. A vasopressor fraction containing substances of 0.6-2.5 kDa was identified in the parathyroid glands. The responsible product was heat sensitive, peptidase-, trypsin- and carboxypeptidase y- sensitive and hydrophilic, as it did not bind to hydrophobic reversed-phase gel. These results suggest that parathyroid glands contain a hydrophilic peptide-like vasopressor substance different from the parathyroid hormone.     

The influence of a single ethanol injection on normal thyroid tissue of the rat

Macro- and microscopic changes in the normal thyroid gland of rats, and in the surrounding tissues 2 and 4 weeks after a single intrathyroidal ethanol injection (IEI), together with the influence of such treatment on the function of the recurrent laryngeal nerves and of the parathyroid glands, were assessed. The intraoperative macroscopic evaluation at 2 weeks (20 rats) and 4 weeks (20 rats) after IEI revealed the presence of a scar at the site of the IEI-treated lobe in seven (35%) and six (30%) rats, respectively, and the reduction of lobe dimensions in thirteen (65%) and fourteen (70%) rats, respectively. The microscopic evaluation of the lobe after IEI showed coagulative necrosis, reduction in thyroid follicle volume, disturbance of follicle structure, haemorrhage, haemosiderin deposits, inflammatory infiltration and fibrosis. No microscopic changes were observed in the tissues surrounding the thyroid, nor in the parathyroid glands located extrathyroidally or in the second thyroid lobe. No vocal cord dysfunction or significant changes in serum calcium levels after IEI were detected.