1-34 Human parathyroid hormone radioimmunoassay: properties of antiserum against synthetic 1-34 human parathyroid hormone and its clinical application.
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Pituitary stimulation of parathyroid hormone secretion: evidence in cattle for a parathyroid stimulating hormone.
A number of previous investigations have indicated that the pituitary may directly stimulate secretion of parathyroid hormone. Others have disagreed. With the recent development of an in vitro bovine parathyroid perfusion system, the direct effect of suspected secretagogues can be assessed on a dynamic, ongoing basis. A partially purified pituitary extract (preparation A) was injected into calves. The plasma calcium increased an average of 1.1 mg/100 ml plasma. No increase of immunoreactive parathyroid hormone (iPTH) was detected, however, in the peripheral plasma prior to the increase in plasma calcium concentration. Since the peripheral plasma iPTH concentration has been shown to be relatively insensitive to changes in the secretion rate, the inability to detect a change in the iPTH concentration does not preclude a direct stimulating effect of the pituitary on the parathyroid. When preparation A was tested on in vitro perfused bovine parathyroid glands, a 30% average increase in secretion of c-iPTH (carboxy terminus) and a 56% average increase in secretion of n-iPTH (amino terminus) was observed under normocalcemic conditions. Under conditions of hypercalcemia, there was an average increase in the c-iPTH secretion rate of 60% and an average n-iPTH secretion rate increase of 88%. A failure of TSH, LH, GH, ADH, oxytocin, and prolactin to stimulate iPTH was observed. Previous reports have eliminated ACTH, MSH, and lipotropin as possible parathyroid secretagogues. The concept of a parathyroid stimulating hormone (PTSH) located in the pituitary that can directly stimulate the parathyroid gland to secrete parathyroid hormone is consistent with the results of this investigation.
Animals↗
Loss of immunoreactivity of human serum parathyroid hormone by the action of rat kidney enzyme, preferentially hydrolyzing parathyroid hormone.
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Animals↗
Parathyroid hormone [PTH(1-34)] and parathyroid hormone-related protein [PTHrP(1-34)] promote reversion of hypertrophic chondrocytes to a prehypertrophic proliferating phenotype and prevent terminal differentiation of osteoblast-like cells.
The effects of parathyroid hormone/parathyroid hormone-related protein (PTH/PTHrP) on late events in chondrocyte differentiation were investigated by a dual in vitro model where conditions of suspension versus adhesion culturing are permissive either for apoptosis or for the further differentiation of hypertrophic chondrocytes to osteoblast- like cells. Chick embryo hypertrophic chondrocytes maintained in suspension synthesized type II and type X collagen and organized their extracellular matrix, forming a tissue highly reminiscent of true cartilage, which eventually mineralized. The formation of mineralized cartilage was associated with the expression of alkaline phosphatase (ALP), arrest of cell growth, and apoptosis, as observed in growth plates in vivo. In this system, PTH/PTHrP was found to repress type X collagen synthesis, ALP expression, and cartilage matrix mineralization. Cell proliferation was resumed, whereas apoptosis was blocked. Hypertrophic chondrocytes cultured in adherent conditions in the presence of retinoic acid underwent further differentiation to osteoblast-like cells (i.e., they resumed cell proliferation, switched to type I collagen synthesis, and produced a mineralizing bone-like matrix). In this system, PTH addition to culture completely inhibited the expression of ALP and matrix mineralization, whereas cell proliferation and expression of type I collagen were not affected. These data indicate that PTH/PTHrP inhibit both the mineralization of a cartilage-like matrix and apoptosis (mimicked in the suspension culture) and the production of a mineralizing bone-like matrix, characterizing further differentiation of hypertrophic chondrocytes to osteoblasts like cells (mimicked in adhesion culture). Treatment of chondrocyte cultures with PTH/PTHrP reverts cultured cells in states of differentiation earlier than hypertrophic chondrocytes (suspension), or earlier than mineralizing osteoblast-like cells (adhesion). However, withdrawal of hormonal stimulation redirects cells toward their distinct, microenvironment-dependent, terminal differentiation and fate.
Animals↗
Potassium stimulates parathyroid hormone release from perifused parathyroid cells.
A method for perifusing dispersed bovine parathyroid cells is described. Using this approach, we have studied the effects of raised extracellular potassium and ouabain on calcium-regulated parathyroid hormone (PTH) secretion in vitro. Decreasing calcium from 1.5 to 0.5 mM stimulated PTH release within 5-10 min, and the increased secretory rate was maintained for the duration of the low calcium administration. High potassium (60 mM) promptly stimulated PTH secretion at 1.5 mM calcium. The effect of high potassium was more transient than that of low calcium. Raised potassium significantly enhanced the response to 0.5 mM calcium. Ouabain (10(-3) M) had no significant effect at 1.5 mM calcium, but depressed the secretory response to 0.5 mM calcium. In conclusion, the effect of raised potassium on parathyroid cells is qualitatively similar to its effect on other endocrine and exocrine systems.
Animals↗
Normalizing effect of Ca2+ ionophore on cytoplasmic Ca2+ and parathyroid hormone release of dispersed parathyroid cells from patients with hyperparathyroidism.
The effects of the Ca2+ ionophore A23187 on parathyroid hormone (PTH) secretion and cytoplasmic free Ca2+ concentration (Ca2+i) were measured at different extracellular Ca2+ concentrations using dispersed cells from patients with hyperparathyroidism (HPT). The addition of a low concentration of the Ca2+ ionophore to quin2-loaded cell preparations resulted in the apparent normalization of calcium-regulated Ca2+i. At all extracellular calcium concentrations Ca2+i reached significantly higher values in the presence of the ionophore and the dose-response relationship was shifted to the left. Under similar conditions calcium-regulated PTH release was correspondingly corrected with an increased suppressibility and left-shifted dose-response relationship. The data render strong support for a disturbed regulation of Ca2+i as a major factor in the pathophysiology of HPT.
Aminoquinolines↗
Interaction between extracellular calcium and endothelin-1 influences parathyroid hormone secretion from bovine parathyroid cells through the increase in intracellular calcium.
Endothelin-1 (ET-1) secretion from bovine parathyroid cells (bPTCs) responds to the changes in extracellular calcium concentrations ([Ca2+]c) and ET-1 inhibits parathyroid hormone (PTH) secretion. However, the effect from the interaction between [Ca2+]e and ET-1 on PTH secretion is unknown. To clarify these issues, a bPTC suspension was used to study the regulation of ET-1 secretion by subtle changes in [Ca2+]e and PTH secretion by the interaction between [Ca2+]e and ET-1. We added [Ca2+]e at varying concentrations, 0.5-2.0 mM, to the bPTC medium to define the relationship between [Ca2+]e and ET-1 secretion and found that the ET-1 secretion was inversely regulated by [Ca2+]e with a low [Ca2+]e stimulating, and a high [Ca2+]e inhibiting ET-1 secretion. It is even suppressed to an undetectable level at a [Ca2+]e of > 1.5 mM. Further, we worked to determine how the interaction between ET-1 and [Ca2+]e influences PTH secretion. ET-1 > or = 10(-10) M, inhibited PTH secretion in a dose-dependent manner and significantly inhibited PTH secretion at a low or normal [Ca2+]e. At an ET-1 concentration of > or = 10(-10) M, the 'calcium-PTH' relation showed significant changes in physiological responses. The effect of ET-1 on intracellular calcium concentrations ([Ca2+]i) of bPTCs was studied using the fura 2 fluorescence method. We found that increasing doses of ET-1 induced a progressive increase in [Ca2+]i of bPTCs. Our results suggest that ET-1 secretion is inversely regulated by [Ca2+]e. ET-1 can inhibit PTH secretion and alter the parathyroid secretion pattern to various calcium stimuli. ET-1 also elevates [Ca2+]i and this may be a part of the intracellular signaling mechanisms involved in the inhibition of PTH secretion from bPTCs.
Animals↗
Alteration in density, morphology and parathyroid hormone release of dispersed parathyroid cells from patients with hyperparathyroidism.
Dispersed parathyroid cells from normal human and bovine glands and from 10 patients with primary (7 adenomas, 3 hyperplasias) and 4 patients with uraemic hyperparathyroidism (HPT) have been investigated with respect to density, morphology and parathyroid hormone (PTH) release. Percoll density gradients enabled an efficient isolation of viable parathyroid cells which generally banded between 1.035-1.090 g/ml. The average density was significantly higher in cells from the normal than the abnormal glands. The pathological glands contained large chief cells, oxyphil and transitional oxyphil cells and, in one case, water-clear cells which were enriched in fractions with densities below 1.055 g/ml. Measurements of cell diameters revealed an increased proportion of enlarged cells in the preparation of abnormal glands. Nuclear diameters were similar in the normal human glands, adenomas and hyperplasias, but the variability was greater among the adenomas. In comparison to normal bovine parathyroid cells, PTH release of cells from the pathological human glands was reduced and abnormally insensitive to extracellular calcium. The oxyphil and water-clear cells secreted similar amounts of PTH as the chief cells of the abnormal glands. The disturbed PTH release in secondary HPT seemed to be confined mainly to cells within nodules of the hyperplastic glands. The results show that the disturbed hormone regulation in HPT is related to morphological changes of the cells and that buoyant density gradients can be used to accumulate the abnormal cells.
Adenoma↗
Hypercalcemia and ectopic secretion of parathyroid hormone by an ovarian carcinoma with rearrangement of the gene for parathyroid hormone.
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Adenocarcinoma↗
Monoclonal antibody-mediated modulation of parathyroid hormone secretion by dispersed parathyroid cells.
Available data suggest that ionized calcium may interact with a cell surface "sensor" or "receptor" to produce changes in one or more intracellular second messengers that ultimately regulate the release of parathyroid hormone (PTH). Recently, we developed a series of monoclonal antibodies directed toward specialized differentiation antigens expressed on endocrine cells. Since many of these monoclonal antibodies displayed exquisite specificity for cell surface molecules on the parathyroid cell, we used these reagents as probes to investigate signal recognition/transduction mechanisms associated with abnormal calcium-regulated PTH secretion. Depending on their binding site on the respective target antigen molecules, these monoclonal antibodies either stimulated or inhibited hormone secretion. Thus, defects in membrane-associated structures may contribute to deranged calcium-regulated PTH secretion in abnormal parathyroid cells.
Antibodies, Monoclonal↗
Parathyroid hormone (PTH) assay of parathyroid cysts examined by fine-needle aspiration biopsy.
The authors report three cases of parathyroid cysts examined by the fine-needle aspiration biopsy technic. A presumptive diagnosis of parathyroid cyst was made when characteristic water-clear fluid was aspirated. The diagnosis was then confirmed by parathyroid hormone (PTH) assay. The authors believe that the C-terminal/midmolecule determination should be the assay of choice, because the N-terminal-specific assay gave normal or slightly elevated results in all the cases studied. If only an N-terminal-specific PTH assay is obtained, potential for a false negative diagnosis exists. With a correct PTH assay, a specific diagnosis of parathyroid cyst can be rendered, which enables appropriate treatment of total fluid aspiration, which thereby eliminates the need for thyroid hormone treatment or surgery in most cases. A discussion of PTH assays is presented along with speculations concerning the secretion of PTH by the parathyroid gland. The previous literature detailing cytologic findings and the PTH assays of parathyroid cysts diagnosed by the fine-needle aspiration biopsy are reviewed.
Adult↗
Role of anions in parathyroid hormone release from dispersed bovine parathyroid cells.
It is known that permeant anions are required for the release of epinephrine from isolated chromaffin granules and of serotonin from intact platelets. We have now investigated the role of anions in the release of a polypeptide hormone, parathyroid hormone, from dispersed bovine parathyroid cells. The release is inhibited 60%-80% by decreasing either [Cl-] or [OH-] and 60%-70% by replacement of NaCl with the impermeant anion isethionate. By contrast, substitution of various monovalent cations in the medium had no effect on the release. Disodium 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS) and probenecid, which are known to block anion transport in the erythrocyte, also cause a dose-dependent 90%-100% inhibition of release. Moreover, kinetic analysis of inhibition by probenecid suggests that it is competitive with respect to either OH- or Cl-. These results suggest that anions and the anion transport system may play a role in exocytosis of a polypeptide hormone. The proton ionophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone was was also found to block hormone release, and the possibility is discussed of a "chemosmotic" mechanism for exocytosis in this system similar to that previously postulated for chromaffin granules and platelets.
Animals↗
A G protein-coupled receptor from zebrafish is activated by human parathyroid hormone and not by human or teleost parathyroid hormone-related peptide. Implications for the evolutionary conservation of calcium-regulating peptide hormones.
Genomic and cDNA clones encoding portions of a putative catfish parathyroid hormone (PTH) 2 receptor (PTH2R) led to the isolation of a cDNA encoding a full-length zebrafish PTH2R (zPTH2R). The zPTH2R shared 63 and 60% amino acid sequence identity with human and rat PTH2Rs, respectively, 47-52% identity with mammalian and frog PTH/PTHrP receptors (PTH1R), and less than 37% with other members of this family of G protein-coupled receptors. COS-7 cells expressing zPTH2R(43), a 5' splice variant that lacked 17 amino acids in the amino-terminal extracellular domain, showed cAMP accumulation when challenged with [Tyr(34)]hPTH(1-34)-amide (hPTH) (EC(50), 1.64 +/- 0. 95 nM) and [Ile(5),Trp(23),Tyr(36)]hPTHrP-(1-36)-amide ([Ile(5), Trp(23)]hPTHrP) (EC(50), 46.8 +/- 12.1 nM) but not when stimulated with [Tyr(36)]hPTHrP-(1-36)-amide (hPTHrP), [Trp(23), Tyr(36)]hPTHrP-(1-36)-amide ([Trp(23)]hPTHrP), or [Ala(29),Glu(30), Ala(34),Glu(35),Tyr(36)]fugufish PTHrP-(1-36)amide (fuguPTHrP). FuguPTHrP also failed to activate the human PTH2R but had similar efficiency and efficacy as hPTH and hPTHrP when tested with cells expressing the human PTH1R. Agonist-dependent activation of zPTH2R was less efficient than that of zPTH2R(43), and both receptor variants showed no cAMP accumulation when stimulated with either secretin, growth hormone-releasing hormone, or calcitonin. The zPTH2R thus has ligand specificity similar to that of the human homolog, which raises the possibility that a PTH-like molecule exists in zebrafish, species which lack parathyroid glands.
Amino Acid Sequence↗
The action of parathyroid hormone on salivary glands in organ culture. 3. The influence of parathyroid hormone on the secretion of the duct cells and on the uptake of calcium by the glands.
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Animals↗
Relation between parathyroid hormone and adrenocorticotropic hormone in primary hyperparathyroidism.
Parathyroid hormone is concerned with urolithiasis, and regulated by serum ionized calcium concentration. We thought that parathyroid hormone might also be regulated by a hormone. 1 mg of ACTH injection was given intramuscularly to 6 patients with primary hyperparathyroidism, 6 patients with urolithiasis, and 5 control subjects. Serum calcium significantly increased 2 h after ACTH injection in primary hyperparathyroidism. However in the other two groups, an increase of serum calcium was not observed. Parathyroid hormone increased after ACTH injection in most subjects of all three groups. Calcium concentration in a culture medium of parathyroidectomy increased in 4 cases, and the parathyroid hormone concentration in the culture medium increased in 3 cases after ACTH addition. From these data, we believe that ACTH directly influences the parathyroid glands, and that calcium is released from the parathyroid cells. Therefore, the decrease in calcium concentration in the parathyroid cells activates the excretion of parathyroid hormone. The fact that serum parathyroid hormone increases in most subjects in all groups supports our hypothesis, namely that ACTH acts directly on the parathyroid gland.
Adenoma↗
Signal transduction pathways mediating parathyroid hormone regulation of osteoblastic gene expression.
Parathyroid hormone (PTH) plays a central role in regulation of calcium metabolism. For example, excessive or inappropriate production of PTH or the related hormone, parathyroid hormone related protein (PTHrP), accounts for the majority of the causes of hypercalcemia. Both hormones act through the same receptor on the osteoblast to elicit enhanced bone resorption by the osteoclast. Thus, the osteoblast mediates the effect of PTH in the resorption process. In this process, PTH causes a change in the function and phenotype of the osteoblast from a cell involved in bone formation to one directing the process of bone resorption. In response to PTH, the osteoblast decreases collagen, alkaline phosphatase, and osteopontin expression and increases production of osteocalcin, cytokines, and neutral proteases. Many of these changes have been shown to be due to effects on mRNA abundance through either transcriptional or post-transcriptional mechanisms. However, the signal transduction pathway for the hormone to cause these changes is not completely elucidated in any case. Binding of PTH and PTHrP to their common receptor has been shown to result in activation of protein kinases A and C and increases in intracellular calcium. The latter has not been implicated in any changes in mRNA of osteoblastic genes. On the other hand activation of PKA can mimic all the effects of PTH; protein kinase C may be involved in some responses. We will discuss possible mechanisms linking PKA and PKC activation to changes in gene expression, particularly at the nuclear level.
Animals↗
[Clinical studies on the action of parathyroid hormone on the kidney. I. Factors affecting the renal phosphaturic response of parathyroid hormone].
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Adolescent↗
Mechanism of resistance to the phosphaturic effect of the parathyroid hormone in the hamster.
The effect of parathyroid hormone and calcitonin on the renal excretion of phosphate, calcium, and cyclic AMP was evaluated in the thyroparathyroidectomized hamster, a mammal apparently reisstant to the phosphaturic effect of parathyroid hormone. Parathyroid hormone did not increase phosphate excretion, although it decreased excretion of calcium and increased urinary excretion of cyclic AMP. This lack of a phosphaturic response to parathyroid hormone was not reversed by administration of 25-OH vitamin D or infusions of calcium or phosphate. Calcitonin, another potentially phosphaturic hormone, also vailed to increase phosphate excretion but markedly elevated urinary excretion of cyclic AMP. In hamsters pretreated with infusion of urinary ammonium chloride, which decreased plasma and urinary pH, both parathyroid hormone and calcitonin increased excretion of phosphate as well as that of cyclic AMP. Acetazolamide had no phosphaturic effect in ammonium chloride-loaded hamsters, and it decreased cyclic AMP and calcium excretion. Alkalinization of urine by acetazolamide did not prevent the phosphaturic effect of parathyroid hormone in ammonium chloride-loaded hamsters, but it blocked the increase in urinary cyclic AMP excretion. Parathyroid hormone and calcitonin both stimulated adenylate cyclase in a cell-free system (600-g pellet) from hamster renal cortex, elevated tissue cyclic AMP levels, and activated protein kinase in tissue slices from hamster renal cortex. In acid medium, the increase in cyclic AMP and activation of protein kinase in response to parathyroid hormone was diminished, but addition of acetazolamide restored responsiveness of both parameters to control values. Acetazolamide, on the other hand, did not influence adenylate cyclase or its response to parathyroid hormone or cyclic AMP phosphodiesterase activity. We conclude that the lack of a phosphaturic effect of parathyroid hormone and calcitonin in the hamster depends on steps in the cellular action of these hormones, steps that are sensitive to pH subsequent to cyclic AMP generation and protein kinase activation. In addition, acetazolamide may potentiate the phosphaturic effect of parathyroid hormone by promoting accumulation of cyclic AMP in tissue. Thus, the hamster is a particularly useful model for studies of syndromes in which there is renal resistance to phosphaturic hormones.
3',5'-Cyclic-AMP Phosphodiesterases↗