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PubMed1986

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↗
PubMed1987

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↗
PubMed2002

Intraoperative parathyroid hormone levels in thyroid and parathyroid surgery.

OBJECTIVE: To determine the utility of intraoperative parathyroid hormone measurement in predicting postoperative hypocalcemia after thyroid and parathyroid surgeries that places total parathyroid function at risk. STUDY DESIGN: Retrospective case review. METHODS: The case records of 23 patients undergoing total or completion thyroidectomy and 30 patients undergoing parathyroid exploration were reviewed. All patients had intraoperative parathyroid hormone levels measured. Samples were taken before dissection and 10 minutes after the resection was completed. Serial ionized calcium levels were measured in the postoperative period. Percentages of reduction in PTH levels from preoperative to postresection levels were calculated. Percentages of reduction in PTH level and the absolute value of the intraoperative PTH values were compared with postoperative ionized calcium levels. RESULTS: In the 23 patients who underwent thyroid surgery, the average preoperative and postoperative PTH values were 50 pg/mL (range, 17-87 pg/mL) and 34 pg/mL (range, 4-93 pg/mL), respectively. The average decrease in PTH was 39% (range, 39%-90%). The incidence of hypocalcemia was significantly higher in patients with intraoperative PTH levels less than 15 pg/mL relative to patients with PTH levels greater than 15 pg/mL in this setting ( P=.006). In the 30 patients who underwent parathyroid exploration, average preoperative and postoperative PTH levels were 291 pg/mL (range, 65-1675 pg/mL) and 113.8 pg/mL (range, 6.5-1263 pg/mL) respectively. The intraoperative PTH level did not correlate with postoperative calcium levels in the parathyroid group. Percentages of decrease in PTH levels greater than 60% was statistically associated with surgical cure in this population. CONCLUSIONS: The study demonstrates that intraoperative PTH levels greater than 15 pg/mL after total or completion thyroidectomy indicate a low risk of postoperative hypocalcemia and that these patients may be candidates for outpatient surgery. In the parathyroid group, intraoperative PTH levels do not correlate well with postoperative calcium levels.

Calcium↗
PubMed1986

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↗
PubMed1978

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↗
PubMed1999

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↗
PubMed1984

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↗
PubMed1994

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↗
PubMed2002

Normocalcemia and persistent elevated serum concentrations of 1-84 parathyroid hormone after operation for sporadic parathyroid adenoma: evidence of increased morbidity from cardiovascular disease.

Elevated serum concentrations of 1-84 parathyroid hormone (PTH) after operation for sporadic parathyroid adenoma have been reported in previous studies, years after operation for primary hyperparathyroidism (pHPT). The cause and significance of this finding have not been elucidated. Primary hyperparathyroidism was diagnosed in 195 patients from January 1987 to December 1998. Operation for pHPT was performed in 124 patients. To evaluate long-term effects of elevated serum 1-84 PTH, biochemical variables and pre- and postoperative diseases were investigated from hospital case records. Of the 124 patients operated on, 103 had a solitary adenoma. Among these patients, 60 had normal serum concentrations of 1-84 PTH and calcium postoperatively, 38 patients had follow-up for more than 12 months (range 12-207 months-group A). Persistent elevated serum concentrations of 1-84 PTH and normocalcemia were found in 23 patients. Fourteen patients had follow-up for more than 12 months (range 15-76 months-group B). Two patients had persistent pHPT, and 18 were normocalcemic, but in this retrospective study data on serum 1-84 PTH were not available. No significant differences were found between groups A and B at the time of diagnosis concerning clinical characteristics. More that 12 months after operation for pHPT, the patients in group B, with persistent elevated serum concentrations of 1-84 PTH, had a significantly (c2 = 11, p = 0.005, and power of test 0.66) higher frequency of cardiovascular diseases from ischemic heart disease and hypertension. Persistent elevated serum concentrations of 1-84 PTH after operation for sporadic parathyroid adenoma may be associated with development of cardiovascular disease. This group of patients therefore needs lifelong control and, possibly, medical intervention.

Adenoma↗
PubMed1977

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↗
PubMed2002

Immunoassays for the detection of parathyroid hormone.

Biologically active parathyroid hormone (PTH) in humans with normal renal function circulates predominantly as an 84 amino acid peptide. PTH fragments of varying length arise either from metabolism of the intact hormone within the parathyroid glands or in peripheral tissues, such as liver, and the resulting carboxyl-terminal peptides are eliminated mainly by glomerular filtration and subsequent tubular degradation. Most of the initially raised anti-PTH antisera were directed against epitopes within the mid- or carboxyl-terminal regions of the hormone. These antibodies were used for the development of conventional, displacement-type radioimmunoassays, but provided only an index of the biologically active PTH(1-84) in the circulation. Subsequently developed immunometric assays use two distinct antibodies, a capture antibody usually directed against a carboxyl-terminal portion of PTH(1-84) and a radio- or enzyme-labeled detection antibody usually directed against the amino-terminal portion of the hormone. Such assays were thought to detect largely, if not exclusively, intact PTH, thus providing the concentration of biologically active hormone in blood, which is especially important for establishing the diagnosis of hyperparathyroidism. However, serum samples from normal subjects and patients with primary or secondary hyperparathyroidism have demonstrated that most immunometric two-site sandwich assays detect, besides PTH(1-84), one or more recently discovered large carboxyl-terminal PTH fragments that lack a portion of the amino-terminal end of the molecule. Some of these amino-terminally truncated PTH molecules [ntPTH(1-84)] exhibit an elution profile on high performance liquid chromatography (HPLC) that is indistinguishable from that of synthetic PTH(784). Such peptides were previously thought to be of minimal if any biological activity, but recent studies have shown that synthetic PTH(7-84) has hypocalcemic properties in vivo and that it inhibits osteoclastic bone resorption and the formation of mature osteoclasts in vitro. It is currently unclear whether important differences in disease states can be revealed by comparing results obtained with older immunometric assays that measure the full-length hormone and ntPTH(1-84) versus newer assays that measure only PTH(1-84). Therefore, whereas most immunometric PTH assay systems are appropriate for the diagnosis of primary hyperparathyroidism, it is possible that immunometric assays designed to detect only PTH(1-84) will be more useful in certain diagnostic studies, for intraoperative PTH monitoring and for assessing the pulsatility of PTH secretion. In addition, the ability to distinguish between the relative concentrations of ntPTH(1-84) versus PTH(1-84) may reveal previously unsuspected roles for the ntPTH(1-84) fragments in the pathophysiology of patients with end-stage renal disease and/or other disorders involving parathyroid hormone.

Chromatography, High Pressure Liquid↗
PubMedDate not supplied

Hormone metabolism and response of adenylate cyclase to parathyroid hormone in kidney.

1. Incubation of parathyroid hormone with plasma membranes from rat kidney cortex resulted in rapid loss of all hormal activity. 2. Chick kidney membranes showed no ability to inactivate parathyroid hormone even with prolonged incubation. 3. Biologically active, labelled parathyroid hormone was degraded to fragments by rat kidney membranes, but not by chick kidney. 4. Hormone-responsive adenylate cyclase activity in a mixture of rat and chick kidney membranes was additive. 5. Parathyroid hormone bound specifically to chick kidney palsma membranes. 6. It is concluded that hormone in activation during incubation has little relevance to the effectiveness of parathyroid hormone in stimulating adenylate cyclase activity in kidney, and furthermore that failure of chick kidney to metabolize the hormone is not the explanation for the greater sensitivity of this species to the hormone.

Adenylyl Cyclases↗
PubMed1976

Impaired release of parathyroid hormone in magnesium deficiency.

Parathyroid hormone release and end-organ responsiveness to parathyroid extract (PTE) were evaluated in a 25-year-old woman with magnesium deficiency associated with hypocalcemia and inappropriately low levels of serum immunoreactive parathyroid hormone (iPTH). End-organ responsiveness to PTE was demonstrated by increases in serum calcium and in urinary phosphorus, cyclic AMP, and hydroxyproline. When the serum calcium was increased from a baseline of 6.9 mg/100 ml to levels of 8.0 mg/100 ml and higher by calcium infusion, the serum iPTH decreased from the low normal range to below the limits of detectability. The intravenous administration of 3 mg/kg of body weight of magnesium led to an abrupt and striking increase in circulating iPTH with a 2-fold increase in one minute, a 6-fold increase in two minutes, and an 8-fold increase in five minutes. The very rapid increase in serum iPTH produced by magnesium infusion in this study suggests an effect of magnesium on hormone secretion rather than an effect on hormone synthesis. The evidence provided by this investigation indicates that the release of parathyroid hormone is impaired in magnesium deficiency and that the level of circulating calcium required for the suppression of parathyroid hormone secretion is lower than that in normal subjects.

Adult↗
PubMed1997

Control of hair growth with parathyroid hormone (7-34).

Parathyroid hormone (PTH) related peptide (PTHrP) is thought to influence the proliferation and differentiation of the epidermis and hair follicle. As a means of elucidating the biologic function of PTHrP on the hair follicle, a PTHrP analog PTH (7-34), which is a PTH/PTHrP receptor antagonist, was given intraperitoneally twice daily to C57 BL/6 mice at different stages of the hair cycle. PTH (7-34) induced 99 +/- 4.5% (mean +/- SEM) of resting telogen hair follicles into a proliferative (anagen) state, whereas 100% of the hair follicles in the control group remained in telogen. To determine whether this peptide influenced the progression of the hair follicles from anagen to catagen (hair follicle maturation and regression), groups of mice that were either spontaneously in or induced to anagen received either PTH (7-34) or placebo. Morphometric analysis of the hair follicles from the middle back region of the spontaneous anagen mice that received PTH (7-34) revealed that 19 +/- 4% (mean +/- SEM) of the follicles were in anagen VI, whereas none (0%) were in anagen in the control group. Similarly, in induced anagen mice treated with PTH (7-34), 22.3 +/- 1.4 (mean +/- SEM) of the follicles were in anagen VI compared to only 1.3 +/- 0.7% in the control mice. Together these observations suggest that PTHrP is a hair follicle morphogen that may be a major factor responsible for controlling the hair cycle. These studies provide a new insight for development of PTHrP analogs for a wide variety of disorders related to disturbances of hair cycling.

Animals↗