Regulation Of Parathyroid Hormone Release Research Articles

Pathophysiology of primary hyperparathyroidism.

Parathyroid gland is the overall regulatory organ within the systemic calcium homeostasis. Through cell surface bound calcium-sensing receptors external calcium inversely regulates release of parathyroid hormone (PTH). This mechanism, which is voltage independent and most sensitive around physiologic calcium concentrations, is regulated through a 120 kDa calcium sensing receptor, CaR. Inherited inactivation of this receptor is the cause for familial hypocalciuric hypercalcemia (FHH). Parallel research identified the 550 kDa glycoprotein megalin, which also is expressed on the parathyroid cell surface, as another potential calcium sensing protein. Although this protein expresses numerous calcium binding sites on its external domain, its main function may be calcium sensitive binding and uptake of steroid hormones, such as 25-OH-vitamin D3 (bound to vitamin D binding protein) and retinol. In hyperparathyroidism (HPT), excessive PTH is secreted and the calcium sensitivity of the cells reduced, i.e. the set-point, defined as the external calcium concentration at which half-maximal inhibition of PTH release occurs, shifted to the right. Pathological cells have reduced expression of both CaR and megalin, and reduced amount of intracellular lipids, possibly including stored steroid hormones. A number of possible genetic disturbances have been identified, indicating multifactorial reasons for the disease. In postmenopausal women, however, the individual group with highest incidence of disease, a causal relation to reduced effect of vitamin D is possible. An incipient renal insufficiency with age, lack of sunshine in the Northern Hemisphere, and an association to the baT haplotype of the vitamin D receptor supports this theory. This review summarizes data on regulation of PTH release, dysregulation in HPT, as well as proliferation of parathyroid cells.

Effect of magnesium on parathyroid cells: evidence for two sensing receptors or two intracellular pathways?

It currently remains controversial as to the intracellular mechanisms coupled to the inhibition of parathyroid hormone (PTH) secretion that are modulated by extracellular divalent cations. To study mechanisms responsible for regulation of PTH release by cations, we investigated the effect of Mg2+ on cytosolic Ca2+ levels ([Ca2+]i) and PTH secretion in single isolated bovine parathyroid cells. Addition of 9.0 mM Mg2+ evoked a spike of [Ca2+]i in approximately 80% of cells in the presence of extracellular Ca2+. Mg2+ decreased steady-state [Ca2+]i, which represented inhibition of influx of extracellular Ca2+ in 13-78% of cells. The percentage of cells that had a decline in steady-state [Ca2+]i after exposure to Mg2+ was dependent on the extracellular Ca2+ concentration. The effect of Mg2+ on intracellular Ca2+ response was dose dependent. Extracellular Mg2+ inhibited PTH secretion in cells that showed decline in steady-state [Ca2+]i, although cells that showed a spike after addition of Mg2+ secreted more PTH than cells that did not show a spike. The spike of [Ca2+]i and decline in steady-state [Ca2+]i that occur in response to extracellular Mg2+ may be caused independently by two distinct mechanisms that differentially regulate secretion of PTH.

Regulation of parathyroid hormone release by protein kinase-C is dependent on extracellular calcium in bovine parathyroid cells.

The purpose of this study was to evaluate regulation of PTH secretion by protein kinase-C (PKC) in adult bovine parathyroid cells. Extracellular calcium (Ca2+e) is the main physiological regulator of PTH secretion. Putative second messengers include intracellular calcium (Ca2+i), cAMP, inositol trisphosphate, and diacylglycerol (DAG). Both DAG and Ca2+i activate PKC. Certain phorbol esters mimic the effect of DAG and cause prolonged stimulation of PKC. The stimulatory phorbol esters 12-O-tetradecanoylphorbol acetate (1 microM) and phorbol-12,13-dibutyrate (1 microM) did not affect PTH secretion at low Ca2+e, but increased both individual cell secretion and recruitment of cells to secrete at high Ca2+e. The PKC inhibitors H7 (1 microM), tamoxifen (10 microM), and sphinganine (5 microM) inhibited PTH release at low Ca2+e (0.1 and 0.2 mM) and decreased cell recruitment over the physiological range of Ca2+e. The nonstimulatory phorbol esters 4 alpha-phorbol-12,13-didecanoate (1 microM) and phorbol-13-monoacetate (1 microM) had no effect on PTH secretion. To assess the mechanism by which certain phorbol esters stimulated PTH secretion, in situ hybridization for PTH mRNA was performed. Phorbol-12,13-dibutyrate (1 microM) qualitatively increased steady state PTH mRNA levels compared to control values. We conclude that 1) PKC stimulation increased PTH secretion at high Ca2+e, but not at low Ca2+e; 2) PKC inhibition decreased PTH secretion at low Ca2+e; and 3) PKC stimulation increased steady state PTH mRNA levels. These data suggest that PKC plays an important regulatory role in the synthesis and secretion of PTH.

Regulation of parathyroid hormone release by protein kinase-C is dependent on extracellular calcium in bovine parathyroid cells [published erratum appears in Endocrinology 1993 May;132(5):2270-2

Regulation of parathyroid hormone release by protein kinase-C is dependent on extracellular calcium in bovine parathyroid cells [published erratum appears in Endocrinology 1993 May;132(5):2270-2

Regulation of parathyroid hormone release in normal and pathological parathyroid cells exposed to modulators of protein kinase C.

Effects of the protein kinase C activating phorbol ester 12-O-tetradecanoyl phorbol 13-acetate and the inhibitor 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7) on parathyroid hormone (PTH) release were studied in normal bovine and pathological human parathyroid cells. An increase of extracellular Ca2+ from 0.5 to 3.0 mmol/l inhibited PTH release by 60% in the bovine cells with half maximal effect (ED50) at 1.31 mmol/l. This inhibition reached less than 50% in the cells from patients with primary and uremic hyperparathyroidism, and the ED50 values were 1.49 and 1.42 mmol/l, respectively. The phorbol ester (0.1 mumol/l) made secretion insensitive to changes of extracellular Ca2+, an action counteracted by H-7 (50 mumol/l) in the bovine cells, whereas H-7 alone had no effects. The phorbol ester and H-7 had opposite actions on regulation of PTH release also from cells from patients with hyperparathyroidism. However, in pathological cells H-7 alone improved Ca2+ inhibition of secretion by stimulating release in low Ca2+ concentrations and decreasing the ED50 values. The magnitude of changes in ED50 values by H-7 increased with the severity of the secretory disturbance of the pathological cells. The results indicate that increased protein kinase C activity may be a factor of importance in the pathophysiology of hyperparathyroidism.

Immunohistochemicaf evidence of parathyroid hormone-related protein in human parathyroid tissue.

Immunohistochemical staining for parathyroid hormone-related protein (PTHrp) was investigated on cryosections of 17 normal-sized human parathyroid glands, 47 adenomatous and hyperplastic glands of hypercalcemic patients with primary or uremic hyperparathyroidism, and 5 metastases of parathyroid carcinoma. Utilizing a polyclonal antiserum recognizing aminoterminal PTHrp, approximately two-thirds of the normal and enlarged glands but none of the parathyroid carcinomas demonstrated a conspicuous immunostaining. The extent and intensity of the reactivity varied between the glands even of individual patients. The staining was found in chief and oxyphilic parathyroid cells, and studies of cell suspensions substantiated that the immunoreaction was present also on the surface of the parathyroid cells. Reduced PTHrp expression in the functionally more dedifferentiated parathyroid tissue was suggested by comparison of the normal (i.e., suppressed) and adenomatous parathyroid tissue from the individual patients and by parallel stainings with the monoclonal El1 antibody, which recognizes a calcium sensor involved in the regulation of parathyroid hormone release. The findings substantiate a functional role for PTHrp in euparathyroid and hyperparathyroid individuals.

Monoclonal antiparathyroid antibodies revealing defect expression of a calcium receptor mechanism in hyperparathyroidism.

AbstractMonoclonal antibodies were generated with a hybridoma technique after immunization of mice with intact human parathyroid cells. Three antibodies of the IgG type reacted in immunohistochemistry and immunofluorescense with parathyroid epithelial cells and proximal tubule cells of the kidney but not with a large number of other human tissues. Adenomatous and hyperplastic parathyroid glands of patients with hyperparathyroidism (HPT) demonstrated a reduced immunohistochemical reactivity with the antibodies as compared to the intense staining of normal human parathyroid tissue. Experiments with dispersed parathyroid cells from the normal and pathological glands showed that 2 of the antibodies blocked the effects of ambient calcium on cytoplasmic calcium and parathyroid hormone release. This indicates that the antibodies interfere with a newly recognized receptor mechanism of parathyroid cells involved in the sensing and gating of calcium and thereby also in the regulation of parathyroid hormone release. A reduced expression of the putative calcium receptor mechanism of abnormal parathyroid cells may, thus, be principally responsible for the hypercalcemia of HPT by causing a decreased sensitivity to extracellular calcium of the parathyroid hormone release from pathological parathyroid glands. The antibodies should improve the parathyroid histological diagnosis by their ability to identify and to distinguish between normal and abnormal parathyroid tissue.

Calcium regulation of parathyroid hormone release.

Calcium regulation of parathyroid hormone release.

Regulation of parathyroid hormone release and cytosolic calcium by extracellular calcium in dispersed and cultured bovine and pathological human parathyroid cells.

Alterations in parathyroid glandular sensitivity to calcium may contribute to the hypersecretion of PTH in hyperparathyroidism. Since the cytosolic calcium concentration may mediate the effects of extracellular calcium on PTH release, we have employed the calcium-sensitive intracellular dye QUIN-2 to examine the relationship between extracellular calcium, cytosolic calcium, and PTH secretion in adult, neonatal, and cultured bovine as well as pathological human parathyroid cells. PTH release was measured using C- and N-terminal radioimmunoassays. Neonatal bovine parathyroid cells showed a greater set-point for secretion (the Ca++ concentration causing half of the maximal inhibition of PTH release) than adult cells (1.27 +/- 0.11 vs. 1.06 +/- 0.11 mM extracellular calcium, P less than 0.01), and a slightly higher extracellular calcium was necessary to raise the cytosolic calcium concentration to a given level in neonatal than in adult bovine parathyroid cells. In individual neonatal and adult cell preparations, there was a close correlation between the set-point for secretion and the "set-point" for cytosolic calcium (r = 0.832, P less than 0.001). In cells from five human parathyroid adenomas, which had an increase in set-point for secretion, the extracellular calcium concentration necessary to raise the cytosolic calcium concentration to a given level was slightly greater than in the neonatal cells. In four preparations of human parathyroid cells there was a significant correlation between the set-points for secretion and cytosolic calcium (r = 0.856, P less than 0.01). Because neonatal bovine and pathological human parathyroid glands show cellular hyperplasia, we studied the temporal relationship between cellular proliferation and the regulation of PTH release and cytosolic calcium concentration in cultured bovine parathyroid cells. Cellular proliferation, estimated by 3H-thymidine incorporation, increased significantly in culture from 104 +/- 10.1 counts/well on day 1 (first 24 h in culture) to 588 +/- 188 and 6,156 +/- 649 counts/well on days 2 and 4, respectively. In cultured cells on day 1, highly Ca++ (2-3 mM) inhibited maximal PTH release by 58.8 +/- 3.2%, which decreased significantly (P less than 0.001) to 38.2 +/- 1.9 and 17.1 +/- 3.7% on days 2 and 4, respectively. The cytosolic calcium observed at 3 mM calcium on day 1 was 701 +/- 43 nM, which declined to 466 +/- 60 and 314 +/- 14 nM on days 2 and 4 (P less than 0.05). There was a close correlation between this progressive decrease in maximal inhibition of PTH release and the cytosolic calcium at high extracellular calcium in cultured cells (r = 0.99, P < 0.001). Thus, during active proliferation of cultured cells, there is an alteration in the regulation of cytosolic calcium at a given extracellular calcium concentration, and changes in the regulation of PTH release and cytosolic calcium by extracellular calcium may be related to enhanced cellular proliferation.

Regulation of parathyroid hormone release in primary and secondary hyperparathyroidism - studies in vivo and in vitro.

The effects of calcium on parathyroid hormone (PTH) release were studied in vivo and in vitro in primary hyperparathyroidism (HPT) and in vitro in secondary HPT. In vivo the serum PTH was clearly reduced by intravenous calcium infusion in all the examined patients with primary HPT caused by adenoma. In vitro the release of PTH from dispersed parathyroid cells was likewise suppressed by raising the calcium concentrations in the incubation media, though in all cases a basal release of PTH still persisted even at high calcium concentrations. The degree of suppressibility in vitro varied, but in both primary HPT with adenoma and in secondary HPT it was inversely related to the patients' serum calcium values. These results suggest that the secretion of PTH in patients with primary and secondary HPT is not autonomous either in vivo or in vitro. Furthermore, the non-suppressible basal release of PTH indicates that a major cause for the increased secretion of PTH is the increased number of parenchymal cells. However, the degree of suppressibility of the individual cells rather than the absolute number of cells, seems to be of great importance for the individual serum calcium values in HPT.

Adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase and the regulation of parathyroid hormone release by divalent cations and agents elevating cellular cAMP in dispersed bovine parathyroid cells.

Divalent cations and agents elevating cellular cAMP were tested for their effects on parathyroid hormone (PTH) secretion and protein kinase activity in dispersed bovine parathyroid cells. After incubation with secretagogue for 5-30 min, cells were sedimented, PTH in the supernatant was determined by RIA, and the pellet was disrupted by sonication for the measurement of protein kinase activity. Preliminary studies established conditions where the protein kinase activity ratio (AR = activity in the absence divided by that in the presence of 10(-6) M cAMP in the kinase assay) remained stable during the preparation and assay of cellular extracts. (-)Isoproterenol caused a rapid (within 5 min) increase in the AR from 0.28 to 0.63, which returned to 0.25-0.3 within 5 min after the addition of the potent beta-adrenergic blocker (-)propranolol. (-)Isoproterenol, dopamine, and the phosphodiesterase inhibitor methylisobutylxanthine caused parallel, dose-dependent increases in PTH release and the protein kinase AR of 2- to 2.5-fold. Calcium and magnesium, on the other hand, despite causing 2- to 4-fold inhibition of secretion at 2 and 5 mM, respectively, had no effect on the AR. Calcium (2.0 mM) likewise had only a modest (0-25%) inhibitory effect on the isoproterenol-stimulated increase in the AR in spite of a 3- to 4-fold inhibition of agonist-stimulated secretion. These results suggest that the stimulation of secretion associated with agents that elevate cAMP is mediated by cAMP. Changes in the degree of activation of protein kinase, on the other hand, cannot quantitatively for the effects of divalent cations on basal or agonist-stimulated secretion.

Abnormal Regulation of Parathyroid Hormone Release by Calcium in Secondary Hyperparathyroidism due to Chronic Renal Failure*

Dispersed parathyroid cells were employed to study calcium-regulated parathyroid hormone (PTH) release in severe secondary hyperparathyroidism due to chronic renal insufficiency. Cell preparations were obtained from 16 parathyroid glands of 6 patients undergoing subtotal parathyroidectomy for parathyroid bone disease and/or hypercalcemia. The effects of increasing ambient calcium concentration on immunoreactive PTH release in vitro were assessed and compared with results observed in cells prepared from 7 adenomas and 6 normal parathyroid glands. There was no difference in maximal PTH release for the 3 types of tissue (mean +/- SEM, 8.48 +/- 1.9 , 8.1 +/- 3, and 10.1 +/- 0.78 ng/10(5) cells. h respectively). In 14 of 16 hyperplastic glands, 6 of 7 adenomas, and all of the normal glands, PTH release was inhibited more than 50% by 2-3 mM calcium (suppressible glands). Of the normal glands, half of the maximal inhibition of PTH release (the set-point) occurred at less than 1.03 mM calcium in 5 of 6 cases. In 12 of 14 suppressible hyperplastic glands and all of the 6 suppressible adenomas, on the other hand, the set-point was 1.03 mM or higher (p less than 0.01 and P less than 0.002, respectively). Thus, in severe secondary parathyroid hyperplasia due to chronic renal insufficiency, there is frequently an increase in the set-point for calcium without a change in the maximal secretory rate per cell. Abnormal calcium-regulated PTH release at the cellular level, therefore, is not limited to parathyroid neoplasia (i.e. adenoma or primary hyperplasia), but may occur in secondary hyperplasia as well.

Calcium-Regulating Hormones

Symposium1 December 1980Calcium-Regulating HormonesBOY FRAME, M.D., SUDHAKER D. RAO, M.B.B.S.BOY FRAME, M.D.Search for more papers by this author, SUDHAKER D. RAO, M.B.B.S.Search for more papers by this authorAuthor, Article, and Disclosure Informationhttps://doi.org/10.7326/0003-4819-93-6-928 SectionsAboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinkedInRedditEmail ExcerptDespite a life span of several decades, the field of bone and mineral metabolism is still in its embryonic stage. Although understanding of diseases affecting parathyroid glands and the skeleton has greatly improved, many questions are still unanswered. This was the overall impression at the VII International Conference on Calcium-Regulating Hormones, recently held in Estes Park, Colorado.Recent advances in molecular biology and genetic bioengineering have paved the way for better understanding of intracellular events in hormone secretion. Until recently it has been difficult to obtain intact human parathyroid hormones (PTH) either for laboratory use or for clinical trials. Synthetic...Symposim Papers1. KRONENBERGRICHPOTTS HAJ. The structure and function of parathyroid hormone genes. Massachusetts General Hospital, Harvard Medical School, Massachusetts Institute of Technology; Boston, Massachusetts. Google Scholar2. ARNAUDNISSENSONTEITELBAUM CRA. Parathyroid hormone receptors. University of California at San Francisco and Veterans Administration Medical Center; San Francisco, California. Google Scholar3. NISSENSONABBOTTTEITELBAUMARNAUD RSAC. Relationship between biologically active and immunoreactive PTH levels in hyperparathyroid man. Department of Medicine, University of California, and Veterans Administration Medical Center; San Francisco, California. Google Scholar4. MARTINHRUSKASLATOPOLSKY KKE. Peripheral metabolism of parathyroid hormone: activation or inactivation. Washington University School of Medicine; St. Louis, Missouri. Google Scholar5. BROWN E. Regulation of parathyroid hormone release in dispersed parathyroid cells. Peter Bent Brigham Hospital; Boston, Massachusetts. Google Scholar6. STEWARTBROADUS AA. Humoral hypercalcemias of malignancy. Yale University School of Medicine; New Haven, Connecticut. Google Scholar7. BOURNEBRICKMANFARFEL HAZ. Molecular basis of pseudohypoparathyroidism. University of California; San Francisco, California. Google Scholar8. LEVINEAURBACHSPIEGEL MGA. Clinical and basic studies in pseudohypoparathyroidism. National Institute of Arthritis, Metabolism, and Digestive Diseases; Bethesda, Maryland. Google Scholar9. MARXATTIESPIEGEL SMA. Familial hypocalciuric hypercalcemia. Metabolic Diseases Branch, National Institute of Arthritis, Metabolism, and Digestive Diseases; Bethesda, Maryland. Google Scholar10. MUNDYYONEDAORR GTF. Monocyte Chemotaxis and interaction with lymphocytes in bone resorption. University of Texas Health Science Center; San Antonio, Texas. Google Scholar11. KAHNMALONETEITELBAUM AJS. Mononuclear phagocytes as bone resorbing cells. Jewish Hospital of St. Louis, Washington University School of Medicine; St. Louis, Missouri. Google Scholar12. MARTINPARTRIDGE TN. Initial events in activation of bone cells by parathyroid hormone, prostaglandins and calcitonin. University of Melbourne; Heidelberg, Victoria, Australia. Google Scholar13. HEERSCHENGJEZ JBD. Regulation of hormone responsiveness of bone in vitro by glucocorticoids, parathyroid hormone, calcitonin and prostaglandins. University of Toronto; Toronto, Canada. Google Scholar14. CANFIELD R. Diphosphonates in treatment of diseases with increased bone resorption. Columbia University; New York, New York. Google Scholar15. PARSONSPODBESEK JR. Parathyroid hormone in treatment of osteoporosis. National Institute For Medical Research; London, England. Google Scholar16. DEFTOS J. Effects of age and sex on calcitonin secretion. University of California and San Diego Veterans Administration Medical Center; La Jolla, California. Google Scholar17. ZANZITHOMPSONCOHN IKS. A two year study of the effects of calcitonin on skeletal mass in osteoporosis. Medical Research Center, Brookhaven National Laboratory; Upton, New York, New York. Google Scholar18. DREZNERLYLESHARRELSON MKJ. Vitamin D—resistant osteomalacias: evaluation of vitamin D metabolisms and response to therapy. Duke University Medical Center; Durham, North Carolina. Google Scholar19. SHIKESTURTRIDGEHARRISON MWJ. Osteopenia associated with hypercalcemia and hypercalciuria induced by total parenteral nutrition: the role of vitamin D. Departments of Medicine and Pathology, University of Toronto; Toronto, Canada. Google Scholar20. KLEINHORSTNORMANAMENTCOBURN GRAMJ. Reduced plasma 1,25 (OH)2—vitamin D levels during long-term total parenteral nutrition: a possible cause of metabolic bone disease. University of California Riverside and National Animal Disease Center; Los Angeles, California. Google Scholar21. HODSMANWONGSHERRARD AED. Use of 24,25-dihydroxyvitamin D3 in dialysis osteomalacia: preliminary results. Veterans Administration Wadsworth Hospital; Los Angeles, California. Google Scholar22. SCHOLZPURNELL DD. Prospective study: asymptomatic and uncomplicated primary hyperparathyroidism. Mayo Clinic and Mayo Foundation; Rochester, Minnesota. Google Scholar This content is PDF only. To continue reading please click on the PDF icon. Author, Article, and Disclosure InformationAffiliations: Division of Bone and Mineral Metabolism Henry Ford Hospital Detroit, Michigan PreviousarticleNextarticle Advertisement FiguresReferencesRelatedDetails Metrics Cited ByRenale Osteopathie: Pathogenese und Möglichkeiten der TherapieCorrection: "Symposium" Article on Calcium-Regulating HormonesGORDON L. KLEIN, M.D., RONALD L. HORST, PH.D., ANTHONY W. NORMAN, PH.D., MARVIN E. AMENT, M.D., JACK W. COBURN, M.D.The influence of infusion rate on the acute intravenous toxicity of phytic acid, a calcium-binding agent 1 December 1980Volume 93, Issue 6Page: 928-930KeywordsBioengineeringBone and mineral metabolismClinical trialsHormonesMolecular biologyParathyroidParathyroid hormoneResearch laboratoriesSkeleton Issue Published: 1 December 1980 PDF DownloadLoading ...