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PubMed1981

Influence of parathyroid hormone on bone cell ultrastructure.

A study in rats demonstrated that morphologic changes in the bone osteocytes and osteoblasts are produced following parathyroid hormone (PTH) injection into thyroparathyroidectomized animals. It further showed that similar changes occur in normal rats as the result of of extended fasting. Plasma calcium concentrations were determined at sacrifice to ascertain that these changes in bone occurred at times when plasma calcium is rising as the result of parathyroid hormone stimulation. Tibias from these animals were removed and prepared for morphologic observation using both transmission (TEM) and scanning (SEM) electron microscopy. Specific structural features characterized bone cells stimulated by exogenous or endogenous PTH. The most significant morphologic alterations involved surface microvilli and blebs as determined by SEM. TEM studies showed alterations in the cisternae of the rough endoplasmic reticulum (RER). Additionally, cell shape varied markedly from the control cuboidal morphology. These morphologic changes occurred during peak periods of plasma calcium change and returned to control morphology as plasma calcium levels normalized. Use of an extracellular electron-dense tracer (lanthanum) confirmed the patency of the intercellular channels and the presence of a fluid space between the bone cell plasma membranes and the mineralized surface. PTH stimulation modified cell activity such that the tracer material entered the cell more readily, possibly by inducing increased pinocytosis (endocytosis). This study supports the concept that the osteocytes and lining cells on the surface of bone play a role in maintenance of plasma calcium concentrations.

Animals↗
PubMed2005

Growth hormone replacement is important for the restoration of parathyroid hormone sensitivity and improvement in bone metabolism in older adult growth hormone-deficient patients.

Alterations in PTH circadian rhythm and PTH target-organ sensitivity exist in adult GH-deficient (AGHD) patients and may underlie the pathogenesis of AGHD-related osteoporosis. GH replacement (GHR) results in increased bone mineral density, but its benefit in AGHD patients over 60 yr old has been debated. To examine the effect of age on changes in PTH circadian rhythm and target-organ sensitivity after GHR, we recruited 22 AGHD patients (12 were <60 yr of age, and 10 were >60 yr of age). Half-hourly blood samples were collected for PTH, calcium, phosphate, nephrogenous cAMP (marker of renal PTH activity), type-I collagenbeta C-telopeptide (bone resorption marker), and procollagen type-I amino-terminal propeptide (bone formation marker) before and after 1, 3, 6, and 12 months of treatment with GHR. Significant PTH circadian rhythms were present in both age groups throughout the study. After GHR, PTH decreased and nephrogenous cAMP, adjusted calcium, and bone turnover markers increased in both groups, suggesting increased PTH target-organ sensitivity. In younger patients, the changes were significant after 1 month of GHR, but, in older patients, the changes were delayed until 3 months, with maximal changes at 12 months. Older AGHD patients derive benefit from GHR in terms of improvement in PTH sensitivity and bone metabolism. Their response appears delayed and may explain why previous studies have not shown a positive effect of GHR on bone mineral density in older AGHD patients.

Adenoma↗
PubMed1975

Metabolism in immunoreactive parathyroid hormone in the dog. The role of the kidney and the effects of chronic renal disease.

The role of the kidney in the metabolism of parathyroid hormone (PTH) was examined in the dog. Studies were performed in awake normal and uremic dogs after administration of bovine parathyroid hormone (b-PTH) or synthetic amino terminal tetratricontapeptide of b-PTH (syn b-PTH 1-34). The renal clearance of immunoreactive PTH was determined from the product of renal plasma flow and the percent extraction of PTH immunoreactivity by the kidney. Blood levels of circulating immunoreactive PTH were determined by radioimmunoassay. The normal dog kidney extracted 20 plus or minus 1% of the immunoreactive b-PTH delivered to it, and renal clearance (RC) of immunoreactivity was 60 ml/min. When RC was compared to an estimate of total metabolic clearance (MCR) of immunoreactivity, it accounted for 61% of the total. Both MCR and RC were markedly decreased in dogs with chronic renal disease. However, the percent extraction of immunoreactive PTH was unchanged in chronic renal disease, and the observed decrease in RC was due to changes in renal plasma flow. The largest portion of the reduction in total MCR was accounted for by the decrease in RC, and there was no compensation for the decrease in RC by extrarenal sites of PTH metabolism.

Animals↗
PubMed2004

Quick intraoperative parathyroid hormone assay: surgical adjunct to allow limited parathyroidectomy, improve success rate, and predict outcome.

Intraoperative parathyroid hormone (PTH) assay (QPTH) has made possible less invasive operative approaches in the treatment of primary hyperparathyroidism with stated advantages. When compared to the traditional bilateral neck exploration (BNE), only the targeted, hypersecreting gland is excised, leaving in situ non-visualized but normally functioning parathyroids. The QPTH-guided limited parathyroidectomy (LPX) must be able to identify multiglandular disease (MGD), predict a successful outcome, and have a low recurrence rate. In our series, 421 patients who underwent LPX were compared to 340 undergoing BNE; all operative failures and patients followed for 6 months or longer were included. Operative failure occurred if serum calcium and PTH levels were elevated within 6 months of parathyroidectomy. Multiglandular disease was defined in the LPX group as more than one gland excision guided by QPTH or operative failure after removal of a single abnormal gland; in the BNE group it was defined as excision of more than one enlarged gland. Recurrence was defined as elevated calcium and PTH after 6 months of eucalcemia. Operative failure and MGD rates were compared using chi-squared analysis. The method of Kaplan-Meier and the log-rank test were used to compare recurrence rates. Operative success was seen in 97% of LPX patients and in 94% of the BNE group ( p = 0.02). Multiglandular disease was identified in 3% of LPX patients and 10% of BNE patients ( p < 0.001). There was no statistical difference in the overall recurrence rates ( p = 0.23). The QPTH-guided parathyroidectomy identifies MGD and allows an improved success rate with the same low recurrence rate when compared to the results of BNE.

Humans↗
PubMed2003

Intraoperative parathyroid hormone testing: what have we learned?

OBJECTIVES/HYPOTHESIS: The development of rapid, sensitive assays for measuring the intact parathyroid hormone (iPTH) molecule has the potential to allow the surgeon to determine the success of parathyroid surgery intraoperatively. The purpose of the study was to review our results in the context of currently held beliefs regarding the ability of the intraoperative iPTH to predict resolution of hyperparathyroidism. STUDY DESIGN: Retrospective review. METHODS: The study series is a retrospective review of 107 consecutive parathyroidectomies performed by a single surgeon. Patients with primary, secondary, and tertiary hyperparathyroidism were included. RESULTS: The intraoperative assay allowed an overall success rate of 93.4% across all patient categories. The success rate in patients with primary hyperparathyroidism was 95.7%. Measuring the iPTH level at 10 versus 15 minutes after the removal of tissue did not significantly affect the predictive value of the test. A decrease of 50% in the iPTH level after the resection of hyperfunctioning tissue was prognostic of successful treatment of the hyperparathyroid state. By contrast, a postexcision iPTH level that was within the normal range was not always predictive of cure. CONCLUSIONS: The intraoperative iPTH assay is particularly useful in the treatment of primary hyperparathyroidism. The assay eliminates the need for intraoperative frozen-section analysis in most cases and allows the surgeon to perform limited resections with confidence. This is especially true in complicated parathyroid surgeries, such as revision surgeries or those requiring concomitant thyroid surgery. The assay is also useful in secondary hyperparathyroidism, although it appears that the inability to identify small nonfunctional or hypofunctional supernumerary parathyroid glands means that long-term normocalcemia may not be assured.

Adenoma↗
PubMed1996

Ectopic production of intact parathyroid hormone by a squamous cell lung carcinoma in vivo and in vitro.

Ectopic tumoral production of intact parathyroid hormone (PTH) is rare. The PTH-related protein is the common cause of hypercalcemia in most solid tumors, particularly squamous and renal carcinomas. We report the case of a 71-yr-old man with a PTH-producing squamous cell lung carcinoma. Immunocytochemical analysis of the tumor tissue as well as of cultured tumor cells revealed PTH positive staining. Cultured tumor cells released PTH and were calcium sensitive, producing 122 +/- 16 pg/microgram DNA of intact PTH (mean +/- SEM) at 0.5 mmol/L calcium compared with 26 +/- 2 pg/microgram DNA at 3.0 mmol/L calcium. Somatostatin analogues have been used in the treatment of humoral hypercalcemia of malignancy (HHM). However, we found that somatostatin (0.1 microgram/L) in cultured tumor cells increased the release of intact PTH (123 +/- 19 versus 82 +/- 1 pg/microgram DNA, P < 0.05) and thus might have a negative effect on the HHM. This report is the first to describe a true ectopic PTH-producing squamous cell lung carcinoma associated with HHM.

Aged↗
PubMed1995

Calcium-regulated parathyroid hormone secretion in adynamic renal osteodystrophy.

Hypercalcemia and low serum parathyroid hormone (PTH) levels are features of the adynamic lesion (AD) of renal osteodystrophy, but there is little information about parathyroid gland function in this disorder. Therefore, the four parameter model was used to evaluate calcium-regulated PTH release in patients with either adynamic bone or secondary hyperparathyroidism (OF) as documented by bone biopsy and in normal volunteers (NL). Patients had undergone CCPD for 20 +/- 4.2 months, and all received calcium carbonate as the sole phosphate-binding agent. During two hours infusions of sodium citrate, the rate of decline in serum ionized calcium levels did not differ among groups; serum PTH levels rose from 136 +/- 38 to 342 +/- 140 pg/ml in AD and from 691 +/- 99 to 869 +/- 121 pg/ml in OF. Maximum PTH levels were 322 +/- 42% of baseline values in AD but only 146 +/- 9.7% of baseline in OF (P < 0.001), and the increase above baseline levels in AD did not differ from that in NL (300 +/- 25%, NS). During calcium infusions, serum PTH levels fell from 164 +/- 75 to 39 +/- 11 pg/ml in AD and from 622 +/- 76 to 171 +/- 29 pg/ml in OF; minimum serum PTH levels, expressed as a percentage of pre-infusion values, were 25 +/- 2% in AD and 26 +/- 5% in OF (NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium↗
PubMed2002

Structure-function studies of analogues of parathyroid hormone (PTH)-1-34 containing beta-amino acid residues in positions 11-13.

The 1-34 N-terminal fragments of human parathyroid hormone (PTH) and PTH-related protein (PTHrP) elicit the full spectrum of bone-relevant activities characteristic of the intact hormones. The structural elements believed to be required for receptor binding and biological activity are two helical segments, one N-terminal and one C-terminal, connected by hinges or flexible points located around positions 12 and 19. To test this hypothesis, we synthesized and characterized the following analogues of PTH-(1-34), each containing single or double substitutions with beta-amino acid residues around the putative hinge located at position 12: I. [Nle(8,18),beta-Ala(11,12),Nal(23),Tyr(34)]bPTH-(1-34)NH(2); II. [Nle(8,18),beta-Ala(12,13),Nal(23),Tyr(34)]bPTH-(1-34)NH(2); III. [Nle(8,18),beta-Ala(11),Nal(23),Tyr(34)]bPTH-(1-34)NH(2); IV. [Nle(8,18),beta-hLeu(11),Nal(23),Tyr(34)]bPTH-(1-34)NH(2); V. [Nle(8,18),beta-Ala(12), Nal(23),Tyr(34)]bPTH-(1-34)NH(2); VI. [Nle(8,18),beta-Ala(13), Nal(23),Tyr(34)]bPTH-(1-34)NH(2) (beta-hLeu = beta-homo-leucine; beta-Ala = beta-alanine; Nal = L-2-naphthyl-alanine; Nle = norleucine). Analogues I and III exhibit very low binding affinity and are devoid of adenylyl cyclase activity. Analogue II, despite its very low binding capacity is an agonist. Biological activity and binding capacity are partially restored in analogue IV, and completely restored in analogues V and VI. The conformational properties of the analogues were investigated in aqueous solution containing dodecylphosphocholine (DPC) micelles as a membrane-mimetic environment using CD, 2D-NMR, and molecular dynamics calculations. All peptides fold partially into the alpha-helical conformation in the presence of DPC micelles, with a maximum helix content in the range of 30-35%. NMR analysis reveals the presence of two helical segments, one N-terminal and one C-terminal, as a common structural motif in all analogues. Incorporation of beta-Ala dyads at positions 11,12 and 12,13 in analogues I and II, respectively, enhances the conformational disorder in this portion of the sequence but also destabilizes the N-terminal helix. This could be one of the possible reasons for the lack of biological activity in these analogues. The partial recovery of binding affinity and biological activity in analogue IV, compared to the structurally similar analogue III, is clearly the consequence of the reintroduction of Leu side-chain of the native sequence. In the fully active analogues V and VI, the helix stability at the N-terminus is further increased. Taken together, these results stress the functional importance of the conformational stability of the helical activation domain in PTH-(1-34). Contrary to expectation, insertion of a single beta-amino acid residue in positions 11, 12, or 13 in analogues III-VI does not favor a disordered structure in this portion of the sequence.

Amino Acid Sequence↗
PubMed1996

Incidence of multiglandular disease in primary hyperparathyroidism determined by parathyroid hormone secretion.

BACKGROUND: Successful parathyroidectomy depends on recognition and excision of all hyperfunctioning parathyroid glands. Because histologic definition is limited, multiglandular disease (MGD) is usually determined grossly by means of estimation of gland size and the experience of the surgeon, resulting in frequency varying from 8% to 33%. Normalization of elevated intraoperative intact parathyroid hormone (iPTH) levels after excision of all hyperfunctioning glands is necessary for postoperative normocalcemia and indicates normal secretion of remaining parathyroids. Abnormal hormone secretion measured during operation has been used to define the extent of excision and the incidence of MGD. METHODS: One hundred ten consecutive parathyroidectomy patients with no previous neck surgery or history of multiple endocrine neoplasia had intraoperative iPTH assays performed before and after excision of any suspected abnormal parathyroid gland(s). A drop in iPTH level after gland excision predicted postoperative normal calcium levels. RESULTS: All patients except one had normalization of serum calcium levels (average follow-up, 15 months). One hundred five patients had only one hyperfunctioning gland removed, and all have remained normocalcemic. Five (5%) patients had more than one gland involved: four had two or more hyperfunctioning parathyroids and one patient, who had a large parathyroid cyst removed, remained hypercalcemic. CONCLUSIONS: By using a biochemical assay, instead of estimated size, to predict which parathyroid glands are hypersecreting, the incidence of MGD in primary hyperparathyroidism was found to be 5%.

Adolescent↗
PubMed1989

Influence of zinc and calcium deficiency on the concentrations of calcitonin, parathyroid hormone, and 25-hydroxy-vitamin D3 in rat serum.

48 male Sprague-Dawley rats with an average live weight of 141 g were assigned to four groups of 12 animals each. Group I was fed the basal diet (63 mg/kg of Zn, 8.8 g/kg of Ca), group II received a Ca-deficient diet (0.043 g/kg of Ca), group III was fed a Zn-deficient diet (1.1 mg/kg of Zn), and group IV received a diet with a combined Zn- and Ca-deficiency (1.1 mg/kg of Zn; 0.043 g/kg of Ca). Each of the four groups was fed the same daily quantity of rations, which was based on the food uptake of the deficient groups III and IV. After 28 days of the experiment, the rats were anesthesized with ether and sacrificed. In the obtained serum, the concentrations of calcitonin, parathyroid hormone, and 25-hydroxy-vitamin D3 were measured by radioimmune assays. The Zn- and Ca-concentrations in the serum served as parameters for the status of Zn- and Ca-supply. 1. Dietary Ca-deficiency had no influence on the development of live weight of the rats in the case of restricted feeding. Zn-deficiency, however, strongly reduced live weight development. 2. Alimentary Ca-deficiency reduced the Ca-concentration of the serum by 34%, the calcitonin concentration by 17%, and the 25-hydroxy-vitamin D3 concentration by 82% as compared to the levels in control animals, whereas the concentrations of Zn and parathyroid hormone remained unchanged. 3. Alimentary Zn-deficiency reduced the Zn-concentration of the serum by 63% as compared to the control animals, whereas the concentrations of 25-hydroxy-vitamin D3 and parathyroid hormone were increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Structure of human parathyroid hormone(1-34) in the presence of solvents and micelles.

The structure of the N-terminal 34-residue fragment of human parathyroid hormone was determined in 40% trifluoroethanol employing two-dimensional 1H nuclear magnetic resonance spectroscopy. The proton chemical shifts were assigned from magnitude and phase-sensitive COSY, relayed COSY, and NOESY spectra. Distance constraints, estimated from NOESY spectra, were used to create a set of structures by distance geometry (DGEOM) which were subsequently refined by restrained energy minimization and restrained molecular dynamics (CHARMm). The resulting structures contained two helices spanning residues 3-12 and residues 17-26. The NOE constraints for residues 13-16 did not provide a single structural solution; however, their conformations were not disordered. The structures prepared by DGEOM and refined with CHARMm contained either an irregular turn or a helical structure at residues 13-16. The secondary structure of human parathyroid hormone(1-34) was also assessed by circular dichroism in the presence of methanol, trifluoroethanol, and dodecylphosphocholine micelles. Under all three conditions, the peptide formed structures containing various amounts of helical content. The formation of helical secondary structure in the presence of micelles supports the proposal that the trifluoroethanol-induced structure of human parathyroid(1-34) was not an artifact of its environment but perhaps was an indication of the conformation that the molecule adopts when in close proximity to a membrane surface and possibly when bound to the parathyroid receptor.

Amino Acid Sequence↗
PubMed2005

25-hydroxyvitamin D3-1alpha-hydroxylase is expressed in human vascular smooth muscle cells and is upregulated by parathyroid hormone and estrogenic compounds.

BACKGROUND: 1,25(OH)2 vitamin D3 exerts multiple effects in human vascular smooth muscle cells (VSMCs). We therefore tested the possibility that VSMCs possess an endogenous 25-hydroxyvitamin D3-1alpha-hydroxylase system, the final enzyme in the biosynthetic pathway of 1,25(OH)2D3. METHODS AND RESULTS: We assessed the expression and activity of 25-hydroxyvitamin D3-1alpha-hydroxylase by real-time polymerase chain reaction and the conversion of 25(OH)D3 into 1,25(OH)2D3. First, 25-hydroxyvitamin D3-1alpha-hydroxylase mRNA was identified in cultured VSMCs by real-time polymerase chain reaction. Second, in cells treated daily (3 days) with parathyroid hormone (66 nmol/L), estradiol-17beta (30 nmol/L), raloxifene (3 micromol/L), and the phytoestrogens genistein (3 micromol/L), biochainin A (3 micromol/L), and 6-carboxy biochainin A (30 nmol/L), 25-hydroxyvitamin D3-1alpha-hydroxylase mRNA increased by 43+/-13%, (P<0.05) 7+/-24% (P=NS), 176+/-28% (P<0.01), 65+/-11% (P<0.05), 152+/-24% (P<0.01), and 71+/-9% (P<0.05), respectively. Third, production of 1,25(OH)2D3 from 25(OH)D3 was seen with a Km of 25 ng/mL and increased dose dependently after treatment with parathyroid hormone, genistein, and the phytosetrogen derivative 6-carboxy biochainin A. Estradiol-17beta and biochainin A also increased the generation of 1,25(OH)2D3 by 40+/-23% (P<0.05) and 55+/-13% (P<0.05), respectively. CONCLUSIONS: We provide here the first evidence for the expression of an enzymatically active 25(OH)D3-1alpha-hydroxylase system in human VSMCs, which can be upregulated by parathyroid hormone and estrogenic compounds. Because exogenous vitamin D inhibits VSMC proliferation, the role of this system as an autocrine mechanism to curb changes in VSMC proliferation and phenotype is a subject for future investigation.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMedDate not supplied

Effects of L-dopa on plasma levels of parathyroid hormone in calves.

After oral administration of l-dihydroxyphenylalanine (L-dopa) to calves, plasma concentrations of L-dopa, dopamine, norepinephrine and parathyroid hormone increased whereas prolactin and calcium decreased while epinephrine remained unchanged. The decrease of prolactin presumably occurred as a consequence of the conversion of L-dopa to dopamine (in the hypothalamus), whereas the increase in parathyroid hormone was caused by hypocalcemia, by elevated dopamine and possibly by norepinephrine.

Administration, Oral↗
PubMed1996

The N-terminal region of the third intracellular loop of the parathyroid hormone (PTH)/PTH-related peptide receptor is critical for coupling to cAMP and inositol phosphate/Ca2+ signal transduction pathways.

Structural determinants within the parathyroid hormone (PTH)/PTH-related peptide (PTHrP) receptor that mediate G-protein activation of adenylate cyclase and phospholipase C are unknown. We investigated the role of the N-terminal region of the third intracellular loop of the opossum PTH/PTHrP receptor in coupling to two signal transduction pathways. We mutated residues in this region by tandem-alanine scanning and expressed these mutant receptors in COS-7 cells and/or Xenopus oocytes. All mutant receptors retained high affinity PTH binding in COS-7 cells, indistinguishable from wild-type receptors. Receptors with tandem-alanine substitutions in two N-terminal segments (377RVL379 and 381TKLR384) demonstrated impaired adenylate cyclase and phospholipase C activation. Receptor mutants with single-alanine substitutions scanning these two segments showed three different signaling defects in COS-7 cells. 1) Two mutant receptors (V378A and L379A) had reduced inositol phosphate (IP), but normal cAMP responses to PTH. 2) Mutant receptor T381A showed reduced cAMP, but wild-type IP responses to PTH. 3) Mutant receptor K382A demonstrated both markedly reduced cAMP and IP production due to PTH. In oocytes, mutants T381A and K382A showed decreased PTH-stimulated cAMP accumulation and intracellular Ca2+ mobilization. Thus, the N-terminal region of the third intracellular loop of this receptor plays a critical role in coupling to both Gs- and Gq-mediated second-messenger generation.

Animals↗
PubMed1981

Effect of secretin on parathyroid hormone and calcitonin secretion.

The effect of secretin on secretion of parathyroid hormone (PTH) and calcitonin (CT) was evaluated by both in vitro and in vivo techniques. In in vitro studies with bovine parathyroid tissue, Secretin-Boots caused significant dose-related increases in PTH secretion. In in vitro studies with rat thyroparathyroid tissue, Secretin-Boots caused significant increases in both PTH and CT secretion. Infusion of Secretin-Boots or of synthetic secretin in biologically equivalent doses into rats caused similar increases in secretion of PTH and of CT. Infusion of multiple doses of synthetic secretin revealed a dose-related stimulation of both PTH and CT secretion. Infusion of Secretin-Boots into normal human subjects caused prompt and progressive significant increases in secretion of both PTH and CT, with return to baseline values within 90 min after termination of the infusion. These data suggest that secretin can stimulate hormonal secretion by parathyroid and thyroid C cells and that secretin may play a modulating role in the secretion of both PTH and CT.

Adult↗
PubMed2002

Parathyroid hormone: what are we measuring and does it matter?

Immunometric assays claiming to determine intact parathyroid hormone (PTH) generally cross-react with N-truncated forms such as PTH(7-84). Laboratories need to examine the relevance of new assays with probable PTH(1-84) specificity. It is logical that assays should measure what they state they do. However, it seems unlikely that use of older 'intact' PTH assays will affect the clinical interpretation of results in primary hyperparathyroidism or vitamin D deficiency. It is plausible that appropriate application of new PTH assays could improve outcome in chronic renal failure. However, it has never been suggested that straightforward replacement of existing assays with new PTH(1-84) assays will lead to this improved outcome. A better understanding of PTH fragments and their interaction with PTH receptors may shed light on the relevance of different PTH assays. In the meantime, older technologies will continue to work well for the vast majority of patients.

Humans↗
PubMed1990

Parathyroid adenoma with conflicting parathyroid hormone levels.

For discrepant diagnoses in a patient with hypercalcemia, the authors utilized three different parathyroid hormone assays. The new two-site immunoradiometric assay (IRMA) proved to be the most accurate and is recommended in the differential diagnosis of hypercalcemia.

Adenoma↗
PubMed1972

Calcium-regulated parathyroid hormone peptidase.

An enzymatic activity that catalyzes the conversion of glandular parathyroid hormone to a smaller-molecular-weight, biologically and immunologically active form of this hormone has been extracted from normal parathyroid and other porcine tissues. The product of the conversion has the immunologic characteristics of the hormone that occurs in peripheral serum and in tissue culture medium from parathyroid explants. The enzyme is activated by chelating agents and is inhibited by high calcium concentrations, suggesting that this enzyme may be important in the regulation of secretion or metabolism of the hormone.

Animals↗