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At least 307 records · Page 17Linked to original sources
PubMed1988

[The measurement of parathyroid hormone in sera of hemodialysis patients with renal insufficiency by employing the various kinds of parathyroid hormone kits].

This study focussed on elucidating difference of blood PTH levels, by employing the various kinds of PTH kits. We carried out the measurements of PTH levels in sera of the hemodialysis patients with renal insufficiency presumably inactivated PTH degradative regulation in kidney. Our results showed the remarkable significant relationships among blood PTH levels of carboxyl and mid-region PTH and intact PTH in hemodialysis patients and was deduced that the difference of PTH levels by using various kinds of PTH kits was responsible of PTH cleavage effect in the kidney.

Adult↗
PubMed1999

Hyperphosphatemia accelerates parathyroid cell proliferation and parathyroid hormone secretion in severe secondary parathyroid hyperplasia.

We studied the role of phosphorus retention in parathyroid cell proliferation and parathyroid hormone (PTH) oversecretion in severe secondary parathyroid hyperplasia. Mice transplanted with human parathyroid tissue from a patient who had undergone parathyroidectomy for severe secondary hyperparathyroidism were divided into four groups; each group was given a diet with a different phosphorus content (0.4, 0.7, 1.0, and 1.2%) to alter serum phosphorus concentrations. Histologic examinations of grafts by hematoxylin-eosin or by bromodeoxyuridine (BrdU) immunohistochemical staining were performed to assess parathyroid cell proliferation. Changes in serum phosphorus concentrations unidirectionally affected PTH secretion from the graft, because human PTH did not cross-react with mouse PTH. Serum phosphorus concentrations of 1.0P and 1.2P groups were significantly higher than those of 0.4P and 0.7P groups (p<0.05). Serum phosphorus concentrations were significantly correlated with the gradient of human PTH elevation with a coefficient of 0.48 and a p<0.05. Furthermore, serum phosphorus concentrations and the gradient of human PTH elevation were significantly higher in mice with BrdU-immunoreactive cells in the parathyroid graft than in mice without immunoreactive cells in the graft. These results indicate that uncontrolled hyperphosphatemia may accelerate the proliferation of parathyroid cells, exacerbating PTH oversecretion.

Animals↗
PubMed1975

Selective proteolysis of the receptor for parathyroid hormone in skeletal tissue.

Parathyroid hormone, calcitonin, and prostaglandin E2 activate the adenylate cyclase-cyclic AMP system in fetal-rat calvaria. These agents presumably interact with the tissue at separate receptor sites. When calvaria were preincubated with trypsin, 500 mug/ml for 45 min, the subsequent increase in 3',5'-AMP in response to parathyroid hormone was markedly diminished, whereas the response to calcitonin and prostaglandin E2 were not altered significantly. The effect was attributable to an action of the enzyme on the tissue and not to hydrolysis of the hormone. Similarily, preincubation of calvaria with trypsin prior to homogenization and preparation of a crude plasma membrane fraction decreased PTH-sensitive adenylate-cyclase activity by 58% but did not alter the degree of stimulation of the enzyme in response to calcitonin, prostaglandin E2, or sodium fluoride. These studies support the hypothesis that the actions of parathyroid hormone and calcitonin on bone are mediated through distinct receptor sites, and the receptors for parathyroid hormone can be altered selectively with trypsin.

Adenylyl Cyclases↗
PubMed1983

Aspiration of enlarged parathyroid glands for parathyroid hormone assay.

Enlarged parathyroid glands were percutaneously aspirated under computed tomographic (CT) control in 7 patients, and levels of parathyroid hormone (PTH) and human thyroglobulin (HTg) were measured. All 7 patients had high levels of PTH in at least 1 specimen. It is concluded that the measurement of high concentrations of PTH in the aspirate from a cervical or mediastinal mass, with CT documentation of needle position, provides absolute localization of parathyroid masses.

Adenoma↗
PubMed1995

Proparathyroid hormone is preferentially cleaved to parathyroid hormone by the prohormone convertase furin. A mass spectrometric study.

Parathyroid hormone (PTH), an 84-amino acid peptide, is the major regulator of blood calcium homeostasis. Its mRNA, in addition to encoding the mature peptide, also encodes a "pre" sequence of 25 amino acids and a basic "pro" hexapeptide. To assess which of the subtilisin-like prohormone convertases can process proPTH to PTH we coinfected cells with a vaccinia virus construct expressing human preproPTH and vaccinia virus constructs expressing furin, PC1 or PC2. BSC-40 cells, having a constitutive secretory pathway, and GH4C1 cells, having a regulated secretory pathway, were used. PTH biosynthetic products in cell extracts and media were purified by high performance liquid chromatography, identified by radioimmunoassay, and unambiguously defined as either proPTH or PTH by ion-spray mass spectrometry. In both cell types, furin was the most effective in processing proPTH to PTH. In all cases only PTH was released into the medium. In addition, partially purified furin and PC1 were tested for their ability to appropriately cleave a tridecapeptide spanning the prohormone cleavage site found in proPTH. Here too furin was much more effective at cleaving at the correct site. Northern blot analysis and in situ hybridization showed that furin and preproPTH mRNA are co-expressed in the parathyroid, whereas PC1, PC2, and PC5 are not and PACE4 is expressed only at very low levels. Taken together these studies strongly suggest that furin is the enzyme responsible for the physiological processing of proPTH to PTH.

Amino Acid Sequence↗
PubMed1975

[Parathyroid response to EDTA: effect of the immune heterogeneity of the parathyroid hormone].

The parathyroid response to EDTA infusion was measured in 23 patients with hypo- or hyperparathyroidism using two different antisera, one predominantly anti COOH-terminal (GP 62) and the other predominantly anti NH2-terminal (WC), and was compared with the responses observed in 16 controls for GP 62 and 18 controls for WC. In primary hyperparathyroidism elevated basal PTH values were found more frequently with GP 62 (6 of 10 cases) than with WC (3 of 9 cases). However, WC more frequently exhibited exaggerated responses to EDTA (8 of 9 cases) than GP 62 (7 of 10 cases). In hypoparathyroidism the basal values were not distinguishable from the normals. However, the EDTA test showed absent or low responses in 10 of 11 cases studied with GP 62. Antiserum WC showed normal responses in 4 cases with postoperative hypoparathyroidism, revealing some residual PTH secretion but not response in the 2 cases with idiopathic hypoparathyroidism. Since one of them had a normal response when measured with GP 62, secretion of an immunologically abnormal PTH may be suspected. In chronic renal failure normal responses can be observed despite an abnormal basal PTH level, since it is falsely elevated by the accumulation of COOH-terminal fragments.

Acids↗
PubMed1977

Beta-adrenergic stimulation of cyclic AMP content and parathyroid hormone release from isolated bovine parathyroid cells.

The effects of beta-adrenergic agonists and antagonists on cyclic AMP (cAMP) accumulation and parathyroid hormone (PTH) release from isolated bovine parathyroid cells have been determined. Beta-adrenergic agonists markedly stimulate cAMP production and PTH release with an order of potency (-) isoproterenol greater than (-)epinephrine greater than greater than (-) norepinephrine, suggesting a beta2-type adrenergically mediated process. Both effects are blocked by the beta-blocker propranolol with the strict stereospecificity expected for a beta-adrenergic response. Low calcium concentrations also stimulate cAMP accumulation, but the cyclic nucleotide response under these conditions is only 3% of that obtained with isoproterenol, raising the possibility that factors other than cAMP may control low calcium-mediated PTH release. The release of PTH by low calcium is also not blocked by propranolol, confirming the independence of the response to low ambient calcium from the beta-adrenergic receptor. These studies substantiate further the utility of the isolated parathyroid cell preparation for studying secretagogue-mediated alterations in cyclic nucleotides and hormone secretion. Isolated cells also also make feasible the direct identification of beta-adrenergic receptors in parathyroid cell membranes and whole cells.

Adrenergic beta-Agonists↗
PubMed2001

The evolution of assays for parathyroid hormone.

Recent progress in the assay of parathyroid hormone has revealed that commercially available assays for intact parathyroid hormone also measure additional parathyroid hormone peptides that appear to be truncated at the amino-terminal region and have the elution position on high-performance liquid chromatography of parathyroid hormone 7-84. Specific assays have been developed that measure only the true or 'whole', 84-amino-acid peptide. Such 'whole' parathyroid hormone assays have led to the discovery of new findings that suggest that parathyroid hormone fragments such as parathyroid hormone 7-84, which have hitherto been considered to be biologically inactive, may actually have biologic effects. These data, coupled with the emerging discovery of additional receptors for parathyroid hormone peptides, suggest that parathyroid hormone fragments might have potentially important actions, at least in the setting of renal failure.

Animals↗
PubMed1986

Parathyroid cell surface autoantibodies that inhibit parathyroid hormone secretion from dispersed human parathyroid cells.

Serum autoantibodies directed toward antigenic determinants on the surface of human parathyroid cells (PTAb-CS) have been demonstrated in a subset (8 of 23) of adult patients with idiopathic hypoparathyroidism (IHP). In sera from 3 of 8 patients with PTAb-CS, binding of these autoantibodies to their respective parathyroid cell surface antigen(s) resulted in marked inhibition of parathyroid hormone (PTH) secretion in an in vitro dispersed human parathyroid cell (dPTC) system. In 1 subject evaluated longitudinally, circulating levels of PTAb-CS, and the magnitude of the inhibitory effect on PTH secretion, temporally correlated with the clinical course of the hypoparathyroidism. These findings suggest a causative role for antibodies directed against cell surface antigens in parathyroid dysfunction in some cases of "autoimmune" hypoparathyroidism.

Aged↗
PubMed1992

[Parathyroid hormone and calcitonin].

Parathyroid hormone (PTH) is essential for the physiologic maintenance of mineral homeostasis. PTH regulates the mineral transport in bone and kidney and through its secondary actions on mineral transport in intestine (mediated by 1.25 (OH)2D). Calcitonin, in many ways, acts as a physiologic antagonist to PTH. Recently the techniques of molecular biology have been applied to the study of these hormones and more precise mechanism of action of these hormones has been elucidated. Last year both PTH receptor and calcitonin receptor were cloned. This review briefly summarizes new informations about their biosynthesis, secretion, metabolism, action, and structures of their receptors.

Amino Acid Sequence↗
PubMed1984

Forskolin increases cellular cyclic adenosine monophosphate content and parathyroid hormone release in dispersed bovine parathyroid cells.

We studied the effects of the positive-inotropic and hypotensive agent forskolin on parathyroid hormone (PTH) release, cAMP accumulation, and adenylate cyclase activity in dispersed bovine parathyroid cells. Forskolin stimulated PTH release 1.7 to 3.7-fold at 10(-5) mol/L and increased cAMP content maximally 37.6-fold at 10(-4) mol/L. Forskolin induced a maximal increase in cAMP accumulation by 5 minutes of incubation. The rate of PTH release in forskolin-treated cells also reached maximal levels at five to ten minutes of incubation. There was a dose-dependent increase in PTH release and cAMP content over the range of 10(-7) to 10(-4) M forskolin with half-maximal stimulation at 10(-7) to 10(-6) mol/L for PTH release and between 10(-5) and 10(-4) mol/L for cAMP content. PTH release and cAMP accumulation were inhibited by increasing extracellular calcium concentrations in both control cells and those incubated with 10(-5) mol/L forskolin. Forskolin stimulated adenylate cyclase activity in lysates from parathyroid cells 15.7-fold with half-maximal activation between 10(-6) and 10(-5) mol/L forskolin. Forskolin-stimulated (10(-5) mol/L) and basal adenylate cyclase activities declined in parallel with increasing calcium concentrations. In contrast, phosphodiesterase activity was unaffected by forskolin at 10(-6) to 10(-4) mol/L. Forskolin, therefore, by directly activating adenylate cyclase, enhances cAMP accumulation and PTH release in dispersed bovine parathyroid cells. As with other agents activating cAMP accumulation in this system, these effects are inhibited by elevated calcium concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1980

Lack of a direct effect of 1,25-dihydroxycholecalciferol on parathyroid hormone secretion by normal bovine parathyroid glands.

Because of differing reports of an effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on parathyroid hormone (PTH) secretion, the present studies were performed in vitro using bovine parathyroid gland slices and isolated parathyroid cells. Both COOH-terminal and NH2-terminal RIAs for PTH were employed. No effect of 1,25(OH)2D3 on PTH secretion was found during a 4-h incubation of parathyroid slices in variable external calcium concentrations. The results from dual RIA measurements also showed no effect of 1,25(OH)2D3 on PTH secretion by isolated parathyroid cells during 90- to 150-min incubations with variable calcium concentrations. In addition, extensive analysis by polyacrylamide gel electrophoresis showed no effect of 1,25(OH)2D3 on cAMP generation. Whereas calcium inhibited and isoproterenol stimulated the production of cAMP, 1,25(OH)2D3 had no effect. We conclude that 1,25(OH)2D3 does not affect parathyroid gland function acutely in vitro.

Animals↗
PubMed1994

Parathyroid hormone analogues inhibit calcium mobilization in cultured vascular cells.

Parathyroid hormone and parathyroid hormone-related protein lower blood pressure and relax contracted arteries. Parathyroid hormone also attenuates angiotensin II-induced vasoconstriction. To determine the cellular mechanism or mechanisms by which parathyroid hormone analogues antagonize pressor effects, we examined the effect of these peptides on angiotensin II-induced calcium mobilization in fura 2-AM-loaded cultured rat vascular smooth muscle cells. Either 100 nmol/L parathyroid hormone or parathyroid hormone-related protein significantly reduced the amount of calcium mobilized by 100 nmol/L angiotensin II. The attenuating effect of these peptides was mimicked by 10 mmol/L forskolin and 10 mmol/L isobutylmethylxanthine and was not dependent on the presence of extracellular calcium. This effect of the parathyroid hormone analogues was reduced when cells were pretreated with 100 mmol/L 2',5'-dideoxyadenosine, an adenylate cyclase inhibitor. Combined inhibition of cyclic nucleotide-dependent protein kinases eliminated the inhibitory effect of parathyroid hormone, whereas protein kinase C inhibition had no effect. Parathyroid hormone analogues decreased the amount of calcium released by inositol 1,4,5-trisphosphate in digitonin-permeabilized vascular smooth muscle cells. This effect was inhibited by treatment with 2',5'-dideoxyadenosine. These results suggest that these peptides attenuate inositol 1,4,5-trisphosphate-sensitive calcium mobilized by angiotensin II via an adenylate cyclase-dependent mechanism. This may be a mechanism by which acute administration of parathyroid hormone or parathyroid hormone-related peptide antagonizes vasoconstriction.

Animals↗
PubMed1996

Anomalous effects of hormone fragments on the measurement of parathyroid hormone by radioimmunoassay.

One of the basic assumptions underlying the use of radioimmunoassay and other competitive protein-binding assays is the homogeneity of the antigen or ligand. This assumption is not valid for the measurement of parathormone (PTH) because of the presence of fragments. Hence, there is a potential for errors and high variability in the measurement of parathyroid hormone (PTH) by radioimmunoassay. Even though region-specific radioimmunological and immunoradiometric assays for PTH measurement can overcome some of the difficulties caused by the presence of hormone fragments, the possibility for serious measurement errors still remains. We therefore examined experimentally and by modeling the impact of fragments on the estimation of the concentration of a highly purified intact bovine parathyroid hormone by radioimmunoassay. Our experimental results show that the mere presence of fragments can lead to a significant underestimation or overestimation of the amount of the intact hormone. The results have been simulated by a model in which fragments bind to the antibodies, thus competing with the intact hormone, and to the intact hormone as well, thereby reducing the amount of free intact hormone in competition with the radioligand. This work indicates that it may be preferable to consider alternative methods, other than competitive protein-binding assays, for the measurement of secreted PTH.

Animals↗
PubMed1975

Effects of parathyroid hormone on renal function.

Parathyroid hormone has been recognized as an important factor in the regulation of renal function since the 1920s. Early investigations mainly characterized the role of the hormone in calcium and phosphorus metabolism. Subsequently, significant contributions have been made to the understanding of the influence of parathyroid hormone on acid-base balance and amino acid excretion. The following is a review of the effects of parathyroid hormone in the regulation of renal function with special emphasis on new developments.

Acid-Base Equilibrium↗
PubMed1988

Relationship between external and cytoplasmic calcium concentrations, parathyroid hormone release and weight of parathyroid glands in human hyperparathyroidism.

Parathyroid hormone (PTH) release and cytoplasmic calcium concentrations were investigated at ambient calcium concentrations of 0.5-3.0 mmol/l in dispersed parathyroid cells from 44 hypercalcaemic patients with primary or uraemic hyperparathyroidism (HPT). In comparison with parathyroid cells from adult cattle, release of PTH by human preparations was reduced and values of the ambient calcium concentration causing half-maximal inhibition of PTH release (median effective dose, ED50) were significantly increased. Half-maximal inhibition of PTH release was obtained with concentrations of cytoplasmic calcium almost identical to the concentrations of ionized calcium in the plasma of the individual patients. Cytoplasmic concentrations of calcium in the parathyroid cells were inversely related to release of PTH. Concentrations of cytoplasmic calcium were significantly lower in human than in bovine cells and the ED50 for ambient calcium increase on cytoplasmic calcium was raised to the same extent as the ED50 for ambient calcium inhibition of PTH release in human compared with bovine cells. The magnitude of the increased ED50 for ambient calcium inhibition of PTH release and increase of cytoplasmic calcium concentration was similar in adenomas and sporadic as well as hereditary primary hyperplasias, but the secretion was the least aberrant in uraemic hyperplasias, although they had by far the largest glandular mass. Serum concentrations of total calcium before surgery correlated with the ED50 for ambient calcium effects of PTH release and cytoplasmic calcium, but not with glandular weight. These findings demonstrate a universally abnormal regulation of cytoplasmic calcium in HPT and its importance for PTH release, and that disturbance of cytoplasmic calcium rather than the increased glandular mass contributes to the hypercalcaemia in adenomatous and hyperplastic HPT.

Calcium↗
PubMed1983

Influence of age, strain and season on diurnal periodicity of thyroid stimulating hormone, thyroxine, triiodothyronine and parathyroid hormone in the serum of male laboratory rats.

The influence of age, strain and season on the diurnal pattern of serum hormone levels from the pituitary-thyro-parathyroid complex was studied in male laboratory rats. Distinct 24 h periodicity in the serum levels of thyroid stimulating hormone (TSH) and triiodothyronine (T3) was observed in all groups of rats. There was no influence of age (40, 60 and 90 days old Sprague-Dawley rats), but a significant influence of strain (Sprague-Dawley vs. BH/Ztm rats) and season (summer vs. winter) on the diurnal pattern of serum TSH and T3 levels. Significant 24 h periodicity in serum thyroxine (T4) levels existed during winter in BH/Ztm rats, but not in Sprague-Dawley (SD) rats of any age. Adult SD rats demonstrated 24 h periodicity in serum levels of T4 only in summer. No diurnal periodicity in serum levels of parathyroid hormone (PTH) was observed in any group of rats. There were significant changes in 24 h mean serum levels of TSH and T3 throughout pubertal development. Twenty-four h mean serum levels of T3 and T4 were significantly higher in summer than in winter. Twenty-four h mean serum levels of T4 were significantly lower in BH/Ztm rats than in SD rats. Significant correlation was observed between serum concentrations of T3 and T4, TSH and T4, and between TSH and T3 in some groups of rats, but not in all. The results indicate that 24 h periodicity of serum hormone levels from the pituitary-thyroid complex of male laboratory rats may vary with age and strain of the animals and with the season of experiment performance.

Age Factors↗