Secretion of parathyroid hormone by abnormal human parathyroid glands in vitro

Radiation survival curves for Lewis lung tumours in the lungs ranging in size from 0-5 to 20 mm3 have been obtained, and a size-dependent variation in hypoxic fraction was found. Cell-survival studies following treatment of various sizes of s.c. tumours indicated that the effects of 60Co gamma-rays and the chemotherapeutic agents 1,3-bas(2-chloroethyl)-1-nitrosourea (BCNU) and cyclophosphamide are all size-dependent. Large pulmonary nodules which had regressed but had not been cured by cyclophosphamide regrew with a radiosensitivity that was characteristic of previously untreated tumours. The results give additional experimental support to the clinical interest in early adjuvant therapy of micrometastases, and sequential combined modality therapy for larger tumours.     

In vitro parathyroid hormone release in patients with secondary hyperparathyroidism

BACKGROUND: The purpose of this study was to determine the precise endocrine characteristics of parathyroid function in secondary hyperparathyroidism (sHPT). METHODS: We examined the effects of extracellular ionized calcium (Ca2+) varying from 0.5 to 2.0 mM on parathyroid hormone (PTH) release in parathyroid cell suspensions using a mid-regional PTH assay. Cells were obtained from 26 patients with sHPT who were divided into two groups according to the type of hyperplasia they exhibited, either nodular (n = 16) or diffuse (n = 10). For comparison, we also analyzed data from nine patients with primary hyperparathyroidism (pHPT; adenomas). RESULTS: Significant in vitro suppression of PTH release by Ca2+ was observed in the majority of subjects, regardless of the histologic abnormality. The pHPT group exhibited no significant relationship between clinical and in vitro data. In contrast, in the sHPT group (taken as a whole), suppression of PTH release by Ca2+ exhibited a plateau at a total serum calcium concentration of 2.5 mmol/L, and a parathyroid gland weight of 2 g. CONCLUSIONS: These findings suggest that there is a curvilinear relationship in sHPT, but not pHPT, between the in vitro calcium sensitivity of parathyroid cells and total serum calcium, as well as gland weight. The in vitro calcium sensitivity in sHPT remains constant when the total serum calcium concentration exceeds 2.5 mmol/L, or when the gland weight exceeds 2 g.     

High phosphate level directly stimulates parathyroid hormone secretion and synthesis by human parathyroid tissue in vitro

Phosphate retention plays an important role in the pathogenesis of secondary hyperparathyroidism in patients with renal failure. In in vitro studies, high extracellular phosphate levels directly stimulate PTH secretion in rat and bovine parathyroid tissue. The present study evaluates the effect of high phosphate levels on the secretion of PTH and the production of prepro PTH mRNA in human hyperplastic parathyroid glands. The study includes parathyroid glands obtained from patients with primary adenomas and from hemodialysis and kidney-transplant patients with diffuse and nodular secondary hyperplasia. The experiments were performed in vitro using small pieces of parathyroid tissue. The ability of high calcium levels to decrease PTH secretion was less in adenomas than in secondary hyperplasia; among the secondary hyperplasia, nodular was less responsive to an increase in calcium than diffuse hyperplasia. In diffuse hyperplasia, PTH secretion was increased in response to 3 and 4 mM phosphate compared with 2 mM phosphate, despite a high calcium concentration in the medium; prepro PTH mRNA levels increased after incubation in 4 mM phosphate. Similar results were obtained with nodular hyperplasia, except that the elevation of PTH secretion in response to 3 mM phosphate did not attain statistical significance. In adenomas, high calcium concentrations (1.5 mM) did not result in inhibition of PTH secretion, independent of the phosphate concentration, and the prepro PTH mRNA was not significantly increased by high phosphate levels. In conclusion, first, the PTH secretory response to an increase in calcium concentration is less in nodular than diffuse hyperplasia; second, high phosphate levels directly affect PTH secretion and gene expression in patients with advanced secondary hyperparathyroidism.     

Dopaminergic actions of parathyroid hormone in the rat medial basal hypothalamus in vitro

Parathyroid hormone (PTH) modulates dopamine (DA) metabolism in the rat medial basal hypothalamus (MBH) in vivo. Direct effects of PTH on MBH DA metabolism were therefore investigated in vitro. Incubation of rat MBHs for 60 min with 10(-7)-10(-5) M human PTH1-34 consistently reduced the tissue DA content and increased the DOPAC (dihydroxyphenylacetic acid) to DA ratio. This ratio was further increased in tissues incubated in 10(-5) M PTH1-34, as a result of an increase in DOPAC content. The tissue content of DOPAC and DA was unaffected by 10(-9) M PTH. The serotonin (5HT) content of the MBH was reduced by 10(-5) M PTH1-34, but concentrations of 5HT, 5-hydroxyindolacetic acid, and norepinephrine were otherwise unaffected by 10(-9)-10(-5) M PTH1-34. Concentrations of DA in the incubation media were reduced after exposure to 10(-6) or 10(-5) M PTH1-34. The uptake of 3H-labelled DA by incubated tissues was also reduced by 10(-6) M PTH1-34, as was the metabolism of 3H-labelled DA into tissue and media DOPAC. Monoamine oxidase (MAO) activities A and B were significantly increased after the incubation of the MBH with 10(-6) or 10(-5) M PTH1-34. These results further demonstrate neuromodulatory actions of PTH on dopaminergic neurons within the rat MBH in vitro, and suggest neural and/or neuroendocrine roles of PTH of central or peripheral origin.     

In vivo parathyroid hormone stimulates in vitro bone resorption by bovine monocytes

Cells of the monocyte-macrophage lineage have been thought to play a role in bone resorption. We examined the effects of in vivo administration of parathyroid hormone and 1,25-dihydroxyvitamin D3 on the ability of monocytes to degrade bone in vitro. Administration of parathyroid hormone for 4 d resulted in sustained hypercalcemia and a transient 1-d increase in plasma 1,25-dihydroxyvitamin D3. Parathyroid hormone significantly stimulated bone degradation by monocytes 2.6 times more than that of pretreatment controls. Parathyroid hormone treatment significantly enhanced (threefold) release of superoxide anion by monocytes stimulated with phorbol 12-myristate 13-acetate and increased migration of monocytes to bone particles in vitro. Continuous 7-d infusion of 1,25-dihydroxyvitamin D3 (50 micrograms/d) elevated plasma 1,25-dihydroxyvitamin D3 until infusions were discontinued. Increased 1,25-dihydroxyvitamin D3 was associated with hypercalcemia, which continued for several days postinfusion. In vivo administration of 1,25-dihydroxyvitamin D3 did not affect in vitro ability of monocytes to degrade bone. We concluded that in vivo administration of parathyroid hormone enhanced in vitro responsiveness of isolated monocytes in a manner consistent with a role for monocytes in bone remodeling. Furthermore, these data suggested that circulating monocytes could be a useful experimental model for further studies on parathyroid hormone responsiveness and bone resorption for the cow with milk fever.     

In vitro cleavage of internally quenched fluorogenic human proparathyroid hormone and proparathyroid-related peptide substrates by furin. Generation of a potent inhibitor

The cleavage of parathyroid hormone (PTH) from its precursor proparathyroid hormone (pro-PTH) is accomplished efficiently by the proprotein convertase furin (Hendy, G. N., Bennett, H. P. J., Gibbs, B. F., Lazure, C., Day, R., and Seidah, N. G. (1995) J. Biol. Chem. 270, 9517-9525). We also showed that a synthetic peptide comprising the -6 to +7 sequence of human pro-PTH is appropriately cleaved by purified furin in vitro. The human pro-PTH processing site Lys-Ser-Val-Lys-Lys-Arg differs from the consensus furin site Arg-Xaa-(Lys/Arg)-Arg that is represented by Arg-Arg-Leu-Lys-Arg in the cleavage site of pro-PTH-related peptide (pro-PTHrP). An earlier study demonstrated that an internally quenched fluorogenic substrate bearing an O-aminobenzoyl fluorescent donor at the NH2 terminus and an acceptor 3-nitrotyrosine near the COOH terminus was appropriately cleaved by the convertases furin and PC1 (Jean, F., Basak, A., DiMaio, J., Seidah, N. G., and Lazure, C. (1995) Biochem. J. 307, 689-695). Here, we have synthesized a series of internally quenched fluorogenic substrates based upon the pro-PTH and pro-PTHrP sequences to determine which residues are important for furin cleavage. Purified recombinant furin and PC1 cleaved the human pro-PTH internally quenched substrate at the appropriate site in an identical manner to that observed with the nonfluorescent peptide. Several substitutions in the P6-P3 sequence were well tolerated; however, replacement of the Lys at the P6 position with Gly and replacement of the P3 Lys by an acidic residue led to markedly compromised cleavage by furin. Furin activity was very sensitive to substitution in P' positions. Replacement of Ser at P1' with Gly and Val at P2' with Ala generated substrates that were less well cleaved. Substitution at the P1' position of Val for Ser in conjunction with Ala for Val at P2', as well as a single substitution of Lys for Val at P2', generated specific inhibitors of furin cleavage. The findings of this study open the way to the rational design of inhibitors of furin with therapeutic potential.     

Family studies in patients with primary parathyroid hyperplasia

The relatives of 25 index patients with primary parathyroid hyperplasia were tested for hypercalcemia. At least 13 of these patients had one or more first degree relatives with hypercalcemia. Two familial syndromes each with autosomal dominant transmission were recognized. Two index patients were part of large kindreds categorized as having familial hypocalciuric hypercalcemia (FHH). Manifestations of multiple endocrine neoplasia type I were present in the kindreds of at least four other index patients (FMEN I). In seven other kindreds there were too few affected members to allow definitive classification. Differences between manifestations of FHH and FMEN I were described. Among offspring of affected persons in kindreds with FHH, as distinct from FMEN I, the prevalence of hypercalcemia approached the theoretic maximum of 50 per cent during the first two decades. In FHH, nephrolithiasis and peptic disease were unusual; moderate hypercalcemia occurred without hypercalciuria; and subtotal parathyroidectomy did not abolish hypercalcemia. Concentrations of peptide hormones other than parathyroid hormone (PTH) were normal in those with FHH; in FMEN I high concentrations of glucagon in plasma were found in five of six patients tested, and high concentrations of gastrin were found in three of 12 patients. Hypergastrinemia generally accompanied obvious peptic disease. Distinction of the two conditions is important since patients with FHH may not benefit from subtotal parathyroidectomy, but they generally have a better clinical prognosis than do patients with FMEN I.     

Effect of age on the response to parathyroid hormone

Serum phosphate (PO4) levels and the tubular threshold for PO4 corrected for glomerular filtration (TP/GF) are age-dependent, being higher in children than in adults. We evaluated the effect of age on the response to infusion of parathyroid hormone(1-34) (PTH) in healthy children (n = 8) and adults (n = 12). In addition, six patients with pseudohypoparathyroidism (PHP) and two with PTH deficiency (hypoparathyroidism [HP]) were also studied. At baseline, TP/GF in normal subjects was inversely correlated with urinary cyclic adenosine monophosphate corrected for glomerular filtration (UcAMP/GF) (P < .0359). After PTH administration in the controls, UcAMP/GF was inversely correlated with TP/GF (P < .0007) and directly correlated with maximal fractional extraction of PO4 (FEP) (P < .0002). The slope of the regression of TP/GF (P < .0076) and FEP (P < .0034) with UcAMP/GF was steeper in children than in adults. Two HP patients had high PTH-stimulated UcAMP/GF levels, but stimulated TP/GF and FEP were not changed commensurate with levels that would expected from the normative data. In six patients with PHP, PTH-stimulated TP/GF was also correlated with peak UcAMP/GF (r = .96, P < .002). PHP patients could be distinguished from normal controls based on the combination of low peak FEP or high TP/GF together with low peak UcAMP/GF. Thus, in normal subjects, the phosphaturic response to PTH is correlated with the increase in urinary cAMP and is age-dependent, with a greater decrease of TP/GF in children than in adults.     

Intra-operative parathyroid hormone assay for simplified localization of parathyroid adenomas

Lack of success in parathyroid surgery is usually due to failure to identify the abnormal parathyroid gland correctly at operation. The surgeon may be helped by rapid parathyroid hormone (PTH) assay in peripheral blood after removal of a suspected adenoma, and by frozen section histology, but these are not true localization techniques. We have adapted a non-isotopic immunoassay for rapid measurement of PTH in samples from the upper, middle and lower thyroid veins taken at operation, before exploration begins. Fifteen patients with primary hyperparathyroidism were operated on. In 10 the parathyroid adenoma was located easily, and was associated with high local venous PTH levels. In four patients the abnormal parathyroid was not immediately apparent but the assay indicated its location, which was confirmed after further exploration. In one patient there was no difference in PTH levels in the six venous samples. An ectopic adenomatous gland was successfully identified behind the thymus. The operation was successful in all patients as shown by a fall in the plasma calcium to the normal range. We conclude that intra-operative selective venous sampling and rapid PTH assay facilitates operative localization of parathyroid adenomas.     

Pseudohypoparathyroidism with osteitis fibrosa cystica: direct demonstration of skeletal responsiveness to parathyroid hormone in cells cultured from bone

The role of aberrant neurodevelopment in the etiology of schizophrenia is reviewed in light of recent neuropathologic, neurochemical, and neuroimaging evidence of cerebral abnormalities in schizophrenic patients. There may exist some genetic defect in the control of brain development. Clinical epidemiologic surveys highlight the importance of obstetric complications, and prenatal exposure to influenza epidemics in contributing to these abnormalities. It is suggested that such environmental hazards and aberrations in the control of early brain development produce the neuronal phenotype that manifests as schizophrenia with early age of onset of symptoms associated with soft neurologic signs and is more common in young males.     

Cortisol stimulation of parathyroid hormone secretion by rat parathyroid glands in organ culture

Addition of cortisol (10(-6) to 10(-8) M) and related glucocorticoid congeners to cultures of rat parathyroid glands stimulated dose-related increases in parathyroid hormone secretion; the addition of deoxycorticosterone or cortexolone was without effect. Cortexolone, however, inhibited the stimulatory activity of cortisol when both were added to the culture medium. This direct stimulatory effect of cortisol on parathyroid gland secretion may account in part for the increased concentration of parathyroid hormone in the serum of cortisol-treated animals.     

Transplantation of parathyroid tissue in experimental hypoparathyroidism: in vitro and in vivo function of parathyroid tissue microencapsulated with a novel amitogenic alginate

Microencapsulation of tissues is an alternative to postoperative immunosuppression in transplantation. In 1994 iso-, allo- and xenotransplantation of microencapsulated parathyroid tissue was achieved in vivo. However, continued analysis of the coating substance (an alginate) determined mitogenic properties. Here, we report on the in vitro and in vivo function of parathyroid tissue microencapsulated with a novel amitogenic alginate suitable for use in humans. To assess in vitro function, parathyroid tissue encapsulated with mitogenic and amitogenic alginate was exposed to rising concentrations of calcium. For in vivo experiments, it was isotransplanted into parathyroidectomized rats. PTH release into medium and PTH serum levels as well as calcium levels of recipient rats were analyzed and compared to native (non-microencapsulated) tissue and empty capsules, respectively. In vivo, transplants were excised and subjected to histologic examination six months after trans-plantation. In vitro, parathyroid tissue encapsulated with amitogenic alginate releases approximately half of the PTH of the native tissue, not different from tissue encapsulated with the mitogenic alginate. In vivo, the novel alginate preserved parathyroid function similar to that of native tissue over the six month period resulting in complete reversal of hypoparathyroidism. Correspondingly, histologic examination revealed vital parathyroid tissue in intact microcapsules. By establishing in vitro function and successful long-term transplantation, we have documented the principle of microencapsulation of parathyroid tissue to be effective also with the novel amitogenic alginate, which is suitable for clinical use.     

Use of a rapid intraoperative parathyroid hormone assay in the surgical management of parathyroid disease

We present recent developments in the area of glycosaminoglycans (GAGs) and their possible interaction with insulin-like growth factor-I (IGF-I). GAGs are constituents of proteoglycans, and the combination of a core protein and a specific GAG makes a unique proteoglycan with a precise developmental pattern and with the ability to bind growth factors. This process is apparently regulated by the moiety of the peripheral GAGs. The supplementation of GAGs promotes neuritogenesis in vitro and stimulates nerve regrowth and muscle reinnervation, an effect correlated with an increase in trophic factor mRNA expression. In the case of neonatal nerve lesion, there is in addition an enhanced motor neuron survival, accompanied by higher levels of IGF-I in plasma and denervated muscle. The neurotrophic and neuroregenerative effects of exogenous GAGs were also observed in motor neuron disease in the wobbler mouse.     

Immunoreactive parathyroid hormone in early and advanced renal failure

Immunoreactive parathyroid hormone (iPTH) was measured in the serum of 20 patients with early renal failure (ERF) using three assays with different specificity. Half of these patients had elevated iPTH in one or more assays, up to twice the upper limit of normal. In contrast, 36 patients with a creatinine clearance below less than 20 ml/min had an 80% elevated iPTH, up to 5 times the upper limit of normal. The patients with ERF and elevated iPTH had a lower serum calcium but no higher serum phosphate than those with normal iPTH. The differences in iPTH in early and end-stage renal failure can be explained by known differences in metabolism of different PTH forms in uremia.     

Serum intact parathyroid hormone and ionised calcium concentration in children with renal insufficiency

We report our experience of the use of an immunoradiometric assay for intact parathyroid hormone (i-PTH) and the measurement of plasma ionised calcium concentration (PCa2+) in 73 children with chronic renal insufficiency (CRI); plasma creatinine concentration (PCr) 52-856 mumol/l. There was a poor correlation between i-PTH and PCr (r = 0.10, n = 552) compared with that for C-terminal PTH and PCr (r = 0.60, n = 248), suggesting that the i-PTH assay is independent of renal function in this group of treated children. A clear response of i-PTH to a low total plasma Ca (tPCa) and PCa2+ was observed. There was a significant positive correlation between both tPCa and PCa2+ (r = 0.50, n = 389) and the fraction of Ca2+ (the fraction of tCa which was ionised) and PCa2+ (r = 0.50, n = 389). The finding of a low or normal PCa2+ with a low calculated fraction of Ca2+ was frequently observed, i.e. the measured tPCa was unexpectedly high, suggesting complexing of Ca2+ by accumulated anions in CRI. There was a poor relationship between the plasma albumin concentration and both bound plus complexed Ca (tPCa minus PCa2+) and the fraction of Ca2+ (r = 0.15 and -0.17, respectively). The positive predictive value for a raised i-PTH of a tubular reabsorption of phosphate of less than 80% was 0.87, and of an alkaline phosphatase greater than 800 U/l was 0.37.(ABSTRACT TRUNCATED AT 250 WORDS)     

Parathyroid hormone-related peptide and the parathyroid hormone/parathyroid hormone-related peptide receptor in skeletal development

Desquamative gingivitis is a fairly common complaint. Typically seen in females who are middle-aged or older, it is predominantly a manifestation of a range of vesiculobullous disorders. The main complaint is of persistent soreness of the gingiva. Most cases are related to lichen planus or pemphigoid, but it is also important to exclude pemphigus, dermatitis herpetiformis, linear IgA disease, chronic ulcerative stomatitis, and other conditions. Biopsy is invariably required to confirm the diagnosis after a full history, general, and oral examination. Apart from improving the oral hygiene, immunosuppressive therapy is typically required to control the condition.