Insensitive to PTH of CD8+ T cells regulate bone marrow mesenchymal stromal cell in aplastic anemia patients.

Aplastic anemia (AA) is a rare disorder characterized by the suppression of bone marrow function resulting in progressive pancytopenia. The pathogenesis of AA is complex and involves an abnormal hematopoietic microenvironment, hematopoietic stem cell/progenitor cell deficiencies, and immunity disorders. However, the underlying mechanism of the disease is still not fully uncovered. In this research, we collected both donor and patient samples and found suppressed proliferation, abnormal differentiation as well as increased apoptosis of patient mesenchymal stem cells (MSCs). Considering the close relationship of parathyroid hormone (PTH) and MSCs differentiation, further studies showed that although patients maintained normal serum PTH level, their CD8+ T cells possessed lower PTH receptors. The insensitive to PTH of patients' CD8+ T cells finally lead to reduced expression of key Wnt factors. In all, bone marrow CD8+ T cells may play an important role in inducing MSCs adipogenesis and osteogenesis imbalancement.

Nitrosoreductase-Like Nanocatalyst for Ultrasensitive and Stable Biosensing.

Enzyme-like nanocatalytic reactions developed for high signal amplification in biosensors are of limited use because of their low reaction rates and/or unwanted side reactions in aqueous electrolyte solutions containing dissolved O2. Herein, we report a nitrosoreductase-like catalytic reaction, employing 4-nitroso-1-naphthol, Pd nanoparticles, and H3N-BH3, which affords a high reaction rate and minimal side reactions, enabling its use in ultrasensitive electrochemical biosensors. 4-Nitroso-1-naphthol was chosen after five hydroxy-nitro(so)arene compounds were compared in terms of high signal and low background levels. Importantly, the nanocatalytic reaction occurs without the self-hydrolysis and induction period observed in the nanocatalytic reduction of nitroarenes by NaBH4. The high signal level results from (i) fast nanocatalytic 4-nitroso-1-naphthol reduction, (ii) fast electrochemical redox cycling, and (iii) the low influence of dissolved O2. The low background level results from (i) slow direct reaction between 4-nitroso-1-naphthol and H3N-BH3, (ii) slow electrode-mediated reaction between 4-nitroso-1-naphthol and H3N-BH3, and (iii) slow electrooxidation of H3N-BH3 at electrode. When applied to the detection of parathyroid hormone, the detection limit of the newly developed biosensor was ∼0.3 pg/mL. The nitrosoreductase-like nanocatalytic reaction is highly promising for ultrasensitive and stable biosensing.

Calcium Ion Channels: Roles in Infection and Sepsis Mechanisms of Calcium Channel Blocker Benefits in Immunocompromised Patients at Risk for Infection.

Immunosuppression may occur for a number of reasons related to an individual's frailty, debility, disease or from therapeutic iatrogenic intervention or misadventure. A large percentage of morbidity and mortality in immunodeficient populations is related to an inadequate response to infectious agents with slow response to antibiotics, enhancements of antibiotic resistance in populations, and markedly increased prevalence of acute inflammatory response, septic and infection related death. Given known relationships between intracellular calcium ion concentrations and cytotoxicity and cellular death, we looked at currently available data linking blockade of calcium ion channels and potential decrease in expression of sepsis among immunosuppressed patients. Notable are relationships between calcium, calcium channel, vitamin D mechanisms associated with sepsis and demonstration of antibiotic-resistant pathogens that may utilize channels sensitive to calcium channel blocker. We note that sepsis shock syndrome represents loss of regulation of inflammatory response to infection and that vitamin D, parathyroid hormone, fibroblast growth factor, and klotho interact with sepsis defense mechanisms in which movement of calcium and phosphorus are part of the process. Given these observations we consider that further investigation of the effect of relatively inexpensive calcium channel blockade agents of infections in immunosuppressed populations might be worthwhile.

Parathyroid Diseases and T Cells.

PURPOSE OF REVIEW: This review summarizes studies into the permissive role of T cells in the bone catabolic effects of hyperparathyroidism and parathyroid hormone (PTH). RECENT FINDINGS: Work in animals combined with recent translational studies in humans now highlight the potent amplificatory action of T cells on PTH-induced bone resorption. Mechanistic animal studies reveal a complex pathway by which PTH exploits natural self-renewal functions of CD4+ T cells, to drive TNFα production that promotes formation of IL-17A secreting Th17 T cells. TNFα and IL-17 further amplify osteoblastic receptor activator of NF-κB ligand (RANKL) production and down-modulate osteoprotegerin (OPG), establishing conditions propitious for osteoclastic bone resorption. These findings are consistent with, and add to, the traditional view of PTH-induced bone loss involving only osteoblast-lineage cells. T cells potently amplify traditional pathways and provide permissive costimulatory signals to bone marrow stromal cells, facilitating the development of an increased RANKL/OPG ratio favourable to bone resorption and bone loss.

Detection of parathyroid hormone-like hormone in cancer cell cultures by gold nanoparticle-based lateral flow immunoassays.

Parathyroid hormone-like hormone (PTHLH) exerts relevant roles in progression and dissemination of several tumors. However, factors influencing its production and secretion have not been fully characterized. The main limitation is the lack of specific, sensitive and widely available techniques to detect and quantify PTHLH. We have developed a lateral flow immunoassay using gold nanoparticles label for the fast and easy detection of PTHLH in lysates and culture media of three human cell lines (HaCaT, LA-N-1, SK-N-AS). Levels in culture media and lysates ranged from 11 to 20 ng/mL and 0.66 to 0.87 µg/mL respectively. Results for HaCaT are in agreement to the previously reported, whereas LA-N-1 and SK-N-AS have been evaluated for the first time. The system also exhibits good performance in human serum samples. This methodology represents a helpful tool for future in vitro and in vivo studies of mechanisms involved in PTHLH production as well as for diagnostics. From the Clinical Editor: Parathyroid Hormone-like Hormone (PTHLH) is known to be secreted by some tumors. However, the detection of this peptide remains difficult. The authors here described their technique of using gold nanoparticles as label for the detection of PTHLH by Lateral-flow immunoassays (LFIAs). The positive results may also point a way to using the same technique for the rapid determination of other relevant cancer proteins.

Thymus-associated parathyroid hormone has two cellular origins with distinct endocrine and immunological functions.

In mammals, parathyroid hormone (PTH) is a key regulator of extracellular calcium and inorganic phosphorus homeostasis. Although the parathyroid glands were thought to be the only source of PTH, extra-parathyroid PTH production in the thymus, which shares a common origin with parathyroids during organogenesis, has been proposed to provide an auxiliary source of PTH, resulting in a higher than expected survival rate for aparathyroid Gcm2⁻/⁻ mutants. However, the developmental ontogeny and cellular identity of these "thymic" PTH-expressing cells is unknown. We found that the lethality of aparathyroid Gcm2⁻/⁻ mutants was affected by genetic background without relation to serum PTH levels, suggesting a need to reconsider the physiological function of thymic PTH. We identified two sources of extra-parathyroid PTH in wild-type mice. Incomplete separation of the parathyroid and thymus organs during organogenesis resulted in misplaced, isolated parathyroid cells that were often attached to the thymus; this was the major source of thymic PTH in normal mice. Analysis of thymus and parathyroid organogenesis in human embryos showed a broadly similar result, indicating that these results may provide insight into human parathyroid development. In addition, medullary thymic epithelial cells (mTECs) express PTH in a Gcm2-independent manner that requires TEC differentiation and is consistent with expression as a self-antigen for negative selection. Genetic or surgical removal of the thymus indicated that thymus-derived PTH in Gcm2⁻/⁻ mutants did not provide auxiliary endocrine function. Our data show conclusively that the thymus does not serve as an auxiliary source of either serum PTH or parathyroid function. We further show that the normal process of parathyroid organogenesis in both mice and humans leads to the generation of multiple small parathyroid clusters in addition to the main parathyroid glands, that are the likely source of physiologically relevant "thymic PTH."

First Japanese patient treated with parathyroid hormone peptide immunization for refractory hypercalcemia caused by metastatic parathyroid carcinoma.

Patients with unresectable parathyroid carcinoma develop severe hypercalcemia, bone fractures and renal failure, and become unresponsive to conventional treatments. It has been shown that successful induction of anti-parathyroid hormone (PTH) antibodies, using PTH peptide fragments for immunisation, normalized serum levels of calcium as well as improved clinical symptoms. Here, we report our experience of PTH immunization in a Japanese female suffering from refractory hypercalcemia and renal failure caused by unresectable metastatic parathyroid carcinoma. Upon immunization, there were apparent clinical responses including reduction of serum levels of Ca along with anti-PTH antibodies induction. Therefore, we concluded that PTH immunization was an effective treatment against hypercalcemia caused by metastatic parathyroid carcinomas that are unresponsive to conventional treatments.

A Rapid Intraoperative Parathyroid Hormone Assay Based on the Immune Colloidal Gold Technique for Parathyroid Identification in Thyroid Surgery.

Objective: A novel immunochromatographic test strip method was developed to detect tissue parathyroid hormone (PTH) using the immune colloidal gold technique (ICGT). The accuracy and application value of this method for intraoperative parathyroid identification were evaluated. Methods: Serum samples were collected to measure PTH by both ICGT and electrochemiluminescence immunoassay (ECLIA). Patients who underwent unilateral and total thyroidectomy were enrolled to evaluate the feasibility and clinical efficacy of rapid intraoperative identification of parathyroid glands via PTH determination using ICGT. Two sample preparation methods, fine needle aspiration (FNA) and tissue block homogenate (TBH), were used for PTH-ICGT analysis. Results: Bablok analysis showed a linear relationship between the serum PTH measurements obtained by ICGT and ECLIA. Non-parathyroid tissues had much lower PTH concentrations (14.8 ± 2.1 pg/ml, n = 97) detected by ICGT, compared to the parathyroid gland tissues (955.3 ± 16.1 pg/ml, n = 79; P < 0.0001), With biopsy results as the standard, ICGT showed higher diagnosis rates as compared with direct visual inspection, for identifying both parathyroid glands (97.4 vs. 78.2%) and non-parathyroid tissues (100 vs. 68.9%). The cut-off values for parathyroid identification by FNA and TBH methods were 63.99 and 136.30 pg/ml, respectively. The detection time was 2 min by TBH method for in vitro tissue detection and 6 min by FNA method for in situ tissue detection, both of which were faster than traditional intraoperative cryopathological examination (usually >30 min). Intraoperative application of ICGT method was associated with higher postoperative serum calcium and blood PTH levels at 1 and 3 months as well as a lower incidence of postoperative transient hypocalcemia, as compared with direct visual inspection. Conclusion: PTH-ICGT assay shows high potential as a rapid, novel alternative for intraoperative parathyroid identification.

PTH induces bone loss via microbial-dependent expansion of intestinal TNF+ T cells and Th17 cells.

Bone loss is a frequent but not universal complication of hyperparathyroidism. Using antibiotic-treated or germ-free mice, we show that parathyroid hormone (PTH) only caused bone loss in mice whose microbiota was enriched by the Th17 cell-inducing taxa segmented filamentous bacteria (SFB). SFB+ microbiota enabled PTH to expand intestinal TNF+ T and Th17 cells and increase their S1P-receptor-1 mediated egress from the intestine and recruitment to the bone marrow (BM) that causes bone loss. CXCR3-mediated TNF+ T cell homing to the BM upregulated the Th17 chemoattractant CCL20, which recruited Th17 cells to the BM. This study reveals mechanisms for microbiota-mediated gut-bone crosstalk in mice models of hyperparathyroidism that may help predict its clinical course. Targeting the gut microbiota or T cell migration may represent therapeutic strategies for hyperparathyroidism.

CD8+ T lymphocytes enhance the anabolic effect of intermittent parathyroid hormone on cementoblasts.

Root resorption is usually inflammatory in nature and has a tight link with immune system. Intermittent parathyroid hormone (iPTH) could promote cementum regeneration. The cross-talk of immune cells and cementoblasts may play an important role in the regeneration which stayed to be elucidated. In this study, a CD8+ T cells-OCCM-30 cells coculture system was established in vitro to investigate whether CD8+ T cells could enhance the anabolic effect of iPTH on cementoblasts and to find out the potential link of the effect with Wnt signal pathway. Determined by real-time PCR and Western Blot, we found an amplified cementogenesis in the OCCM-30 cells from coculture system, including increased mRNA and protein expression of Alp, Opn and Runx2, ALP activity and mineralization. We also found iPTH could increase the expression of Wnt10b in CD8+ T cells by ELISA. In addition, Wnt10b would promote the proliferation of OCCM-30 cells, while the effect on differentiation was various in different culture medium. These results demonstrated that the stimulating effect of iPTH on cementoblasts could be mediated through an interaction with CD8+ T cells, and T-cell-induced Wnt10b might be a key mechanism in the mediation.

PTH Immunoassay Interference Due to Human Anti-Mouse Antibodies in a Subject With Obesity With Normal Parathyroid Function.

CONTEXT: Immunoassay interference has been most often found with prolactin measurement. However, only few data exist on immunoassay interference for other hormones. CASE DESCRIPTION: A 36-year-old woman with obesity (body mass index, 31 kg/m2) had regularly attended our endocrine unit for type 2 diabetes therapy. When she was included as a control subject in a study for obesity management, detailed laboratory testing was performed, including PTH. In the absence of clinical symptoms, she presented with normal calcium, phosphate, and vitamin D levels. However, the PTH levels were >5000 ng/L. These results were obtained using the Roche Elecsys electrochemiluminescence assay. Repeated measurements with this assay (mouse antibody) led to the same findings. However, using an Euroimmun assay (goat antibody), the exact PTH values were measured at 18.0 ng/L. After pretreatment with a heterophilic antibody blocking reagent, the results of the Roche assay had decreased to a normal level. This phenomenon was explained by the detection of human anti-mouse antibodies in the proband's serum. CONCLUSIONS: In cases of prolactin immunoassay interference, endogenous antibodies will bind to the hormone in vivo, resulting in complexes of a high molecular weight that are less efficiently cleared by the kidneys and, thus, accumulate in the blood. In contrast, the PTH values >5000 ng/L detected in our subject most likely had resulted from the specific interference of the human anti-mouse antibodies present in the proband's serum with the assay antibody, resulting in artificial stimulation of the Roche assay detection system ex vivo.

Ultrasensitive Detection of Parathyroid Hormone through Fast Silver Deposition Induced by Enzymatic Nitroso Reduction and Redox Cycling.

Enzymatically induced silver deposition and subsequent electrochemical oxidation have been widely used in electrochemical biosensors. However, this method is ineffective for producing highly enhanced silver deposition for use in ultrasensitive detection. Herein, we report a fast silver deposition method that simultaneously uses three signal amplification processes: (i) enzymatic amplification, (ii) chemical-chemical (CC) redox cycling, and (iii) chemical-enzymatic (CN) redox cycling. DT-diaphorase (DT-D) is used for enzymatic amplification to convert a nitroso compound, a species incapable of directly reducing Ag+ to an amine compound, which can directly reduce Ag+. NADH acts as a reducing agent for the indirect reduction of Ag+ via the two redox cycling processes. 4-Nitroso-1-naphthol is converted to 4-amino-1-naphthol (NH2-N) in the presence of DT-D. NH2-N initiates two redox cycling processes: NH2-N, along with Ag+ and NADH, are involved in the CC redox cycling, whereas NH2-N, along with Ag+, DT-D, and NADH, are involved in the CN redox cycling. Finally, the deposited silver is electrochemically oxidized to produce a signal. When this triple signal amplification strategy for fast silver deposition is applied to an electrochemical immunosensor for detecting parathyroid hormone (PTH), a detection limit as low as ∼100 fg/mL is obtained. The concentrations of PTH in clinical serum determined using the developed immunosensor are found to agree with those measured using a commercial instrument. Thus, the use of this strategy for fast silver deposition is highly promising for ultrasensitive electrochemical detection and biosensing applications.

Selective uptake of intact parathyroid hormone by the liver: differences between hepatic and renal uptake.

Hepatic and renal extraction of immunoreactive parathyroid hormone (i-PTH) was studied in awake dogs with explanted kidneys and chronic indwelling hepatic vein catheters. After a single injection of bovine PTH 1-84 (b-PTH 1-84), hepatic arteriovenous (A-V) differences for immunoreactive PTH (i-PTH) was 39% at 2 min after injection but decreased to 0% by 25 min, despite high levels of i-PTH in the arterial circulation. Gel filtration of arterila and hepatic venous samples obtained when hepatic A-V differences for i-PTH were demonstrable revealed hepatic uptake of the intact hormone and addition of a smaller COOH-terminal fragment, eluting just after the intact hormone, to the hepatic venous blood. Gel filtration of samples obtained 20-30 min after injection of b-PTH was demonstrable) revealed no detectable intact hormone in the circulation. Levels of COOH-terminal fragments of the hormone at the time were identical in arterial and hepatic venous samples. In additional experiemtns no hepatic A-V difference was observed after the injection of the synthetic bovine PTH 1-34 (syn b-PTH 1-34). By comparison there was a demonstrable A-V difference of 20% across the kidney for both intact PTH and COOH-terminal fragments that persisted until i-PTH disappeared from the circulation. The kidney also demonstrated an A-V difference of 22% after injection of syn b-PTH 1-34. These studies demonstrate selective extraction of intact PTH but not of its fragments by the liver. The kidney, on the other hand, extracted the intact hormone and both COOH and NH2 terminal fragments. The studies demonstrate that the kidney was the only organ of those examined that detectably removed the fragments of PTH from the circulation.

Direct release of parathyroid hormone fragments from functioning bovine parathyroid glands in vitro.

To determine the origin of circulating parathyroid hormone fragments, hormonal peptides released from bovine parathyroid tissue in a physiologically responsive in vitro "perifusion" system were analyzed by gel exclusion chromatography and region-specific radioimmunoassays. When exposed to low Ca++, the tissue released large quantities of intact hormone (parathyroid hormone 1--84) as well as amino- and carboxyl-terminal fragments. Fragments of the hormone were also released when the tissue was exposed to high Ca++, but the carboxyl fragments comprised a much greater proportion of the hormonal peptides released. Control experiments indicated that fragmentation of the hormone occurred within the gland and not after it was secreted. These experiments provide direct evidence, therefore, that release of fragments from the parathyroid gland may contribute to the immunologic heterogeneity of the hormone in the circulation.

Human parathyroid hormone. Immunological characterization of antibodies against a glandular extract and the synthetic amino-terminal fragments 1-12 and 1-34 and their use in the determination of immunoreactive hormone in human sera.

Antibodies to a urea-trichloroacetic acid extract [hPTH-(TCA)] of human parathyroid tumors and to the synthetic NH(2)-terminal fragments of human parathyroid hormone hPTH-(1-12) and -(1-34) were developed in goats to characterize immunochemically various PTH preparations and to estimate immunoreactive PTH (iPTH) in human sera. They were quantitated on the basis of their capacity to bind [(131)I]-hPTH-(1-12), [(131)I]hPTH-(1-34) or [(131)I]bovine PTH (bPTH-(1-84)). The quality of the antibodies was assessed by reference to inhibition of their interaction with labeled peptides by synthetic hPTH comprising 34 NH(2)-terminal amino acid residues or fragments thereof [hPTH-(1-12), -(13-34), -(18-34), -(25-34), -(18-24)] or by the Sephadex G-100-purified full-length peptide hPTH-(1-84) [hPTH-(1-84)G-100]. The synthetic peptides used in this work correspond in their structure to the NH(2)-terminal amino acid sequence 1-34, as elucidated by Brewer and collaborators (1972. Proc. Natl. Acad. Sci. U. S. A.69: 3583-3588). Inhibition studies were also carried out with bPTH-(1-34) and bPTH-(1-84). Anti-hPTH-(TCA) exhibited specificities directed to determinants in the COOH-terminal and NH(2)-terminal part of hPTH-(1-84) and exhibited cross-reactivity with bPTH-(1-84). Anti-hPTH-(1-34), on the other hand, showed immunological specificities mainly directed to antigenic determinants located in the COOH-terminal half of hPTH-(1-34). In addition, some reactivity with the NH(2)-terminal hPTH-(1-12) and with the extractive full-length peptides of human and bovine origin was observed. Antibodies to hPTH-(1-12) cross-reacted with hPTH-(1-34) and -(1-84)G-100.IPTH WAS RADIOIMMUNOLOGICALLY DETERMINED IN HUMAN SERA BY THE FOLLOWING SYSTEMS: (a) [(131)I]bPTH-(1-84), anti-hPTH-(TCA) and hPTH-(1-84)G-100 as standard; (b) [(131)I]hPTH-(1-34), anti-hPTH-(1-34) and hPTH-(1-34) as standard. With system (a), COOH-terminal fragments of hPTH-(1-84) having a molecular weight of approximately 7,000 were detected, and there was an almost total discrimination of serum iPTH levels in normal and in hyperparathyroid subjects. With system (b), on the other hand, several molecular species of iPTH were detected, including a component larger than hPTH-(1-84) and others similar to hPTH-(1-84) and to a fragment co-eluting with the NH(2)-terminal fragment hPTH-(1-34). When serum iPTH was assayed in system (b), there was a large overlap of iPTH levels in control subjects and in patients with primary hyperparathyroidism.

Metabolism of bovine parathyroid hormone. Immunological and biological characteristics of fragments generated by liver perfusion.

The metabolism of bovine parathyroid hormone (PTH) by the perfused rat liver was studied. Labeled hormone, with or without cold hormone, was infused into the circulating perfusion medium containing various calcium concentrations. Pefusate samples at various time periods after the introduction of PTH into the system were chromatographed on Bio-gel P-10; radioactivity and/or immunoreactivity were measured in eluted fractions. Before the perfusion, all immuno- and radioactivity eluted in a single peak, with an apparent mol wt of 9,500 (peak I). After perfusion for 15 min, two other peaks with approximate mol wt of 7,000 (peak II) and 3,500 (peak III) were discernible. Peak I contained both NH2-terminal and COOH-terminal immunoreactivity and was biologically active at all time periods tested. The relative contribution of NH2-terminal and COOH-terminal immunoreactivity to the total immunoreactivity remained constant in this peak throughout the perfusion. In every respect, peak I had the characteristics of intact hormone. At all times, peak II consisted of only COOH-terminal immunoreactivity and was biologically inactive. At early time periods, peak III contained predominantly NH2-terminal immunoreactivity and was biologically active. With time, the relative contribution of NH2-terminal immunoreactivity decreased strikingly while that of COOH-terminal immunoreactivity increased. The three peaks identified in these experiments were analogous in size, biological activity, and immunological characteristics to those we have previously described for fractionated human hyperparathyroid serum. The rate of metabolism of PTH appeared to be regulated by the calcium concentration in the medium. At a high concentration of calcium (greater than 11 mg/100 ml), PTH metabolism was greatly retarded. At a low concentration of calcium (smaller than 5 mg/100 ml), the rate of metabolism was greatly increased. The physiological significance of our observations on the metabolism of PTH by isolated perfused rat liver is not known. However, since such metabolism results in a biologically active fragment, it is suggested that metabolism of intact hormone may be required before full biological expression is possible.

Decrease in serum immunoreactive parathyroid hormone in rats and in parathyroid hormone secretion in vitro by 1,25-dihydroxycholecalciferol.

The present study determined the effects of 1,25-dihydroxycholecalciferol on serum immunoactive parathyroid hormone and on parathyroid hormone secretion in vitro. Rats injected i.p. with 1,25-dihydroxycholecalciferol, 130 pmol (2 U)/140 g body wt, which is probably a physiologic dose, had a significant 43% decrease in serum immunoreactive parathyroid hormone at 4 h. In addition, this dose of 1,25-dihydroxycholecalciferol inhibited the serum immunoreactive parathyroid hormone response to hypocalcemia induced by phosphate injection. Because the increment in serum immunoreactive parathyroid hormone was less but the decrement in serum calcium more in phosphate plus 1,25-dihydroxycholecalciferol-treated than in phosphate plus vehicle-treated rats, the impaired serum immunoreactive parathyroid hormone response to 1,25-dihydroxycholecalciferol could not be attributed to the change in serum calcium. In studies of parathyroid hormone secretion from bovine parathyroid tissue in vitro, the concentration of 1,25-dihydroxycholecalciferol used for most experiments was 1nM, which is in the range found in rat serum. 1,25-Dihydroxycholecalciferol at 1 or 100 nM significantly inhibited parathyroid hormone secretion when medium calcium concentration was normal (1.5 mM), high (3.0 mM), and low (1.0 mM). Maximum inhibition ranged from 19 to 74%; inhibition was generally seen after 2 h of incubation; and inhibition was sustained or progressive thereafter. Vitamin A, 0.1 muM, caused a marked stimulation of parathyroid hormone secretion. 1,25-Dihydroxycholecalciferol at 1 nM markedly reduced (44%) the effect of vitamin A to stimulate parathyroid hormone secretion. This effect of 1,25-dihydroxycholecalciferol was maximal at 1 h and persisted thereafter. Another steroid, hydrocortisone, 10 muM, did not inhibit parathyroid hormone secretion, suggesting that the 1,25-dihydroxycholecalciferol effect was not a nonspecific inhibitory effect on parathyroid cells. Because other workers have shown that parathyroid hormone directly stimulates 1,25-dihydroxycholecalciferol secretion, our results are consistent with the concept that there is a feedback loop where parathyroid hormone directly stimulates secretion of 1,25-dihydroxycholecalciferol, which in turn directly inhibits secretion of parathyroid hormone.

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.

The role of 1 alpha, 25-dihydroxyvitamin D in the mediation of intestinal hyperabsorption of calcium in primary hyperparathyroidism and absorptive hypercalciuria.

The cuase for the intestinal hyperabsorptionof calcium (Ca) in various forms of hypercalciurias was explored by a careful measurement of plasma 1 alpha, 25-dihydroxycholecalciferol [1 alpha, 25-(OH)I D] and by an assessment of intestinal Ca absorption and of parathyroid function. In 18 cases of primary hyperparathyroidism (PHPT), the mean plasma concentration of 1 alpha, 25-(OH)2D was significantly increased (4.9 +/- 2.2 SD ng/dl vs. 3.4 +/- 0.9 ng/dl for the control group), and was significantly correlated with fractional Ca absorption (alpha) (r = 0.80, P less than 0.001). Plasma 1 alpha, 25-(OH)2D was also correlated with urinary Ca (P less than 0.05), but not with serum Ca or phosphorus (P), P clearance, urinary cyclic AMP, or serum immunoreactive parathyroid hormone. In 21 cases of absorptive hypercalciuria (AH), plasma 1 alpha, 25-(OH)2D was elevated in one-third of cases, and the mean value of 4.5 +/- 1.1 ng/dl was significantly higher than that of the control group (P less than 0.01). Since relative hypoparathyroidism may be present, the normal absolute value of plasma 1 alpha, 25-(OH)2D, found in two-thirds of cases of AH, may be considered to be inappropriately high. Moreover, in the majority of cases of AH, the data points relating plasma 1 alpha, 25-(OH)2D and alpha fell within 95% confidence limits of values found in non-AH groups (including PHPT). The results suggest that the intestinal hyperabsorption of Ca in PHPT aw AH may be vitamin D dependent. However, the disturbance in vitamin D metabolism may not be the sole cause for the high Ca absorption in AH, since in some patients with AH, the intestinal Ca absorption appears to be inapp

Parathyroid hormone secretion in vivo. Demonstration of a calcium-independent nonsuppressible component of secretion.

The response of normal bovine parathyroid glands to hypercalcemia was assessed in vivo by radioimmunoassay of immunoreactive parathyroid hormone concentrations in parathyroid effluent blood obtained by surgical cannulation of both anesthetized and nonanesthetized calves. Hypercalcemia was induced for periods of 0.3-35 h by intravenous infusion of a solution of calcium chloride. Assessment of immunoreactivity in effluent and peripheral blood included measurements of selected samples by use of a radioimmunoassay specific for a site residing in the biologically active portion of the hormone molecule. In all instances, the concentration of immunoreactive parathyroid hormone in hypercalcemic venous effluent from a superior parathyroid gland exceeded that of the peripheral blood. Failure of hypercalcemia to suppress completely secretion by normal parathyroids indicates that a portion of parathyroid hormone secretion occurs independent of blood calcium concentration. Consequently, continued parathyroid hormone secretion despite hypercalcemia can no longer be regarded as a unique feature of parathyroid neoplasia.