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PubMed1990

Renal osteodystrophy. Radiological diagnosis compared with a new radioimmunoassay method of parathyroid hormone.

The parathyroid hormone concentration in the blood measured by the 'two-site radioimmunoassay', which is specific for the biologically active parathyroid molecule (parathyrine), was compared with the radiological manifestations of secondary hyperparathyroidism (HPT) on magnification radiographs of the phalanges in patients undergoing maintenance hemodialysis and in patients with renal allografts. Sensitivity of radiology for the diagnosis of HPT proved to be high (88%), whereas specificity was low (30%). Statistical analysis showed that there was a good correlation between the parathyrine levels and the intensity of radiological changes in the phalanges in patients with renal allografts (coefficient of Krueger-Spearman = 0.65). In patients undergoing hemodialysis the correlation between laboratory parameters and radiological changes was poor.

Adult↗
PubMed1976

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.

Amino Acids↗
PubMed1986

CAP survey of parathyroid hormone assays.

Parathyroid hormone (PTH) analysis was recently added to the College of American Pathologists ligand assay survey. Synthetic whole-molecule PTH was used as the test hormone. This material was found to be stable in lyophilized serum for at least 10.7 days at 35 degrees C and 3.9 days at 45 degrees C. The survey results showed wide ranges of answers yielding within-assay coefficients of variation from 12% to 93%. The median percentage of the spiked hormone that was recovered by the various assay methods ranged from 24% to 390%. Separation of the spiked and endogenous measured PTH concentrations ranged from a twofold separation to an approximate 50% overlap of results. The survey may not be a valid indicator of PTH assay efficacy since whole-molecule human PTH may not be the most clinically important form of circulating PTH; however, the survey shows that there is a large heterogeneity in commercial PTH assays.

Cold Temperature↗
PubMed1987

A simplified diagnostic test in hypoparathyroidism and pseudohypoparathyroidism type I with synthetic 1-38 fragment of human parathyroid hormone.

Bovine parathyroid extract of E. Lilly (Indianapolis), which has been used to differentiate pseudohypoparathyroidism (PHP) and hypoparathyroidism (HP) is no longer available. We therefore evaluated the usefulness of the synthetic 1-38 fragment of human parathyroid hormone (1-38 hPTH), the biologically active part of the intact hormone, in a simplified modification of the traditional Ellsworth-Howard test. 1-38 hPTH was slowly injected over 2 min at a dose of 0.5 micrograms/kg body weight in healthy children and adults (n = 7), as well as in children with HP (n = 4) and PHP (n = 4). In the controls PTH administration induced a significant rise of plasma cAMP (at least 146 nmol/l), urine cAMP and serum prolactin, as well as a decrease of the tubular phosphate reabsorption. The respective responses were similar in the children with HP but markedly impaired in the patients with PHP. In four healthy adults a second PTH administration at an interval of 3 h induced a comparable response of cAMP and prolactin, indicating that these PTH effects are reproducible and not impaired by the first injection. The two PTH administrations caused a significant but variable rise of serum 1,25-dihydroxy-vitamin D in all four adults. In conclusion 1-38 hPTH has effects on the kidney and anterior pituitary similar to purified parathyroid extracts but has the advantage of being chemically and biologically defined and well tolerated. Since timed urine collections may be unreliable in young children, the plasma cAMP measurement at 5 and 10 min after the PTH injection is a good substitute for the traditional Ellsworth-Howard test, peak values over 100 nmol/l being regarded as a normal response.

Adolescent↗
PubMed1987

Plasma thyrocalcitonin and parathyroid hormone concentrations in early neonatal hypocalcaemia.

During the first week of life serum calcium, phosphorus, magnesium, immunoreactive thyrocalcitonin hormone, and parathyroid hormone concentrations were determined daily in 36 preterm and 29 small for gestational age, full term, healthy infants. Preterm babies with early neonatal hypocalcaemia had significantly higher concentrations of serum thyrocalcitonin hormone in the first four days of life than normocalcaemic preterm babies. Parathyroid hormone concentrations were similar in hypocalcaemic and normocalcaemic infants. In contrast, in the full term group no significant differences were detected in thyrocalcitonin hormone and parathyroid hormone patterns between hypocalcaemic and normocalcaemic subjects. This suggests two different pathogeneses for early hypocalcaemia in low birthweight infants. Hyperthyrocalcitoninaemia seems to be the main determining factor in preterm infants, while a non-hormonal pathogenesis should be considered in full term infants who are small for gestational age.

Calcitonin↗
PubMed1991

Thrombin and H64A subtilisin cleavage of fusion proteins for preparation of human recombinant parathyroid hormone.

Human parathyroid hormone, hPTH, an 84 amino acid polypeptide, was produced intracellularly in Escherichia coli as a fusion protein, linked to the C-terminus of a 15 kD IgG-binding protein. Approximately 100 mg fusion protein was obtained per liter fermentation medium. To test the efficiency of two alternative enzymatic cleavage methods, two fusion proteins differing only in the linker region were constructed. Cleavage of a Phe-Phe-Pro-Arg linker was obtained with bovine thrombin and cleavage of a Phe-Ala-His-Tyr linker with recombinant H64A subtilisin. Both enzymes yielded the correct N-terminus and cleaved their respective linkers quantitatively, although additional internal cleavage sites in hPTH were detected and characterized. The linker cleavage conditions were optimized and hPTH was purified to homogeneity. Thrombin cleavage resulted in a final yield of 5 mg hPTH/L, while H64A subtilisin cleavage was more specific and gave 8 mg/L. The purified recombinant product was identical to native hPTH and exhibited full biological activity in an adenylate cyclase assay.

Amino Acid Sequence↗
PubMed1992

Dissociation of phosphaturia and 25(OH)D-1 alpha-hydroxylase trophism using a novel analogue of parathyroid hormone.

Certain parathyroid hormone (PTH) analogues have been shown to selectively impair some but not all physiological actions of PTH. In this study, transaminated rat (r) PTH [TA-rPTH-(1-34)], a PTH analogue that differs from the rPTH-(1-34) fragment in that the NH2-terminal alanine is converted to pyruvate, was infused into mice to determine its properties in vivo and specifically to determine whether stimulation of 25-hydroxyvitamin D-1 alpha-hydroxylase (1 alpha-hydroxylase) activity was more dependent on concomitant renal handling of phosphate or on generation of adenosine 3',5'-cyclic monophosphate (cAMP). High-performance liquid chromatography-purified TA-rPTH-(1-34) was infused into C57BL mice at 10 or 30 pmol/h for 24 h. At 30 pmol/h, TA-rPTH-(1-34) was comparable with rPTH-(1-34) in its hypophosphatemic and phosphaturic effects but was less potent than rPTH-(1-34) in raising serum calcium. TA-rPTH-(1-34) was markedly less effective in stimulating renal 1 alpha-hydroxylase than rPTH-(1-34). Stimulation of urinary cAMP excretion occurred after infusion with TA-rPTH-(1-34), but this effect was significantly less than that seen with rPTH-(1-34). These findings indicate that PTH-induced hypophosphatemia and phosphaturia can be uncoupled from PTH stimulation of 1 alpha-hydroxylase. Furthermore, cAMP-related signal transduction appears to be more significant in regulation of 1 alpha-hydroxylase than mechanisms that mediate PTH-sensitive phosphate transport, independent of cAMP.

Animals↗
PubMed1990

Mechanisms of impaired insulin secretion after chronic excess of parathyroid hormone.

Excess parathyroid hormone (PTH) in presence or absence of chronic renal failure impairs insulin release from pancreatic islets. This abnormality has been attributed to PTH-induced accumulation of Ca in the cytosol of the islets. Direct evidence for the latter phenomenon is lacking. This study examined the effect of chronic administration of PTH to rats with normal renal function on resting cytosolic Ca of the islets and evaluated the mechanisms through which a rise in resting cytosolic Ca may inhibit insulin secretion. After 42 days of PTH administration, glucose-induced insulin secretion was impaired, and this defect was corrected by the use of D-glyceraldehyde as secretagogue for insulin. Resting cytosolic Ca of islets from PTH-treated rats was markedly increased compared with that of islets from normal animals (288 +/- 27.1 vs. 135 +/- 3.7 nM, P less than 0.01), and their content of ATP in the presence of both 2.8 and 16.7 mM D-glucose was reduced (2.8 mM D-glucose, 4.6 +/- 0.17 vs. 6.0 +/- 0.42 pmol/islet, P less than 0.01; and 16.7 mM D-glucose, 6.9 +/- 0.25 vs. 11.1 +/- 0.95 pmol/islet, P less than 0.01). D-Glyceraldehyde increased ATP content in islets of PTH-treated rats from 4.6 +/- 0.17 to 8.8 +/- 0.71 pmol/islet. Glucose uptake by the islets, their insulin content, and both the Vmax and the apparent Km for fructose 6-phosphate of phosphofructokinase 1 (EC 2.7.1.11) in PTH-treated rats were not different from normal. The two major cellular derangements in the islets of PTH-treated rats were a reduction in ATP content and a rise in resting cytosolic Ca.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1986

Regulation by calcium of parathyroid hormone mRNA in cultured parathyroid tissue.

We have examined the effect of changes in the concentration of extracellular calcium on parathyroid hormone mRNA in both short-term (hours) and long-term (days) cultures of bovine parathyroid tissue. Using a 32P-labeled PreProPTH cDNA probe, PTH mRNA was measured by gel blot hybridization of total RNA from tissue slices incubated for 4 h in low (0.5 mM) or high (5 mM) calcium concentrations and also by dot blot hybridization of cytoplasmic RNA extracted from aggregates of partially dispersed cells cultured up to 72 h in low (0.4 mM), normal (1 mM), or high (3 mM) calcium concentrations. PTH mRNA was unchanged over 4 h while high calcium had suppressed PTH secretion. However PTH mRNA did respond during long-term culture. By 24 h in high calcium there was a 50% suppression which was maintained for a further 48 h. PTH mRNA in normal calcium remained unchanged over 72 h while in low calcium it had increased slightly by 48 h. In contrast to the effect seen in cultured bovine parathyroid cells, PTH mRNA in human parathyroid adenoma cells cultured for 48 h in high calcium was decreased by only 10%.

Adenoma↗
PubMed1978

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.

Animals↗
PubMed1989

Periparturient hypocalcemia in cows: prevention using intramuscular parathyroid hormone.

Intravenously administered parathyroid hormone has recently been reported to prevent parturient paretic hypocalcemia in dairy cows. In the present study, Parathyroid hormone was administered intramuscularly prior to parturition to study its effects on Ca homeostasis and the incidence of periparturient hypocalcemia. Ten Holstein cows were fed a high Ca diet prepartum to predispose them to parturient paretic hypocalcemia. Five cows received intramuscular injections of synthetic bovine parathyroid hormone three times per day beginning about 6 d before parturition and continuing at a reduced dose for about 6 d after parturition. One of five control cows developed parturient paresis, and all five control cows exhibited hypocalcemia within 24 h of calving. None of the treated cows became paretic, and plasma calcium was normal or slightly elevated in these cows during the first 24 h after calving. Parathyroid hormone administration increased plasma concentrations of 1,25-dihydroxyvitamin D and hydroxyproline prior to parturition, suggesting that both intestinal Ca absorption and bone calcium resorption were increased by administration of the hormone. One hormone-treated cow became recumbent and required euthanasia. Although metastatic calcification of soft tissues was not observed, the death of this cow raises the possibility that there are unknown side effects of parathyroid hormone when administered intramuscularly.

Animals↗
PubMed1987

The effect of phorbol ester on in vitro release of parathyroid hormone from abnormal human parathyroid cells.

Intracellular events that regulate parathyroid hormone (PTH) release are not well understood. Cyclic AMP (cAMP) and cAMP-dependent protein kinases play a role in the regulation of release due to several agonists, but these factors do not fully explain PTH release that is mediated by extracellular ionized calcium (Ca++). A calcium-phospholipid-dependent (non-cAMP-dependent) protein kinase can be activated by 12-O-tetradecanoylphorbol-13-acetate (TPA). To determine whether this protein kinase regulates PTH release, we examined the effect of TPA on PTH release from human parathyroid tissue. Cell suspensions of abnormal parathyroid tissue removed at surgery were prepared by enzymatic dispersion and incubated for several hours with and without 10(-7) mol/L TPA at low and high calcium levels. In ten preparations in the absence of TPA, increasing Ca++ from 0.25 to 2.5 mmol/L reduced PTH release to an average of 39% of maximal release (range, 11% to 67%). The effect on TPA on Ca++-regulated PTH release appeared biphasic. At low (0.25 mmol/L) Ca++ level, TPA suppressed PTH release to an average of 78% of maximal release without TPA (95% confidence interval, 67% to 88%) (p less than 0.01 compared to cells incubated without TPA). At high (2.25 mmol/L) Ca++ level, TPA augmented PTH release from an average of 39% of maximal release without TPA to 62% of maximal release without TPA (95% confidence level, 48% to 78%), an average augmentation of 22% (95% confidence level, 9% to 36%) (p less than 0.01 compared with cells incubated without TPA). TPA appeared to make PTH release independent of Ca++. Both inhibitory and stimulatory effects were dose dependent. Incubations with TPA demonstrated no toxicity as judged by trypan blue dye exclusion, linearity of PTH release, and cellular incorporation of tritiated leucine. TPA had no effect on the radioimmunoassay for PTH. We conclude that a calcium/phospholipid-dependent, non-cAMP-dependent protein kinase may play a role in mediating Ca++-regulated PTH release from abnormal human parathyroid cells. Its site of action and integration with other regulatory pathways remain to be determined.

Adenoma↗
PubMed1985

A "carboxyl terminal" clinical radioimmunoassay for parathyroid hormone with apparent recognition preference for the intact hormone.

A radioimmunoassay for Parathyroid Hormone which is used in a clinical setting was characterized by immunoreactivity with various synthetic fragments of the hormone, serum parathyroid hormone response to oral calcium intake in normocalcemic calcium stone-formers, and ability to detect fragments of parathyroid hormone secreted by abnormal human parathyroid tissue in vitro. Although almost all of the recognition sites for the antiserum were within the 53-84 carboxyl terminal amino acid sequence of the hormone, the radioimmunoassay mainly detected the "intact" hormone rather than the carboxyl terminal fragment(s) which most "carboxyl-terminal" assays of parathyroid hormone are claimed to preferentially detect. Differences in tertiary structure between the intact hormone and its fragments probably account for the relative inability of this antiserum to detect the carboxyl terminal fragment(s).

Adenoma↗
PubMed1989

Immunocytochemical demonstration of a novel system of neuroendocrine peptidergic neurons in the pond snail Lymnaea stagnalis, with antisera to the teleostean hormone hypocalcin and mammalian parathyroid hormone.

Immunocytochemical staining with antisera raised against trout hypocalcin, the hypocalcemic hormone of the Stannius corpuscles and against bovine parathyroid hormone (bPTH1-84), revealed a new system of neuroendocrine neurons in the pond snail Lymnaea stagnalis. The neurons are located in small groups or single cells in the visceral, parietal, and pedal ganglia of the central nervous system. The axons of these cells are running to the periphery of the pleuroparietal, visceroparietal, and pleuropedal connections, the dorsopedal commissure, and to several nerves originating in the visceral, parietal, and pedal ganglia. The axons are ending with characteristic axonal distensions in the periphery of these connectives, commissure, and nerves. These regions probably act as neurohaemal areas. The affinity of this neuroendocrine system for both the anti-hypocalcin and anti-PTH sera is another indication for a special relationship between hypocalcin and PTH, which possess some immunological resemblance and similar biological activities, although no similarity in primary structure.

Animals↗
PubMed1990

Characterization of fully active biotinylated parathyroid hormone analogs. Application to fluorescence-activated cell sorting of parathyroid hormone receptor bearing cells.

[Nle8,18,Tyr34]bPTH-(1-34)amide (NlePTH) was biotinylated using sulfosuccinimidyl 6-(biotinamido)hexanoate, in dimethyl sulfoxide, and the multiple resulting peptides peaks were separated by reverse-phase high performance liquid chromatography. Their biological activities were compared with those of NlePTH, the parent compound, in radioreceptor and cAMP accumulation bioassays using rat osteosarcoma 17/2.8 cells; the earliest two eluting products, bioPTH 1 and 2, were equipotent, a third, bioPTH 3, was only 10% as potent, and the remaining, later eluting derivatives all were less than 0.1% as active. Competitive avidin binding assays using [3H]biotin suggested that bioPTH 1 and 2 had a single biotin congener per molecule, while bioPTH 3 contained two biotin residues. Upon Edman degradation, bioPTH 1 contained biotin on the lysine at position 13 of NlePTH; bioPTH 2's biotin was on the lysine at position 26 (or 27) and bioPTH 3 had biotins on lysines at both positions 13 and 26 (or 27). Avidin tagged with 125I, peroxidase, or fluorescein isothiocyanate was detected on bone-derived cells which had been incubated initially with bioPTH 2 (1, 10, and 100 nM) for 4 h, but not when NlePTH (1 microM) was added with bioPTH 2. A fluorescence-activated cell sorter detected a symmetrical shift in fluorescence of bone-derived cells incubated with 10 nM of bioPTH 2 and 10 micrograms/ml fluorescein isothiocyanate-avidin. Addition of a 30-fold molar excess of NlePTH, or omission of bioPTH 2, completely reversed this fluorescence shift, and no shift in fluorescence was seen with cells lacking PTH receptors. This fully active, high affinity biotinylated PTH-derivative should prove useful in the study of PTH receptor-bearing cells.

Animals↗