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At least 181 records · Page 10Linked to original sources
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↗
PubMed1983

High-performance liquid chromatographic methods for the analysis of human parathyroid hormone in reference standards, parathyroid tissue and biological fluids.

Reversed-phase high-performance liquid chromatography (RP-HPLC) has been used to fractionate human parathyroid hormone (hPTH) from a variety of natural sources and to compare it with synthetic hPTH and hPTH fragments. Multiple radioimmunoassay systems for amino, mid and carboxyl regions of hPTH were used to monitor various preparations of hPTH previously prepared by conventional methods and ampouled in nanogram amounts for reference standard and reagent purposes. Results confirmed that they were free of detectable cleavage products, but showed that the intact hPTH comprised three or four closely associated components. A similar pattern of heterogeneity was obtained when hPTH was extracted from stored human parathyroid adenomata by a simple rapid HPLC bulk fractionation method. Comparison with synthetic 1-84 hPTH and modification of sample handling to minimize oxidative conditions, indicate that some of these components are probably intermediate oxidation products. A number of less hydrophobic components, with carboxyl region immunoreactivities, were obtained from the individual adenoma samples, human parathyroid cyst fluid, ampouled samples of human adenoma tissue culture medium, and secondary hyperparathyroid plasma ultrafiltrate when they were fractionated by RP-HPLC. The results strongly suggest that the biological degradation of hPTH is more complex than generally believed, and that RP-HPLC offers a new dimension in its analysis.

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↗
PubMed1984

Effects of 1,25- and 24,25-dihydroxycholecalciferol on parathyroid hormone release from human parathyroid cells in vitro.

The effects of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) and 24,25-dihydroxycholecalciferol (24,25-(OH)2D3) on parathyroid hormone (PTH) release from human parathyroid cells were investigated using an in vitro system of dispersed cells. The cells were obtained from 7 patients with primary hyperparathyroidism (HPT) and adenoma, 4 patients with primary HPT due to hyperplasia and 2 patients with parathyroid hyperplasia secondary to chronic renal failure. The dispersed cells were incubated in tissue culture medium at low, normal and high external calcium concentrations for 2-16 h. There was a gradual suppression of PTH release (5-55%) when the calcium concentration in the medium was increased from 0.5 to 3.0 mM, thus indicating retained regulation of hormone release. The addition of 1,25-(OH)2D3 in concentrations of 0.1 and 1 ng/ml and of 24,25-(OH)2D3 in concentrations of 1.0 and 10 ng/ml during the incubations did not further affect the amount of PTH released by the cells. The concentrations of the different vitamin D metabolites tested closely correspond to levels observed under normal physiological conditions and during treatment with high doses of vitamin D in vivo. Thus, the findings contradict the idea of any direct short-term regulatory effect of either 1,25-(OH)2D3 or 24,25-(OH)2D3 on the secretion of PTH from hyperfunctioning human parathyroid tissue.

24,25-Dihydroxyvitamin D 3↗