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PubMed1976

[Studies on the biosynthesis and secretion of parathyroid hormone in monolayer cultures of bovine parathyroid cells (I) (author's transl)].

We have developed a preparation of monolayer cultures of bovine parathyroid cells in order to elucidate the control mechanism of the biosynthesis and secretion of parathyroid hormone (PTH) at cellular level. Dispersion of parathyroid cells was performed by stirring minced bovine parathyroid tissues in Hanks' BSS containing 0.3 yields to 0.5 percent collagenase at 37 degrees C for 60 min. Dispersed cells were cultured at 37 degrees C in MEM-Hanks' BSS containing 10 percent fetal calf serum and 15 mM HEPES. On the 5th day of the culture, the medium was replaced with 1 percent BSA-MEM-Hanks-HEPES buffer, and the cells were incubated with 3H-leucine or in the media containing various concentrations of calcium, magnesium, PGE1, PGE2 or DBcAMP. At the end of incubation, the cells were detouched and homogenized in 8M urea, 0.2 N HCL and 0.01 M cysteine solution. The isolation of proparathyroid hormone (ProPTH) and PTH was performed through the preparation of TCA-powder followed by CMC column chromatography. PTH in the incubation medium was determined by radioimmunoassay. It was demonstrated that the monolayer cultures of bovine parathyroid cells were synthesizing ProPTH and converting it to PTH. The cultures exhibited linear secretion rates of PTH into the medium. The secretion of PTH was markedly increased by PGE1, PGE2 or DBcAMP in the range of 10(-7) yields to 10(-5)M in the former and 10(-5) yields to 10(-3)M in the latter, while calcium or magnesium changed secretion rate in the range of 0.3 yields to 4.4 mM.

Animals↗
PubMed1979

Regulation of hormone-induced cyclic AMP response to parathyroid hormone and prostaglandin E2 in cells cultured from human giant cell tumors of bone.

Cells dispersed from human giant cell tumors of bone and grown in monolayer culture increase intracellular cyclic AMP (cAMP) when incubated with parathyroid hormone (PTH) or prostaglandin E2 (PGE2). When cells are continuously exposed to PTH, cAMP levels increase acutely but then decrease rapidly to pretreatment values despite continued presence of hormone or addition of new hormone. Preincubation of cells with PTH for periods as short as 10 min results in a decrease in the capacity of cells to increase cAMP content when re-exposed to maximal stimulatory concentrations of PTH. The decrease in the magnitude of the PTH-induced cAMP response observed in cells pretreated with this hormone is dependent on the concentration of PTH present during the preincubation. The loss of cAMP response in cells pretreated with either PGE2 or PTH is hormone specific in that cells made refractory by pretreatment with one hormone still increase cAMP content when exposed to the other. Although the cells are not releasing measurable amounts of prostaglandins into the medium, pretreatment with indomethacin results in an increase in the magnitude of the cAMP response to PGE2. The PTH-induced cAMP response is not affected by indomethacin pretreatment. The loss of PTH responsiveness produced by hormone preincubation is consistent with the phenomenon of "down-regulation" observed with ligand-receptor interactions in a variety of tissues.

1-Methyl-3-isobutylxanthine↗
PubMed1975

A comparison of the effects of the calcitonins, steroid hormones and thyroid hormones on the response of bone to parathyroid hormone in tissue culture.

A bone culture system was used to compare the effects of several hormones on the response of 5-day-old mouse calvaria to parathyroid hormone (PTH). The results showed that salmon calcitonin was almost 10-5 times more active than any other hormone in preventing the PTH-induced release of calcium and caused a dose-related inhibition of calcium release over a range of 0-2-200 milli MRC units/culture. A high dose of calcitonin (200 milli MRC units) caused a net accretion of calcium in the absence of PTH. Progesterone and testosterone were more active than the naturally occurring oestrogens although a synthetic oestrogen (stillboestrol diphosphate) had approximately the same potency. High concentrations of these hormones caused a net accretion of calcium whether or not PTH was present. Cortisol was only effective at high doses, as was the steroid precursor cholesterol. In the present culture system the thyroid hormones (triiodothyronine and thyroxine) inhibited the action of PTH. It was concluded that these agents acted in a similar fashion to the oestrogens. That is, they prevented the accumulation of citric acid induced by PTH by reducing the rate of glycolysis. None of the hormones affected the inhibition of citrate oxidation caused by PTH. The results also showed that, whilst these hormones inhibited PTH-mediated bone resorption, they had an action on bone independent of PTH. Experiments with clomiphene citrate failed to demonstrate an oestrogen receptor in bone.

Animals↗
PubMed1978

Effect of parathyroid hormone on plasma prolactin in man.

The iv infusion of parathyroid extract or the synthetic fragments of 1-34 bovine or human parathyroid hormone produced a rapid and marked increase of plasma PRL in normal subjects. The stimulation of the release of endogenous parathyroid hormone by administration of disodium EDTA also resulted in a parallel increase of plasma PRL. Parathyroid hormone did not act via plasma cAMP, as the plasma level reached by this nucleotide was too small to produce PRL release. The ingestion of L-dopa 2 h before parathyroid hormone infusion suppressed the PRL response, suggesting that dopamine and parathyroid hormone interact at a common site. As it has been recently shown that PRL stimulates the renal synthesis of 1,25-dihydroxycholecalciferol, the present data suggest that the effect of parathyroid hormone on this synthesis may be due to the increase in plasma PRL.

Adult↗
PubMed1979

The interrelationships among prolactin, 1,25-dihydroxyvitamin D, and parathyroid hormone in humans.

Serum PRL, parathyroid hormone (PTH), and plasma 1,25-dihydroxyvitamin D [1,25(OH)2D]concentrations were measured in 6 women and 2 men with hyperprolactinemia, 6 normal men and 7 normal women, 4 men and 4 women with primary hyperparathyroidism, and 16 men and 4 women with Ca nephrolithiasis. Plasma 1,25(OH)2D and serum parathyroid hormone (PTH) concentrations were normal in the women and men with hyperprolactinemia. In patients with primary hyperparathyroidism and elevated serum PTH, plasma 1,25(OH)2D concentrations were elevated but serum PRL levels were normal. Likewise, serum PRL levels were normal in patients with Ca nephrolithiasis who had significantly elevated plasma, 1,25(OH)2D concentrations and normal serum PTH concentrations. Thus, hyperprolactinemia due to pituitary adenoma or idiopathic hypersecretion is not accompanied but elevated plasma concentrations of 1,25(OH)2D.

Adenoma↗
PubMed1975

Selective proteolysis of the receptor for parathyroid hormone in renal cortex.

Studies were carried out to determine if the receptors for parathyroid hormone, calcitonin, and prostaglandin E1 could be differentiated in renal cortex. Slices of rabbit renal cortex were incubated in buffer containing theophylline for 1 hr and then in fresh buffer with and without hormone for an additional period of 15 to 30 min. Parathyroid hormone caused a marked increase in 3',5'-AMP in both the tissue and the reaction medium. The maximal increase in 3',5'-AMP in response to prostaglandin E1 was similar to that of parathyroid hormone in the tissue but significantly less in the medium. The maximal response to calcitonin was less in both the tissue and the medium. Addition of 200 mug/ml trypsin to the first incubation abolished the subsequent response to parathyroid hormone in both the tissue and the reaction medium but did not affect the basal concentration of 3',5'-AMP or the response to calcitonin or prostaglandin E1. Controls were carried out to show that the lack of response to parathyroid hormone could not be attributed to hydrolysis of the hormone by residual trypsin. Slices were also homogenized after preincubation with and without trypsin and assayed for adenylate cyclase activity. Incubation with trypsin markedly diminished the increase in enzyme activity in response to parathyroid hormone but did not alter the basal activity or the response to calcitonin or sodium fluoride. The response to prostaglandin E1 was significantly increased. Combinations of any two or the three hormones at maximal concentrations caused an additive increase in adenylate cyclase activity. The results indicate that the receptors for parathyroid hormone, calcitonin and prostaglandin E1 in renal cortex are separate and the receptor for parathyroid hormone can be selectively hydrolyzed by proteolytic digestion.

Adenylyl Cyclases↗
PubMed1978

Autoantibodies to parathyroid hormone receptor.

Autoantibodies which block the binding of parathyroid hormone to membrane receptors for the hormone were detected in the sera (especially in the IgG fraction) of 49 out of 50 uraemic patients with secondary hyperparathyroidism (patients with high levels of C-regional parathyroid hormone). These antibodies are species-specific. Their presence in the serum in unaffected by dialysis. Inhibition of binding appears to be related to the rise in C-regional parathyroid-hormone levels and the duration of uraemia. The production of cyclic adenosine monophosphate by parathyroid-hormone-stimulated adenyl cyclase was reduced by the blocking antibodies. The findings show that secondary hyperparathyrodism in uraemia is another example of a receptor-antibody disease, but it is not known whether the antibodies act by modifying the affinity of the receptors for the hormone or by reducing the concentration of receptors available.

Animals↗
PubMed1978

Effects of calcium intake and renal function on plasma immunoreactive parathyroid hormone levels in rats.

Parathyroid hormone (PTH) was estimated with a radioimmunoassay system which recognised presumably intact rat PTH as the major circulating species. A low calcium diet was found to increase PTH levels in shamoperated and in 5/6-nephrectomized rats. In rats with normal renal function, a low calcium intake resulted in a significant mean increase of PTH levels, while changes in plasma calcium, magnesium, phosphate and protein concentrations were not detectable; at the same time the ability of the duodenum to transport calcium in vitro was accelerated. In 5/6-nephrectomized rats, on the other hand, PTH levels were dramatically increased in hypocalcemic animals kept on a calcium deficient diet, while intestinal calcium transport was impaired. These data support the concept that hypocalcemia is the most important stimulus for increased PTH release. Since increased PTH levels can be seen in situations where increased 1,25-dihydroxy-cholecalciferol synthesis is known to occur, it appears that this metabolite cannot inhibit a rise in plasma PTH levels.

Animals↗
PubMed1977

Renal effects of native parathyroid hormone and synthetic biologically active fragments in pseudohypoparathyroidism and hypoparathyroidism.

To gain further insight into the biological significance of parathyroid hormone (PTH) metabolism, native parathyroid hormone and synthetic peptides, similar to PTH metabolites generated in vivo, have been given intravenously to human subjects. The resultant changes in renal excretion of adenosine 6':5' monophosphate (cyclic AMP) and inorganic phosphate have been measured in five pseudohypoparathyroid, four hypoparathyroid, and one pseudopseudohypoparathyroid patient. As anticipated, native PTH promptly increased urinary cyclic AMP and phosphate excretion in the hypoparathyroid and pseudo-pseudohypoparathyroid patients, and had little or no effect on their excretion in the pseudohypoparathyroid patients. Synthetic bovine parathyroid hormone 1-34 and synthetic human parathyroid hormone 1-34 had effects essentially identical to each other and to native PTH. We conclude that the PTH resistance of pseudohypoparathyroidism is probably not caused by a defect in PTH metabolism. We further conclude that synthetic human or bovine parathyroid hormone 1-34 could be used for diagnostic evaluation of patients.

Creatinine↗
PubMed1979

Effect of parathyroid hormone on bicarbonate absorption by proximal tubules in vitro.

The effect of parathyroid hormone on bicarbonate absorption was tested in rabbit proximal renal tubules perfused in vitro. In proximal straight tubules 0.05 U/ml of parathyroid hormone caused a large and reversible increase in the steady-state bicarbonate concentration in tubule fluid. Further, the rates of bicarbonate and fluid absorption (measured at faster flow rates) were inhibited approximately 50% by the hormone. We conclude that parathyroid hormone directly inhibits fluid and bicarbonate absorption by proximal straight tubules, causing an increase in the bicarbonate concentration in the tubule fluid, and we suggest that this action of the hormone contributes to the increase in renal bicarbonate excretion that is generally caused by the hormone. In proximal convoluted tubules, parathyroid hormone was previously demonstrated by other investigators to inhibit fluid and bicarbonate absorption approximately proportionally, so that there was little or no change in the bicarbonate concentration in tubule fluid. In agreement we found in the present studies that 0.05 U/ml of the hormone did not affect the steady-state bicarbonate concentration in proximal convoluted tubule fluid and that 5 U/ml caused only an equivocal increase in tubule fluid bicarbonate concentration.

Absorption↗
PubMed1978

[Renal receptors of parathyroid hormone and calcitonin (author's transl)].

The two first steps of the renal cellular action of parathyroid hormone and of calcitonin are the hormonal binding onto specific receptors and the stimulation of adenylate cyclase by the hormone-receptor complex producing an increase in the intra-cellular concentration of 3'-5' cyclic adenosine monophosphate (cyclic AMP). Specific glomerular and tubular receptors for parathyroid hormone have been demonstrated using either tritiated parathyroid hormone or an indirect technique with 125 I labelled specific antibodies. Tubular receptors are localized both in the proximal and distal segments of the nephron. Parathyroid hormone stimulates glomerular and tubular adenylate cyclase. The main unsolved problem is the difficulty for demonstrating high affinity binding sites and stimulation of adenylate cyclase at low physiological concentrations of parathyroid hormone. In man, administration of parathyroid hormone produces a marked increase in the urinary excretion of cyclic AMP chiefly concerning its nephrogenous fraction. The peak of excretion is early and precedes the decrease in phosphate tubular reabsorption. Tubular receptors for calcitonin have been demonstrated using 125 I labelled salmon calcitonin. Calcitonin stimulates renal adenylate cyclase in only some segments of the nephron allowing receptors for calcitonin to be localized in the wide ascending branch of Henle's loop and the initial part of the convoluted distal tubule. In the presence of guanylnucleotides, binding of calcitonin onto its receptors and activation of adenylate cyclase are observed in the range of physiological concentrations of calcitonin in the rat. In man, administration of calcitonin produces a moderate increase in the urinary excretion of cyclic AMP coming from a non renal tissue.

Adenosine Monophosphate↗
PubMed1976

Reversible resistance to the renal action of parathyroid hormone in man.

1. Normal subjects showed a highly reproducible, rapid increase in plasma adenosine 3':5'-cyclic monophosphate (cyclic AMP) after an intravenous injection of 200 MRC units of highly purified bovine parathyroid hormone. 2. No significant increase in plasma cyclic AMP was observed after administration of bovine parathyroid hormone to patients with severe chronic renal failure. 3. Even when renal function was not impaired, some patients with primary hyperparathyroidism, who had high concentrations of endogenous parathyroid hormone, showed resistance to bovine parathyroid hormone and when this was injected intravenously it caused only a small increase in plasma cyclic AMP. This resistance was reversible since there was marked improvement in the response after parathyroidectomy, when endogenous parathyroid hormone concentration had fallen. 4. It was possible to reproduce this resistance to the hormone by intravenous infusion of bovine parathyroid hormone into normal subjects. When the hormone (1000 MRC units) was infused over 2 h, after an initial increase there was a progressive decline in plasma cyclic AMP concentration and a fall in urinary cyclic AMP excretion. The response to a standard test stimulus (200 MRC units of bovine parathyroid hormone given as a rapid intravenous injection) was examined at intervals after 1000 units of bovine parathyroid hormone had been infused. Initially, the response was severely impaired; at 4 h, partial recovery had occurred and, 24 h after the infusion, recovery of the response was complete. The resistance was therefore reversible. Infusion of the amino-terminal peptide, fragment 1-34, gave the same effect as infusion of intact hormone. Region-specific assays for the hormone were used to show that the concentration of immuno-assayable hormone remained high during the infusions. 5. The mechanism of this reversible resistance to parathyroid hormone remains to be elucidated; it seems unlikely that circulating hormone fragments could account for the prolonged impairment in the responsiveness to the intact hormone. It is possible that alteration in the formation, intracellular degradation or, perhaps, release of cyclic AMP from the cells, is the cause. Changes in the characteristics of the hormone receptor sites might also explain the phenomenon.

Aged↗
PubMed1979

Binding of bovine parathyroid hormone to surface receptors of cultured B-lymphocytes.

Binding of parathyroid hormone onto B-lymphocytes is detected by the utilization of the labelled antibody membrane assay. The amount of parathyroid hormone bound to the receptor sites was depending on the quantity of cells in the incubation milieu. Each cell line showed typical characteristics in time course of parathyroid hormone binding and maximal receptor capacity. Fragmentation of intact parathyroid hormone, also varying with the cell line tested, was very rapid, even at 24 degrees C. Within 20 min most of the cell lines destroyed 20% of the native hormone in the incubation mixture, indicating a fragmentation rate of up to 2.25 ng/min at 37 degrees C. Bmax and KD for the different lymphocytes was 5.3--19 . 10(11) M and 1.8--18,5 . 10(11) M, respectively. These values are in the range of reported plasma concentrations and may therefore represent more physiological values for the capacity and affinity of membrane receptors.

Animals↗