Effect of aluminum and parathyroid hormone on osteoblasts and bone mineralization in chronic renal failure

Bone aluminum, quantitative bone histology, and plasma parathyroid hormone (PTH) were compared in 29 patients undergoing chronic hemodialysis. Histologic techniques included double tetracycline labeling and histochemical identification of osteoclasts and osteoblasts. Bone aluminum was measured chemically by flameless atomic absorption spectrophotometry, and histochemically. When measured chemically, the bone aluminum was 67 +/- 46 (SD) mg/kg dry weight (normal 2.4 +/- 1.2 mg/kg); histochemically, aluminum was present at 2.9 +/- 4.4% of trabecular surface. The biochemical and histochemical results agreed well (r = 0.80, P less than 0.001). No double tetracycline labels were seen at the mineralization front where aluminum was deposited, indicating cessation of mineralization at these sites. The osteoblast surface correlated positively with plasma PTH (r = 0.67, P less than 0.001) and negatively with bone aluminum level (r = -0.42, P less than 0.05). Multiple linear regression showed a correlation of aluminum with osteoblasts additional to that of PTH, consistent with a direct effect of aluminum in depressing osteoblast numbers. Though a relationship between PTH and chemically determined bone aluminum level could not be demonstrated, there was a negative correlation between osteoclast count and aluminum, and the nine patients with severe hyperparathyroid bone disease had lower chemically determined aluminum levels than the other patients. These results suggest that aluminum (a) directly inhibits mineralization, (b) is associated with decreased PTH activity and hence osteoblast numbers, and (c) directly reduces osteoblast numbers. In addition to inducing severe, resistant osteomalacia, aluminum appears to contribute to the mild osteomalacia commonly seen in renal failure, characterized by extensive thin osteoid and low tetracycline and osteoblast surfaces.     

Frusemide therapy and intact parathyroid hormone plasma concentrations in chronic renal insufficiency.

It has been suggested that frusemide affects plasma parathyroid hormone (PTH) concentrations. To further investigate this issue we analysed plasma intact PTH in 77 patients with chronic renal failure (CCr 8.0-89.8 ml/min per 1.73 m2) as a function of frusemide therapy. The rate of increase of plasma PTH observed with progression of renal failure was faster in patients who received frusemide as compared to patients who did not receive the drug. The slope of the regression line of PTH on CCr was steeper (P less than 0.02) for patients with frusemide (n = 40, slope -0.34) than without frusemide (n = 37, slope -0.20). This effect was specific for frusemide therapy since therapy with other antihypertensive drugs (including thiazides and beta-blockers) was not correlated with PTH plasma concentrations. Frusemide therapy was also associated with a significantly greater urinary calcium excretion in uraemic patients but did not influence other parameters of calcium metabolism. To clarify mechanisms involved in the effect of frusemide on plasma PTH values, seven normal subjects were studied for 24 h before and for 24 h after oral administration of 80 mg frusemide. The main findings were: (1) Median PTH values were higher than on a control day (P less than 0.05) 3 h after frusemide (3.9 pmol/l vs 1.8) and 6 h after frusemide (4.0 vs 2.6); (2) ionised plasma calcium did not change significantly, whereas mean calcium/creatinine ratio increased from 0.20 to 0.46 after frusemide treatment through an increase in absolute calcium excretion; (3) plasma 1 alpha,25-dihydroxyvitamin D3, catecholamines, and magnesium concentrations did not change significantly after frusemide.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of erythropoiesis in chronic renal failure: the role of parathyroid hormone

Sera from 20 anemic patients with chronic renal failure (CFR) were studied for their effect on bone marrow in vitro erythroid colony formation (CFUE) and the observations correlated with parathyroid hormone (PTH) and ionized calcium levels in the patients' sera. Results demonstrated that 17 out of 20 patients' sera significantly inhibited in vitro erythropoiesis by 47% to 97%. No significant elevation in ionized calcium was found in 16 of the patients tested. Furthermore, assay of PTH levels in these patients revealed that 9 out of 20 had elevated levels of PTH. No correlation was found between PTH serum levels and the degree of in vitro inhibition of erythropoiesis (CFUE) by the patients' sera. Addition of up to 2,000 pg/mL (far above the patients' levels) of exogenous N-terminal or C-terminal PTH with in vitro bone marrow cultures resulted in no inhibitory effect on CFUE. It is concluded that the circulating inhibitor of erythropoiesis which has been shown to exist in the sera of this particular group of patients with CRF, is not PTH.     

Parathyroid hormone and its fragments in children with chronic renal failure

Parathyroid hormone (PTH) immunoradiometric assays (IRMA) exhibit cross-reactivity between 1-84 PTH and long carboxyl-terminal-PTH (C-PTH) molecules. C-PTH antagonizes the biological actions of 1-84 PTH and circulates in excess in chronic renal failure (CRF), partially explaining why supra-physiological PTH levels are recommended to maintain bone turnover. Furthermore, the ratio 1-84 PTH/C-PTH may be related to bone turnover. This study characterizes the 1-84 PTH/C-PTH ratio in children with varying severity of CRF and levels of PTH. Two hundred and forty-one children with CRF, managed with the aim of preventing the development of hyperparathyroidism, had PTH measured by intact IRMA and a new more specific Cyclase-Activating-PTH (CAP) IRMA. C-PTH levels were calculated by subtracting CAP-IRMA from intact IRMA. Fifty-three controls with normal renal function were also recruited. Mean intact IRMA correlated with CAP-IRMA (r=0.98), but was higher (P<0.001). The mean 1-84 PTH/C-PTH ratio was lower than controls in dialysis patients (P=0.022) and those with a glomerular filtration rate <30 ml/min per m² (P=0.033). This ratio was comparable to controls when the PTH level was normal, but was lower with PTH levels outside the normal range (P<0.01). These data suggest that CAP-IRMA gives a more accurate assessment of actual PTH levels than intact IRMA in CRF. Maintenance of normal PTH levels throughout the course of CRF permits the maintenance of a normal 1-84 PTH/C-PTH ratio, the clinical significance of which requires further investigation in children.     

Abnormal skeletal response to parathyroid hormone and the expression of its receptor in chronic uremia

Chronic renal failure is characterized by a resistance to the hypercalcemic action of parathyroid hormone (PTH). This resistance probably involves several mechanisms, including a disturbance of vitamin D metabolism, a desensitization of the skeleton by high PTH levels, hyperphosphatemia, uremic toxins, and acidosis. We have explored the possibility that a downregulation of the recently cloned PTH/PTHrp receptor might also be involved. We found a marked decrease in the expression of the receptor mRNA in the kidney and the bone of uremic rats; other authors have found a decrease in the heart and the liver. The reduced expression in the kidney was accompanied by a diminished stimulability of renal adenylate cyclase activity, suggestive of a functional depression of the hormonal response in this target tissue. It is probable that the downregulation of the PTH/PTHrp receptor plays an important role in the skeletal resistance to the calcemic effect of PTH in chronic renal failure.     

慢性肾脏病患者甲状旁腺激素水平对肾性贫血的影响

目的 探讨慢性肾脏病（CKD）患者甲状旁腺激素（PTH）升高致红细胞寿命缩短的机制。 方法 以住院初治的CKD患者75例（按eGFR分为1～2期、3～4期和5期）和健康对照组30例为对象。免疫发光法测全段甲状旁腺激素（iPTH）;流式细胞术测红细胞表面磷脂酰丝氨酸（PS）外翻水平及红细胞内钙离子浓度（[Ca2+]i）。 结果 （1）随着肾功能的减退,CKD3～4期及5期患者 iPTH、[Ca2+]i及红细胞表面PS外翻水平逐渐升高、贫血逐渐加重,明显高于CKD1～2期和对照组（均P < 0.05）。（2）CKD3～4期或5期患者Hb与iPTH和红细胞表面PS外翻水平呈负相关（r = -0.830和-0.791,均P < 0.01）;iPTH与 [Ca2+]i和红细胞表面PS外翻水平呈正相关（r = 0.882和0.924,均P < 0.01）,与血钙浓度呈负相关（r = -0.544, P < 0.01）;红细胞表面PS外翻水平与 [Ca2+]i呈正相关（r = 0.923,P < 0.01）,与血钙浓度无相关（r = -0.138,P = 0.365）。（3）[Ca2+]i（Y）对iPTH（X）的直线回归方程：Y=3.327+0.213X（F=21.529,P < 0.05）;红细胞表面PS外翻水平（Y）对iPTH（X1）及[Ca2+]i（X2）的多元线性回归方程：Y=-0.303+0.283X2+0.139X1（F = 6.59,P < 0.01）。 结论 iPTH增加红细胞内钙离子浓度,引起红细胞表面PS外翻增多,致红细胞寿命缩短而加重肾性贫血。     

Intestinal calcium absorption,serum phosphate,and parathyroid hormone in patients with chronic renal failure and osteodystrophy before and during hemodialysis

Summary In 34 patients with chronic renal failure (CRF), fractional⁴⁷calcium absorption (Fa⁴⁷Ca) was measured by an external counting method. A significant correlation was found with impairment of renal function, as expressed by the creatinine clearance. There was also a significant correlation of Fa⁴⁷Ca with the serum phosphate (SeP) level and of immunoreactive parathyroid hormone (iPTH) with renal function. When the relationship of both SeP and Fa⁴⁷Ca with creatinine clearance was excluded, no partial correlation between SeP and Fa⁴⁷Ca appeared to exist. A significant increase of Fa⁴⁷Ca and serum Ca and a significant decrease of SeP and iPTH were found in 12 patients 2 to 15 months after they were put on intermittent hemodialysis. The possible influence of SeP on intestinal calcium absorption is discussed, and it is suggested that impairment of intestinal absorption of calcium is not a main factor in development of renal osteodystrophy.     

Phosphorus deficiency,parathyroid hormone and bone resorption in the growing rat

Sham-operated and parathyroidectomized (PTX) rats were divided into two pair-fed groups, one on a normal mineral intake (0.5% Ca, 0.3% P), the other on a regimen low in phosphorus (0.5% Ca, 0.03% P). P depletion led to a drop in plasma P and urine P, a rise in plasma Ca and a marked rise in urine Ca, a drop in serum magnesium and a rise in urine Mg. The changes were more pronounced in the PTX animals, but final values were the same in both groups. Parallel bone-seeking isotope (⁸⁵Sr,¹⁷⁷Lu,²³⁷Np) studies in nonablated animals revealed an increased in the urinary nuclide output and in the urine/tibia ratio in P-deficient animals. Normal and primary bone osteocytes decreased and enlarged osteocytes increased as a result of P deficiency; osteoclasts and osteoblasts also increased. Bone composition showed a drop in ash content and a rise in water, with a light decrease in both Ca and P, and a corresponding rise in hydroxyproline and nitrogen in the P-deficient animals. The results are interpreted to mean that P-deficiency in the young growing rat leads to an increase in bone resorption which occurs also in the absence of parathyroid hormone (PTH). The fact that final values were similar in the control and PTX P-deficient animals suggests that steady-state regulation can also occur without PTH. Because P-deficiency leads to rapid hypercalcemia and rapid marked hypercalciuria, there may exist a mechanism for phosphate regulation which would then supersede Ca homeostasis. The change in serum and urine Mg levels may reflect a decrease in tubular Ca and Mg reabsorption associated with P-deficiency.     

Effects of parathyroid hormone on the osteoclastic pool,bone resorption and formation in rat alveolar bone

Summary The osteoclast number and its relation to parathyroid hormone have been studied in rat alveolar bone by quantitative histology and fluorescent labeling. The osteoclast number decreases 60 h after parathyroidectomy and remains constant for the next 132 h. Parathyroid hormone administration to parathyroidectomized animals 96 h after the operation induces an increase in osteoclast number within 12 h to some-what above those of control animals. The elevated osteoclast counts remain constant for 60 h then rapidly fall over the next 24 h to the level seen in untreated parathyroidectomized animals. As determined by fluorescent labeling, normal alveolar bone resorption and formation were disturbed by parathyroidectomy, such that significant bone formation occurred for only 6 days after surgery, after which a quiescent state followed.     

Skeletal actions of intermittent parathyroid hormone: effects on bone remodelling and structure

Intermittent administration of parathyroid hormone peptides has anabolic skeletal effects and reduces fracture risk in postmenopausal women with osteoporosis but the cellular and structural mechanisms by which these effects are mediated have not been fully established. In cancellous and endocortical bone, there is evidence that both modelling and remodelling-based formation contribute to the increase in bone mass although the contribution of these at different time points in the response to PTH has not been established. Despite the large increase in spine bone mineral density, however, significant increases in iliac crest cancellous bone volume and trabecular thickness have not been consistently demonstrated, possibly reflecting site-specific differences in PTH-induced skeletal effects and/or the large sampling and measurement variance associated with assessment of iliac crest cancellous bone volume and structure. In iliac crest cortical bone, increased cortical thickness has been demonstrated, due at least in part to increased endosteal bone formation; there is also some evidence for increased formation on periosteal surfaces. At some sites an increase in cortical porosity may also occur and the overall effects on cortical bone strength, particularly at the hip, remain to be established. Studies in iliac crest bone indicate a trend towards a lower mineralisation density of bone matrix and increased heterogeneity of mineralisation, consistent with new bone formation. In addition, there is a reduction in mineral crystallinity and a shift towards more divalent collagen cross-links, indicating a change towards a younger bone profile.

The potential clinical implications of these effects on bone are currently unknown. The stimulatory effect of PTH peptides on bone formation may favour their use in low turnover bone disease and in states of advanced bone loss. Furthermore, if beneficial effects on cortical bone strength are confirmed, efficacy at non-vertebral sites might be superior to those observed with antiresorptive drugs. Better definition of the effects of intermittent PTH administration on cancellous and cortical bone remodelling and structure at different skeletal sites may inform these speculations and is an important area for future research.     

Effect of lithium on parathyroid hormone-induced calcium release from bone rudiments

Summary Lithium treatment of humans and animals has been associated with adverse effects on bone and mineral metabolism. In order to determine whether lithium was altering the skeletal response to parathyroid hormone, we incubated bone rudiments for 5 days in the presence or absence of the drugs. Lithium had no effect on either parathyroid hormone-induced cyclic AMP generation or⁴⁵Ca release from the bone rudiments. The data are consistent with the hypothesis that the skeletal effects of lithium are not mediated via inhibition of the parathyroid hormone-adenyl cyclase-cyclic AMP system.     

老年男性甲状旁腺激素与骨密度的关系

本文的目的在于探讨在健康老年人中，甲状旁腺素（ＰＴＨ），钙（Ｃａ）、磷（Ｐ）、镁（Ｍｇ）、碱性磷酸酶（ＡＫＰ）、肌酐（Ｃｒ）与骨密度（ＢＭＤ）之间的关系。选择７０名健康老人，抽血查Ｃ－ＰＴＨ、Ｃａ、Ｐ、Ｍｇ、ＡＫＰ和Ｃｒ的水平。并在左侧桡骨远端１／３处，用单能光子骨密度测定仪测定ＢＭＤ。以正常参考值为标准（０．６２９７～０．７６９５ｇ／ｃｍ２），将对象分为ＢＭＤ降低组和ＢＭＤ正常组。结果显示：（１）在ＢＭＤ正常组（ＢＭＤ值为０．７３±０．０７ｇ／ｃｍ２）中，ＰＴＨ的水平为１５５．３６±９３．４５（ｎｇ／Ｌ），在ＢＭＤ降低组（ＢＭＤ值为０．５７±０．０４ｇ／ｃｍ２）中，ＰＴＨ的水平为２１４．１１±９１．９３（ｎｇ／Ｌ）。二组间差异有统计学意义。（２）在ＢＭＤ正常组中，血清钙的水平为２．１２±０．２２（ｍｍｏｌ／Ｌ），在ＢＭＤ降低组中，血清钙的水平为２．２３±０．１９（ｍｍｏｌ／Ｌ）。两组相比，差别有统计学意义（Ｐ＜０．０５）。实验结果提示：在老年男性与年龄有关的骨密度降低中，ＰＴＨ的分泌起到重要作用。     

Plasma calcitonin in rats with renal failure

Summary To study the effect of the kidney on blood calcitonin (CT), rats were made uremic by either total or partial nephrectomy or bilateral ligation of the ureters. Plasma CT concentrations were measured by radioimmunoassay before and after calcium infusion. Uremia induced by total or partial nephrectomy produced an increase in plasma CT. Rats had higher plasma CT levels (49.3±1.7 pg/ml, mean ±SE) after total nephrectomy than after ureteral ligation (30.9±1.5 pg/ml) even though no significant difference was observed between the blood urea nitrogen (BUN) levels of these two groups. These results indicate that the kidney contributes to the degradation of CT.     

Abnormal skeletal response to parathyroid hormone in dogs with chronic uremia

Summary The release of cyclic AMP from bone in response to stimulation with PTH 1–34 was examined in 20 dogs with long-term chronic renal failure (CRF) produced by unilateral nephrectomy and contralateral partial renal artery ligation. After 9 to 15 months of uremia, the tibiae were removed and perfused in vitro. Seven dogs with CRF served as controls, 7 dogs with CRF were treated with 24,25(OH)₂D₃ — 2.5 μg per day, and 6 CRF dogs underwent thyroparathyroidectomy (TPTX) 42 h before they were sacrificed. The release of cyclic AMP from bone in response to PTH 1–34 in the CRF dogs was severely reduced compared to the response observed in 7 dogs with normal renal function (net accumulation of cyclic AMP release 86±8.5 versus 426±59.0 pmol/30 min). Long-term treatment of uremic dogs with 24,25(OH)₂D₃ had no effect on the release of cyclic AMP by bone. However, the release of cyclic AMP was restored to normal levels in the CRF dogs that underwent thyroparathyroidectomy. All CRF dogs had secondary hyperparathyroidism and the fact that TPTX returned the cyclic AMP response to normal values suggests that desensitization to PTH of the adenylate cyclase system of bone exists in chronic uremia.     

慢性肾衰竭患者腰椎骨密度测定分析

目的 观察慢性肾衰竭病人骨密度（BMD）值的变化.方法 采用双能X线骨密度测定的方法测定201例慢性肾衰竭病人的1～4腰椎前后位BMD值,并与年龄、性别相匹配的正常人1～4腰椎前后位BMD值进行比较分析.结果 慢性肾衰竭早期（氮质血症期）、肾衰竭期与尿毒症期患者BMD测定值无明显差异（P＞0.05）.慢性肾衰竭患者BMD测定值明显低于正常对照组（P＜0.05）.结论 慢性肾衰竭早期BMD值已明显降低,骨量丢失在慢性肾衰竭出现前已经开始.BMD测定敏感性较高,可以在慢性肾衰竭早期反映患者骨含量变化,是目前早期诊断肾性骨病的较好方法.     

Role of carbonic anhydrase in bone resorption: Effect of acetazolamide on basal and parathyroid hormone-induced bone metabolism

Summary The effects of the carbonic anhydrase inhibitor acetazolamide on basal and parathyroid hormone (PTH)-induced bone metabolism were studied to evaluate the manner in which acetazolamide inhibits bone resorption. Half-calvaria from 5 to 6-day-old mice were cultured using the following treatments: control; acetazolamide (10, 33, or 100 μM); PTH (16.7 nM bovine PTH 1-34); acetazolamide + PTH. The effects of acetazolamide on PTH-induced cAMP accumulation and protein synthesis were determined. Media from bones cultured for 48 hours were analyzed for calcium to assess bone resorption, glucose to assess calvarial glucose utilization, and lactic acid to assess calvarial lactic acid release. Media were also assayed for β-glucuronidase activity as an indicator of lysosomal enzyme release and for lactate dehydrogenase activity as an indicator of cytosolic enzyme release and cytotoxicity. Acetazolamide at 100 μM completely inhibited PTH-induced bone resorption. This inhibition did not appear to be due to cell death, as acetazolamide did not increase lactate dehydrogenase release. Acetazolamide had no effect on PTH-enhanced cAMP levels, indicating that receptor binding and adenylate cyclase activation were unaffected. Acetazolamide alone did not alter calvarial protein synthesis, but did significantly inhibit protein synthesis in the presence of PTH. PTH significantly enhanced calvarial glucose utilization, lactic acid release, and β-glucuronidase release. Acetazolamide inhibited all of these PTH-induced parameters in a manner that roughly paralleled its inhibition of bone resorption; acetazolamide alone had no effect on the basal values. Our results indicate that acetazolamide inhibition of bone resorptionin vitro may involve general alterations in hormonally stimulated bone cell metabolism secondary to carbonic anhydrase inhibition.     

Effects of parathyroid hormone on alkaline phosphatase activity and mineralization of cultured chick embryo tibiae

Summary The objectives of this study were (a) to determine if decreased bone alkaline phosphatase (AlPase) activity, resulting either from exposure to parathyroid hormone (PTH) or from direct inhibition of AlPase with levamisole, was concomitant with net changes in bone Ca and P content; and (b) to determine the duration of the effect of PTH on bone AlPase activity after the hormone was removed. Tibiae from 7-day chick embryos were incubated in chemically defined medium for 3–4 days. The Ca and P content of bones incubated for 72 h in this system increased from 2-to 9-fold. Addition of PTH (1 U/ml) to the medium resulted in a 60% decrease in bone AlPase activity, and this decrease was accompanied by a marked inhibition of Ca and P accumulation in bone. When levamisole, a specific inhibitor of AlPase activity, was added to the medium, a similar inhibition of bone mineral accumulation resulted. A 24-h incubation in medium containing PTH (1 U/ml) resulted in a 30% decrease in bone AlPase activity. Following the 24-h exposure to PTH, incubation was continued in medium containing no hormone. After 72 h in hormone-free medium, bones that had been exposed to PTH earlier contained more AlPase activity than paired control bones never exposed to PTH. The PTH-treated bones also recovered their ability to accumulate Ca and P. The results of this study show that: (a) decreased bone AlPase activity resulting from either exposure to PTH or direct inhibition by levamisole is associated with a marked decrease in mineral accumulation in bone; (b) exposure to PTH followed by removal of the hormone leads to recovery and even an increase in bone AlPase activity; and (c) following removal of PTH from the culture system, tibiae recover their ability to accumulate Ca and P. These results suggest that one of the ways PTH may alter mineral accretion is through its effects on bone AlPase activity.     

Effect of endogenous and infused parathyroid hormone on plasma concentrations of recently administered45Ca

Summary The net rate of loss of⁴⁵Ca from plasma was monitored in normal, thyroparathyroidectomized (TPTX), and nephrectomized rats. Also studied was the effect of a 24 h intravenous infusion of PTH in TPTX rats. The⁴⁵Ca was injected after an overnight fast and 1 to 4 h prior to the time the first blood sample was obtained.In normal rats, the net rate of loss of⁴⁵Ca from plasma was slower than in TPTX rats for at least 12 h after radionuclide injection. Nephrectomy did not affect this difference between control and TPTX rats until 8 h after⁴⁵Ca injection or about 18 h after nephrectomy. At this time a reversal occurred and the net rate of plasma⁴⁵Ca loss in nephrectomized rats with parathyroids became faster than in TPTX nephrectomized rats.When PTH was infused at a constant rate (3 mU/g body weight/h) plasma calcium concentrations rose gradually for approximately 12 h after which a constant plasma calcium level was maintained with continued PTH infusion. During the period when plasma calcium concentrations were rising, the net rate of loss of⁴⁵Ca from plasma was slower than in TPTX controls infused only with saline. However, when plasma levels stabilized, plasma⁴⁵Ca disappearance rates changed such that the rate loss of⁴⁵Ca from plasma became faster in PTH-infused than in TPTX controls.It is concluded that PTH increases calcium efflux from the same compartment in bone which receives calcium from plasma, thereby returning some recently deposited⁴⁵Ca to plasma. In the non-equilibrated state, this returns additional⁴⁵Ca to plasma causing anet decrease in the rate of loss of⁴⁵Ca from plasma. However, in the equilibrated condition, when both calcium efflux from bone and influx into bone are in balance but at higher flux rates, PTH stimulates the diffusion of⁴⁵Ca into other bone compartments.