Zoledronic acid efficacy and safety over five years in postmenopausal osteoporosis

In a 5-year study involving 119 postmenopausal women, zoledronic acid 4 mg given once-yearly for 2, 3 or 5 years was well tolerated with no evidence of excessive bone turnover reduction or any safety signals. BMD increased significantly. Bone turnover markers decreased from baseline and were maintained within premenopausal reference ranges.

INTRODUCTION

After completion of the core study, two consecutive, 2-year, open-label extensions investigated the efficacy and safety of zoledronic acid 4 mg over 5 years in postmenopausal osteoporosis.

METHODS

In the core study, patients received 1 to 4 mg zoledronic acid or placebo. In the first extension, most patients received 4 mg per year and then patients entered the second extension and received 4 mg per year or calcium only. Patients were divided into three subgroups according to years of active treatment received (2, 3 or 5 years). Changes in BMD and bone turnover markers (bone ALP and CTX-I) were assessed.

RESULTS

All subgroups showed substantial increases in BMD and decreases in bone markers. By the end of the core study, 37.5% of patients revealed a suboptimal reduction (< 30%) of bone ALP levels. After subsequent study drug administration during the extensions, there was no evidence of progressive reduction of bone turnover markers. Furthermore, increased marker levels after treatment discontinuation demonstrates preservation of bone remodelling capacity.

CONCLUSIONS

This study showed that zoledronic acid 4 mg once-yearly was well tolerated and effective in reducing biomarkers over 5 years. Detailed analysis of bone marker changes, however, suggests that this drug regimen causes insufficient reduction of remodelling activity in one third of patients.

The effect of intranasal salmon calcitonin on postmenopausal bone turnover as assessed by biochemical markers: evidence of maximal effect after 8 weeks of continuous treatment

Although treatment with intranasal salmon calcitonin (sCT) has been shown to effectively inhibit postmenopausal bone loss, there is still controversy over both timing and the duration of its application. In an open prospective study, we therefore assessed the effect of shortterm intranasal sCT on postmenopausal bone turnover, employing biochemical markers of bone metabolism. Ten early postmenopausal, previously untreated women (1-5 years after menopause) with biochemical evidence of increased bone resorption and a low bone mineral density at baseline were treated with intranasal sCT (100 IU B.I.D.) for a period of 3 months. Oral calcium (500 mg/day) was administered simultaneously, and during a further 3 month follow-up interval. Treatment with sCT resulted in a pronounced suppression of bone resorption markers with a maximum effect reached after 8 weeks of therapy: as compared to the respective baseline values, mean levels decreased by -26.2% +/- 3.4% (P < 0.001) for pyridinoline, -32.7% +/- 3.5% (P < 0.001) for deoxypyridinoline, -32.7% +/- 3.3% (P < 0.001) for hydroxyproline, and -24.1% +/- 8.2% (P < 0.001) for the amino-terminal telopeptide. In contrast, changes in bone formation markers of osteocalcin (-14.4% +/- 4.8%, P < 0.05) and C-terminal procollagen type I propetide (-7.9% +/- 3.9%, ns) were much less pronounced. Unexpectedly, after week 8 of the study all resorption markers showed a plateau and a trend to increase, although intranasal sCT was continued for a total of 12 weeks. This effect could not be attributed to the formation of anti-sCT antibodies. After cessation of treatment, both bone formation and resorption markers rapidly returned to baseline levels. Bone mineral density of both spine and hip showed no significant change during the observation period. Our results demonstrate that in postmenopausal women with a high bone turnover, intranasal treatment with 200 IU of sCT effectively reduces bone turnover and maintains bone mass, the maximum effect being reached after 8 weeks of treatment.

The effect of rat parathyroid hormone (1-34) infusion on urinary 3-hydroxypyridinium cross-link excretion in the rat

The utility of measurement of the urinary excretion of the 3-hydroxypyridinium cross-links, pyridinoline (Pyr) and deoxypyridinoline (Dpyr) as indices of bone resorption in rats was investigated. Total Pyr and Dpyr excretion were measured in young rats treated by s.c. infusion with rat parathyroid hormone (1-34) (PTH) at 22-30 micrograms/kg/day or with diluent (controls) for 14 days. During infusion, average urinary excretion of both cross-links was significantly higher in PTH rats (Pyr: 11.77 +/- 0.44 nmol/day), Dpyr: 15.81 +/- 0.95 nmol/day) than in controls (Pyr: 10.17 +/- 0.35 nmol/day, Dpyr: 12.03 +/- 0.67 nmol/day). These results were consistent with the magnitude of the expected increase in bone resorption rate with this dose of PTH. The method appears to provide a sensitive measure of bone resorption for in vivo bone studies in rats.

N-terminal truncation of salmon calcitonin leads to calcitonin antagonists. Structure activity relationship of N-terminally truncated salmon calcitonin fragments in vitro and in vivo

Structural requirements for binding to the bone calcitonin (CT) receptor and for CT bioactivity both in vitro and in vivo were assessed for a series of N-terminally truncated, N alpha-acetylated, fragments of salmon calcitonin (sCT). Sequential deletion of amino acid residues from the amino-terminus of [Ala7]sCT-(2-32) peptide amide first led to partial agonists and, upon deletion of residues 1 to 7, to a high affinity antagonist, N alpha-acetyl-sCT-(8-32)-NH2. The presence of two separate domains within the sCT sequence is proposed: (I) a binding domain comprising residues 9-32 and (II) an activation domain requiring residues 3 to 6. N alpha-acetyl-sCT-(8-32)-NH2, in several bioassays including plasminogen activator release from LLC-PK1 cells (pA2 = 7.31), cAMP production in UMR-106-06 cells (pA2 = 7.81) and in the fetal rat long bone resorption assay showed potent antagonistic properties.

Somatostatin receptors are restricted to a subpopulation of osteoblast-like cells during endochondral bone formation

Specific binding sites for the peptide hormone somatostatin have previously been demonstrated in long bones from neonatal rats. In the present study, the distribution of somatostatin receptors during embryonic bone formation has been investigated using the stable radioiodinated somatostatin analogue, SDZ 204-090. Somatostatin receptors in rat long bones were first detectable at the time of invasion of the cartilage model by osteogenic cells. Initially, receptors were detectable throughout the region occupied by osteogenic cells. As bone growth proceeded, however, receptors were restricted to the region of most recent invasion of the hypertrophic cartilage, where osteoid had not yet been deposited. In vivo labelling studies in neonatal rats were carried out to identify the cells bearing somatostatin receptors. Receptors were present in a restricted region of the metaphysis, immediately adjacent to the hypertrophic cartilage. Chondrocytes, osteoclasts, and mature osteoblasts were not labelled by the radioligand. The labelled cells were often apposed to remnants of cartilage matrix and stained positively for the osteoblast marker, alkaline phosphatase. Thus the cells with specific somatostatin-binding sites were probably osteoblast precursor cells. Specific binding was detectable in all endochondral bones examined, including those of the skull, but no specific binding was found in the membrane bones of the skull. These data suggest that somatostatin is involved in the regulation of osteoblast differentiation during endochondral bone formation.

Phosphate transport adaptation in rat jejunum and plasma level of 1,25-dihydroxyvitamin D3

Intestinal absorption of inorganic phosphate (Pi) increases in response to a reduction in the dietary supply of Pi. In this work this adaptive response has been characterized in jejunal brush border membrane vesicles and studied in temporal relationship with the change in the plasma level of 1,25(OH)2D3. The results indicate that in rat jejunal brush border membrane vesicles the activity of the sodium-dependent Pi transport system is stimulated by a low Pi diet. This adaptive response was the result of an increase in the Vmax and a reduction in the Km of the cotransport system. This change in Pi transport was correlated with an increase in the circulating level of 1,25(OH)2D3 in a time-related fashion. In conclusion, these results are consistent with the notion that Pi restriction leads to an increase in Pi transport activity in the luminal membrane of the intestine. A time course study suggests that the elevation in plasma 1,25(OH)2D3 might be involved in the adaptation of the intestinal Pi transport system to Pi restriction.

Stimulation of bone formation in vivo by transforming growth factor-beta: remodeling of woven bone and lack of inhibition by indomethacin

Local effects of transforming growth factor-beta (TGF beta) on bone have been investigated in growing mice. The influence of indomethacin on TGF beta effects was also examined. Five daily injections of TGF beta-1 or -2 were administered subcutaneously over the frontal and parietal bones of seven-week-old mice. In animals treated with TGF beta alone or TGF beta and indomethacin, then killed on day 19 (day 1 = day of first TGF beta injection), the combined frontal and parietal bones were heavier and the frontal bones were thicker than in controls. On day 4, multiple layers of differentiating osteoblasts were visible in the periosteum of calvariae from TGF beta-treated animals. On day 8, highly vascularised periosteal woven bone was seen in the calvariae of TGF beta-treated animals. On day 19 (14 days after the last injection) the woven bone had been partially remodeled into lamellar bone containing bone marrow, and was still actively being remodeled. The histological appearance of bones from animals treated concurrently with TGF beta and indomethacin was identical to that of animals treated with TGF beta alone, and there appeared to be no difference between TGF beta-1 and TGF beta-2. Thus TGF beta-stimulated bone formation in vivo is a long term effect that appears to be independent of prostaglandins. Osteoclast counts in sections of TGF beta-treated animals were not elevated on day 4, although at this stage effects on osteoblastic cells were already morphologically apparent. Osteoclast counts in TGF beta-treated bones were significantly increased over control values on days 8 and 19.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-6 is produced by bone and modulated by parathyroid hormone

Interleukin-6 (IL-6) is a cellular regulatory molecule, the diverse functions of which relate to cells both within and outside the immune system. In this report we demonstrated that bone tissue, specifically osteoblasts, produce interleukin-6 and that this function can be modulated by the osteotrophic hormone parathyroid hormone (PTH). Given that the complex process of bone remodeling is now thought to be regulated not only by systemic hormones but also by locally produced factors, the existence of a parathyroid hormone-stimulated production of interleukin-6 by osteoblasts may have important physiological significance.

Short- and long-term effects of a single dose of bisphosphonates on retinoid-induced bone resorption in thyroparathyroidectomized rats

The inhibitory effect of a single subcutaneous (s.c.) dose of three different bisphosphonates (Bps)--4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP), 2-(2-pyridinyl)-ethylidene-1,1-bisphosphonate (2-PEBP), and dichloromethylene-bisphosphonate (Cl2MBP)--was studied in a model of retinoid-induced bone resorption, which consists of assessing the hypercalcemic effect of the arotinoid Ro 13-6298 given s.c. for three days in thyroparathyroidectomized (TPTX) rats. The retinoid was given on day 0, 1, and 2. Bps were administered together with or at different times prior to the first dose of retinoid. A dose-dependent inhibition was obtained with all three compounds. AHBuBP produced complete inhibition which remained for 3 weeks at 0.1 mg P/kg. The dose-response curves were identical when the compound was given on the first day of retinoid administration (day 0) or 6 days earlier. With 2-PEBP, the dose-response curve was the same as that for AHBuBP when given on day 0. When given 6 days earlier, the curve was shifted to 30 times less potency. Cl2MBP was about 100 times less potent than AHBuBP when given on day 0, with 3 mg P/kg producing complete inhibition. When given 6 days earlier, the curve was also shifted to 10 times less potency, and even 30 mg P/kg failed to produce complete inhibition. With 10 mg P/kg, the inhibitory effect was maintained partially for up to 3 weeks. This study shows that in this model of bone resorption the inhibitory effect of a single dose of certain Bps is effective for at least 3 weeks and that the compounds vary in their activity over time.

Bisphosphonates inhibit 1,25-dihydroxyvitamin D3-induced increase of osteocalcin in plasma of rats in vivo and in culture medium of rat calvaria in vitro

In order to test whether bisphosphonates, which are potent inhibitors of osteoclastic bone resorption, may also act upon osteoblasts, we studied the effect of dichloromethylenebisphosphonate (Cl2MBP) and 4-amino-1-hydroxybutylidene-1,1-bisphosphonate (AHBuBP) on in vivo levels and in vitro release of osteocalcin, a bone-specific protein produced by osteoblasts. In rats, 161 mumol/kg of Cl2MBP or 1.61 mumol/kg AHBuBP strongly inhibited the increase of plasma osteocalcin induced by 1,25(OH)2D3. The inhibition was measurable within 24 hours after the administration of bisphosphonate and was independent of any change in bone resorption. The effect upon osteocalcin release was also present in calvaria cultures. 250 microM Cl2MBP strongly inhibited the osteocalcin release induced by 10(-8) M 1,25(OH)2D3. In the presence of 1,25(OH)2D3, protein synthesis and DNA synthesis were also decreased, whereas in the absence of 1,25(OH)2D3, protein synthesis was increased. Thus, bisphosphonates affect the production of a bone-specific protein by osteoblasts in addition to their inhibitory action on osteoclasts.

Parathyroid hormone-independent regulation of 1,25(OH)2D in response to inhibition of bone resorption

Both plasma level of 1,25-dihydroxyvitamin D [1,25(OH)2D] and intestinal Ca absorption increase after biphosphonate-induced inhibition of bone resorption. Parathyroid hormone (PTH) has been considered a key mediating element of this homeostatic response. In the present work, the role of PTH was assessed by studying the influence of 1-hydroxypentane-1,1-bisphosphonate (HPeBP) on vitamin D and Ca metabolism in both intact and thyroparathyroidectomized (TPTX) rats. In intact rats, HPeBP given at 0.1 mg P/kg body wt sc for 10 days strongly inhibited bone resorption without affecting bone formation. This effect was associated with a marked stimulation of intestinal Ca absorption and Ca balance. In this condition, HPeBP caused a marked rise in plasma 1.25(OH)2D without affecting the level of 25-hydroxyvitamin D. In TPTX rats, HPeBP given at same dose also inhibited bone resorption and enhanced plasma 1,25(OH)2D, intestinal Ca absorption and Ca balance. In summary, this study shows that bisphosphonates such as HPeBP with prevailing inhibitory activity on bone resorption induce a marked stimulation of both 1,25(OH)2D production and intestinal Ca absorption. This homeostatic response is not attenuated after PTH removal. Thus, as previously shown for the response to low Ca diet, PTH does not appear to be an essential mediating factor for stimulating 1,25(OH)2D production in response to an increase in bone mineral retention.

Production of hemopoietic growth factors by bone tissue and bone cells in culture

This study was carried out to determine whether bone might be a source of hemopoietic growth factors. Both neonatal murine calvaria and primary cultures of cells isolated from calvaria released, upon stimulation with lipopolysaccharide, an activity that stimulated the growth of the interleukin (IL) 3-dependent cell lines, 32D cl, 123, and NSF 60. Upon gel filtration, this activity eluted with a molecular weight of 30,000 kDa. Further characterization, however, revealed that the major activity in conditioned medium was not IL 3. Activity was absorbed by DEAE-Sephacel at low salt concentration, whereas IL 3 does not adhere. Furthermore, an IL 3-specific antiserum did not neutralize the activity from cells and only partly neutralized the activity generated by whole calvaria. After gel filtration, the 30-kDa activity stimulated the growth of very large colonies in semisolid medium consisting mainly of granulocytes with the remainder being macrophages. No colony types belonging to other hemopoietic lineages were found, indicating, again, that the activity was not identical to IL 3. Subsequently, conditioned medium was fractionated by hydrophobic chromatography on Phenyl-Sepharose CL-4B, yielding two peaks of activity. Neutralization of activity with antisera to granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL 3 and use of colony assays showed that medium conditioned by whole calvaria contained GM-CSF and granulocyte CSF (G-CSF) in similar amounts together with a little IL 3, and medium conditioned with calvaria cells contained GM-CSF and little G-CSF. We conclude that bone releases hemopoietic growth factors that could contribute both to hemopoiesis and to the recruitment of osteoclasts from progenitors resident in the adjacent marrow.

Hypercalcemia induced with an arotinoid in thyroparathyroidectomized rats. New model to study bone resorption in vivo

A model of stimulated bone resorption was developed using a synthetic retinoid in thyroparathyroidectomized rats. The retinoid induced an increase in bone resorption and in the number of vertebral subperiosteal osteoclasts. The resulting increase in plasma Ca could be used as an easily measured index of bone resorption. Three bisphosphonates produced a dose-related prevention and reversal of retinoid-induced hypercalcemia. Their potencies were similar to those previously obtained by histomorphometry. Irradiation (600 rad) of the rats prevented hypercalcemia but failed to reverse it, showing that proliferation of osteoclast precursor cells was important in inducing, but not in maintaining, bone resorption. Calcitonin produced similar effects on calcemia and prevented the increase in osteoclast number but failed to reverse the increase, suggesting that it inhibited precursor proliferation. This model represents a new tool to study mechanisms of bone resorption and the action of inhibitors in vivo.

Effect of synthetic calcium pyrophosphate and hydroxyapatite crystals on the interaction of human blood mononuclear cells with chondrocytes, synovial cells, and fibroblasts

Synthetic calcium pyrophosphate dihydrate crystals and, to a lesser extent, synthetic hydroxyapatite crystals increased the amount of interleukin-1/mononuclear cell factor released by human blood monocytes, as measured by collagenase and prostaglandin E2 production by rabbit chondrocytes, human dermal fibroblasts, and adherent rheumatoid synovial cells. The same crystals also directly induced collagenase and prostaglandin E2 secretion by rabbit chondrocytes, and potentiated the action of interleukin-1/mononuclear cell factor on chondrocytes. These mechanisms may be important in the pathogenesis of the destructive arthropathies associated with these crystals.

Effect of a single injection of two new bisphosphonates on the hypercalcemia and hypercalciuria induced by Walker carcinosarcoma 256/B in thyroparathyroidectomized rats

The effect of one single injection of two new bisphosphonates, 4-amino-1-hydroxybutylidene-1,1-bisphosphonate and 2-(2-pyridyl)ethylidene-1,1-bisphosphonate, and of dichloromethylenebisphosphonate on the hypercalcemia and hypercalciuria induced by the Walker carcinosarcoma 256/B in the thyroparathyroidectomized rat was evaluated. When given either before or after the development of hypercalcemia and hypercalciuria, 16.1 mumol/kg 4-amino-1-hydroxybutylidene-1,1-bisphosphonate or 2-(2-pyridyl)ethylidene-1,1-bisphosphonate totally inhibited hypercalciuria, whereas hypercalcemia was only partially reduced over the 14 days of the experiment. At 10 and 100 times lower doses, the effect was strongest the first days, but still partially present 14 days later. The difference of activity on calcemia and calciuria appears to be due to the fact that the tumor increased both bone resorption and renal reabsorption of calcium. Only the former was altered by the bisphosphonates. The two new compounds appeared to be of similar potency and more active than dichloromethylenebisphosphonate. These compounds could be promising for the treatment of malignant hypercalcemia and other conditions with increased bone resorption in humans, even when given only over short periods of time.

The increase in skin 7-dehydrocholesterol induced by an hypocholesterolemic agent is associated with elevated 25-hydroxyvitamin D3 plasma level

Vitamin D3 is generated in skin by UV irradiation of 7-dehydrocholesterol (7-DEHC). Whether the 7-DEHC amount in skin affects vitamin D3 formation, and thereby the plasma level of 25-hydroxyvitamin D3 (25[OH]D3) is not known. In the present work we report on the influence on vitamin D and Ca metabolism of a new hypocholesterolemic agent, HCG-917 (0-2-[hydroxy-3-]N'-(2-chlorophenyl)-N-piperazinyl-1- [propyl]-4-chloro-benz-aldoxim-hydrochloride) which inhibits 7-DEHC reductase and thereby increases skin 7-DEHC. Rats were treated with HCG 917 (0.3 and 5.0 mg/kg, orally) for 13 days. HCG 917 caused a dose-dependent decrease in cholesterol and concomitant accumulation of 7-DEHC in plasma and skin. In skin, 7-DEHC was: control: 1.05 +/- 0.20; HCG 917, 0.3 mg/kg: 1.41 +/- 0.22; HCG 917, 5.0 mg/kg: 2.35 +/- 0.35 mg/g. At a dose of 0.3 mg/kg, HCG 917 had no significant influence on the plasma level of neither 25(OH)D3 nor 1,25(OH)2D3. However, at a dose of 5.0 mg/kg, HCG 917 induced a significant increase in plasma 25(OH)D3 (control: 36.2 +/- 2.2; HCG 917 5.0 mg/kg: 57.6 +/- 6.5 nmol/l) and a slight but not significant rise in 1,25(OH)2D3. Calcium balance studies indicated that HCG 917 did not influence intestinal Ca absorption nor urinary Ca excretion. At a dose of 5.0 mg/kg HCG 917 slightly induced a decrease in total plasma Ca. In conclusion, HCG 917 treatment can induce a significant rise in skin 7-DEHC with an increase in plasma 25(OH)D3. These results suggest that variation in the skin level of 7-DEHC can directly influence the cutaneous production of vitamin D3 and thereby the vitamin D status of the organism.

Murine osteoblastlike cells and the osteogenic cell MC3T3-E1 release a macrophage colony-stimulating activity in culture

The osteoclast may be of hematopoietic lineage and as such its development could be regulated by colony-stimulating factors. Since there is much interest as to whether osteoblasts influence bone resorption, we examined whether bone cells produce colony-stimulating activity. Both cells isolated from neonatal calvaria and the osteogenic cell MC3T3-E1 were found to constitutively release a colony-stimulating activity possessing characteristics of a macrophage colony-stimulating factor, as determined by basic biochemical purification and by identity of colonies induced in cultures of bone marrow cells. Release could be increased by the presence of the bone-resorbing agents lipopolysaccharide and 1,25 dihydroxyvitamin D3. We conclude that the osteoblast may contribute to both the processes of osteoclast formation and of hematopoiesis through the secretion of colony-stimulating activity into the adjacent bone marrow.

[The regulation of bone remodeling]

The adult skeleton is subject to a remodeling process which must be tightly regulated to keep bone mass constant. Bone resorption and bone formation are coupled. After a brief review of the cellular mechanisms of bone remodeling, its regulation is discussed. Bone resorption is modulated by parathyroid hormone, 1,25-dihydroxyvitamin D and other hormones. Locally, agents such as prostaglandins and factors from the immune system are important. Bone formation is stimulated by insulin and somatomedin C (= insulin like growth factor 1) which mediates the effect of growth hormone. Other hormones and local factors also play a role.

Influence of vitamin D3 metabolites on the production of interleukins 1,2 and 3

We investigated the effect of vitamin D3 metabolites on the release of the three interleukins (IL) IL 1, IL 2 and IL 3 by mononuclear cells. Models for the production of these mediators were the release of IL 1 by the murine macrophage cell line P388D1, of IL2 by rat spleen cells, and of IL 3 by the murine WEHI-3 cell line. IL 1 production was significantly increased with 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) at 10(-10)M and above. 1,25(OH)2D3 did not stimulate cell proliferation as assessed with [methyl-3H]thymidine (3H-TdR) incorporation. 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) and 25-hydroxyvitamin D3 (25(OH)D3) were about 1000 times less effective than 1,25(OH)2D3. IL 2 production, by cultured rat spleen cells stimulated with Concanavalin A, was decreased by increasing concentrations of 1,25(OH)2D3. The minimal effective dose varied between experiments and ranged from 10(-11) to 10(-8) M. Moreover, proliferation (3H-TdR incorporation) of mouse thymocytes treated with phytohemagglutinin and IL 1 was decreased in a dose-dependent fashion by 1,25(OH)2D3 starting at 10-11) M. This effect might be secondary to a decrease of endogenous IL 2 production. IL 3 release by WEHI-3 cells was significantly increased with 10(-11)-10(-9) M 1,25(OH)2D3, whereas higher concentrations were less effective or decreased IL 3 production. These results show that 1,25(OH)2D3 and, to a lesser extent, 24,25(OH)2D3 and 25(OH)D3 have selective effects on lymphokine production. It is tempting to speculate that the actions of 1,25(OH)2D3 on bone might in part be mediated by lymphokines. Moreover, we suggest that 1,25(OH)2D3 might not be an immunoregulator per se, but makes use of the immune system to exert its influence on one of its classical targets, namely the bone, and possibly on other connective tissues.

Suppression of parathyroid secretion after administration of WR-2721 in a patient with parathyroid carcinoma

WR-2721 is an organic thiophosphate, known as a radioprotective agent, which also inhibits parathyroid hormone (PTH) secretion and reduces the plasma calcium level in euparathyroid animals and human subjects. In this study we present evidence that WR-2721 is also able to reduce an abnormal PTH secretion in a case of parathyroid carcinoma. The intravenous infusion of a single dose (750 mg/m2) of WR-2721 was followed within 3 h by a reduction in the plasma concentration of PTH by 60%, and of Ca by about 0.45 mmol/l. These changes were associated with a diminution in urinary cAMP excretion. Based on this observation it appears that WR-2721 merits further investigation as a possible agent for the medical treatment of hyperparathyroidism.

Stimulation of interleukin 1 and 3 production by retinoic acid in vitro

Retinoic acid and other retinoids stimulate or inhibit a number of immune responses, but their mechanism of action on immune cells is not fully understood. However, retinoids have been shown to inhibit interferon production, so they could act by influencing the production of lymphokines. Hence we have studied the effect of retinoic acid on the production of interleukins (ILs) 1 and 3 in vitro. Models for the production of ILs were the murine macrophage cell line P388D1 and human peripheral blood mononuclear cells for IL 1 and the murine WEHI-3 cell line for IL 3. Retinoic acid stimulated IL 1 release by P388D1 cells in a dose-related fashion, starting at 10(-9) M and maximally at 10(-8)-10(-6) M. With peripheral blood mononuclear cells a maximal stimulation of IL 1 release was observed with 10(-7) M-retinoic acid. IL 3 release by WEHI-3 cells was also stimulated by retinoic acid in a dose-related fashion. The maximal response was obtained with 10(-8) M-retinoic acid. These results show that retinoic acid, in physiological concentrations, exerts selective effects on interleukin production in vitro, and this stimulation of IL 1 and IL 3 release may explain some of the immunostimulatory effects of retinoids in vivo. Moreover, since IL 1 is known to influence connective tissues and bone, an increase in IL 1 might also explain some of the changes observed in these tissues in vitamin A poisoning and with high-dose retinoid therapy.

Effect of bisphosphonates on production of interleukin 1-like activity by macrophages and its effect on rabbit chondrocytes

Bisphosphonates are potent inhibitors of bone resorption, but their mode of action is still unknown. Since interleukin 1 (IL-1)-like activity has been shown to stimulate bone resorption in vitro, we have studied whether bisphosphonates inhibit either the production of IL-1-like activity or its effect on one type of connective tissue cell, chondrocytes. The production of IL-1-like activity was examined using rabbit peritoneal macrophages and the murine macrophage cell line P388D1, and the effect of IL-1-like activity was assessed by measuring the secretion of collagenase and prostaglandin E2 (PGE2) by rabbit chondrocytes. Production of IL-1-like activity was unaffected by bisphosphonates, whereas the effect of IL-1-like activity on collagenase and prostaglandin E2 secretion by rabbit chondrocytes was increased rather than inhibited by bisphosphonates. Finally, bisphosphonates increased DNA and cell number in chondrocyte cultures, but this effect was blocked when IL-1-like activity was added to the cultures. Thus, our results provide no evidence for a direct inhibitory effect of bisphosphonates on either the production of IL-1-like activity or the action of IL-1-like activity on chondrocytes.

Evidence for a particularly severe secondary hyperparathyroidism in analgesic abuse nephropathy

Ca metabolism was compared in two groups of patients with chronic interstitial nephritis: in 21 patients (analgesic abuse nephropathy (AAN) group), nephropathy was due to exposure for 5-50 years (mean 21.1) to phenacetin-containing analgesics, whereas in 21 other patients (controls) it was due to exposure for 1-80 years (mean 21.4; NS) to other causes. Patients were followed for 2.5 +/- 0.6 and 1.6 +/- 0.6 years, respectively (mean +/- SEM; NS). Blood Ca, P, protein, creatinine, alkaline phosphatase, parathyroid hormone (PTH), 25-hydroxyvitamin D (25(OH)D), 1,25-dihydroxyvitamin D (1,25(OH)2D) as well as arterial acid-base status and urinary excretion rate of Ca, P and creatinine were determined serially. Results were included only when P was maintained between 0.7 and 1.9 mmol/l. The range of creatinine levels studied was 95-1,600 mumol/l. No differences were found between the two groups with respect to creatinine clearance, blood P, protein, arterial pH and bicarbonate, and urinary excretion rates of Ca and P. Mean plasma Ca was significantly lower, and PTH was significantly higher in the AAN group than in the control group; mean plasma alkaline phosphatase activity was also significantly higher in the AAN group. In both groups Ca was negatively correlated with creatinine, but the slope of the regression line was steeper in the AAN group than in controls. The degree of hypocalcemia was related to the increase in plasma PTH and alkaline phosphatase, but not to the plasma level of 25(OH)D or 1,25(OH)2D.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin 2-independent stimulation of rabbit chondrocyte collagenase and prostaglandin E2 production by an interleukin 1-like factor

In the present study, interleukin 1 (IL 1)-containing media from different sources, namely a murine macrophage cell line (P388D1), rabbit peritoneal macrophages, and human peripheral blood mononuclear cells, were compared for their effect on thymocyte proliferation and on collagenase and PGE2 secretion by chondrocytes. A high correlation was found between the enhancement of thymocyte proliferation and the induction of collagenase and PGE2 secretion by chondrocytes. Furthermore, a highly purified IL 1-like factor, namely mononuclear cell factor (MCF) was also active on chondrocytes. The addition of highly purified IL 2 to rabbit chondrocytes had no effect on collagenase and PGE2 secretion induced by IL 1-containing media. Our findings suggest that the factor which induced collagenase and PGE2 secretion by rabbit chondrocytes was an IL 1-like factor. Thus, collagenase secretion by chondrocytes may be used as an IL 2-insensitive assay for the detection of IL 1-like factors.

Influence of macrophage products on the release of plasminogen activator, collagenase, beta-glucuronidase and prostaglandin E2 by articular chondrocytes

We describe the effects of products of mononuclear phagocytes on the secretory activity of chondrocytes. The primary confluent cultures of rabbit articular chondrocytes were exposed to standard medium alone or enriched with conditioned medium obtained from cultures of rabbit peritoneal macrophages, the mouse macrophage cell line P388D1 or human blood mononuclear cells. Four markers of release were assessed, the neutral proteinases plasminogen activator and collagenase, the acid hydrolase beta-glucuronidase and prostaglandin E2, and the kinetics of their changes were monitored. Chondrocytes that were cultured in standard medium secreted large amounts of plasminogen activator, some beta-glucuronidase, but no collagenase, and released only minor amounts of prostaglandin E2. The addition of conditioned medium from rabbit macrophages induced a rapid release of large quantities of prostaglandin E2 and an abundant secretion of collagenase, while abolishing or strongly decreasing plasminogen activator secretion. In addition, beta-glucuronidase secretion was markedly enhanced. The decrease in secretion of plasminogen activator appeared to reflect a diminished production, since no evidence was found for the generation of inhibitors or for an accelerated extracellular breakdown of the enzyme. Conditioned media of the mouse and human mononuclear cells influenced the secretory activities of rabbit articular chondrocytes in a similar way, suggesting that the factor (or factors) acting on chondrocytes is produced by a variety of macrophages, and that its action is not species-restricted. The time course and concentration-dependence of the effects observed indicate that the secretion of plasminogen activator and collagenase are influenced in a strictly reciprocal fashion by the macrophage products. The release of prostaglandin E2 paralleled that of collagenase.

Lack of effects of 1,25- and 24,25-dihydroxy vitamin D on parathyroid hormone response to hypocalcemia in cattle

Effects of 1,25(OH)2D3 or 24,25(OH)2D3 on plasma PTH were examined following induced hypocalcemia with EGTA. EGTA infusions caused an elevation of plasma PTH within 10 min. Sixty min after the start of EGTA infusions, 1,25(OH)2D3 or 24,25(OH)2D3 were IV administered. Transient (within 5 min) elevations in plasma PTH were observed in two of five animals following the administration of 1,25(OH)2D3 or of 24,25(OH)2D3. Neither secosterol had an effect on the induced elevations in plasma PTH during the remaining 60 min of the EGTA infusions. Twenty-two hr following 24,25(OH)2D3 administration, plasma PTH, ionized and total calcium, inorganic phosphate, and magnesium were normal, while plasma 24,25(OH)2D was elevated. The plasma PTH response to EGTA-induced hypocalcemia was not significantly altered from that observed prior to the administration of 24,25(OH)2D3. Animals, which were IV injected with 1,25(OH)2D3 received the same amount IM 60 min later. Twenty-two h following IM 1,25(OH)2D3, plasma 1,25(OH)2D, ionized and total calcium, and plasma inorganic phosphate were elevated. Plasma PTH and magnesium were lowered. The PTH response to EGTA-induced hypocalcemia was significantly reduced in these animals. A similar reduction in the PTH response to induced hypocalcemia was observed in animals receiving 7 hr IV infusions of calcium chloride. The findings suggest that the blunted response was, in part, the consequence of the preceding hypercalcemia. These results indicate that 1,25(OH)2D3 does not directly regulate plasma PTH secretion and that 24,25(OH)2D3 has no effect on plasma PTH during induced hypocalcemia in the bovine species.

Rapidity of plasma 1,25-dihydroxyvitamin D responses to hypo- and hypercalcemia in steers

Experiments were designed to study the rapidity of changes in plasma 1,25-dihydroxyvitamin D [1,25-(OH)2D] levels in response to hypercalcemia and hypocalcemia induced by 10-h infusions of CaCl2 or EGTA in steers. In response to CaCl2 infusions, 1,25-(OH)2D was decreased within 4 h (P less than 0.05) and remained lower (P less than 0.05) than preinfusion concentrations for up to 14 h after termination of the infusions. PTH and inorganic phosphate (Pin) transiently decreased in response to the CaCl2 infusions, whereas total magnesium (Mg) continuously fell for up to 24 h after the start of the infusions. In response to infusions with EGTA, on the other hand, 1,25-(OH)2D continuously increased and was raised significantly (P less than 0.05) between 12 and 24 h after the start of the infusions. PTH increased within 2 h (P less than 0.05) and remained elevated (P less than 0.05) for up to 2 h after the end of the EGTA infusions, whereas Pin and Mg were not significantly changed. During and after 10-h control infusions of sodium chloride, the levels of 1,25-(OH)2D, PTH, Ca, Ca++, Pin, and Mg remained unaltered. In conclusion, plasma levels of 1,25-(OH)2D were lowered in response to hypercalcemia within 4 h and increased in response to hypocalcemia within 12 h. After termination of the infusions with CaCl2 or EGTA, levels of 1,25-(OH)2D remained decreased or elevated for at least 14 h, even though Ca, Ca++, and PTH levels were normalized. The slow changes in 1,25-(OH)2D contrast with the rapid responses of PTH to hyper- and hypocalcemia.

Unilateral nephrectomy and 1,25-dihydroxyvitamin D3

Several renal functions respond to nephron loss by a compensatory adaptation. Whether the production of 1,25(OH)2D3 also adapts to a renal mass reduction is still a matter of controversy. In the present study we have investigated in rats the influence of unilateral nephrectomy, in both the acute (48 hr) and chronic (2 to 6 weeks) state, on plasma 1,25(OH)2D3 level measured by competitive protein binding assay. In the acute state no difference in plasma 1,25(OH)2D3 level between sham-operated (SHAM) and unilateral-nephrectomized (UNI-NX) rats was found. The presence of the thyroparathyroid glands was not required for maintaining plasma 1,25(OH)2D3 at a normal level 48 hr after UNI-NX. In the chronic state in rats fed at 1.1% Ca diet, plasma 1,25(OH)2D3 (means +/- SEM) was 94 +/- 4 in SHAM and 98 +/- 8 pM in UNI-NX. In rats fed a 0.1% Ca diet it was 252 +/- 16 in SHAM and 239 +/- 20 pM in UNI-NX. Analysis of 3H-1,25(OH)2D3 plasma decay curve indicated that in UNI-NX under a high calcium diet the normalization of plasma 1,25(OH)2D3 appears to be entirely due to an increase in production, whereas under a low calcium diet part of it may also result from a moderate decrease in the elimination rate. In conclusion, this study indicates that unilateral nephrectomy does not affect the level of plasma 1,25(OH)2D3 even under a calcium restriction challenge. This compensatory adaptation appears to be independent of parathyroid hormone.

Nature of calcemic effect of 1,25-dihydroxyvitamin D3 in experimental hypoparathyroidism

The influence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] treatment on the daily fluctuation of plasma calcium concentration ( [Ca]P1) in relation to the feeding-fasting alternation has been studied in vitamin D-replete sham-operated (sham) and thyroparathyroidectomized (TPTX) rats fed a normal Ca diet. 1,25(OH)2D3 was given (26 or 39 pmol/day) intraperitoneally either by single injection or constant infusion using osmotic minipumps. After 7 days of treatment [Ca]P1 was measured at 4-h intervals for 24 h. Pair-fed, sham and TPTX animals received the solvent vehicle intraperitoneally. The results show that in sham rats the very moderate daily fluctuation of [Ca]P1 was not accentuated by 1,25(OH)2D3. A marked fluctuation of [Ca]P1 in relation to the food intake was observed in untreated TPTX as compared with sham rats. In TPTX rats 1,25(OH)2D3 increased the fasting [Ca]P1. In contrast the rise in [Ca]P1 during feeding was not significantly accentuated by 1,25(OH)2D3. The daily fluctuation of [Ca]P1 was the same whether the dose of 1,25(OH)2D3 was given in one single injection or by constant infusion, suggesting that this hormone is not involved in the hour-to-hour regulation of [Ca]P1. In conclusion, in the absence of parathyroid glands, 1,25(OH)2D3 given in doses that stimulate intestinal calcium absorption has a much more pronounced effect on the fasting calcemia than on the rise in calcemia observed during the feeding period. These results suggest that the mobilization of calcium from bone could play an important role in the calcemic effect of 1,25(OH)2D3 when given in the hypoparathyroid state.

[Particularly severe calcium metabolic disorder in nephropathy from analgesic abuse]

Calcium (Ca) metabolism was compared in 2 groups of patients with chronic interstitial nephritis: in 21 patients (AAN-group) nephropathy was due to exposure for 5 to 50 years (mean 21.1) to phenacetin containing analgesics, whereas in 21 other patients (controls) it was due to exposure for 1 to 80 years (mean 21.4) (NS) to other causes. Patients were followed for 2.5 +/- 0.6 and 1.6 +/- 0.6 years respectively (mean +/- SEM) (NS). Blood Ca, P, protein, creatinine, alkaline phosphatase, parathyroid hormone (PTH), 25-hydroxyvitamin D (25-OH-D), together with arterial acid-base status and urinary excretion rate of Ca, P and creatinine were measured serially. For each patient the results were averaged for 2 degrees of renal failure, i.e. for creatinine levels below and above 400 mumol/l (logarithmic mean). Results were included only when P was maintained between 0.7 and 1.9 mmol/l. The range of creatinine levels studied was 95 to 1600 mumol/l. No differences were found between the 2 groups with respect to creatinine clearance, blood, P, protein, arterial pH and urinary excretion rates of Ca and P. There was a trend for blood HCO3 to be lower in the AAN group. Mean plasma Ca was significantly lower, and PTH was significantly higher, in the AAN than in the control group at both degrees of renal failure; mean plasma alkaline phosphatase activity was also significantly higher in the AAN group, but at severe degrees of renal failure only. Significant correlations were observed between individual values of both Ca and PTH (r = -0.747) and PTH and alkaline phosphatase (r = 0.603). The degree of hypocalcemia and of hyperparathyroidism was not related to the plasma level of 25-OH-D. It is concluded that at comparable degrees and duration of renal failure patients with AAN, when compared with patients with interstitial nephritis of other origins, have lower blood Ca and consequently higher PTH levels and alkaline phosphatase activities, suggesting more severe osteodystrophy.

[Primary hyperparathyroidism of the aged female: effect of estrogens on calcium metabolism]

Serum calcium, urinary calcium and a calcium loading test were evaluated twice in 5 elderly women with primary hyperparathyroidism, once not under and once under estrogen therapy. The treatment produced a significant lowering of blood calcium and normalization of urinary calcium excretion in the fasting state, per 24 h and after calcium load. Estrogen therapy might be useful in conservative treatment of asymptomatic hyperparathyroidism and in symptomatic cases where surgery is impossible.

Effects of products from macrophages, blood mononuclear cells and or retinol on collagenase secretion and collagen synthesis in chondrocyte culture

Collagenase secretion was studied on cultures of rabbit articular chondrocytes. Differentiation of the cells was assessed by characterizing the type of 3H-labelled collagen produced during treatment with (1) conditioned media from rabbit peritoneal macrophages and human blood mononuclear cells, and (2) with retinol, a potent cartilage resorbing agent in tissue culture. Conditioned media stimulated collagenase secretion. Total collagen synthesis was reduced due to a decrease of synthesis of alpha 1 chains; the amount of alpha 2 chains synthesized was unchanged. This is thought to be due to a reduction in type II synthesis. Retinol did not stimulate collagenase secretion. Total collagen synthesis was reduced by retinol. alpha 2 chain synthesis, however, was significantly increased, suggesting a switch of collagen synthesis in favor of type I collagen, and therefore, dedifferentiation. These results demonstrate that dedifferentiation of chondrocytes with respect to collagen synthesis is not necessarily associated with a stimulation of collagenase secretion.

Increase of whole-body calcium and skeletal mass in normal and osteoporotic adult rats treated with parathyroid hormone

1. The effect of long-term administration of parathyroid hormone (PTH) on whole-body calcium and ash weight of individual bones has been studied in normal and osteoporotic adult female rats in order to examine whether such a treatment could induce a positive calcium balance. 2. Osteoporosis was induced by calcium restriction during pregnancy and lactation. Sequential measurements of whole-body calcium were made by neutron activation. 3. In non-osteoporotic intact and thyroparathyroidectomized rats a daily dose of 75 units of human PTH 1-34 given subcutaneously for 3 weeks increased whole-body calcium. 4. In osteoporotic animals 25-50 units of either bovine PTH 1-84 or human PTH 1-34 given subcutaneously twice daily for 6 weeks increased both whole-body calcium and ash weight of individual bones. Microradiographic examination of the tibiae indicates, however, that PTH administration does not result in the restoration of individual trabeculae lost during the development of osteoporosis. 5. The results show that PTH can enhance skeletal mass in both normal and osteoporotic rats. In osteoporotic animals the restoration of whole-body calcium and ash weight of individual bones is not accompanied by a return of the morphological structure of the tibia to normal.

Plasma levels of vitamin D metabolites in diphosphonate-treated rats

1. Protein-binding assays have been used to measure plasma 1,25-dihydroxy-vitamin D [1,25-(OH)2D] as well as 25-hydroxy-vitamin D [25-(OH)D] in rats given 10 mg of phosphorus (P) day(-1) kg(-1) as ethane-1-hydroxy-1,1-diphosphonate (EHDP). 2. In control animals given a normal laboratory chow plasma 25-(OH)D and 1,25-(OH)2D were about 40 nmol/l and 300 pmol/l respectively. 3. EHDP produced a decrease of plasma 1,25-(OH)2D to below 50 pmol/l in 2 days. 4. Both in control and in EHDP-treated rats plasma 1,25-(OH)2D increased when dietary calcium (Ca) was restricted to 0.1%, or dietary P to 0.2%, indicating that the well-known stimulatory effect of Ca or P deprivation was at least partially effective in EHDP-treated rats. 5. In response to an increase of the oral supply of vitamin D3 to 65 nmol/day the plasma level of 25-(OH)D rose in both control and EHDP groups. Plasma 1,25-(OH)2D was not increased above the normal value in control rats. In EHDP-treated rats, however, plasma 1,25-(OH)2D rose to a level equal to that in controls, suggesting that the effect of EHDP on plasma 1,25-(OH)2D can be overcome at high precursor concentration.

Perinatal parathyroid hormone, vitamin D metabolites, and calcitonin in man

Plasma levels of calcium and of parathyroid hormone (PTH) were comparable in the mothers at delivery and in nonpregnant controls; magnesium was decreased (P < 0.001) in maternal blood; and phosphate (P < 0.001), 1,25-dihydroxyvitamin D (1,25(OH)2D) (P < 0.001), and calcitonin (CT) (P < 0.01) were raised. Cord levels of calcium (P < 0.01), magnesium (P < 0.05), and CT (P < 0.01) were higher, and PTH (P < 0.01) was lower than in the maternal blood. Levels of 25(OH)D, 1,25(OH)2D, and 24,25(OH)2D lower in fetal than in maternal blood (P < 0.01) and significant linear correlations between the vitamin D metabolites examined in mothers and neonates (P < 0.001) are consistent with a diffusion barrier across the placenta and/or different affinities of binding proteins. Plasma levels of 25(OH)D and 24,25(OH)2D were significantly related (P < 0.01), suggesting precursor product type, relationships. Levels of 1,25(OH)2D higher in arterial than in venous umbilical blood (P = 0.06, sign test; P < 0.005, paired t test) suggest that the fetus participates in the synthesis of 1,25(OH)2D. Maternal PTH was significantly related to the arteriovenous difference of 1,25(OH)2D levels (P < 0.01) in cord blood, and it possibly enhances the synthesis of 1,25(OH)2D during the final stage of fetal development.

Calcium-dependent, parathyroid hormone-independent regulation of 1,25-dihydroxyvitamin D

The increase of plasma 1,25-dihydroxyvitamin D (1,25(OH)2D) in response to Ca restriction has been suggested to be essentially mediated by parathyroid hormone (PTH). In this study, we have assessed the influence of variations in calcium intake on plasma 1,25(OH)2D in pair-fed sham-operated (sham) and in hypocalcemic hypoparathyroid rats after thyroparathyroidectomy (TPTX). In sham rats, plasma 1,25(OH)2D increased from 189 +/- 16 to 486 +/- 41 pM when dietary calcium was inreased from 1.2% Ca to 0.2% Ca. This increase was associated with an increase in plasma PTH level. In TPTX rats, plasma 1,25(OH)2D increased from 112 +/- 9 to 332 +/- 36 pM when dietary calcium was decreased. In this case, the increase was not associated with a rise in plasma PTH level nor with an increase in urinary cyclic AMP. When TPTX rats were infused chronically with PTH (60 U/day), plasma 1,25(OH)2D was 62 +/- 9 pM when the 1.2% Ca diet was given and 281 +/- 45 pM with the 0.2% Ca diet. These reults confirm that the thyroparathyroid glands influence plasma 1,25(OH)2D but they also provide evidence for a PTH-independent response of plasma 1,25(OH)2D to Ca restriction.

Use of dermestid beetles for cleaning bones

Various parts of the skeleton of normal and osteoporotic rats were compared with respect to their dry weight, ash weight, and calcium content when the bones were cleaned by Dermestes maculatus beetles or manually. Both techniques gave similar results. This was also true when whole body calcium measured by neutron activation and total skeletal calcium from bones cleaned by the beetles were compared. Thus dermestid beetles are useful as a technique to clean bones, especially for the parts of the skeleton which are difficult to dissect by hand.

Effects of disodium dichloromethylene diphosphonate on Paget's disease of bone

19 patients with Paget's disease were treated orally for 6 months with disodium dichloromethylene diphosphonate. 1600 mg/day (10 patients) significantly reduced urine hydroxyproline, serum alkaline phosphatase, urine calcium, and the number of pagetic bone osteoclasts. Tetracycline double labelling revealed undisturbed bone mineralisation. There was improvement on quantitative bone-scans and bone pain diminished. There was a transient increase in parathyroid hormone level in 13 of the 19 patients during treatment, which was associated with a high serum 1,25 (OH)2D3. No adverse clinical side-effects have been observed and biochemical remission has persisted for 9 months.

Regulation of the metabolism of 25-hydroxyvitamin D3 in primary cultures of chick kidney cells

A primary chick kidney cell culture is described, capable of forming 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], 24,25-dihydroxyvitamin D3 [24,25(OH)2D3], and 1,24,25-trihydroxyvitamin D3 [1,24,25(OH)3D3] over several days. The apparent Km values were 0.125 microM for the 1-hydroxylase and 2.1 microM for the 24-hydroxylase. Exogenous 1,25(OH)2D3 decreased 1-hydroxylase and increased 24-hydroxylase within 4 h. 24,25(OH)2D3 produced similar effects, but only in the absence of fetal calf serum. R and S isomers of 1,24,25(OH)3D3 were about fives times less active than 1,25(OH)2D3. Bovine parathyroid hormone stimulated the 1- and reduced the 24-hydroxylase in 6 h, but this only occurred in cultures either previously treated with 1,25(OH)2D3 and EGTA to lower Ca to 0.8 mM or in cultures grown in the presence of 25-hydroxyvitamin D3 (25(OH)D3). Under the latter condition, the sensitivity to bovine parathyroid hormone was enhanced, 0.04 U/ml producing a maximum response. Synthetic aminoterminal tetratriacontapeptide (1-34) human parathyroid hormone was equally effective. In the absence of D metabolites, estradiol for 6 h produced a dose-dependent inhibition of the 1-hydroxylase, but no change in the 24-hydroxylase. Progesterone, testosterone, and corticosterone had no significant effect. In cultures grown in the presence of 25(OH)D3 no reproducible effects were obtained with either 1 microM estradiol or 1 microM testosterone, alone or in combination, but 5 microM corticosterone decreased the 1- and increased the 24-hydroxylase. Changes in Ca and P concentrations of the medium as well as addition of ethane-l-hydroxy-1, 1-diphosphate for 48 h did not affect any of the hydroxylase activities. The modulation of the hydroxylase activities by vitamin D3 metabolites and parathyroid hormone suggests that these factors regulate the renal hydroxylase by direct actions, whereas it would appear that ethane-1-hydroxy-1,1-diphosphate, Ca, P, and steroid may exert their influence indirectly.

Relation between bone mineralization, Ca absorption, and plasma Ca in phosphonate-treated rats

Disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP) is known to inhibit the crystallization of calcium phosphate salts in vitro. Large doses of EHDP administered in vivo inhibit skeletal mineralization, decrease intestinal calcium absorption, and produce hypercalcemia. In the present study, EHDP or one of 13 other phosphonates were given to rats at 10 mg P/kg-day sc for 7 days in order to better define the nature of the relationship between bone mineralization, intestinal absorption, and plasma calcium in the regulation of calcium homeostasis. Each of the phosphonates which inhibited skeletal mineralization in vivo also inhibited crystallization in vitro, but the converse was not true. A very close correlation was found between inhibition of skeletal mineralization, decreased intestinal calcium absorption, and slight hypercalcemia. A dose-response study with two compounds also revealed the same close correlation. It is argued that the impairment of intestinal calcium absorption in phosphonate-treated rats may represent a secondary homeostatic response to the primary effect of the drugs on bone mineralization. This response may be mediated by an elevation of a fraction of plasma calcium.

Calcium absorption in diphosphonate-treated rats: effect of parathyroid function, dietary calcium and phosphorus

1. The role of parathyroid hormone (PTH) and 1, 25-dihydroxy-cholecalciferol (1,25-(OH)2D3) in modulation of intestinal Ca absorption was studied in rats, using disodium ethane-1-hydroxy-1,1-diphosphonate (EHDP), which is known to reduce 1,25-(OH)2D3 formation. 2. EHDP decreased intestinal Ca absorption. This effect could be abolished by small amounts of 1,25-(OH)2D3, whereas even large doses of PTH were ineffective. EHDP also decreased Ca absorption in thyroparathyroidectomized (TPTX) rats. Therefore the effect of EHDP on 1,25-(OH)2D3 production is unlikely to be mediated through PTH. 3. The correction by PTH of the decreased Ca absorption in TPTX rats was inhibited by EHDP. Since EHDP inhibits formation of 1,25-(OH)2D3 the effect of PTH on Ca absorption is likely to be mediated through this vitamin D3 metabolite. 4. In normal rats both a low Ca and a low P diet stimulated Ca absorption. In EHDP-treated intact rats low Ca still stimulated Ca absorption, whereas the effect of low P abolished. This indicates that low Ca and low P diets affect Ca absorption through different mechanisms. 5. Intestinal adaptation to a low Ca diet was still observed in EHDP-treated TPTX rats. Thus, in the rat, intestinal adaptation to low Ca diet can occur without PTH.

A new device for ultrafiltration. The ultrafiltrability of calcium and inorganic phosphate in human serum

The various problems concerning the ultrafiltration of blood serum are outlined, and a novel ultrafiltration device, which overcomes all these problems is presented. Its main advantages are the following: (1) The deposition of protein on the filter is prevented by producing a flow across the filter surface. (2) The pCO2 remains constant, since the fluid is not in contact with a gas space. (3) The minimum serum volume is only 0.4 ml (4) Six samples can be processed simultaneously. (5) All commercially available filter types can be used. The machine, tested by measuring the ultrafiltrability of calcium, inorganic phosphate, sodium and chloride in human serum, proved to be a reliable laboratory tool. The precision of the determinations were comparable to respective serum analyses. The ultrafiltrabilities obtained, without correction for water content of serum, were 55.6 +/- 2.9% for calcium, 88.3 +/- 5.0% for inorganic phosphate, 95 +/- 1.7% for sodium, and 103 +/- 0.7% for chloride (means +/- S.D.).