Genetic models show that parathyroid hormone and 1,25-dihydroxyvitamin D3 play distinct and synergistic roles in postnatal mineral ion homeostasis and skeletal development

In humans, loss-of-function mutations in parathyroid hormone (PTH) and 25-hydroxyvitamin D3-1alpha-hydroxylase [1alpha(OH)ase] genes lead to isolated hypoparathyroidism and vitamin D-dependent rickets type I, respectively. To better understand the relative contributions of PTH and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] to skeletal and calcium homeostasis, we compared mice with targeted disruption of the PTH or 1alpha(OH)ase genes to the double null mutants. Although PTH-/- and 1alpha(OH)ase-/- mice displayed only moderate hypocalcemia, PTH-/-1alpha(OH)ase-/- mice died of tetany with severe hypocalcemia by 3 weeks of age. At 2 weeks, PTH-/- mice exhibited only minimal dysmorphic changes, whereas 1alpha(OH)ase-/- mice displayed epiphyseal dysgenesis which was most severe in the double mutants. Although reduced osteoblastic bone formation was seen in both mutants, PTH deficiency caused only a slight reduction in long bone length but a marked reduction in trabecular bone volume, whereas 1alpha(OH)ase ablation caused a smaller reduction in trabecular bone volume but a significant decrease in bone length. The results therefore show that PTH plays a predominant role in appositional bone growth, whereas 1,25(OH)2D3 acts predominantly on endochondral bone formation. Although PTH and 1,25(OH)2D3 independently, but not additively, regulate osteoclastic bone resorption, they do affect the renal calcium transport pathway cooperatively. Consequently, PTH and 1,25(OH)2D3 exhibit discrete and collaborative roles in modulating skeletal and calcium homeostasis and loss of the renal component of calcium conservation might be the major factor contributing to the lethal hypocalcemia in double mutants.     

The effects of 1,25-dihydroxycholecalciferol, parathyroid hormone, and thyroxine on trabecular bone remodeling in adult dogs. A histomorphometric study.

The effects of 1,25-dihydroxycholecalciferol (1,25-(OH)2D3), parathyroid hormone (PTH), and L-thyroxine (T4) on trabecular bone remodeling were evaluated by histomorphometric methods in adult female beagle dogs. Intravenous 1,25-(OH)2D3 (1.25 micrograms/day in equally divided doses) was administered intermittently for 6 days and withdrawn 14 days for three complete cycles. PTH was administered intravenously (2.5 U/kg/day) in divided doses 6 hours apart for 60 days. Thyroxine was given orally (1.0 mg/kg/day) in divided doses for a similar interval. Static and dynamic changes were evaluated using tetracycline and DCAF (2,4 BIS) N, N', Di (carboxymethyl) (amino methyl fluorescein) in vivo double labeling of bone from the iliac crest taken before treatment and after 60 days. The intermittent administration of 1,25-(OH)2D3 stimulated the bone resorption rate and depressed the formation rate. 1,25-(OH)2D3 increased trabecular resorption surfaces; osteoid surface, volume, and thickness; mineralization lag time; and osteoblast number but decreased the bone volume. Multiple small daily doses of PTH resulted in an overall negative balance in trabecular bone. This was associated with an increased trabecular surface-to-volume ratio, bone resorption and formation rates, active forming surfaces, osteoid volume and surface, life span of bone forming and resorbing sites, and the number of osteoclast nuclei. Thyroxine appeared to increase bone mass by enhancing the switch-over from the resorptive to the formative phase of remodeling. Coupling between osteoid apposition and mineralization was increased by recruiting more forming sites and prolonging their life span. Thyroxine increased bone resorption and formation rates, trabecular bone volume and balance, number of osteoclast nuclei, and life span of bone forming sites. The osteoid seam thickness and mineralization lag time were decreased. The present study demonstrated that 1,25-(OH)2D3, PTH, and thyroxine at the dose and schedule used, markedly altered stimulators of remodeling in trabecular bone of adult dogs.     

腹膜透析患者骨代谢的评估

了解腹膜透析患者的骨代谢状况。用IRMA、RRA和RIA对24例持续不卧床腹膜透析（CAPD）患者测定血清PTH（1－84）、25（OH）D3、1,25（OH）2D3、BGP以及血Ca和P的变化。结果表明：尿毒症患者PTH和BGP升高,CAPD可以命名其降低;25（OH）D3和1,25（OH)2D3降低,CAPD对其无明显影响;PTH与25（OH）D31,25（OH）2D3呈负相关,P分别小于0．05和0．01;PTH与BGP呈相相关（P＜0．01）,CAPD可使其相关性降低。提示PTH分泌亢进是骨代谢紊乱的主要因素之一,CAPD患者骨转化率降低。     

Modulation of ovariectomy-related bone loss by parathyroid hormone in rats

Studies were carried out to examine whether parathyroid hormone (PTH) will prevent the age-related bone loss that results from ovarian hormone deficiency and to explore the mechanism of its action. Ovariectomy caused a significant decrease in bone density in the distal metaphysis and mid-diaphysis, but not in the vertebra and proximal metaphysis. The decrease was prevented by PTH injection and in all the bones examined PTH administration increased bone density and bone calcium content above the levels in sham-operated controls. Similar findings were made in bone hydroxyproline levels. PTH treated ovariectomized animals had lower serum 25(OH)vitamin D and higher 1,25(OH)2 vitamin D levels than ovariectomized and sham operated animals that received solvent vehicle. Compared to the sham operated controls, ovariectomy caused a 4.5-fold increase in the number of tartrate resistant acid phosphatase (TRAP) positive multinuclear cells. This increase did not occur in PTH-treated animals. We conclude that PTH is effective in preventing ovarian hormone deficiency bone loss in rats. PTH may mediate this effect partly by stimulating osteoblastic bone formation and partly by increasing 1,25(OH)2 vitamin D-mediated calcium absorption. The data from TRAP positive multinuclear cells indicate that an etiologic component of ovarian hormone deficiency bone loss is the expansion of a pool of osteoclast progenitors and that the bone anabolic action of PTH involves, in part, a decrease in bone resorption as a result of the suppression of the proliferation of osteoclast progenitors.     

Overexpression of the transcriptional factor Runx2 in osteoblasts abolishes the anabolic effect of parathyroid hormone in vivo

There is convincing evidence that Runx2 could be a regulator of the anabolic action of parathyroid hormone (PTH) in bone. We therefore decided to determine how Runx2 overexpression in osteoblasts affects the anabolic response to PTH. Transgenic osteoporotic female mice overexpressing Runx2 (TG) and their wild-type littermates (WT) were treated with PTH (100 microg/kg/day, 7 days a week) or with the vehicle for 6 weeks. Unexpectedly, Runx2 overexpression blunted the increase in the mineral density and volume of bone induced by intermittent PTH in WT mice. Our findings also indicate that PTH failed to increase bone formation in TG mice overexpressing Runx2. This abolition of the effect of PTH by Runx2 overexpression was attributable to a decrease in the differentiation of osteoblastic cells both in vivo and in vitro. Finally, we showed that less cAMP was induced by PTH and that there were fewer PTH binding sites in TG than WT osteoblasts. In conclusion, our findings demonstrate that in vivo a high level of Runx2 abolishes the anabolic effect of PTH, probably via a decrease in the sensitivity of TG osteoblasts to PTH, and that the level of expression of Runx2 is critical if PTH is to produce its anabolic effect on bone in vivo.     

1,25（OH）2D3对甲状旁腺素诱导的肾小管上皮细胞转分化和TGF-β1的表达的影响

目的:探讨1,25(OH)2D3对甲状旁腺素(PTH)诱导的肾小管上皮细胞转分化和转化生长因子-β1(TGF-β1)表达的影响。方法:人肾小管上皮细胞(HK-2细胞)培养在含50 mL/L FCS的DMEM/F12培养液中。对照组:加入等体积含50 mL/L FCS的DMEM/F12培养液;PTH刺激组:加入终浓度为10-10 mol/L PTH的含50 mL/L FCS的DMEM/F12培养液;PTH+1,25(OH)2D3干预组:加入10-10 mol/L PTH,同时加入不同浓度(10-10、10-9、10-8、10-7 mol/L)的1,25(OH)2D3。刺激HK-2细胞48 h。半定量RT-PCR法检测细胞中α-平滑肌肌动蛋白(α-SMA)和TGF-β1的基因表达;Western blot法检测细胞中α-SMA和TGF-β1的蛋白表达;免疫细胞化学法检测细胞中α-SMA的表达;ELISA法检测细胞培养上清液中TGF-β1的含量。结果:半定量RT-PCR结果显示,对照组HK-2细胞中几乎无α-SMA的mRNA表达,仅有少量的TGF-β1 mRNA表达;PTH刺激组α-SMA和TGF-β1mRNA表达量与对照组比较明显增加;PTH+1,25(OH)2D3干预组表达量比PTH刺激组显著降低,且随着1,25(OH)2D3浓度的升高呈一定的剂量依赖性(P<0.05)。Western blot结果显示,对照组HK-2细胞中无α-SMA的蛋白表达,仅有少量的TGF-β1蛋白表达;10-10 mol/L的PTH能够明显诱导HK-2细胞中α-SMA的蛋白表达,增加TGF-β1的蛋白表达量;PTH+1,25(OH)2D3干预组,α-SMA和TGF-β1的蛋白表达量比PTH刺激组显著降低(P<0.05)。免疫细胞化学法结果显示,对照组几乎无α-SMA阳性表达的细胞,PTH刺激组可见大量细胞α-SMA表达阳性;PTH+1,25(OH)2D3干预组α-SMA表达阳性的细胞数明显低于PTH刺激组(P<0.05)。ELISA结果显示,对照组细胞上清液中可检测到少量的TGF-β1,PTH刺激组含量显著升高,PTH+1,25(OH)2D3干预组与PTH刺激组比较含量明显降低(P<0.05)。结论:1,25(OH)2D3能够部分拮抗PTH诱导的HK-2细胞转分化和TGF-β1的表达。     

Inhibited anabolic effect of insulin-like growth factor-I on stromal bone marrow cells in endothelial nitric oxide synthase-knockout mice

AIMS: Insulin-like growth factor-I (IGF-I), parathyroid hormone (PTH) and PTH-related protein (PTHrP) are hormones that have anabolic effects on bone formation. The aim of this study was to investigate whether production of nitric oxide (NO) is involved in the effect of IGF-I and PTH/PTHrP on osteoblast-like cells. METHODS: Bone marrow stromal cells from adult endothelial nitric oxide synthase (eNOS)-knockout (eNOSKO) mice and wild type (WT) counterparts were cultivated with osteogenic substances. The cells showed an osteoblastic phenotype measured as osteocalcin production and alkaline phosphatase activity. DNA synthesis was measured as [3H] thymidine incorporation in the bone marrow cells and in a human osteosarcoma cell-line (SaOS-2). RESULTS: The stimulatory effect of IGF-I on thymidine incorporation seen in WT animals was absent in eNOSKO mice. Addition of a NO donor to eNOSKO cells recovered the effect of IGF-I on thymidine incorporation. PTH/PTHrP stimulated cell proliferation in both WT and eNOSKO mice. In SaOS-2 cells, incubation with IGF-I together with a NOS inhibitor resulted in an inhibition of the anabolic effect of IGF-I on cell proliferation. CONCLUSIONS: The stimulatory effect of IGF-I on WT cell proliferation was abolished in eNOSKO cells, recovered by an NO donor and inhibited in osteosarcoma cells by a NOS inhibitor. The results indicate that the effect of IGF-I is dependent on NO production. The impaired IGF-I response may contribute to the bone defect formation seen in eNOSKO animals.     

Inhibited anabolic effect of insulin‐like growth factor‐I on stromal bone marrow cells in endothelial nitric oxide synthase‐knockout mice

Aims: Insulin‐like growth factor‐I (IGF‐I), parathyroid hormone (PTH) and PTH‐related protein (PTHrP) are hormones that have anabolic effects on bone formation. The aim of this study was to investigate whether production of nitric oxide (NO) is involved in the effect of IGF‐I and PTH/PTHrP on osteoblast‐like cells. Methods: Bone marrow stromal cells from adult endothelial nitric oxide synthase (eNOS)‐knockout (eNOSKO) mice and wild type (WT) counterparts were cultivated with osteogenic substances. The cells showed an osteoblastic phenotype measured as osteocalcin production and alkaline phosphatase activity. DNA synthesis was measured as [³H] thymidine incorporation in the bone marrow cells and in a human osteosarcoma cell‐line (SaOS‐2). Results: The stimulatory effect of IGF‐I on thymidine incorporation seen in WT animals was absent in eNOSKO mice. Addition of a NO donor to eNOSKO cells recovered the effect of IGF‐I on thymidine incorporation. PTH/PTHrP stimulated cell proliferation in both WT and eNOSKO mice. In SaOS‐2 cells, incubation with IGF‐I together with a NOS inhibitor resulted in an inhibition of the anabolic effect of IGF‐I on cell proliferation. Conclusions: The stimulatory effect of IGF‐I on WT cell proliferation was abolished in eNOSKO cells, recovered by an NO donor and inhibited in osteosarcoma cells by a NOS inhibitor. The results indicate that the effect of IGF‐I is dependent on NO production. The impaired IGF‐I response may contribute to the bone defect formation seen in eNOSKO animals.     

Regulation and function of the FGF23/klotho endocrine pathways

Calcium (Ca(2+)) and phosphate (PO(4)(3-)) homeostasis are coordinated by systemic and local factors that regulate intestinal absorption, influx and efflux from bone, and kidney excretion and reabsorption of these ions through a complex hormonal network. Traditionally, the parathyroid hormone (PTH)/vitamin D axis provided the conceptual framework to understand mineral metabolism. PTH secreted by the parathyroid gland in response to hypocalcemia functions to maintain serum Ca(2+) levels by increasing Ca(2+) reabsorption and 1,25-dihydroxyvitamin D [1,25(OH)(2)D] production by the kidney, enhancing Ca(2+) and PO(4)(3-) intestinal absorption and increasing Ca(2+) and PO(4)(3-) efflux from bone, while maintaining neutral phosphate balance through phosphaturic effects. FGF23 is a recently discovered hormone, predominately produced by osteoblasts/osteocytes, whose major functions are to inhibit renal tubular phosphate reabsorption and suppress circulating 1,25(OH)(2)D levels by decreasing Cyp27b1-mediated formation and stimulating Cyp24-mediated catabolism of 1,25(OH)(2)D. FGF23 participates in a new bone/kidney axis that protects the organism from excess vitamin D and coordinates renal PO(4)(3-) handling with bone mineralization/turnover. Abnormalities of FGF23 production underlie many inherited and acquired disorders of phosphate homeostasis. This review discusses the known and emerging functions of FGF23, its regulation in response to systemic and local signals, as well as the implications of FGF23 in different pathological and physiological contexts.     

Panostotic fibrous dysplasia: A congenital disorder of bone with unusual facial appearance,bone fragility,hyperphosphatasemia, and hypophosphatemia

We report a boy with unusual facial appearance, melanotic patches (“coast-of-Maine” type), myelofibrosis, recurrent femoral fractures, and widespread fibrous dysplasia of bone. Biochemical findings included raised serum alkaline phosphatase (bone isozyme) and 1,25-(OH)₂ vitamin D, and low serum phosphorus levels. Elevated urinary excretion rates of total hydroxyproline, glycylproline, and γ-carboxyglutamic acid indicated increased turnover of bone matrix. Transiliac bone biopsy showed a dearth of marrow elements, greatly increased bone turnover, and absence of normal trabecular organization. Serial radiographs showed progressive cortical thinning and loss of bony trabeculae. Calcitonin and etidronate treatments had no lasting effect on the progressive bone disease. The term “panostotic fibrous dysplasia” is suggested for this condition.     

Bone increase in rat tibiae by local administration of amino-terminally truncated rhFGF-4(73-206)

Fibroblast growth factor 4 (FGF-4) plays important roles in bone development during embryogenesis. Human FGF-4 consists of 206 amino acid residues. We produced amino-terminally truncated rhFGF-4, named rhFGF-4(73-206), that increases bone mineral density when systemically administered to mice. In the present study, we examined the effects of rhFGF-4(73-206) in bone after local administration. We injected 1 microg of rhFGF-4(73-206) into tibiae of 10-week-old Sprague-Dawley rats. At days 4 and 7, sets of animals were subjected for tibial bone marrow cell culture in an osteogenic medium. The bone marrow cells from FGF-4-injected tibiae produced more alkaline phosphatase-positive cells and mineralized nodules than those from control tibiae, indicating that local injection of rhFGF-4(73-206) increased the osteoblastic population in the bone marrow. The remaining sets of animals were killed on days 7 and 10. The tibiae were then analyzed with soft X-ray, dual energy X-ray absorptiometry, peripheral quantitative computed tomography, and histomorphometry. The radiographic analyses revealed increases in trabecular bone in the tibiae but no difference in the cortical bone between the rhFGF-4(73-206) group and the control group. High bone turnover and a derived increase of trabecular bone mineral density were demonstrated by histomorphometry in the rhFGF-4(73-206) group. The present results indicate that local injection with rhFGF-4(73-206) elicited an increase in the osteogenic cell population in the tibial bone marrow, which resulted in more trabecular bone.     

Low bone turnover and reduced angiogenesis in streptozotocin-induced osteoporotic mice

It is known that type 1 diabetes (T1D) reduces bone mass and increases the risk for fragility fractures, an effect that has been largely ascribed to decreased bone formation. However, the potential role of decreased angiogenesis as a factor in osteogenesis reduction has not been extensively studied. Furthermore, there is controversy surrounding the effect of T1D on bone resorption. This study characterized bone microstructure, bone strength, and bone turnover of streptozotocin (STZ)-induced diabetic mice (T1D mice) and explored the role of angiogenesis in the pathogenesis of T1D-induced osteoporosis. Results demonstrate that T1D deteriorated trabecular microarchitecture and led to reduced bone strength. Furthermore, T1D mice showed reduced osteoblast number/bone surface (N.Ob/BS), mineral apposition rate, mineral surface/BS, and bone formation rate/BS, suggesting attenuated bone formation. Decreased angiogenesis was shown by a reduced number of blood vessels in the femur and decreased expression of platelet endothelial cell adhesion molecule (CD31), nerve growth factor, hypoxia-inducible factor-1α, and vascular endothelial growth factor was observed. On the other hand, reduced bone resorption, an effect that could lead to impaired osteogenesis, was demonstrated by lower osteoclast number/BS and decreased tartrate-resistant acid phosphatase and cathepsin K mRNA levels. Reduced number of osteoblasts and decreased expression of receptor activator for nuclear factor-κB ligand could be responsible for compromised bone resorption in T1D mice. In conclusion, T1D mice display reduced bone formation and bone resorption, suggesting decreased bone turnover. Furthermore, this study points to impairments in angiogenesis as a pivotal cause of decreased bone formation.     

CELLS OF THE MONONUCLEAR PHAGOCYTE SERIES DIFFERENTIATE INTO OSTEOCLASTIC LACUNAR BONE RESORBING CELLS

Although the osteoclast shares several features with other cells of the mononuclear phagocyte system (MPS), its precise cellular ontogeny is unknown, and its membership of the MPS is controversial. This study examined whether various cells of the MPS can be induced to differentiate into cells capable of the highly specialized osteoclastic function of lacunar bone resorption. We isolated mouse and rat monocytes, mouse (liver, peritoneal, alveolar, brain) tissue macrophages, and spleen and marrow haemopoietic cells, as well as foreign body macrophages and macrophage polykaryons derived from subcutaneous granulomas formed by implantation of latex beads and coverslips in mice. When these cells were incubated with UMR106 osteoblast-like cells on glass coverslips and human cortical bone slices in the presence of 1,25-dihydroxy vitamin D₃ [1,25(OH)₂D₃] for 7 and 14 days, numerous tartrate-resistant acid phosphatase-positive cells formed in these co-cultures and scanning electron microscopy revealed extensive lacunar resorption of the bone surface. Bone resorption was seen as early as 4 days after monocytes were co-cultured with UMR106 cells. With the exception of bone marrow-derived cells, lacunar resorption was not seen in the absence of UMR106 cells. These findings show that a bone-derived stromal cell element is necessary for differentiation of monocytes and tissue and inflammatory macrophages into osteoclast-like cells capable of extensive lacunar bone resorption, and would argue in favour of osteoclast membership of the MPS.     

Parathyroid Hormone in the Treatment of Osteoporosis

Parathyroid hormone (PTH), especially intact human PTH [hPTH(1–84)] and its various fragments [hPTH(1–31), (1–34), (1–36), (1–38) and their modifications], has been used for the treatment of osteoporosis over the last 10 years. Although chronic continuous excess of PTH markedly increases bone resorption, as seen in the typical example of primary hyperparathyroidism and osteitis fibrosa generalisata, intermittent PTH administration has been found to stimulate bone formation in animals, providing a basis for the use of PTH as a therapeutic agent for osteoporosis. In addition to dramatically increasing trabecular bone density and also sustaining cortical bone density, PTH administration increases bone strength and reduces the fracture rate, despite occasional increases in cortical porosity. Administration of PTH in combination with antiresorptive agents such as estrogen, calcitonin, vitamin D and bisphosphonates augments its effect. Because of its bone anabolic action, PTH is expected to be effective for osteoporosis in those of advanced age with suppressed bone remodelling, which might not respond favourably to antiresorptive agents.     

Hypercalcemia in dogs with lymphosarcoma. Biochemical, ultrastructural, and histomorphometric investigations

Dogs with lymphosarcoma and hypercalcemia had decreased trabecular bone volume and increased osteoclastic osteolysis, whereas dogs with lymphosarcoma that were normocalcemic did not have increased bone resorption. Increased osteoclastic resorption was present only in bone from hypercalcemic dogs that contained neoplastic tissue but not in bone free of tumors, suggesting that the factor(s) responsible for stimulating bone resorption were elaborated locally by the tumor tissue. Hypercalcemic dogs with lymphosarcoma had decreased concentrations of plasma immunoreactive parathyroid hormone and serum 1,25-(OH)2D compared with normocalcemic dogs with lymphosarcoma and control dogs with and without other neoplasms. Immunoreactive parathyroid hormone was not detected in lymphosarcoma tissue. The plasma concentration of 13,14-dihydro-15-keto-prostaglandin E2 (PGE2M) was increased approximately 2-fold in hypercalcemic dogs with lymphosarcoma as compared with other groups. Urine excretion of calcium, phosphorus, and hydroxyproline were increased in hypercalcemic dogs with lymphosarcoma. Ultrastructurally, lymphosarcomas were composed of tumor cells with large nuclei and a paucity of cytoplasmic organelles. Light and electron microscopic examination of parathyroid glands revealed inactive or atrophic chief cells in dogs with lymphosarcoma and hypercalcemia. The increased osteoclastic bone resorption in hypercalcemic dogs with lymphosarcoma was not mediated by increased circulating levels of immunoreactive parathyroid hormone and 1,25-(OH)2D but was dependent upon infiltration of bone marrow by neoplastic cells and, presumably, the local production of a bone resorption-stimulating factor.     

Different inhibitory actions of cyclosporine A and cyclosporine A-acetate on lipopolysaccharide-, interleukin 1-, 1,25 dihydroxyvitamin D3- and parathyroid hormone-stimulated calcium and lysosomal enzyme release from mouse calvariain vitro

The effects of cyclosporine A (CsA) and one of its immunologically inactive structural analogues, cyclosporine A acetate (CsA-A) on lipopolysaccharide (LPS)-, interleukin-1 (IL-1)-, 1,25 dihydroxyvitamin D₃ (1,25 D₃)- and parathyroid hormone (PTH)-stimulated bone resorption were tested in mouse calvaria cultures. The release of calcium and a lysosomal enzyme, N-acetylglycosaminidase (NAG) was determined after 3 days of culture. All bone resorbing agents potently stimulated calcium and NAG release. At therapeutic concentration levels of 0.1 and 1.0 g/ml, the immunologically active CsA was signficantly more potent than the inactive CsA-A against LPS- and 1,25 D₃-induced calcium and NAG release. The inhibition by both cyclosporines of IL-1 and PTH stimulated calcium release was not significantly different. CsA was however more potent than CsA-A against IL-1 stimulated NAG release. PTH-stimulated NAG release was not inhibited by CsA or CsA-A. These findings suggest that both cyclosporines interfere with more than one mechanism of activation of bone resorption. The specific effect of CsA against LPS and 1,25 D₃ may be related to its known inhibition of immune cell derived cytokine expression.     

Histomorphometric Evaluation of the Effects of Intermittent 1,25-Dihydroxycholecalciferol Administration on Cortical Bone Remodeling in Adult Dogs

The effects of intermittent low doses (1.25 μg daily, administered intravenously for 6 days and withdrawn for 14 days for 3 complete cycles) of 1,25-dihydroxycholecalciferol (1,25-[OH]₂D₃) on cortical bone were determined and compared in ribs with steady state and regionally accelerated remodeling in adult intact female dogs. The bone changes were analyzed by dynamic bone histomorphometric methods, using tetracycline and DCAF (2,4 BIS) N, N' di (carboxymethyl) (amino methyl fluorescein) in vivo double labeling of bones before treatment and after 60 days of intermittent 1,25-(OH)₂D₃ administration. Serum calcium and phosphorus levels increased during 1,25-(OH)₂D₃ administration. Urinary hydroxyproline excretion increased during the first interval of 1,25-(OH)₂D₃ administration but was not changed significantly during the last two intervals. In normal cortical bone (11th rib) following the administration of 1,25-(OH)₂D₃ there was a marked decrease in the activation frequency, bone formation rate, osteoid seam thickness, seam circumference, and mean appositional rate. Although recruitment of new remodeling sites was decreased after 1,25-(OH)₂D₃, previously existing remodeling units continued to completion. These effects resulted in a preponderance of mature osteons in normal cortical bone. The morphometric changes in cortical bone (9th rib) exposed to both 1,25-(OH)₂D₃ and periosteal elevation were characterized by a marked increase in both the activation frequency and bone formation rate and associated with a decrease in the osteon formation time. Other morphometric parameters that were increased included radial closure rate, numbers of osteoid seams and resorption cavities, ratio of bone resorbing to forming sites, percentage labeled and circumference of osteoid seams, and total and cortical bone areas. The combined effect of periosteal elevation and 1,25-(OH)₂D₃ were markedly different from those observed with 1,25-(OH)₂D₃ alone. These findings suggest that the rapid bone turnover induced by tissue injury will mask or alter the effects of hormones on bone remodeling when studied over a relatively short period of time.     

Calcium homeostasis, bone metabolism and safety aspects during long-term treatment with a GnRH agonist.

Thirty-five women with symptomatic fibroids were treated with monthly injections of 3.2 mg microcapsulated D-Trp-6-LHRH for 6 months. During treatment serum 17 beta-oestradiol levels decreased, falling to castration levels associated with a reduction in the volume of the fibroids. In 16 patients a complete calcium homeostasis and bone metabolism work-up was carried out during treatment and subsequently for a 6-month follow-up period. Bone mineral content (BMC) and Compton bone densitometry readings remained unchanged. There were significant increases in serum calcium phosphate and alkaline phosphatase concentrations. A slight although not significant increase was observed in osteocalcin and parathyroid hormone (PTH) serum levels. Serum 1,25(OH)2D3 values decreased significantly after 3 months of treatment. Urinary hydroxyproline/creatinine and calcium/creatinine ratios as well as 24-h urinary calcium values increased significantly during the treatment period but decreased rapidly to pretreatment values after 3 months in the follow-up period. The endocrine changes induced by the GnRH-agonist treatment were associated with reversible biochemical signs of increased bone turnover and no significant changes in bone mass, suggesting that the treatment can be administered safely for a period of 6 months in patients with oestrogen-dependent diseases.