ISSN:0884-0431    

DOI:10.1002/jbmr.5650100402

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100403

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractStable transfectants expressing a recombinant human calcitonin receptor respond to calcitonin via increased cyclic adenosine 3′,5′ monophosphate (cAMP, EC50= 0.06 nM salmon calcitonin [sCT]) and a transient mobilization of intracellular calcium ([Ca2+]i) coincident with turnover of inositol phosphate (IP; EC50= 6 nM sCT). Millimolar increases in extracellular calcium ([Ca2+]o, EC50= 8 mM) cause a rapid elevation in [Ca2+]i after a calcitonin dose‐dependent pretreatment of cells (pretreatment EC50= 0.2 nM sCT). Cells exhibit persistent sensitivity to increased [Ca2+]o up to 3 h after hormone exposure and even after multiple cycles of increased [Ca2+]o followed by wash. Calcitonin pretreatment of cells also allows apparent influx of elevated extracellular strontium and manganese, but little or no effect is observed on addition of barium, cadmium, or lanthanum. Human amylin (100 nM) causes a rapid and transient increase in [Ca2+]i comparable to that of calcitonin; however, no significant response to increased [Ca2+]o is observed after amylin addition. Human calcitonin gene‐related product (hCGRP) (300 nM) and forskolin do not increase [Ca2+]i or activate a sensitivity to increased [Ca2+]o. Nevertheless, human amylin and human calcitonin gene‐related product (hCGRP) activate adenylate cyclase with EC50s of 0.7 nM and 8 nM, respectively. The calcium‐channel drugs verapamil, BAY K 8644, diltiazem, and nifedipine have little effect on [Ca2+]i increases. The calcitonin‐induced transient mobilization of calcium is inhibited by treatment of cells with cholera toxin or 8‐(diethylamino)‐octyl‐3,4,5‐trimethoxybenzoate (TMB‐8); whereas, the response to subsequent increased [Ca2+]o is inhibited by lanthanum chloride (200 μM) and lower pH (6.0). These studies suggest that a recombinant human calcitonin receptor activates three unique signal transduction pathways in BHK cells. Subnanomolar calcitonin persistently activates adenylate cyclase and a novel pathway coupled to calcium influx while much higher calcitonin levels increase inositol phosphate turnover and generate a transient mobili

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100404

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractEndochondral ossification in fracture healing of rats at 4, 8, 11, 14, and 21 days was analyzed using immunological and molecular probes for markers of the chondrocyte and osteoblast phenotype. These markers were osteocalcin, type I and type II collagen, including the probes homologous to the alternatively spliced forms of α1 type II collagen, type IIA and type IIB. Histologic examination was performed on serial sections of the same tissue blocks to correlate cellular morphology with the immunohistochemical and in situ hybridization findings. At the junction of the cartilaginous and osseous tissue, an overlap of phenotype and morphology was noted. At the 8‐day time point, the cells with chondrocyte morphology expressed intracellular message for osteocalcin and type I collagen. Immunohistochemical analysis of these cells also demonstrated intracellular osteocalcin. However, high levels of the type IIA collagen mRNA, which has previously been associated with less differentiated mesenchymal precursor cells, were expressed in both chondrocytes and osteoblasts. At the later time point (21 days) there was a substantial decrease in the number of cells displaying shared phenotypic characteristics. In situ hybridization and immuno‐histochemistry have permitted identification of an overlapping or shared phenotype in osteoblasts and chondroblasts in fracture callus. The findings raise important questions regarding the possible plasticity of mesenchymal cell phenotypes within the dynamic environment of fracture healing. Additional examination of these issues will further define factors involved in origin, differentiation, and maturation of bone and cartilage c

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100405

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractThe incidence of nutritional rickets in the southern part of Argentina is 8–12 times higher than in the rest of the country. Winter 25(OH)D serum levels in normal population of southern areas are lower than in central and northern areas. To elucidate these differences, we compared the photoconversion of provitamin D3(7‐DHC) to previtamin D3in two cities: Ushuaia (latitude 55°S) and Buenos Aires (34°S). Ampules containing 7‐DHC were exposed to sunlight one day in the middle of each month either from 10:30 a.m. to 2:30 p.m. or from 8:00 a.m. to 5:00 p.m. The percentages of photoproducts formed were determined by high performance liquid chromatography (HPLC). Previous studies have proved that this is a valid model to assess “in vitro” the photoproduction of vitamin D3in human skin. Previtamin D3+ vitamin D3formed in Ushuaia were less (p<0.02) than those found in Buenos Aires during all seasons: summer, (X ± SEM) 6.4 ± 0.8% vs. 13.2 ± 1.8%; autumn, 1.2 ± 0.7% vs. 63 ± 1.3%; winter, 0.8 ± 0.7% vs. 3.6 ± 0.7%; spring, 3.4 ± 0.5% vs. 9.1 ± 1.1%. The photoproducts produced from 10:30 a.m. to 2:30 p.m. were similar for each month and latitude to those formed when the ampules were exposed from 8:00 a.m. to 5:00 p.m. We conclude that in Ushuaia there is a prolonged “vitamin D winter” during which cutaneous synthesis of vitamin D is absent, leading to lower serum values of 25(OH)D and contributing to the hig

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100406

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractMechanical loading plays an important role in the development and maintenance of skeletal tissues. Subnormal mechanical stress as a result of bed rest, immobilization, but also in spaceflight, results in a decreased bone mass and disuse osteoporosis, whereas supranormal loads upon extremities result in an increased bone mass. In this first in vitro experiment with complete fetal mouse cartilaginous long bones, cultured under microgravity conditions, we studied growth, glucose utilization, collagen synthesis, and mineral metabolism, during a 4‐day culture period in space. There was no change in percent length increase and collagen synthesis under microgravity compared with in‐flight 1× gravity. Glucose utilization and mineralization were decreased under microgravity. In addition, mineral resorption, as measured by45Ca release, was increased. These data suggest that weightlessness has modulating effects on skeletal tissue cells. Loss of bone during spaceflight could be the result of both impaired mineralization as well as increased resorp

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100407

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractThis cross‐sectional twin study aimed to quantify the roles of constitutional and lifestyle factors on bone mass in adolescent and young adult women. Areal bone density (BMD) at the lumbar spine, femoral neck, Ward's triangle, and total hip, total body bone mineral content (BMC), and lean mass and fat mass were measured using dual energy X‐ray absorptiometry (DXA) in 215 female volunteer twin pairs (122 monozygotic [MZ], 93 dizygotic [DZ]) aged 10 to 26 years. Height, weight, menarchial history, dietary calcium intake, physical activity, current tobacco use, and alcohol consumption were determined by questionnaire. Mean BMD increased with age to around 16 years, when it reached a plateau. Within‐pair differences in BMD at the lumbar spine (expressed as a percentage of the pair mean BMD) were univariately associated with pair differences in menarchial status (14 ± 3%), height (0.7 ± 0.1% per cm), weight (0.4 ± 0.1% per kg), lean mass (1.0 ± 0.1% per kg), and fat mass (0.5 ± 0.1% per kg). Only menarchial status, height, and lean mass, however, were independent predictors. At the proximal femoral sites, within‐pair BMD differences were associated with within‐pair lean mass differences (1.0 to 1.1 ± 0.2%/kg), and no other factor was significant. The same conclusions applied to within‐pair differences in BMD/height. Total body BMC was independently associated with menarchial status, height, lean mass, and fat mass; the effects of the latter two variables were stronger in pairs both premenarchial. After adjusting for constitutional factors, no lifestyle factor was independently predictive. By reducing collinearity, the cotwin method clearly identified that lean mass, not fat mass, was the major independent determinant of bone mass at the hip, both pre

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100408

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractAlkaline phosphatase (AP) is required for the proper mineralization of cartilage and bone. The enzyme is localized to the outer surface of cells through a phosphatidylinositol‐glycolipid anchor, which is covalently attached to the carboxyl terminus of the protein. In calcifying cartilage, AP‐rich matrix vesicles (MVs) are released into the matrix from chondrocytes, and apatite formation is initiated within and around these particles. In this paper we examine the role of the AP glycolipid anchor using an in vitro mineralization assay system. AP was purified to homogeneity, and the purified enzyme was used to drive mineral formation in vitro with and without the anchor. Mineral formation was initiated through phosphate release from β‐glycerol phosphate (β‐GP). The amount of PO−34released was similar whether the anchor was present or absent. However, SEM and X‐ray microanalysis revealed that the mineral produced by anchored AP was indistinguishable from that produced by MVs and that both of those minerals were more apatite‐like than mineral formed by soluble AP or through spontaneous precipitation. Taken together, the data suggest that in addition to providing PO−34to drive mineralization, AP influences the nature of the mineral formed. Further, AP containing its glycolipid anchor produces mineral comparable with that formed by tissue‐derived MVs. Thus, in the absence of extracellular matrix, MV mineralization in vitro can be emulated by glycolipid

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100409

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious research suggests that physical activity may have a beneficial effect on bone mineral density (BMD) in women. This relationship was explored in a 2‐year, randomized, intervention trial investigating the efficacy of exercise and calcium supplementation on increasing peak bone mass in young women. One hundred and twenty‐seven subjects (ages of 20–35 years) were randomly assigned either to an exercise program that contained both aerobics and weight training components or to a stretching program. Calcium supplementation (up to 1500 mg/day including dietary intake) or placebo was given in a double‐blinded design to all subjects. Spinal trabecular BMD was determined using quantitative computed tomography (QCT). Spinal integral, femoral neck, and trochanteric BMD were measured by dual X‐ray absorptiometry (DXA) and calcaneal BMD by single photon absorptiometry (SPA). Fitness variables included maximal aerobic capacity (VO2max), and isokinetic muscle performance of the trunk and thigh. Measurements were made at baseline, 1 year, and 2 years. Sixty‐three subjects (32 exercise, 31 stretching) completed the study, and all the measured bone parameters indicated a positive influence of the exercise intervention. There were significant positive differences in BMD between the exercise and stretching groups for spinal trabecular (2.5%), femoral neck (2.4%), femoral trochanteric (2.3%), and calcaneal (6.4%) measurements. The exercise group demonstrated a significant gain in BMD for spinal integral (1.3 ± 2.8%,p<0.02), femoral trochanteric (2.6 ± 6.1%,p0.01) measurements. In contrast to exercise, the calcium intervention had no positive effect on any of the bone parameters. In regard to fitness parameters, the exercise group completed the study with significant gains in VO2maxand isokinetic (peak torque) values for the knee flexion and extension and trunk extension. This study indicates that over a 2‐year period, a combined regimen of aerobics and weight training has beneficial effects on BMD and fitness parameters in young women. However, the addition of daily calcium supplementation does not add significant benefit to

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100410

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY

摘要:

AbstractTo examine the role of skeletal loading patterns on bone mineral density (BMD), we compared eumenorrheic athletes who chronically trained by opposite forms of skeletal loading, intensive weight‐bearing activity (gymnastics,n= 13), and nonweightbearing activity (swimming,n= 26) and 19 nonathletic controls. BMD (g/cm) of the lumbar spine, femoral neck, trochanter, and whole body was assessed by dual energy X‐ray absorptiometry (DXA). Subregion analysis of the whole body scan permitted BMD evaluation of diverse regions. Swimmers were taller (p= 0.0001), heavier (p>0.005), and had a greater bone‐free lean mass (p<0.001) than gymnasts and nonathletic controls. When adjusted for body surface area, there was no difference in lean mass between swimmers and gymnasts, and both were higher than controls (p0.05). These results suggest that the intensive weight‐bearing activity characteristic of gymnastics is a powerful osteogenic stimulus and that long‐term nonweightbearing training that incorporates forceful muscular contractions, as in swimming, confers no beneficial skeletal effects on bone mass

ISSN:0884-0431    

DOI:10.1002/jbmr.5650100411

出版商:John Wiley and Sons and The American Society for Bone and Mineral Research (ASBMR)    

年代:1995

数据来源: WILEY