ISSN:0884-0431    

DOI:10.1002/jbmr.5650040402

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

年代:1989

数据来源: WILEY

摘要:

AbstractTrue calcium absorption can only be measured by the time‐consuming and expensive metabolic balance method and is not predicted well by measuring the fractional absorption (FA) of radiocalcium from a fixed calcium carrier. We describe here a 1 day method for measuring the actual fraction of calcium absorbed from the habitual diet (true fractional calcium absorption, TFCA) using stable isotopes of calcium. Oral and intravenous isotopes were administered with each of the three daily meals, and then the ratio of the two isotopes in the urine was measured by mass spectroscopy. In 12 subjects, TFCA determined from stable Ca correlated well with TFCA measured by the balance method (r= 0.71,P<0.01), and the mean values were not different (0.26 and 0.26). In contrast, no significant correlation was found between FA and TFCA. The weak relationship between FA and TFCA underscores the importance of tracing dietary calcium rather than a fixed calcium carrier in tests of calcium absorption. Using the new method, TFCA was inversely related to dietary calcium (r= −0.45,P<0.05), demonstrating that it could detect physiological changes in calcium absorption. Thus, this test has two important advantages: (1) it provides a simple way to measure TFCA and true fractional calcium absorption (the product of TFCA and dietary calcium), the physiologically relevant variables, and (2) because there is no radiation exposure, the test can be used in pregnant women and children, the isotopes can be prepared in advance, and several isotopes can be used simultaneou

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040403

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

年代:1989

数据来源: WILEY

摘要:

AbstractA total of 526 absorption studies, using both the double‐isotope and balance‐based methods, were performed in 189 middle‐aged women in good general health. The study extended over 17 years of observation, with most subjects studied from two to four times at 5 year intervals. Each study was done on the woman's own self‐selected calcium intake and was carried out under inpatient, metabolic balance controls.There was a highly significant inverse correlation between calcium intake and absorption fraction, with the best fit provided by an hyperbola in which absorption fraction is approximately inversely proportional to the square root of intake. The range of absorptive performance was very broad at all intake levels. Mean absorption fraction declined from a value of 0.45 at very low intakes (approximately 200 mg Ca per day) to approximately 0.15 at intakes above 2000 mg/day. There was a highly significant fall in absorption efficiency with age, amounting to approximately 0.0021 per year and a one‐time decrease, amounting to approximately 0.022 at the time of menopausal estr

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040404

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe effects of fluoride at concentrations of 2.0 and 4.5 mM in drinking water on growth rate, vitamin D, water and mineral metabolism, bone histomorphometry, and osteoinduction of demineralized allogenic bone matrix (DABM) were compared in the rat. Whereas fluoride did not influence fluid intake or growth rate at the lower concentration, it increased fluid intake and inhibited growth rate at the higher concentration. Fluoride produced dose‐related increases in serum fluoride and alkaline phosphatase but did not alter serum 25‐hydroxyvitamin D or 1,25‐dihydroxyvitamin D. Serum calcium and phosphate were reduced by fluoride at concentrations of 2.0 mM but not 4.5 mM. Cancellous bone fractional area was increased by fluoride at 2.0 mM and was reduced by fluoride at 4.5 mM. Fluoride had no effect on cancellous bone surface length or the percentage surface lined by osteoblasts and osteoclasts. Fluoride increased medullary area and decreased the endosteal bone formation rate. Fluoride increased periosteal bone formation and apposition rates at concentrations of 2.0 mM but not 4.5 mM. Fluoride inhibited mineralization in DABM implants, and at the higher concentration, fluoride increased the formation of new bone matrix. These results indicate that in the rat, fluoride increases cortical and trabecular bone at therapeutic doses and reduces trabecular bone at toxic doses. The serum concentration of flouride at therapeutic doses in the rat is similar to that in patients with osteoporosis who are on treatment with fluoride. In the rat, there is a narrow range between toxic and therapeutic

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040405

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

年代:1989

数据来源: WILEY

摘要:

AbstractInduction of ornithine decarboxylase (ODC, E.C. 4.1.1.17) activity by parathyroid hormone (PTH) in cultured fetal rat osteoblasts was studied. PTH induced ODC activity and stimulated cAMP production in a dose‐dependent manner, the ED50for cAMP being five times as high as that for ODC. Induction of ODC activity by PTH was partly inhibited by actinomycin D and cycloheximide, with 40 and 55% inhibition, respectively. PTH increased the intracellular ionized calcium concentration ([Ca2+]1), which was absent in a Ca2+‐free medium. Blocking calcium influx, lowering the extracellular calcium concentration, and adding trifluoperazine inhibited both induction of ODC activity and stimulation of cAMP production by PTH. A23187 (100 nM and 1 μM), combined with a low dose of PTH (4 nM), resulted in a synergistic induction of ODC activity and an inhibition of cAMP production. A23187 inhibited induction of ODC activity as well as stimulation of cAMP production by the dose of PTH (20 nM) maximally effective in inducing ODC activity. Forskolin together with this maximal dose of PTH resulted in an additive effect on ODC activity and a synergistic stimulation of cAMP production. The current results show similarities and differences with respect to results obtained with osteoblasts from other species and osteoblast cell lines. The present data indicate that (1) PTH stimulates ODC activity and this is partly due to new enzyme synthesis; (2) calcium is involved in induction of ODC activity and stimulation of cAMP production by PTH; furthermore, it is suggestive that calmodulin and/or protein kinase C are involved; and (3) stimulation of cAMP production by PTH depends on an optimal intracellular calcium concentration r

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040406

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

年代:1989

数据来源: WILEY

摘要:

AbstractReduced renal tubular reabsorption of phosphate of unknown etiology is characteristic ofX‐linked hypophosphatemia in both humans and mice. To test whether a humoral abnormality is involved in the renal effect, parabiosis was performed betweenHypand normal mice at 4 weeks of age. The normal mice joined toHypmice showed a progressive diminution of plasma phosphate over the next 3 weeks to approach the level of theHypmice. These normal mice had a greater renal phosphate excretion index (urine P/plasma P/urine creatinine) than normal‐normal pairs, thus suggesting a reduced renal tubular reabsorption of phosphate. At the same time the expected rises in plasma calcium and plasma 1,25‐dihydroxyvitamin D did not occur. There was a significant reduction in their femoral mineral content but not in their femoral length or body growth relative to normal‐normal pairs. This change in renal handling of phosphate was specific since the urinary losses of potassium and magnesium were not significantly changed. Separation of normal‐Hyppairs 3 or 6 weeks after parabiosis caused the normal mice to achieve normal plasma phosphate levels within 24 h. At 48 h and 7 days after separation these normal mice had plasma phosphate levels higher than normal mice separated from normal‐normal pairs. In summary, the data suggest the presence of a phosphaturic factor in theHypmice that can cross a parabiotic union into normal mice and induce many of the symptoms ofX‐linked hyp

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040407

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

年代:1989

数据来源: WILEY

摘要:

AbstractAfter histochemical staining of tartrate‐resistant acid phosphatase (TRAP) activity, the total and active trabecular resorption surfaces and the number of osteoclasts were determined by histomorphometry on iliac crest biopsies from 36 healthy volunteers. The subjects were separated into three groups according to age and sex. Total trabecular resorption surface showed no significant variation in any group, but the fraction of active resorption surface was significantly higher in the older population. The number of TRAP cells per mm2of section area, related to trabecular bone volume or surface, showed a significant increase in elderly subjects. The mean osteoclast interface was similar in all the groups. We found a significant decrease in resorption depth between young and old populations. These results are consistent with a reduced activity of bone‐resorbing cells in advancing age. These normal values, established after histochemical identification of osteoclasts, may be applied for evaluating abnormal bone‐resorbing cell activity in metabolic bone dis

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040408

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

年代:1989

数据来源: WILEY

摘要:

AbstractBone mineral content (BMC) was measured in the os calcis of 232 normal subjects aged 17–82 years. The mean reproducibility (coefficient of variation) of the measurement was 1.8%. Substantial bone loss occurred between the ages of 20 and 50 years, and in females the menopause was associated with additional bone loss. There was no significant difference in the rate of bone loss in females and males, but the mean BMC was greater at all ages in males than in females.We also compared os calcis BMC with spinal bone mineral density (BMD), measured by quantitative computed tomographic (CT) scanning, in 85 subjects: 33 were normal controls, 19 had osteoporosis defined by the presence of one or more pathological fractures, and in the remainder the CT examination was performed at the patient's request. Os calcis BMC correlated with spinal BMD in both females (r= 0.69,p<0.001) and males (r= 0.84,p<0.001). However, the os calcis BMC did not reliably predict spine values around the CT “fracture threshold” of 90–100 mg/cm3and did not correlate with osteoporotic fracture as well as did spinal BMD. It is concluded that measurement of the os calcis BMC is of limited clinical usefulness for the early diagnosis of osteo

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040409

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

年代:1989

数据来源: WILEY

摘要:

AbstractThe effect of long‐distance running on bone mass was assessed in 10 premenopausal and 9 estrogen‐deprived postmenopausal women and compared to that in closely matched sedentary control women. Vertebral trabecular bone density (VBD) was determined by computed tomography and radial cortical bone density (CBD) by single‐photon absorptiometry. Physical fitness was assessed by determining maximal oxygen consumption (VO2max) on a treadmill run to exhaustion. VBD was 183 + 7 mg/cm3andVO2maxwas 48 + 1 ml/kg per minute in young women runners and 163 + 8 mg/cm3and 32 + 2 ml/kg per minute in sedentary young women. A positive correlation was noted between VBD andVO2maxin these groups (r= 0.509,p<0.03). Despite a significantly higherVO2maxin postmenopausal women runners compared with sedentary controls (37 + 2 versus 24 + 2 ml/kg per minute), VBD was identical (112 + 5 versus 111 + 5 mg/cm3) and no correlation was seen between VBD andVO2max(r= 0.187,p= 0.457). Radial cortical bone density was not different between the runners or sedentary groups in young women (0.738 + 0.01 versus 0.732 + 0.1 g/cm2) or postmenopausal women (0.617 + 0.3 versus 0.665 + 0.4 g/cm2). These results suggest that although physical fitness enhances vertebral bone density in premenopausal women, it does not appear to prevent age‐and/or sex steroid deficiency‐induced bone loss in postmenopau

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040410

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

年代:1989

数据来源: WILEY

摘要:

AbstractTheX‐linked hypophosphatemic (Hyp) mouse is a model for humanX‐linked hypophosphatemia. Surgical joining of normal toHypmice by parabiosis results in the normal mice developing low renal retention of phosphate and hypophosphatemia. These results suggest a humoral component to the renal defect. To test whether this component could be parathyroid hormone, surgical parathyroidectomy (PTX) or sham surgery was performed in mice 3 weeks after parabiotic union (n>20 per group). After an overnight fast, PTX mice were hypocalcemic and hyperphosphatemic relative to sham‐operated control mice. PTX normal mice joined to PTXHypmice were significantly lower in plasma phosphate and higher in fractional excretion of phosphate [U/P phosphate/(U/P creatinine)] when compared with PTX normal mice joined to other PTX normals. To test for more specific evidence of altered renal transport function, renal brush‐border membrane vesicles (BBMV) were prepared from these mice, and phosphate and glucose uptakes were measured. The phosphate/glucose transport ratio was lower in BBMV fromHypmice, joined to either normal mice or toHypmice, when compared with that from normal‐normal pairs. Moreover, BBMV from normal mice joined toHypmice had a significantly lower phosphate/glucose uptake ratio than BBMV from normal mice joined to other normal mice, and their activity approached that of BBMV derived fromHypmice. Glucose uptake in BBMV was unaffected by parabiosis or genotype. In summary, parabiosis of normal mice toHypmice resulted in the development of phosphaturia and decreased BBMV phosphate transport in the normal mice. The persistence of the phosphate transport defect in parathyroidectomized mice suggests that parathyroid hormone is not the humoral factor contributing to thes

ISSN:0884-0431    

DOI:10.1002/jbmr.5650040411

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

年代:1989

数据来源: WILEY