Increased bone resorption precedes increased bone formation in the ovariectomized rat

This study describes an increase in biochemical and histomorphometric markers of bone resorption prior to increased bone formation and trabecular bone loss in the ovariectomized rat. Six-month-old, female Sprague Dawley rats were either sham operated or ovariectomized (Ovx) and killed at 0, 6, 9, 15, 18, 21, and 42 days postOperation when femora were collected and trabecular bone volume (BV/TV) was determined from von Kossa silver-stained sections using the Quantimet 520 image analysis system in the distal region. A number of these sections were also examined unstained for fluorochrome labels, and stained for acid phosphatase to detect osteoclast-like cells (ACP surface). At 18 days postoperation, lumbar vertebrae were examined. Blood and urine specimens were analyzed for bone-related biochemical variables. ACP surface was significantly greater in Ovx rats compared with sham at 6 days postoperation (mean ACP surface (%TS) ± SEM: sham 36.4 ± 1.9; Ovx 40.3 ± 1.2,P < 0.05) as was urinary hydroxyproline excretion. Serum osteocalcin and alkaline phosphatase activity were not elevated in Ovx rats compared with Sham until 9 days postoperation. Mineral apposition rate (MAR) was increased at 12 days after ovariectomy (mean MAR (Μm/day) ± SEM: sham 0.85 ± 0.06; Ovx 1.23 ± 0.06,P < 0.05). Trabecular bone volume (BV/TV) at a specific site in the metaphyseal-diaphyseal core area was significantly lower at 15 days postoperation (mean (%) ± SEM: Sham 7.40 ± 1.23, Ovx 4.25 0 0.65,P < 0.05). There was no difference in lumbar vertebral BV/TV between the two groups at 18 days postoperation, however, ACP surface was elevated in the Ovx rats (P < 0.05). A systemic increase in bone resorption at 6 days postovariectomy precedes increased formation whereas the length of time required for the dissolution of trabeculae postoperation is determined locally.     

Zoledronic acid efficacy and safety over five years in postmenopausal osteoporosis

Summary 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.     

Evidence that type I osteoporosis results from enhanced responsiveness of bone to estrogen deficiency

Type I osteoporosis occurs within 20 years after menopause and is associated with excessive cancellous bone loss and fractures of the vertebrae and distal radius. We have suggested that it may be caused by estrogen deficiency plus some additional factor predisposing to excessive bone loss. One such factor might be a greater degree of sex steroid deficiency, a possibility that could not be previously excluded because assays of sufficient sensitivity have only recently become available. Thus, we studied 36 women with vertebral fractures due to typical high turnover type I postmenopausal osteoporosis and 36 normal postmenopausal women using new ultrasensitive assays with detection limits of 1 pg/ml for estradiol, 5 pg/ml for estrone and 5 ng/dl for testosterone to test if type I osteoporosis results from enhanced responsiveness of bone to estrogen deficiency. Mean levels of serum sex steroids were identical in both groups, but bone turnover was increased by up to 55% in the women with type I osteoporosis. Moreover, compared with controls, the osteoporotic women had a 51% higher (P<0.01) serum osteoprotegerin level, which was likely a compensatory response to the increased bone turnover. In the osteoporotic women, 1-year treatment with transdermal estrogen in 14 women reduced total deoxypyridinoline, an index of bone resorption, by 58% as compared with placebo treatment in 17 women (P<0.001). Thus, as compared to controls, postmenopausal osteoporotic women had comparable sex steroid levels but higher bone turnover levels that were responsive to estrogen therapy. This is consistent with the hypothesis that the greater bone loss in type I osteoporosis is the result of impaired responsiveness of bone to low postmenopausal levels of sex steroids.     

两种糖皮质激素导致骨质疏松过程中骨量、骨转换标志物及雌激素水平的差异

目的 对比泼尼松龙（PRE）和地塞米松（DXM）致骨质疏松过程中对大鼠骨量和骨转换标志物、雌激素水平的差异。方法 选取3月龄SPF级雌性大鼠46只,随机分成4组：基线组（BL组）6只、年龄对照组（AM组）12只、泼尼松龙组（PRE组）14只、地塞米松组（DXM组）14只。BL组于实验开始时麻醉处死,其余各组分别予常规饲养,PRE组以5mg/kg PRE每天一次皮下注射,DXM组以1mg/kg DXM每周两次皮下注射,于干预后1、2、3个月（M1、M2、M3）分3批麻醉处死取材。每次取材时立即取子宫、肾上腺称重,并收集血清以检测血清内雌激素、PINP及β-CTX水平、收集腰1-3椎体以检测腰椎骨密度（BMD）。结果 PRE组各时间点BMD值[（0.183±0.027、0.230±0.005、0.259±0.014）g/cm2]及DXM组各时间点BMD值[（0.191±0.010、0.208±0.012、0.200±0.004）g/cm2]均较AM组[（0.251±0.014、0.275±0.009、0.281±0.008）g/cm2]明显下降（P＜0.05）,其中DXM组下降更为显著（P＜0.01）,且在M2及M3,DXM组BMD值明显低于PRE组（M2：P＜0.05;M3：P＜0.01）。PRE组干预初期,其血清雌激素水平（36.54±20.40μg/L）较AM组（148.74±40.33 μg/L）明显降低（P＜0.01）,但随着干预时间延长, M3时（130.85±18.95 μg/L）增长至与AM组（126.64±69.12 μg/L）相接近水平（P＞0.05）,但在DXM干预下,雌激素水平在各时间点[（93.13±31.27、91.77±33.14、98.83±10.58）μg/L]均低于AM组[（148.74±40.33、140.01±28.46、126.64±69.12）μg/L]（P＜0.05）。两种GC干预下,PINP及β-CTX均显著高于AM组（P＜0.01）,且PRE干预后各时间点PINP水平[（1410.33±882.40、2089.23±1623.61、1546.88±644.68）μg/L]显著高于DEX组[（258.70±139.42、220.89±92.82、483.36±225.82）μg/L]（P＜0.05）。结论 地塞米松诱导骨量减少的能力明显强于泼尼松龙,这可能与其更大程度地降低血清雌激素水平以及更有效地限制成骨有关。     

Increased circulating levels of γ-carboxyglutamic acid-containing protein and decreased bone mass in children on anticonvulsant therapy

Summary In order to investigate the pathophysiology of anticonvulsant-induced osteopenia, circulating levels of bone γ-carboxyglutamic acid-containing protein (Bone Gla Protein: BGP) and urinary excretion of BGP were measured in 16 chidren on chronic anticonvulsant therapy and in 12 control children. Using microdensitometry analysis, osteopenia was found in 25% of the anticonvulsant therapy group, but it was not observed in the control group. Serum BGP and A1-P levels were significantly increased in the anticonvulsant group compared with the control group (P<0.05 andP<0.01, respectively), and a positive correlation was found between serum BGP and A1-P levels (P<0.05). Urinary excretion of BGP and hydroxyproline showed an increase in the anticonvulsant group, but it was not statistically significant. On the other hand, there was no significant difference between the two groups in serum levels of vitamin D metabolites, PTH, calcitonin, Ca, or P or in urinary excretion of Ca or P. It is suggested, therefore, that the increased BGP level in children receiving anticonvulsant therapy is a reflection of high bone turnover due to anticonvulsant drug complications.     

Low body mass index and declining sex steroids explain most age-related bone loss in Brazilian men

Summary  Osteoporosis in men is underestimated, but our data point to an increasing prevalence rate in those over 70 years old with body mass index (BMI) <25 kg/m², bioavailable testosterone <2.7 nmol/L, bioavailable estradiol <40 pmol/L, and high bone turnover, defined in this study as serum carboxyterminal cross-linked telopeptide of type I collagen (ICTP) >4.3 μg/L. Introduction  The association of sex steroids and osteoporosis was evaluated in 104 men, aged 50–93 years old. Methods  Bone mineral density (BMD), bone turnover (ICTP), testosterone (T), and estradiol (E₂) were measured; free and bioavailable hormones (free testosterone index [FTI], BioT, free estradiol index [FEI], and BioE₂) were calculated from T, E₂, sex hormone-binding globulin (SHBG), and albumin. Nonparametric analysis and Poisson regression models were used. Results  Significant increases in SHBG and ICTP and decreases in femoral neck BMD, FTI, FEI, BioT, and BioE₂ were observed with each additional decade of age. Femoral neck BMD was inversely correlated with ICTP, and both were significantly associated with SHBG, FTI, BioT, FEI, and BioE. There was a direct and graded association between age and osteoporosis prevalence rate (OP PR; p = 0.028). Compared to participants less than 70 years old, the crude OP PR of those 80 years and older was 3.2 (95%CI = 1.4–7.3). Adjusting sequentially for BMI and bioavailable sex hormones attenuated the association between age and osteoporosis prevalence by 55% and 77%, respectively. Conclusion  Our data support the view that low BMI and declining sex steroids explain most of the association between aging, increased bone turnover, and osteoporosis in men.     

Rates of cancellous bone remodeling and turnover in osteopenia associated with primary biliary cirrhosis

Osteoporosis and fracturing are well-recognized manifestations of primary biliary cirrhosis (PBC), but the abnormalities of bone remodeling and turnover that result in bone loss are poorly understood. We used dynamic histomorphometric techniques to measure tissue level rates of cancellous bone resorption, formation, and turnover in 12 premenopausal women with PBC and in 12 normal premenopausal women. We compared these values with estimates of bone resorption and formation obtained concurrently in the same subjects by radiocalcium kinetics and biochemical markers. Rates of bone turnover were analyzed as a function of a risk score that reflects the severity of hepatic disease and cholestasis (Mayo proportional-hazards model). Positive correlations were observed between tissue level and whole skeletal estimates of bone remodeling. At the remodeling site (bone multicellular unit [BMU]), the depth of eroded lacunae was unaltered by PBC, but wall thickness was decreased. At the level of bone tissues, mean bone turnover was increased in PBC patients but varied widely and increased as hepatic disease and cholestasis worsened. We conclude that PBC causes a reduction in the volume of bone formed at the remodeling site and that the overall level of bone remodeling and turnover in PBC is strongly influenced by the severity of hepatic disease and cholestasis. We hypothesize that the rate of bone loss in PBC may be decreased by therapeutic agents that slow bone turnover, and that further bone loss may be halted by liver transplantation.     

Treatment of denervation/disuse osteoporosis in the rat with a capacitively coupled electrical signal: effects on bone formation and bone resorption

Utilizing a sciatic neurectomy model of disuse osteoporosis, the effects on rates of bone formation and bone resorption were examined when a capacitively coupled electrical signal was applied to the denervated tibia in the rat. It was found that a low-voltage, symmetrical sine wave, 60-kHz, capacitively coupled signal had no significant effect on the amount of bone resorption occurring in denervated right tibiae in rats previously labeled with [3H]tetracycline. This was true whether the signal was applied while osteoporosis was developing (prevention of osteoporosis) or after it had been established (treatment of osteoporosis). If a similar capacitively coupled signal was applied to rats in which osteoporosis was well established, and the rats were labeled with [3H]tetracycline daily during a 12-day treatment period, it was found that there was statistically significant enhancement of the amount of new bone formation (increased [3H]tetracycline incorporation) in the tibiae that received the signal as compared with that of the controls. These results indicate that prevention or amelioration of disuse osteoporosis that occurs with a capacitively coupled electrical signal is due not to a change in the rate of bone resorption, but to an increase in the rate of bone formation.     

Link between obstructive sleep apnea and increased bone resorption in men

SUMMARY: The bone metabolic abnormalities in patients with obstructive sleep apnea (OSA) were examined. Severity-dependent increases in the serum/urinary levels of bone resorption markers and their attenuation following continuous positive airway pressure therapy in subjects with OSA provide the first evidence of a link between OSA and abnormal bone metabolism. INTRODUCTION: Hypoxia, microinflammation and oxidative stress, well-known pathophysiological features of obstructive sleep apnea (OSA), are also known to affect bone metabolism. We examined the bone metabolic abnormalities in patients with OSA and also the effects of continuous positive airway pressure (CPAP) therapy on these abnormalities. METHODS: A cross-sectional and prospective study was conducted in 50 consecutive male subjects visiting a sleep clinic and 15 age-matched control subjects without OSA. Plasma concentrations of IL-1beta, IL-6, TNF-alfa, 3-nitrotyrosine, osteocalcin, bone-specific alkaline phosphatase (BAP), and urinary concentrations of cross-linked C-terminal telopeptide of type I collagen (CTX) were examined before and after 3 months' CPAP in subjects with OSA. RESULTS: The plasma levels of the cytokines as well as the urinary CTX levels were higher in subjects with severe OSA than in those with mild OSA or control subjects. Significant decrease of the urinary excretion of CTX (before: 211+/-107 vs. after: 128+/-59 microg/mmol/creatinine; p<0.01) as well as of the plasma levels of the cytokines was observed following 3 months' CPAP. CONCLUSIONS: Severity-dependent increases in the serum/urinary levels of bone resorption markers and their reversal following CPAP in subjects with OSA provide the first evidence of a link between OSA and abnormal bone metabolism.     

Protamine: A powerfulin vivo inhibitor of bone resorption

Summary Protamine is shown to be a powerful disrupter of calcium homeostasis, acutely inducing a severe hypocalcemia in both rabbits and rats. The magnitude of its effect correlates with bone turnover. Protamine does not significantly alter the renal excretion of calcium, and is effective whether or not there is calcium present in the gut. Protamine causes a significant fall in the specific activity of⁴⁵Ca in the blood in animals whose bone has been prelabeled with⁴⁵Ca. These data suggest that protamine induces hypocalcemia by blocking calcium efflux from bone. Further work seems indicated to define the biochemical mechanism of this action.     

Long-term effects of ovariectomy and aging on the rat skeleton

Summary The long-term skeletal effects of ovariectomy and aging were studied in female Sprague-Dawley rats sacrificed at 270, 370, and 540 days after bilateral ovariectomy (OVX) or sham surgery at 90 days of age. The proximal tibia was processed undecalcified for quantitative bone histomorphometry. For continuity, data from these late time points were combined with previously published data from earlier time points (0–180 days). A biphasic pattern of cancellous bone loss was detected in the proximal tibial metaphysis of OVX rats. An initial, rapid phase of bone loss out to 100 days was followed by an intermediate period of relative stabilization of cancellous bone volume at the markedly osteopenic level of 5–7%. After 270 days, a slow phase of bone loss occurred during which cancellous bone volume declined to 1–2%. Both the initial, rapid phase and the late, slow phase of bone loss in OVX rats were associated with increased bone turnover. In control rats, cancellous bone volume remained constant at 25–30% out to 270 days (12 months of age), then decreased to ∼10% by 540 days (21 months of age). This age-related bone loss was also associated with increased bone turnover. It is interesting to note that the proximal tibial growth plates were closed in approximately a quarter of the control rats by 15–21 months of age. Our data indicate that a slow rate of bone loss and increased bone turnover persist in OVX rats during the later stages of estrogen deficiency. Therefore, the development of osteopenia is coincident with increased bone turnover in OVX rats as well as in aged, control rats.     

Differential effects of estrogen treatment on bone mineral density of the spine,hip, wrist and total body in late postmenopausal women

It is commonly believed that estrogen is effective only in preventing menopause-related loss of bone mineral. However, recent studies found significant increases in bone mineral density (BMD) of the spine in response to estrogen, particularly in older women. The degree to which estrogen can restore BMD of the hip is uncertain. In the present study, changes in BMD of the lumber spine (L2–4), hip (neck, trochanter and Ward's triangle), wrist (ultradistal) and total body in response to 1 year of hormone replacement therapy (HRT) were evaluated by dual-energy X-ray absorptiometry (DXA) in women 10 or more years past menopause. Twelve women, aged 61–74 years, received conjugated estrogens 0.625 mg and cyclic medroxyprogesterone acetate 5 mg; 12 women who did not receive HRT were controls. Calcium intake was adjusted to approximately 1500 mg/day in all subjects. There were no differences between the groups in BMD prior to treatment. Increases in BMD of the lumbar spine (mean±SD, 0.041±0.030 g/cm²), hip (neck, 0.019±0.018 g/cm²; trochanter, 0.017±0.012 g/cm²; Ward's triangle, 0.026±0.029 g/cm²) and total body (0.013±0.016 g/cm²) occurred in response to HRT, and these changes were significantly different from those in controls (spine, 0.005±0.020 g/cm²; neck, –0.007±0.026 g/cm²; trochanter, 0.002±0.014 g/cm²; Ward's triangle, 0.003±0.019 g/cm²; total body, –0.001±0.017 g/cm²). HRT appears to be most effective at weight-bearing sites that have a high cancellous bone content. This study demonstrates that HRT significantly increases bone mass of the lumbar spine and proximal femur in osteopenic, late postmenopausal women, and may, therefore, be effective in preventing osteoporotic fractures at these sites in this population.     

Bone mineral density and bone turnover in patients with Bartter syndrome

The aim of this investigation was to evaluate bone mineral density (BMD), by use of DXA, and bone turnover, in patients with Bartter syndrome (BS). Ten patients (2 with BS type II and 8 with BS type III) were included in the procedure. Age at study varied between 2 and 30 years. During the studies usual treatment with indomethacin, spironolactone, and potassium chloride was maintained. Results were compared with those obtained in the 20 asymptomatic parents. Height of the patients at the time of the study did not differ from reference values (Z-score –1.2 to +0.8). Three patients (1 with BS type II and 2 with BS type III) presented reduced lumbar spine BMD or overt osteopenia (BMD Z-scores: –2.3, –1.3, and –1.1). BMD did not correlate significantly with age. Paternal and maternal femoral neck BMD values correlated significantly with lumbar spine BMD of the patients (r=0.65, P<0.05, and r=0.80, P<0.01). Lumbar spine BMD Z-scores correlated negatively with urinary Ca excretion when values both from patients and parents were jointly analyzed (r=–0.43, P<0.05). Plasma calcium concentration was significantly higher (P<0.001) and plasma phosphate Z-score was significantly lower (P<0.05) in the patients than in the parents. However, no significant differences were observed in values for intact PTH, 1,25 (OH)₂D₃ and 25 (OH)D₃. Intact PTH values correlated positively with BMD Z-scores at lumbar spine (r=0.45, P<0.05) and at femoral neck (r=0.63, P<0.01). Age-corrected biochemical markers of bone formation (plasma alkaline phosphatase and osteocalcin concentrations) were normal whereas age-corrected markers of bone reabsorption (urinary PYD and DPD excretion) were significantly higher than parental values (P<0.01 and <0.05, respectively). We conclude that: (1) reduced BMD is not an exclusive feature of neonatal BS and it can be also observed in classic BS; (2) the loss of bone mineral is not progressive, probably because of the hypocalciuric effect of indomethacin therapy; and (3) this study did not determine whether loss of bone mass is the cause or the consequence of hypercalciuria although the beneficial effect of indomethacin therapy implies the latter.     

Skeletal size and bone mineral content in Turner's syndrome: Relation to karyotype,estrogen treatment,physical fitness,and bone turnover

Summary Bone mineral content (BMC), bone mineral density, and metacarpal dimensions were studied in 50 women with Turner's syndrome aged 21–45 years in relation to karyotype, estrogen treatment, physical fitness, and biochemical markers of bone turnover. No differences were found between the 25 women with karyotype 45,X and women with other karyotypes. Forty-six women had received estrogen. Significant partial correlations were found between bone mineral density of the forearm and duration of estrogen treatment and physical fitness. BMC of the lumbar spine corrected for vertebral height (BMC(C)_spine) was directly correlated with duration of estrogen treatment and height, marginally correlated with physical fitness, and inversely correlated with age. Outer metacarpal width was positively correlated with duration of estrogen treatment, age at initiation of therapy, and body weight. The diameter of medullary space showed negative correlation with physical fitness and height, and positive correlation with age at initiation of estrogen treatment. Cortical thickness was positively correlated with duration of estrogen treatment, physical fitness, and height. No convincing effects of estrogen could be demonstrated in women below the age of 30. Above the age of 30, all bone mineral measurements were markedly elevated in women treated for longer than the average of this age group. BMC(C)_spine was inversely correlated with biochemical markers of bone formation. Our results demonstrate that estrogen treatment and physical fitness are important determinants of bone mineral status in Turner's syndrome and add to the evidence that estrogen treatment increases BMC in Turner's syndrome.     

Screening for osteopenia and osteoporosis: Selection by body composition

There is a great need for simple means of identifying persons at low risk of developing osteoporosis, in order to exclude them from screening with bone mineral measurements, since this procedure is too expensive and time-consuming for general use in the unselected population. We have determined the relationships between body measure (weight, height, body mass index, lean tissue mass, fat mass, waist-to-hip ratio) and bone mineral density (BMD) in 175 women of ages 28–74 years in a cross-sectional study in a county in central Sweden. Dual-energy X-ray absorptiometry was performed at three sites: total body, L2-4 region of lumbar spine, and neck region of the proximal femur. Using multiple linear regression models, the relationship between the dependent variable, BMD, and each of the body measures was determined, with adjustment for confounding factors. Weight alone, in a multivariate model, explained 28%, 21% and 15% of the variance in BMD of total body, at the lumbar spine and at the femoral neck according to these models. The WHO definition of osteopenia was used to dichotomize BMD, which made it possible, in multivariate logistic regression models, to estimate the risk of osteopenia with different body measures categorized into tertiles. Weight of over 71 kg was associated with a very low risk of being osteopenic compared with women weighing less than 64 kg, with odds ratios (OR) of 0.01 (95% confidence interval (CI) 0.00–0.09), 0.06 (CI 0.02–0.22) and 0.13 (CI 0.04–0.42) for osteopenia of total body, lumbar spine and femoral neck, respectively. Furthermore a sensitivity/specificity analysis revealed that, in this population, a woman weighing over 70 kg is not likely to have osteoporosis. Test specifics of a weight under 70 kg for osteoporosis (BMD less than 2.5 SD compared with normal young women) of femoral neck among the postmenopausal women showed a sensitivity of 0.94, a specificity of 0.36, positive predictive value (PPV) of 0.21, and negative predictive value (NPV) of 0.97. Thus, exclusion of the 33% of women with the highest weight meant only that 3% of osteoporotic cases were missed. The corresponding figures for lumbar spine were sensitivity 0.89, specificity 0.38, PPV 0.33, and NPV 0.91. All women who were defined as being osteoporotic of total body weighed under 62 kg. When the intention was to identify those with osteopenia of total body among the postmenopausal women we attained a sensitivity of 0.92 and a NPV of 0.91 for a weight under 70 kg, whereas we found that weight could not be used as an exclusion criterion for osteopenia of femoral neck and lumbar spine. Our data thus indicate that weight could be used to exclude women from a screening program for postmenopausal osteoporosis.     

Inflammation-mediated osteopenia in the rat: The effects of artificial granuloma and sham operation on cortical and trabecular bone

Recent studies have established that generalized loss of trabecular bone occurs in the growing rat following day-to-day inflammatory irritation for a period of 3 wk. We can now demonstrate that there are similar effects on bone in milder but more prolonged chronic inflammation (14 wk). Thus, there were significant decreases in trabecular bone mass as well as in cortical bone after weekly subcutaneous injections or implantations of nonspecific irritants. Osteopenia, induced by a single but extensive inflammatory lesion, remained apparent even 14 wk after induction. This indicates that inflammation-mediated osteopenia is at least incompletely reversible. A less pronounced but similar reduction of cortical and trabecular bone was observed in rats following sham operation. This might be of importance in all animal studies on bone metabolism that include surgical procedures.     

Temporal relationship between bone loss and increased bone turnover in ovariectomized rats

Summary To characterize osteopenic changes in ovariectomized (OVX) rats as a function of time, female Sprague Dawley rats (240 g body weight, 90 days old) were subjected to bilateral ovariectomy or sham surgery and killed at various times from 14–180 days postovariectomy. The proximal tibial metaphysis was processed undecalcified for quantitative bone histomorphometry. Osteopenia and increased indices of bone resorption and formation were detected in OVX rats as early as 14 days. Longitudinal bone growth was also significantly increased by ovariectomy at 14 days, but returned to control levels at all later times. In OVX rats, osteopenia became progressively more pronounced with time up to 100 days postovariectomy, after which trabecular bone volume appeared to stabilize at the markedly reduced level of 5%. Changes in osteoclast surface, osteoblast surface, and fluoro-chrome-based indices of bone formation in OVX rats followed a similar time course. The maximal increase in these parameters occurred during the first several months postovariectomy followed by a gradual decline toward control levels. Our results indicate that the initial rapid phase of bone loss in OVX rats is coincident with the maximal increase in bone turnover. At later times postovariectomy, bone loss and bone turnover both subside. These findings emphasize the close temporal association between the development of osteopenia and increased bone turnover in OVX rats.     

Effect of body weight on osteopenia in ovariectomized rats

Summary Bilateral ovariectomies or sham surgeries were performed in female Sprague Dawley rats that were 78 days of age and weighed an average of 210 g. Food was available ad libitum to the control rats and to a group of ovariectomized rats (obese OVX). The food consumption of a second group of ovariectomized rats (weight-matched OVX) was restricted to match their body weights to those of the control rats. All rats were sacrificed at 14 weeks postovariectomy. Radioimmunoassay of terminal serum estradiol confirmed the success of ovariectomy. The estradiol concentration in control rats was 24.9±20.2 pg/ml, whereas the hormone was undetectable (<10 pg/ml) in both groups of OVX rats. The final body weights of control and weight-matched OVX rats were nearly identical (∼260 g). In contrast, obese OVX rats weighed significantly more than both of the above groups (∼320 g,P<0.001). The proximal tibia and lumbar vertebra were processed undecalcified for quantitative bone histomorphometry. Tibial trabecular bone volume (TBV) was determined to be 17.6±4.5%, 7.9±5.3%, and 3.6±3.1% for the control, obese OVX, and weight-matched OVX groups, respectively. Tibial TBV for both OVX groups was significantly less than the control value (P<0.001). The difference in tibial TBV between obese OVX and weight-matched OVX rats was also statistically significant (P<0.02). Histologic indices of bone resorption and formation were indicative of increased bone turnover in the proximal tibia of both OVX groups. In comparison to control rats, both groups of OVX rats exhibited a strong trend for a reduction in vertebral TBV, but no significant differences were observed among the three groups. Our results suggest that increased body weight provides partial protection against osteopenia in the long bones of OVX rats. However, it is important to note that this protective effect is only partial and that marked osteopenia develops in the long bones of OVX rats regardless of body weight.     

Effects of long-term calcium intake on body weight, body fat and bone in growing rats

Increased calcium intake may reduce body weight and fat in non-growing individuals. This study explored the long-term effects of high versus low calcium intake on body weight, body fat, BMC, BMD and bone size in growing male and female rats. Ninety male and 90 female Sprague-Dawley rats were randomly assigned either to a high calcium (1%) or low calcium (0.25%) diet from age 3 weeks until 40 weeks. Half of the animals were fed ad libitum, and half of the animals were on an adjusted feeding schedule (the food intake of the low calcium animals was reduced to maintain equal body weight with high calcium animals of the same gender). DXA and radiographic measurements (femur and skull length and width) were collected at the age of 4, 13 and 34 weeks. Growing male rats fed the low calcium diet ad libitum gained more weight and more fat than rats on a high calcium diet. When food intake was controlled, male rats on the low calcium diet still had a greater fat mass (despite their similar body weight) and smaller skeletal measurements than the high calcium animals. Growing female rats initially responded like the males: when fed ad libitum low calcium animals had an increased body weight and fat mass; when food intake was controlled the low calcium animals had a greater fat mass and smaller skeletal measurements. However, these differences were found at 13 weeks and not at 34 weeks, suggesting a transient effect with no long-term differences between high and low calcium intake in the growing female rats.