Alfacalcidol increases cancellous bone in low turnover, fatty marrow sites in aged, orchidectomized rats.

The objectives of this study were to determine the responses of cancellous bone in the distal tibial metaphysis (DTM), a low turnover, fatty (yellow) marrow site, to sham-aged, orchidectomy (ORX) and alfacalcidol treatment in sham-aged and ORX rats. Eighteen-month-old male sham and ORX rats were treated with 0.1 and 0.2 microg/kg alfacalcidol 5 days/wk p.o. for 12 weeks, double fluorescent labeled, and the DTM were processed for bone histomorphometry analyses. The current study found the DTM in sham-aged male rats were resistant to age-related and ORX-induced cancellous bone loss and alfacalcidol-induced bone gain, findings that differ from that in the proximal tibial metaphysis (PTM) and lumbar vertebral body (LVB), two high turnover, red marrow bone sites. However, alfacalcidol treatment increased DTM bone mass in ORX rats where bone turnover was elevated by androgen deficiency. These results in concert with the previously positive findings in red marrow bone sites following alfacalcidol treatment suggest that alfacalcidol is more effective in increasing cancellous bone mass in the skeletal sites with higher bone turnover.

Continuous PGE2 leads to net bone loss while intermittent PGE2 leads to net bone gain in lumbar vertebral bodies of adult female rats.

The present study examined the effects of continuous and intermittent PGE2 administration on the cancellous and cortical bone of lumbar vertebral bodies (LVB) in female rats. Six-month-old Sprague-Dawley female rats were divided into 6 groups with 2 control groups and 1 or 3 mg PGE2/kg given either continuously or intermittently for 21 days. Histomorphometric analyses were performed on the cancellous and cortical bone of the fourth and fifth LVBs. Continuous PGE2 exposure led to bone catabolism while intermittent administration led to bone anabolism. Both routes of administration stimulated bone remodeling, but the continuous PGE2 stimulated more than the intermittent route to expose more basic multicellular units (BMUs) to the negative bone balance. The continuous PGE2 caused cancellous bone loss by stimulating bone resorption greater than formation (i.e., negative bone balance) and shortening the formation period. It caused more cortical bone loss than gain, the magnitude of the negative endocortical bone balance and increased intracortical porosity bone loss was greater than for periosteal bone gain. The anabolic effects of intermittent PGE2 resulted from cancellous bone gain by positive bone balance from stimulated bone formation and shortened resorption period; while cortical bone gain occurred from endocortical bone gain exceeding the decrease in periosteal bone and increased intracortical bone loss. Lastly, a scheme to take advantage of the marked PGE2 stimulation of lumbar periosteal apposition in strengthening bone by converting it to an anabolic agent was proposed.

Greater efficacy of alfacalcidol in the red than in the yellow marrow skeletal sites in adult female rats.

The present study compared the bone anabolic effects of graded doses of alfacalcidol in proximal femurs (hematopoietic, red marrow skeletal site) and distal tibiae (fatty, yellow marrow skeletal site). One group of 8.5-month-old female Sprague-Dawley rats were killed at baseline and 4 groups were treated 5 days on/2 days off/week for 12 weeks with 0, 0.025, 0.05 and 0.1 microg alfacalcidol/kg by oral gavage. The proximal femur, bone site with hematopoietic marrow, as well as the distal tibia bone site with fatty marrow, were processed undecalcified for quantitative bone histomorphometry. In the red marrow site of the proximal femoral metaphysis (PFM), 0.1 microg alfacalcidol/kg induced increased cancellous bone mass, improved architecture (decreased trabecular separation, increased connectivity), and stimulated local bone formation of bone 'boutons' (localized bone formation) on trabecular surfaces. There was an imbalance in bone resorption and formation, in which the magnitude of depressed bone resorption greater than depressed bone formation resulted in a positive bone balance. In addition, bone 'bouton' formation contributed to an increase in bone mass. In contrast, the yellow marrow site of the distal tibial metaphysis (DTM), the 0.1 microg alfacalcidol/kg dose induced a non-significant increased cancellous bone mass. The treatment decreased bone resorption equal to the magnitude of decreased bone formation. No bone 'bouton' formation was observed. These findings indicate that the highest dose of 0.1 microg alfacalcidol/kg for 12 weeks increased bone mass (anabolic effect) at the skeletal site with hematopoietic marrow of the proximal femoral metaphysis, but the increased bone mass was greatly attenuated at the fatty marrow site of the distal tibial metaphysis. In addition, the magnitude of the bone gain induced by alfacalcidol treatment in red marrow cancellous bone sites of the proximal femoral metaphysis was half that of the lumbar vertebral body. The latter data were from a previous report from the same animal and protocol. These findings indicated that alfacalcidol as an osteoporosis therapy is less efficacious as a positive bone balance agent that increased trabecular bone mass in a non-vertebral skeletal site where bone marrow is less hematopoietic.

Cancellous bone minimodeling-based formation: a Frost, Takahashi legacy.

The current dogma is that in adult human beings, remodeling creates nearly all the new cancellous bone tissue. However, Frost, Takahashi and colleagues hypothesized that minimodeling can go on in trabeculae throughout life. The current perspective will review the available reports on minimodeling-based formation to determine whether there is any support for his hypothesis. One: describe the methodology employed to characterize remodeling and minimodeling formation sites or packets, which restrict the analyses of these packets to a known age of the specimen. Two: present quantitative minimodeling data on cancellous bone of aging rats and transiliac bone biopsy of adult humans. Three: describe the occurrence and quantitation of mixed remodeling-minimodeling formation sites that could be misinterpreted as minimodeling sites. Fourth: present irrefutable evidence that bone anabolic agents initiate minimodeling-based formation sites. Fifth: discuss the mechanism of minimodeling-based formation may be the resumption of osteoblastic activity by bone lining cells to increase cancellous bone mass and trabecular connectivity. The findings of minimodeling is a rare activity in normal individuals, but may occur in a select population, and bone anabolic agents can initiate minimodeling-based formation are in support of Frost's hypothesis that minimodeling can continue throughout human life. Thus, another Frost, Takahashi legacy lives on.

Rolipram, a phosphodiesterase 4 inhibitor, prevented cancellous and cortical bone loss by inhibiting endosteal bone resorption and maintaining the elevated periosteal bone formation in adult ovariectomized rats.

Cyclic AMP (cAMP) is a continually produced nucleotide inactivated by hydrolysis to 5'AMP via phosphodiesterase (PDE) enzymes. Rolipram is a selective PDE4 inhibitor reported to have anti-inflammatory effects and used in the treatment of asthma and chronic obstructive pulmonary disease (COPD). The current study was designed to determine whether Rolipram could prevent and restore bone loss in ovariectomized (OVX) rats. Six-month-old Sprague Dawley rats underwent either sham-operated or bilateral ovariectomy, and were left untreated for 60 days to develop osteopenia. Then they were treated with vehicle, 6 mg/kg PGE(2), 3 microg/kg Alendronate or 0.1-1.0 mg/kg Rolipram for 60 days. At sacrifice, the right tibiae were processed for quantitative bone histomorphometric measurements. The right femurs were measured by dual energy A-ray absorptiometry and the 5th lumbar vertebrae were subjected to micro-computed tomography to access bone mass and architecture changes. Our results indicated that OVX induced negative bone balance in all five bone sites we tested, with bone resorption exceeding bone formation. Rolipram at 0.1-0.6 mg/kg dose levels prevented while at 1 mg/kg restored ovariectomy-induced cancellous and cortical bone loss in the tibia, femur and lumbar vertebra. Dynamic bone histomorphometry suggested that these beneficial effects were achieved by partially maintaining the elevated bone formation at the trabecular bone surface and increasing bone formation at the periosteal bone surface of the cortex. Furthermore, it reduced bone turnover at the trabecular and the endocortical bone surfaces. The prevention of further bone loss effects were comparable to those of an anti-resorption agent (Alendronate) but were not as great as those of an anabolic agent (PGE(2)). In addition, Rolipram treatment increased body and muscle weights compared to the vehicle-treated OVX rats. In conclusion, our study in an osteopenic rat model suggested that a selective PDE4 inhibitor may be used for the treatment of established osteoporosis.

Continuous infusion of PGE2 is catabolic with a negative bone balance on both cancellous and cortical bone in rats.

It is well documented that intermittent PGE(2) treatment increases both trabecular and cortical bone mass. However, the effects of continuous PGE(2) administration remain undocumented. The aim of the study was to investigate the effects of continuous prostaglandin E(2) (PGE(2)) on different bone sites in skeletally mature rats. Six-month-old Sprague Dawley rats were treated with PGE(2) at 1 or 3 mg/kg/d continuously via infusion pump for 21 days. Two other groups of rats received PGE(2) at the same doses by intermittent (daily) subcutaneous injections and served as positive controls. Histomorphometry was performed on cancellous bone of the proximal tibial metaphysis and cortical bone of the tibial shaft. As expected, intermittent PGE(2) treatment increased both cancellous and cortical bone mass by stimulating bone formation at the cancellous, periosteal and endocortical bone surfaces. In contrast, continuous PGE(2) treatment decreased cancellous bone mass with bone resorption exceeding bone formation. In addition, continuous PGE(2) treatment increased endocortical and intracortical bone remodeling, inducing bone loss which was partially offset by stimulating periosteal expansion. We conclude that continuous PGE(2) treatment induces overall catabolic effects on both cancellous and cortical bone envelopes, which differs from intermittent PGE(2) treatment that is anabolic. Lastly, we speculate that superior bone mass may be achieved by co-treatment of continuous PGE(2) in combination with an anti-catabolic agent.

Simvastatin did not prevent nor restore ovariectomy-induced bone loss in adult rats.

Current published results on whether statins have beneficial effects on bone metabolism have been conflicting so far. In order to further investigate if statins were promising candidates for the treatment for osteoporosis, we conducted a study in which rats were ovariectomized (OVX) at 6 months of age, allowed to lose bone for 60 days and followed by oral administration of simvastatin at the dose levels of 0.3-10 mg/kg/d for 60 days. PGE2 (6 mg/kg) was used as a positive control. Study endpoints included bone histomorphometry on the proximal tibial metaphysis (PTM) and the tibial diaphysis (TX), dual-energy X-ray absorptiometry on the right femur and micro computed tomography (ICT) on the 5th lumbar vertebra (LV). After 120 days of OVX, cancellous bone lost by 80% in the PTM and 18% in the LV accompanied by increased bone formation and resorption. Simvastatin at all dose levels did not affect bone volume, bone formation rate and bone erosion surface when compared to 120 day ovariectomized animals at all bone sites studied. By contrast, PGE2 restored cancellous and cortical bone area to sham control levels. In conclusion, this study demonstrated that unlike PGE2, oral administration of simvastatin did not have effects on cancellous or cortical bone formation and resorption; and consequently was not able to prevent further bone loss or restore bone mass in the osteopenic, OVX rats.

Ancestry of beagles in lifespan studies of radionuclide toxicity at the University of Utah.

Analysis of the ancestry of the 1,262 lifespan beagles (LSB) entered into lifespan studies at the Radiobiology Division, University of Utah, beginning in 1952 and ending in 1980, indicated that about 97% of ancestor citations in the various pedigrees were of only 10 breeding animals (breeders) among breeders within the beagle colony. In turn, just 18 AKC-registered "champion" beagles from outside of this colony (founders) accounted for about 98% of all ancestor citations among founders for the LSB. We conclude from this study that the animals used in the lifespan radionuclide experiments can be considered to be somewhat genetically interrelated.

The benefit of combining non-mechanical agents with mechanical loading: a perspective based on the Utah Paradigm of Skeletal Physiology.

The Utah Paradigm of Skeletal Physiology with its key component, the mechanostat hypothesis, suggest plausible explanations of some of the tissue-level changes occurring from combining selected non-mechanical agents (anabolic and anti-resorptive/( re)modeling agents) with mechanical loading (osteogenic exercise) to increase bone mass and strength. The evidence for combining selected anabolic agents like parathyroid hormone, prostaglandin E(2), growth hormone, etc. with mechanical loading can increase bone mass is strong. Anabolic agents influence loading-related bone formation changes in a permissive manner and modulate (increase) the responsiveness of bone tissue to mechanical loading by changing thresholds for bone formation and resorption. However, any beneficial effect of combining selected anti-resorptive/(re)modeling agents like estrogen with loading is marginal, especially in adult skeletons. Postulated changes in modeling and remodeling thresholds (set points) and known direct effects on bone cells by non-mechanical agents may explain the observed tissue-level changes associated with large and minor increases in bone mass. Although the pharmaceutical industry has avoided considering osteogenic loading in the treatment of osteoporosis, a methodical dose-response study of anabolic agents combined with loading should: (1) provide opportunities for therapeutic intervention to imitate or enhance the osteogenic response to loading in order to correct osteopenias; (2) provide the potential to diminish the dosage of drugs required to induce bone formation in ways that enhanced efficacy and reduced any side effects; and (3) improve the quality of life and reduce the risk of falls by improving balance, gait speed and muscle strength with a non-mechanical agent like GH that could improve both muscle and bone mass and strength. Lastly, more studies are needed which determine bone strength instead of only "mass" in aged skeletons so one can assess how effective such treatments would reduce the risk of fracture in the clinic.

Variation of long-lived free radicals responsible for the EPR native signal in bone of aged or diseased human females and ovariectomized adult rats.

The purpose of this study was to gain insights into the variations seen in the electron paramagnetic resonance (EPR) spectroscopy of the native signals of teeth and bones used for retrospective dosimetry measurements. We determined that changes occur in the long-lived free radicals responsible for the native signal of cortical bone in aging or diseased human females and aged ovariectomized rats. This was done by measuring the magnitude of the broad (BC) and narrow (NC) components of the native EPR signal of bone following chemical extraction, aging, crushing and thermal annealing. Bone from the upper midshaft of femora of young (17-34 years old, n=5) and elderly (70-92 years old, n=18) females was examined. The results showed that the elderly women had significantly higher BC than the younger women (P<0.01). A similar interpretation was made of the data from an aging female rat osteoporosis model. The results for the NC signals were similar. Finally, dramatic decreases in both NC and BC signals were seen in HIV positive and uncontrolled diabetic (one each) patients indicating the need for studying this signal for a broad spectrum of metabolic disorders. Experiments were performed which strongly indicate that iron liganded with organic molecules is the source of the BC signal. Finally, the accuracy achieved in this study indicates that resolving the dosimetric signal (g=2.0018) should be improved by subtraction of the deconvoluted NC and BC signals from the original spectrum.

Restoring and maintaining bone in osteopenic female rat skeleton: I. Changes in bone mass and structure.

This experiment contains the crucial data for the lose, restore, and maintain (LRM) concept, a practical approach for reversing existing osteoporosis. The LRM concept uses anabolic agents to restore bone mass and architecture (+ phase) and then switches to an agent with the established ability to maintain bone mass, to keep the new bone (+/- phase). The purpose of this study was to learn whether switching to an agent known chiefly for its ability to maintain existing bone mass preserves new bone induced by PGE2 in osteopenic, estrogen-depleted rats. The current study had three phases, the bone loss (-), restore (+), and maintain (+/-) phases. We ovariectomized (OX) or sham ovariectomized (sham-OX) 5.5-month-old female rats (- phase). The OX rats were treated 5 months postovariectomy with 1-6 mg PGE2 per kg/day for 75 days to restore lost cancellous bone mass (+ phase), and then PGE2 treatment was stopped and treatment began with 1 or 5 micrograms/kg of risedronate, a bisphosphonate, twice a week for 60 days (+/- phase). During the loss (-) phase, the cancellous bone volume of the proximal tibial metaphysis in the OX rat fell to 19% of initial and 30% of age-matched control levels. During the restore (+) phase, the cancellous bone volume in OX rats doubled. When PGE2 treatment was stopped, however, and no special maintenance efforts were made during the maintain (+/-) phase, the PGE2-induced cancellous bone disappeared. In contrast, the PGE2-induced cancellous bone persisted when the PGE2 treatment was followed by either a 1 or 5 micrograms treatment of risedronate per kg given twice a week for 60 days during the maintain (+/-) phase. The tibial shaft demonstrated very little cortical bone loss during the loss (-) phase in OX rats. The tibial shaft cortical bone fell some 8%. During the restore (+) phase, new cortical bone in OX rats increased by 22%. When PGE2 treatment was stopped and nothing was given during the maintain (+/-) phase, however, all but the PGE2-induced subperiosteal bone disappeared. In contrast, when PGE2 treatment was stopped and 1 micron risedronate per kg twice a week for 60 days was administered during the maintenance (+/-) phase, the PGE2-induced subperiosteal bone and some of the subendocortical bone and marrow trabeculae persisted.(ABSTRACT TRUNCATED AT 400 WORDS)

Prostaglandin E2 increases the skeletal response to mechanical loading.

The study tested the influence of prostaglandin E2 (PGE2) on the skeletal response to increased in vivo mechanical loading through a four-point bending device. One hundred and twenty Sprague-Dawley female rats (6 months old, 354 +/- 34 g) were divided into 12 groups to accommodate all possible combinations of doses of loads (25, 30, or 35 N) and PGE2 (0, 0.1, 0.3, or 1 mg/kg). Rats received subcutaneous injections of PGE2 daily and in vivo loading of the right tibia every Monday, Wednesday, and Friday for four weeks. Histomorphometric analysis of the periosteal and endocortical surfaces following in vivo dual fluorochrome labeling was performed on both the loaded region of the right tibial diaphysis and a similar region of the left tibial diaphysis. Without PGE2, the threshold for loading to stimulate bone formation was 30 N (peak strain 1360 mu epsilon) at the periosteal surface and 25 N (peak strain 580 mu epsilon) at the endocortical surface. Without loading, the minimum dose of PGE2 to stimulate bone formation at all surfaces was 1 mg/kg/day. When 1 mg/kg/day PGE2 was combined with the minimum effective load, an additive effect of PGE2 and loading on bone formation was observed at the endocortical surface, but a synergistic effect was noted at the periosteal surface. No combined effect of ineffective doses of loading and PGE2 was found. A synergistic effect at peak strains of approximately 1625 mu epsilon on the periosteal surface could suggest either the involvement of locally produced growth factors or autoregulation of endogenous synthesis of PGE2 by exogenously administered PGE2.

Extra cancellous bone induced by combined prostaglandin E2 and risedronate administration is maintained after their withdrawal in older female rats.

Prostaglandin E2 (PGE2) has been recognized for its marked anabolic effect on bone, but the bone gain is lost after the cessation of PGE2 treatment. In previous studies, we were successful in maintaining the new bone by administering a bisphosphonate after the withdrawal of PGE2 treatment. The objective of this study was to determine the fate of the extra bone induced by a combination with PGE2 and risedronate after discontinuing treatment. Ninety-six 9-month-old virgin female Sprague-Dawley rats were treated with 1 or 5 micrograms of risedronate/kg/twice weekly, 6 mg of PGE2/kg/day alone or 6 mg of PGE2/kg/day plus 1 or 5 micrograms of risedronate/kg/twice weekly for 60 days (day 0) and followed by 60 days without treatment (day 60). We have reported the results from the groups treated for 60 days previously. This report is restricted to the histomorphometric findings on the secondary spongiosa of the proximal tibial metaphysis in the groups after withdrawal for 60 days. We found that the only group that maintained the PGE2 induced new bone after withdrawal was the group treated with 6 mg of PGE2/kg/day plus 5 micrograms of risdronate/kg/twice a week. Withdrawal of this combined treatment depressed bone turnover (bone-based bone formation rate, activation frequency) and bone resorption (percent eroded perimeter). The tissue mechanisms responsible for the protection drew from the previously deposited risedronate.

Making rats rise to erect bipedal stance for feeding partially prevented orchidectomy-induced bone loss and added bone to intact rats.

The objectives of this study were to investigate the different effects on muscle mass and cancellous (proximal tibial metaphysis [PTM]) and cortical (tibial shaft [TX]) bone mass of sham-operated and orchidectomized (ORX) male rats by making rats rise to erect bipedal stance for feeding. Specially designed raised cages (RC) were used so that the rats had to rise to erect bipedal stance to eat and drink for 12 weeks. Dual-energy X-ray absorptiometry (DEXA) and peripheral quantitative computerized tomography (pQCT) were used to estimate the lean leg mass and bone mineral. Static and dynamic histomorphometry were performed on the triple-labeled undecalcified sections. We found that making the intact rats rise to erect bipedal stance for feeding increased muscle mass, cortical bone volume, and periosteal bone formation. Orchidectomy increased net losses of bone next to the marrow by increasing bone turnover. Making the ORX rats rise to erect bipedal stance increased muscle mass, partially prevented cancellous bone loss in the PTM, and prevented net cortical bone loss in TX induced by ORX by depressing cancellous and endocortical high bone turnover and stimulating periosteal bone formation. The bone-anabolic effects were achieved mainly in the first 4 weeks in the PTM and by 8 weeks in the TX. These findings suggested that making the rats rise to erect bipedal stance for feeding helped to increase muscle mass and cortical bone mass in the tibias of intact rats, increase muscle mass, and partially prevented cancellous and net cortical bone loss in ORX rats.

Bone mineral metabolism in T lymphocyte-deficient and -replete strains of rat.

The immune and skeletal systems are known to interact. We have repeatedly shown that in contrast to in vitro data, the administration of T lymphocyte immunosuppressants, such as cyclosporin A, leads to an increase in bone resorption and a high turnover osteopenia. The purpose of this study was to characterize the bone metabolism of the T lymphocyte deficient Rowett athymic homozygous (rnu/rnu) nude rat. We wished to determine whether these rats share the bone abnormalities of cyclosporin A-treated rats. Eleven 10-week-old Sprague-Dawley rats and 12 similarly aged nude rats were studied over a 4-week period. Metaphyseal cancellous bone histomorphometry was similar in the two groups of rats and only differed with regard to percentage eroded perimeter (lower in nude rats, p = 0.0008) and longitudinal growth rate (49% lower in nude rats, p < 0.001). The nude rats had less body mass (p < 0.001) but nevertheless gained the same percentage of their body weight over the study period. The athymic rats had lower levels of serum, 1,25-dihydroxyvitamin D (p < 0.014) and serum osteocalcin(p < 0.009), and at the age of 14 weeks the nude rats had lower concentrations of serum creatinine (p = 0.001) and blood ionized calcium (p = 0.0002), yet serum PTH was similar throughout. RNA isolated from the contralateral tibias revealed that the nude group had lower steady-state levels of osteocalcin mRNA despite similar rates of bone formation. In its entirety, the data suggest that T cell deficiency per se is not necessarily associated with high turnover osteopenia.

Raloxifene analog (LY117018 HCL) ameliorates cyclosporin A-induced osteopenia in oophorectomized rats.

Cyclosporin A (CsA) administered to the oophorectomized (Ox) rat exacerbates the high turnover osteopenia associated with estrogen deficiency. 17 beta-estradiol replacement therapy prevent this bone loss. The aim of this study was to see whether an estrogen-like compound, Raloxifene analog (LY117018 HCL, Ral) could likewise ameliorate CsA-induced osteopenia in the Ox rat. Sixty 6-month-old Sprague-Dawley rats, divided into five groups, underwent oophorectomy. One group acted as a basal group and the others received either vehicle (group B), CsA 15 mg/kg/day (group C), Ral 3 mg/kg/day (group D), or CsA 15 mg/kg/day and Ral 3 mg/kg/day (group E) for 28 days by gavage. A sixth sham operated group of 12 rats received vehicle only (group A). Rats were weighed and bled on days 0, 14, and 28 for measurement of ionized calcium, glucose, osteocalcin (BGP), 17 beta-estradiol, and 1,25-dihydroxyvitamin D3 (1,25[OH]2D3). Tibiae were removed on day 28 for bone histomorphometry after double tetracycline and calcein labeling. Oophorectomy caused a significant gain in weight in groups B and C which was prevented by Ral in groups D and E. Randomized blood glucose levels and 1,25(OH)2D3 levels were elevated in both CsA-treated groups. Blood ionized calcium levels were lower in vehicle (group B) compared with sham (group A) on day 28. Ox (group B) had significantly higher serum BGP levels compared with sham-operated rats. Serum BGP levels were further elevated in group C compared with vehicle and were lowered in both Ral-treated groups to vehicle levels by day 28. Bone histomorphometry revealed a high turnover osteopenia with increased parameters of bone formation and resorption and loss of cancellous bone volume postoophorectomy (group B). CsA (group C) exacerbated the effects of oophorectomy. Ral (group D) completely prevented the high turnover osteopenia caused by oophorectomy and was able to attenuate substantially the effects of CsA in the Ox rat (group E). Ral therapy ameliorated CsA-induced osteopenia in the Ox rat and might prove a useful agent in preventing bone loss in postmenopausal women receiving CsA.

Human parathyroid hormone-(1-38) restores cancellous bone to the immobilized, osteopenic proximal tibial metaphysis in rats.

The purpose of this study was to determine if human parathyroid hormone-(1-38) (hPTH(1-38)) can restore cancellous bone mass to the established osteopenic, immobilized proximal tibial metaphyses of female rats. The right hindlimbs of 6-month-old female Sprague-Dawley rats were immobilized by bandaging the right hindlimbs to the abdomen. After 30 days of right hindlimb immobilization, the rats were subcutaneously injected with 200 micrograms hPTH(1-38)/kg/day for 15 days (short-term treatment) or 75 days (longer-term treatment). Static bone histomorphometry was performed on the primary spongiosa, and both static and dynamic histomorphometry were performed on the secondary spongiosa of the right proximal tibial metaphyses. Immobilization for 30 days without treatment decreased trabecular bone area, number, and thickness in both primary and secondary spongiosa, and induced an increase in eroded perimeter and a decrease in tissue referent-bone formation rate in the secondary spongiosa. These changes reached a new steady state thereafter. Treatment with 200 micrograms hPTH(1-38)/kg/day for 15 days, beginning 30 days after immobilization, significantly increased trabecular bone area, thickness, and number in both primary and secondary spongiosa despite continuous immobilization when compared with controls. The short-term PTH treatment (15 days) significantly increased labeling perimeter, mineral apposition rate, and tissue referent-bone formation rate in the secondary spongiosa and stimulated longitudinal bone growth as compared with the controls. Longer PTH treatment (75 days) further increased trabecular bone area, thickness, and number as compared with controls and groups given short-term PTH treatment (15 days). The bone formation indices in the secondary spongiosa of the longer-term treated rats were lower than those of the short-term treated group, but they were still higher than those of controls. Our findings indicate that PTH treatment stimulates cancellous bone formation, and restores and adds extra cancellous bone to the established, disuse-osteopenic proximal tibial metaphysis of female rats with continuously immobilized right hindlimbs. These results suggest that PTH may be useful in treating disuse-induced osteoporosis in humans.

Prostaglandin E2 administration prevents bone loss induced by orchidectomy in rats.

The objects of this study were to investigate whether prostaglandin E2 (PGE2) can prevent orchidectomy (ORX)-induced cancellous bone loss in growing male rats, and to determine the differential effects of PGE2 on sham-operated (sham) and ORX male rats. Fourteen-week-old Sprague-Dawley male rats were divided into groups of basal, vehicle-treated sham, PGE2-treated sham, vehicle-treated ORX, and PGE2-treated ORX rats for either 3 or 9 weeks. PGE2 was given at 6 mg/kg body weight daily by subcutaneous injection. Static and dynamic cancellous bone histomorphometry were performed on double-fluorescent labeled undecalcified proximal tibial metaphyseal sections. No effect was observed by ORX on body weight or longitudinal bone growth rate when compared with sham-operated controls. However, androgen deficiency caused significant increases in percent eroded perimeter, mineral apposition rate, and bone turnover (bone-volume-referent-bone formation rate), which resulted in a significant decrease in trabecular bone number, increase in trabecular separation, and a nonsignificant decrease in trabecular bone area by 3 weeks of ORX. After 9 weeks of ORX, trabecular bone area and number were significantly decreased, and trabecular separation, percent eroded perimeter, and the index of bone turnover (bone-volume-referent-bone formation rate) remained significantly increased while the index of bone formation (tissue-volume-referent-bone formation rate) was nonsignificantly decreased when compared with sham controls. When 6 mg PGE2/kg/day was given for 3 and 9 weeks, similar anabolic effects were observed in sham and ORX rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Rapamycin: a bone sparing immunosuppressant?

Immunosuppressant therpay is associated with osteoporosis both clinically, post-transplantation, and experimentally. In rats, cyclosporin A (CsA) and FK506 induce a state of high turnover rapid bone loss. After 14 days of administration in immunosuppressive doses, the more recently discovered immunosuppressant, rapamycin, resulted in no change of cancellous bone volume. A longer study over 28 days has now been carried out; contrasting the new drug with CsA and FK506. Sixty, 10-week-old Sprague-Dawley rats were randomly divided into five groups of 12 rats each. The first group served as an aging control. The remaining four groups received, by daily gavage, a combined vehicle placebo, CsA 15 mg/kg, FK506 5 mg/kg, and rapamycin 2.5 mg/kg, respectively. CsA- and FK506-treated rats, but not those treated with rapamycin, demonstrated high turnover osteoporosis with raised serum 1,25(OH)2D (p < 0.05) and elevated serum osteocalcin (p < 0.05). The trabecular bone area was decreased by 66% (p < 0.01) in the CsA group and 56% (p < 0.05) in the FK506-treated group compared with the control animals. The CsA- and the rapamycin-treated groups failed to gain weight and developed severe hyperglycemia (> 20 mmol/l, p < 0.001) by day 14 but which largely resolved by day 28. Unlike the groups treated with CsA and FK506, rapamycin-treated rats had no loss of trabecular bone volume but there was increased modeling and remodeling and a decreased longitudinal growth rate. Rapamycin may thus confer a distinct advantage over the established immunosuppressants in not reducing bone volume in the short term.(ABSTRACT TRUNCATED AT 250 WORDS)

Droloxifene prevents ovariectomy-induced bone loss in tibiae and femora of aged female rats: a dual-energy X-ray absorptiometric and histomorphometric study.

Our previous studies indicated that droloxifene (DRO), a tissue-specific estrogen antagonist/agonist, prevented bone loss without causing uterine hypertrophy in growing ovariectomized (OVX) rats. Using dual-energy X-ray absorptiometry (DXA) and bone histomorphometry, the current study compared the efficacy of DRO to 17 beta-estradiol (E2) in preventing OVX-induced bone loss in tibiae and femora of 19-month-old rats to determine whether DRO had similar skeletal effects as E2 in aged female rats. Sprague-Dawley female rats were OVX or sham-operated (sham) at 19 months of age. The sham-operated rats were treated with vehicle (oral), while the OVX rats were treated with vehicle (oral), E2 at 30 micrograms/kg/day (sc), or DRO at 2.5, 5, or 10 mg/kg/day (oral) for 8 weeks. Bone mineral density (BMD) of whole femora (WF), distal femoral metaphyses (DFM), femoral shafts (FS), and proximal femora (PF) was determined using DXA. Static and dynamic cancellous bone histomorphometric analyses were performed in double-labeled undecalcified longitudinal sections from proximal tibial metaphyses. Ovariectomy for 8 weeks significantly reduced the BMD of WF, DFM, FS, and PF (from -6 to -15%). Treatment with E2 completely prevented the decreases in BMD of WF and DFM and had no significant effects in BMD of FS and PF in aged OVX rats. The decrease in BMD of DFM induced by OVX was prevented by treatment with DRO at all dose levels. In addition, DRO at 10 mg/kg/day prevented OVX-induced decreases in BMD of WF, FS, and PF.(ABSTRACT TRUNCATED AT 250 WORDS)