Effects of two non-endurance exercise protocols on established bone loss in ovariectomized adult rats

Virtual Design of 3D-Printed Bone Tissue Engineered Scaffold Shape Using Mechanobiological Modeling: Relationship of Scaffold Pore Architecture to Bone Tissue Formation

Large bone defects are clinically challenging, with up to 15% of these requiring surgical intervention due to non-union. Bone grafts (autographs or allografts) can be used but they have many limitations, meaning that polymer-based bone tissue engineered scaffolds (tissue engineering) are a more promising solution. Clinical translation of scaffolds is still limited but this could be improved by exploring the whole design space using virtual tools such as mechanobiological modeling. In tissue engineering, a significant research effort has been expended on materials and manufacturing but relatively little has been focused on shape. Most scaffolds use regular pore architecture throughout, leaving custom or irregular pore architecture designs unexplored. The aim of this paper is to introduce a virtual design environment for scaffold development and to illustrate its potential by exploring the relationship of pore architecture to bone tissue formation. A virtual design framework has been created utilizing a mechanical stress finite element (FE) model coupled with a cell behavior agent-based model to investigate the mechanobiological relationships of scaffold shape and bone tissue formation. A case study showed that modifying pore architecture from regular to irregular enabled between 17 and 33% more bone formation within the 4-16-week time periods analyzed. This work shows that shape, specifically pore architecture, is as important as other design parameters such as material and manufacturing for improving the function of bone tissue scaffold implants. It is recommended that future research be conducted to both optimize irregular pore architectures and to explore the potential extension of the concept of shape modification beyond mechanical stress to look at other factors present in the body.

Influence of treadmill training on bone structure under osteometabolic alteration in rats subjected to high-fat diet

Nutrition and physical training have important roles in the accumulation and maintenance of bone mass. The aim of this study was to evaluate, in ovariectomized rats (OVX), the effects of treadmill training (T) with high-fat diet (F) on weight gain and bone tissue properties with eight groups (n = 10) for 12 weeks: OVX SC (OVX, sedentary lifestyle, diet control); OVX SF; OVX TC; OVX TF; SH SC (SHAM, sedentary lifestyle, diet control); SH SF; SH TC; and SH TF. Weekly weight gain and final body composition were assessed. After euthanasia, tibiae were analyzed. The trained animals had higher body weight (P = 0.001), bone mineral density (P < 0.001), and trabecular bone (P < 0.001). The animals with a high-fat diet showed higher global fat (P < 0.001), percentage of global fat (P < 0.001) and deformation at impact (P = 0.031) and reduced tibial bone mineral content (P = 0.036). Physical training improves bone microarchitecture, without presenting an increase in impact resistance, and a high-fat diet increases body fat and impairs bone mineralization.

Skeletal deterioration following ovarian failure: can some features be a direct consequence of estrogen loss while others are more related to physical inactivity?

Findings on experimental animals show that ovarian failure is accompanied by a decrease in motor activity. As mechanical loading has a vital role in the maintenance of skeletal health, our aim was to determine to what extent this decrease in motor activity contributes to ovariectomy-induced bone loss. Thirty-two female Wistar rats were ovariectomized or sham-operated and housed in standard cages or with access to running wheels for 36 weeks with their running distance monitored. Markers of bone turnover were assayed in the serum, and bone geometry, trabecular and cortical bone microarchitecture, mineralization degree, and biomechanical properties were assessed in the femur. Differences between groups were determined by one-way ANOVA. Although reduced motor activity and sex steroid deficiency both resulted in decreases in trabecular bone volume, trabecular number decreases were mostly associated with sex steroid deficiency, whereas trabecular thickness decreases were mostly associated with sedentary behavior. Cortical bone appeared to be more sensitive to variations in motor activity, whereas bone turnover rate and bone tissue mineralization degree seemed to be primarily affected by sex steroid deficiency, even though they were further aggravated by sedentary behavior. Increases in femur length were mostly a consequence of sex steroid deficiency, whereas femoral neck length was also influenced by sedentary behavior. Differences in mechanical properties resulted mostly from differences in physical activity. Both the direct effect of sex steroid deficiency and the indirect effect of motor activity changes are implicated in bone loss following ovariectomy.

Vitamin E exhibits bone anabolic actions in normal male rats

Recently, vitamin E has been found to promote the bone structure of nicotine-treated rats well above their baseline values, thus suggesting that vitamin E may have some anabolic action. A bone anabolic agent acts by improving the bone structure leading to stronger bone. To assess the possible anabolic action vitamin E on bone, we supplemented alpha-tocopherol (ATF) or gamma-tocotrienol (GTT) at 60 mg/kg or vehicle [normal control (NC) group] for 4 months to normal male rats and measured their bone structure and biomechanical properties. Histomorphometric analysis revealed that vitamin E-supplemented rats have better trabecular volume, thickness, number, and separation than rats receiving vehicle only. For the first time we reported that GTT improves all the parameters of bone biomechanical strength, while ATF only improved some of the parameters compared to the NC group. Vitamin E supplementation, especially with the gamma isomer, improves bone structure, which contributed to stronger bone. Therefore, vitamin E has the potential to be used as an anabolic agent to treat osteoporosis or as bone supplements for young adults to prevent osteoporosis in later years.

Doping dose of salbutamol and exercise training: impact on the skeleton of ovariectomized rats

Previous studies in healthy rats have demonstrated a deleterious bone impact of β-agonist treatment. The purpose of this study was to examine the trabecular and cortical effects of β2-agonists at doping dose on treadmill exercising rats with estrogen deficiency. Adult female rats were ovariectomized (OVX; n = 44) or sham operated ( n = 12). Then, OVX rats received a subcutaneous injection of salbutamol (SAB) or vehicle with (EXE) or without treadmill exercise for 10 wk. Bone mineral density (BMD) was analyzed by densitometry. Microcomputed tomography and histomorphometric analysis were performed to study trabecular bone structure and bone cell activities. After 10 wk, SAB rats presented a much more marked decrease of BMD and trabecular parameters. Exercise did not change the high level of bone resorption in OVX EXE SAB compared with OVX SAB group (both on COOH-terminal collagen cross-links and osteoclast number). These results confirm the deleterious effect of β2-agonists on bone quantity (femoral BMD gain: OVX EXE, +6.8%, vs. OVX EXE SAB, −1.8%; P < 0.01) and quality (−8.0% of femoral trabecular thickness in OVX EXE SAB vs. OVX EXE), indicating that SAB suppresses the effect of EXE in OVX rats. Furthermore, we notice that the slight beneficial effect of exercise was mainly localized in the tibia. These findings indicate the presence of a bone alteration threshold below which there is no more alteration in structural bone quantity and quality. The negative effects of SAB on bone observed in this study in trained rats may indicate potential complications in doping female athletes with exercise-induced amenorrhea.

Doping dose of salbutamol and exercise: deleterious effect on cancellous and cortical bones in adult rats

Animal studies suggest that bone remodeling is under β-adrenergic control via the sympathetic nervous system. To our knowledge, the impact of β-agonist substances, at doping doses, has not been studied in adult rats. The purpose of this study was to examine the effects of salbutamol injections with or without treadmill exercise on trabecular and cortical bone in adult rats. Adult (36 wk of age) female Wistar rats ( n = 56) were treated with salbutamol (3 mg·kg−1·day−1 sc, 5 days/wk) or vehicle (sham) with or without subsequent treadmill exercise (13 m/min, 60 min/day, 5 days/wk) for 10 wk. Tibial and femoral bone mineral density was analyzed by dual-energy X-ray absorptiometry. Metaphysic trabecular bone structure was analyzed by micro-CT at the time of the animals' death. Bone cell activities were assessed histomorphometrically. After 10 wk, the increase in bone mineral density was less in salbutamol-treated than in sham rats (+3.3% vs. +12.4%, P < 0.05), and trabecular parameters were altered and bone resorption was increased in salbutamol-treated rats compared with controls. The negative effect on bone architecture in salbutamol-treated rats persisted, even with treadmill exercise. These results confirm the deleterious effect of β2-agonists on bone mass during chronic treatment and describe its effects on bone mechanical properties in adult rats. Bone loss occurred independently of a salbutamol-induced anabolic effect on muscle mass and was equally severe in sedentary and exercising rats, despite a beneficial effect of exercise on the extrinsic and intrinsic energy to ultimate strain. These bone effects may have important consequences in athletes who use salbutamol as a doping substance.

The effects of fructo-oligosaccharides in combination with soy protein on bone in osteopenic ovariectomized rats

OBJECTIVE

The intestinal microflora is important in rendering soy isoflavones bioavailable by facilitating their conversion to equol. Hence, substances that can modulate the intestinal microflora could affect the bioavailability of isoflavones. In this study, we examined the effects of fructo-oligosaccharides (FOS), a prebiotic, on enhancing the effects of soy isoflavones on bone in ovariectomized osteopenic female rats.

DESIGN

Sixty-three 9-month-old female Sprague-Dawley rats were either sham-operated (Sham; one group) or ovariectomized (Ovx; four groups) and were fed a control diet for 3 months to induce bone loss. After bone loss was confirmed via dual-energy x-ray absorptiometry, rats were placed on dietary treatment for 4 months. The Sham and one Ovx group received a control diet, and the remaining Ovx groups received either a soy protein-based diet (Soy), a FOS-supplemented diet (FOS), or a soy protein-based and FOS-supplemented diet (Soy+FOS). Before the termination of the study, whole-body bone mineral density (BMD) and bone mineral content (BMC) were assessed under anesthesia. Immediately after euthanasia, bone specimens were collected for the assessments of BMD, BMC, and biomechanical and microarchitectural properties.

RESULTS

Whole-body BMD values were significantly higher in FOS and Soy+FOS groups compared with Ovx controls. The tibial BMC increased by 10%, 6%, and 4% in Soy, FOS, and Soy+FOS groups, respectively, compared to the Ovx control group. FOS and FOS+Soy treatments had the most pronounced effects in enhancing lumbar BMC and BMD. The FOS+Soy combination effectively improved tibial microarchitectural properties by enhancing trabecular number and lowering trabecular separation compared with Ovx controls. The effects of dietary treatments on lumbar microarchitectural properties were minimal and biomechanical properties of the femur were not affected by any of the dietary treatments.

CONCLUSION

Our findings suggest that, although incorporation of either soy or FOS in the diet of Ovx rats can improve BMD of the whole body, tibiae, and lumbar vertebrae, their combination had no any additive effects. However, in terms of microarchitecture, the combination of soy and FOS had a greater effect in reversing the loss of certain microarchitectural parameters such as tibial trabecular number, separation, and thickness.

Effect of treadmill exercise on bone mass in female rats

Increasing peak bone mass at skeletal maturity, minimizing bone loss during middle age and after menopause, and increasing bone mass and preventing falls in advanced age are important measures for preventing osteoporotic fractures in women. Exercise has generally been considered to have a positive influence on bone health. This paper reviews the effects of treadmill exercise on bone in young, adult, ovariectomized, and osteopenic female rats. Treadmill exercise increases cortical and cancellous bone mass of the tibia as a result of increased bone formation and decreased bone resorption in young and adult rats. The increase in lumbar bone mass seems to be more significant when long-term exercise is applied. Treadmill exercise prevents cancellous bone loss at the tibia as a result of suppressed bone resorption in ovariectomized rats, and increases bone mass of the tibia and mechanical strength of the femur, as a result of suppressed bone resorption and increased bone formation in osteopenic rats after ovariectomy. Treadmill exercise transiently decreases the serum calcium level as a result of accumulation of calcium in bone, resulting in an increase in serum 1,25-dihydroxyvitamin D(3) level and a decrease in serum parathyroid hormone level. We conclude that treadmill exercise may be useful to increase bone mass in young and adult rats, prevent bone loss in ovariectomized rats, and increase bone mass and bone strength in osteopenic rats, especially in the long bones at weight-bearing sites. Treadmill exercise may have a positive effect on the skeleton in young, and adult, ovariectomized, and osteopenic female rats.

How many days per week should rats undergo running exercise to increase BMD?

The aim of the present study was to examine the effect of different frequencies of running exercise on increasing bone mineral density (BMD) and improving bone histomorphology at various sites of the skeleton (tibia, femur, and second lumbar vertebra) in young rats. Twenty-five female Wistar rats, 8 weeks old, were divided into five groups, of 5 animals each according to running load: control group, no running (A group); running load (RL), 4 days per week (d/w; B group); RL, 5 d/w (C group); RL, 6 d/w (D group); and RL, 7 d/w (E group). Rats ran on a treadmill at a speed of 15 m/min for 30 min per day over an 8-week period. The results indicated that the BMD of the tibia in the B, C, D, and E groups and that of the femur in the B and E groups increased significantly over that of the A group. However, the cortical BMD and trabecular BMD of the second lumbar vertebra did not change. In regard to bone histomorphometry of the tibia, a parameter of bone resorption (eroded surface/bone surface) was significantly lower in the B and D groups than in the A group. There were no differences in the parameters of bone formation. Tartaric acid-resistant acid phosphatase (TRACP) values were significantly lower in the B and C groups than in the A group. There were significant increases in body weight in the B group and in muscle weight in the C group. From the data obtained in this study, it was concluded that increases in BMD were obtained by a moderate running load at frequencies of 4 and 5 days per week.

Muscle-bone interactions in dystrophin-deficient and myostatin-deficient mice

We have investigated muscle-bone interactions using two mouse mutants that are known to differ from normal mice in skeletal muscle growth and development: mice lacking myostatin (GDF8) and mice lacking dystrophin (mdx). Myostatin-deficient mice show increased muscle size and strength compared to normal mice, whereas the mdx mouse is a well-established animal model for Duchenne muscular dystrophy. The mdx mice have significantly larger hindlimb muscles than controls, and histological sections of the quadriceps muscles show dystrophic changes with extensive fibrosis. Femoral bone mineral density (BMD) and fracture strength (Fu) are significantly greater in mdx mice than controls, and these variables are more strongly correlated with quadriceps muscle mass than with body mass. In contrast, mdx mice do not shower high bone mineral density in the spine relative to controls, whereas myostatin-deficient mice have significantly increased BMD in the lumbar spine compared to normal mice. Both mdx mice and myostatin-deficient mice have expanded femoral trochanters for attachment of large hindlimb muscles, and both mutant strains show increased cross-sectional area moments of inertia mediolaterally (Iyy) but not anteroposteriorly (Ixx) compared to normal mice. These data suggest that lean (muscle) mass is a significant determinant of bone mineral density and strength in the limb skeleton, even when accompanied by a dystrophic phenotype. Likewise, increased muscle mass produces a marked increase in the external dimensions of muscle attachment sites, even when increased muscle size is accompanied by extensive fibrosis and muscle weakness.

High-impact exercise strengthens bone in osteopenic ovariectomized rats with the same outcome as Sham rats

The effect of jump exercise on middle-aged osteopenic rats was investigated. Forty-two 9-mo-old female rats were either sham-operated (Sham) or ovariectomized (OVX). Three months after surgery, the rats were divided into the following groups: Sham sedentary, Sham exercised, OVX sedentary, and OVX exercised. Rats in the exercise groups jumped 10 times/day, 5 days/wk, for 8 wk, with a jumping height of 40 cm. Less than 1 min was required for the jump training. After the experiment, the right tibia and femur were dissected, and blood was obtained from each rat. OVX rats were observed to have increased body weights and decreased bone mass in their tibiae and femurs. Jump-exercised rats, on the other hand, had significantly increased tibial bone mass, strength, and cortical areas. The bone mass and strength of OVX exercised rats increased to approximately the same extent as Sham exercised rats, despite estrogen deficiency or osteopenia. Our data suggest that jump exercise has beneficial effects on lower limb bone mass, strength, bone mineral density, and morphometry in middle-aged osteopenic rats, as well as in Sham rats.

Vitamin E improves bone quality in the aged but not in young adult male mice

It is generally viewed that with advancing age, humans and other animals including mice experience a gradual decline in the rate of bone formation. This, in part, may be due to the rise in oxygen-derived free radical formation. Vitamin E, a strong antioxidant, functions as a free radical scavenger that potentially can suppress bone resorption while stimulating bone formation. Although the effects of vitamin E on immune functions are well documented, there is a paucity of information on its effect on skeletal health in vivo. The purpose of this study was to explore the influence of vitamin E supplementation on bone in young adult and old mice. Six and twenty-four month-old male C57BL/6NIA mice each were divided into two groups and fed a diet containing either adequate (30 mg/kg diet) or high (500 mg/kg diet) levels of vitamin E. Thirty days later, mice were killed and bones were removed for analyses including biomechanical testing using three-point bending and mRNA expressions of insulin-like growth factor-I (IGF-I), osteocalcin, and type 1alpha-collagen using Northern blot. In old but not the young adult mice, high-dose vitamin E enhanced bone quality as evident by improved material and structural bone properties in comparison with adequate. This improved quality was accompanied by increases in bone dry weight, protein, and mRNA transcripts for osteocalcin, type Ialpha-collagen, and IGF-I. These data demonstrate that high-dose vitamin E has pronounced effects on bone quality as well as matrix protein in old mice by augmenting bone matrix protein without reducing bone mineralization as evidenced by unaltered bone density.

Cooperative effects of exercise training and genistein administration on bone mass in ovariectomized mice

We reported that genistein, a soybean isoflavone, prevents bone loss caused by estrogen deficiency, without undesirable effects on the uterus. In this study, we examined cooperative effects of genistein administration and running exercise on bone mass in ovariectomized (OVX) mice. Female mice aged 7 weeks were either sham-operated or OVX and divided into six groups: (1) sham; (2) OVX; (3) OVX, treated with genistein at a submaximal dose (0.4 mg/day) subcutaneously (G); (4) OVX, exercised on a treadmill daily for 30 minutes/day at 12 m/minute on a 10 degree uphill slope (Ex); (5) OVX, given genistein and exercised (ExG); and (6) OVX, treated with 17beta-estradiol (0.03 microg/day) in the same manner as genistein (E2). Four weeks after intervention, bone mass was estimated by dual-energy X-ray absorptiometry (DXA) and peripheral quantitative computed tomography (pQCT). Bone mineral density (BMD) of the whole femur measured by DXA was higher in both the G and the Ex groups than in the OVX group. Furthermore, BMD in the ExG group was significantly higher than that in the groups receiving either intervention alone. Bone area in distal region of the femur was significantly higher in Ex and ExG groups as compared with those in the OVX and G groups. pQCT analysis showed that the cross-sectional areas (CSAs) and periosteum perimeter at midshaft of the femur did not differ in the sham and OVX groups but were significantly higher in Ex and ExG groups. Histomorphometric analysis showed that bone formation rate/bone surface (BFR/BS) was significantly higher in both Ex and ExG groups as compared with that in non-exercised groups. The bone volume (BV/TV) in the distal femoral cancellous bone was lower in the OVX than that in the sham group, and it was restored completely in the ExG group, as in the E2 group. Thickness of the trabecular bone (Tb.Th) was higher in Ex and ExG groups than that in the OVX and G groups. These results indicate that the combined intervention of moderate exercise and the submaximal dose of genistein administration show a cooperative effect in preventing bone loss in OVX mice.

Effect of high-impact and low-repetition training on bones in ovariectomized rats

This study was designed to investigate the effect of high-impact and low-repetition jump training on bones in ovariectomized (OVX) rats. Forty female Wistar rats were sham-operated (sham) or OVX at the age of 11 weeks. The rats were divided randomly into the following four groups: sham-sedentary (SS; n = 10), sham-exercised (SE; n = 10), OVX-sedentary (OS; n = 10), and OVX-exercised (OE; n = 10). The rats started the jump training at the age of 12 weeks. The jump-training protocol was 10 times/day, 5 days/week and the jumping-height was 40 cm. After 8 weeks of training, the mass and breaking force in the tibia and ulna, cross-sectional areas of diaphysis in the tibia, and serum bone turnover markers were measured. The jump training significantly increased the fat-free dry weight, ash weight, and ultimate breaking force in the tibia. The rate of increase in these parameters was similar in both the sham and the OVX groups. On the other hand, in the ulna, there were no significant changes in the ultimate breaking force. The jump training significantly increased the periosteal perimeter and cortical area, although the increase in these parameters in OE compared with OS was lower than that in SE compared with SS. The jump training significantly increased serum osteocalcin in the OVX groups, as well as in the sham groups. These results suggest that high-impact and low-repetition training had beneficial effects on bone formation and bone biomechanical properties in OVX rats, as well as in sham rats.

Alteration in the mechanical competence and structural properties in the femoral neck and vertebrae of ovariectomized rats

The structural and mechanical properties of bone in the femoral neck and various other sites were investigated in intact (INT), sham-operated (Sham), and ovariectomized (OVX) rats. Six weeks after operation, the maximal load and energy absorption of the femoral neck were significantly lower in the OVX than in the INT or Sham groups, being 73.2 +/- 1.4 (SE) N, 86.3 +/- 4.1 N, and 87.1 +/- 3.2 N, respectively (p < 0.01) for load. The total cross-sectional area of the femoral neck did not change after OVX, but the marrow cavity area was enlarged, leading to a reduced bone area (including both cortical and trabecular bone) (p < 0.01). Histomorphometric analysis showed that new bone formation could not be detected at the periosteum of the femoral neck below the femoral head, but at the endocortical surfaces the double tetracycline labeling revealed an increased mineral apposition rate (MAR) and bone formation rate (BFR) in OVX animals (p < 0.001). In contrast, MAR and BFR were significantly increased in both periosteal and endocortical surfaces of the tibia, humerus, and femoral shaft, thus preventing a decrease in cortical bone area. The maximal bending loads of the tibia and humerus were not different in the various groups of animals. The correlation coefficient between maximal load and bone area revealed positive relationships in the femoral neck (r = 0.54, p < 0.01), tibia (r = 0.46, p < 0.01), and humerus (r = 0.51, p < 0.01). Ovariectomy resulted in a decreased trabecular bone volume of lumbar vertebra VI (L6) decreased compressive loads of lumbar vertebrae I, III, and IV. These lumbar bone loads were positively related to their L6 bone area (L4/L6: r = 0.66, p < 0.001). Element analyses (energy dispersion spectrometer) from trabecular and cortical areas of bone showed some changes related to aging but not to OVX. These results indicate that ovariectomy influences the biomechanical properties of rat bone by changing structural properties rather than material ones.

Additive effect of voluntary exercise and growth hormone treatment on bone strength assessed at four different skeletal sites in an aged rat model

The aim of the study was to assess the effect of growth hormone (GH), voluntary exercise (Ex), and the combination of GH and Ex on bone strength, mass, and dimensions in aged, intact female rats. In addition, the effect of food restriction (FR) was studied. Fourteen-month-old virgin F-344 rats were divided into 6 groups with 13 animals in each: (1) baseline (BSL); (2) control + solvent vehicle (CTRL); (3) GH 2.5 mg/kg/day (GH); (4) exercise, voluntary: 0.6-0.7 km/day (Ex); (5) GH treatment and voluntary exercise (GH + Ex); and (6) FR. Group 1 was killed at the beginning of the study and served as baseline. All the other groups were killed after 18 weeks' treatment. The effects of aging and treatment regimes were measured at four different skeletal sites: lumbar vertebrae, femoral cortical bone, femoral neck, and the distal femoral metaphysis. Aging in itself induced a decline in vertebral body strength and ash density. At the appendicular skeletal sites, bone mass and strength were unchanged or increased. Treatment with GH alone induced a significant increase in the biomechanical parameters at the vertebral body and the femoral diaphysis, but not at the femoral neck or the distal femoral metaphysis. Voluntary exercise on its own increased load values significantly over CTRL at the vertebral body site, but not at any of the appendicular skeletal sites. The combination of GH and voluntary exercise resulted in an additive effect at the vertebral site and at the femoral diaphysis, and a synergistic (potentiating) effect at the two femoral metaphyses. FR, on the other hand, had a negative effect on cortical bone area and strength at the femoral diaphysis, but no significant effect on the other sites tested. We conclude that GH treatment and voluntary exercise both have skeletal anabolic effects; however, these effects are exerted to differing degrees at different sites. Importantly, when dosed together, GH and Ex have either an additive or synergistic anabolic effect on all sites (axial and appendicular).

Effect of exercise on tibial and lumbar vertebral bone mass in mature osteopenic rats: bone histomorphometry study

The effect of moderate running exercise on tibial and lumbar vertebral bone mass was examined in mature osteopenic rats by bone histomorphometry. Ten 37-week-old female Wistar rats, with bone loss resulting from being fed a relatively low-calcium diet for 14 weeks after ovariectomy at the age of 23 weeks, were randomly divided into two groups of five animals each; control and exercise groups. The exercise consisted of treadmill running at 12 m/min for 1 h per day on 5 days per week for 12 weeks. During the exercise period, all animals were fed a standard calcium diet. After 12 weeks of exercise, bone histomorphometry was evaluated for cancellous bone (secondary spongiosa) of the proximal tibia and the fourth lumbar vertebra and for cortical bone of the tibial shaft. The findings suggested that in the mature osteopenic rat, there was a beneficial effect of moderate running exercise with adequate calcium intake on bone mass only in a weight-bearing long bone, the tibia. The mechanism for increased bone mass appeared to be both decreased bone resorption and increased bone formation in cancellous bone and increased bone formation in cortical bone.

Effects of exercise on bone mineral density in mature osteopenic rats

Dual-energy X-ray absorptiometry (DXA) was used to examine the effects of quantitative application of treadmill running exercise on bone mineral density (BMD) of the tibia and the fourth and fifth lumbar (L4 + L5) vertebrae in mature osteopenic rats. Twenty 37-week-old rats with bone loss, resulting from feeding a relatively low calcium diet for 14 weeks after ovariectomy at the age of 23 weeks, were divided into four groups of five rats each according to the intensity and duration of the exercise: 12 m/minute, 1 h/day in group EX1; 18 m/minute, 1 h/day in group EX2; 12 m/minute, 2 h/day in group EX3; and sedentary control in group CON. With a standard calcium diet, the exercise was performed 5 days a week for 12 weeks, and the BMD of both the right tibia and the L4 + L5 vertebrae was measured using DXA at weeks 0, 4, 8, and 12. At the end of 12 weeks of exercise, the right femur and the L5 vertebra were dissected and the mechanical strength was measured using a three-point bending test and a compression test, respectively. After 12 weeks of exercise, a significant increase in the tibial BMD was observed in only group EX1 compared with that in group CON (p = 0.0039, by two-way analysis of variance). However, any significant increase in the L4 + L5 vertebral BMD was not observed in any exercise groups compared with that in the control group. While a maximum breaking force of the femoral shaft in group EX1 was significantly greater than that in group CON (p < 0.05, by Mann-Whitney's U-test), that in groups EX2 and EX3 did not significantly differ from that in group CON. However, there was no significant difference in a maximum breaking force of the L5 vertebral body among all the exercise and control groups. These results indicated that the beneficial effects of treadmill running exercise under a standard calcium diet were recognized only in the weight-bearing bones of the mature osteopenic rats resulting from estrogen deficiency and inadequate calcium intake only when an optimal level of exercise was applied.

Effect of resistance exercise training on cortical and cancellous bone in mature male rats

The effect of resistance training on tibial cancellous and cortical bone was evaluated in rats by using static histomorphometry and Northern analysis. Five-month-old male Sprague-Dawley rats were randomly assigned to exercise (Ex; n = 8) or control (Con; n = 4) groups. Animals were operantly conditioned to press two levers, facilitating full extension and flexion of the hindlimbs ("squats"), while wearing an unweighted vest. After an 8-wk familiarization period, Ex animals performed 3 sessions/wk for 17-19 sessions with progressively increased amounts of weight applied to the vest. Con rats completed the same exercise protocol without applied resistance. No difference in cross-sectional, medullary, or cortical bone area was observed between Ex and Con rats in the tibial diaphysis. In contrast, the cancellous bone area in the proximal tibial metaphysis was significantly larger in trained rats. Trabecular number, trabecular thickness, and the percentage of cancellous bone covered by osteoid were significantly greater in the Ex animals compared with Con animals. In addition, steady-state mRNA levels for osteocalcin for the Ex group were 456% those expressed in the Con group. The data demonstrate that resistance training increases cancellous bone area in sexually mature male rats and suggest that it does so, in part, by stimulating bone formation.

Estrogen regulates the rate of bone turnover but bone balance in ovariectomized rats is modulated by prevailing mechanical strain

Estrogen deficiency induced bone loss is associated with increased bone turnover in rats and humans. The respective roles of increased bone turnover and altered balance between bone formation and bone resorption in mediating estrogen deficiency-induced cancellous bone loss was investigated in ovariectomized rats. Ovariectomy resulted in increased bone turnover in the distal femur. However, cancellous bone was preferentially lost in the metaphysis, a site that normally experiences low strain energy. No bone loss was observed in the epiphysis, a site experiencing higher strain energy. The role of mechanical strain in maintaining bone balance was investigated by altering the strain history. Mechanical strain was increased and decreased in long bones of ovariectomized rats by treadmill exercise and functional unloading, respectively. Functional unloading was achieved during orbital spaceflight and following unilateral sciatic neurotomy. Increasing mechanical loading reduced bone loss in the metaphysis. In contrast, decreasing loading accentuated bone loss in the metaphysis and resulted in bone loss in the epiphysis. Finally, administration of estrogen to ovariectomized rats reduced bone loss in the unloaded and prevented loss in the loaded limb following unilateral sciatic neurotomy in part by reducing indices of bone turnover. These results suggest that estrogen regulates the rate of bone turnover, but the overall balance between bone formation and bone resorption is influenced by prevailing levels of mechanical strain.

Long-term effects of ovariectomy on the mechanical properties and chemical composition of rat bone

One hundred Sprague-Dawley rats were ovariectomized (OVX) or sham-operated (Sham) at the age of 12 weeks. Eight or six animals from each group were sacrificed at the following time points: 0, 2, 4, 8, 16, 28, and 40 weeks. Mechanical testing of the bones showed that the maximal load of the femoral neck remained at the baseline level in OVX rats but clearly increased in Sham animals. However, after 28 weeks (at the age of 40 weeks) of ovariectomy, the femoral neck strength in Sham animals started to decrease, reaching the OVX level at the age of 1 year. The gain of torsional strength of the humerus was first slowed down after ovariectomy, but 16 weeks after operation this difference between the OVX and Sham animals disappeared. In OVX rats incorporation of 45 Ca2+ into the tibia and the number of osteoclasts on the trabecular bone surfaces were increased at 4-16 weeks and at 2-28 weeks, respectively, but they returned later to the levels observed in Sham animals. This indicates that the OVX-induced increase in bone turnover is transient. The trabecular bone volume at the distal femur decreased and the area of the marrow cavity in the distal third of the femur increased after OVX and did not show any recovery. Analysis of the inorganic composition of bone by energy-dispersion spectrometry showed that the percentage of magnesium was transiently decreased after OVX in both trabecular and cortical bone. Despite the OVX-induced loss of trabecular bone, increasing body weight or some metabolic changes may induce structural changes which may be responsible for maintaining the mechanical force of the femoral neck in aging OVX rats.

Total and regional bone mineral content in Spanish professional ballet dancers

Total body bone mineral content (TBBMC) and regional bone mineral content (BMC) was measured in the members of the Spanish National Dance Company (15 female, mean age 25.1 +/- 3.8 years, and 15 male, mean age 28.2 +/- 2.1 years) and in 30 controls (15 women, mean age 26.1 +/- 1.8 years, and 15 men, mean age 28.0 +/- 1.5 years). Ca, P, and Mg intake were greater in the group of ballet dancers than in controls analysis of variance (ANOVA, all P < 0.0001). BMC was similar in the group of ballet dancers and controls except in the trunk without pelvis (P < 0.001). Both male and female dancers weighed less than controls (P < 0.05). The BMC of the male dancers was less than that of male controls only in the trunk (P < 0.05) and in the trunk without pelvis (P < 0.005); BMC was lower in female dancers than in female controls only in the arms and in the trunk without pelvis (P < 0.05 and P < 0.005, respectively). TBBMC, adjusted for weight and age, was correlated partially with caloric intake (kcal/day) and with Ca, P, Mg, and Zn intake (g/day), and yielded significant differences between the dancers and controls only in P intake (P < 0.01), and between male dancers and male controls only in caloric intake and in Ca, P, and Zn intake (all P < 0.01, except for Ca, P < 0.05). The lower trunk bone mass observed in the female dancers is a risk factor for eventual osteoporosis.

The development of femoral osteopenia in ovariectomized rats is not reduced by high intensity treadmill training: a mechanical and densitometric study

The effect of treadmill running on the development of osteopenia was investigated in adult ovariectomized (OVX) rats compared with sedentary OVX and sedentary sham-operated rats. The rats were 3 months old with a mean weight of 214 g. OVX rats were fed a low calcium diet (0.01%), and the sham rats received the normal diet (1.1% calcium). The training consisted of treadmill running at a speed of 27 m/minute for 1 hour 5 out of 7 days during a period of 8 1/2 weeks. The weight gain was higher in the sedentary OVX (108 g) than in the training OVX (62 g) and sham-operated rats (61 g) (P < 0.001). Comparing the two OVX groups, training had no significant effects on the development of femoral osteopenia as assessed by mechanical testing of the femoral shaft and neck, and by bone mass measurements by dual energy X-ray absorptiometry (DXA) or by ashing. Comparing all three groups bone mineral content (BMC) and bone mineral density (BMD) were reduced by more than 40% in both the OVX groups compared with the sham-operated rats (P < 0.001). Ash weight and calcium content were reduced by approximately 40% in both OVX groups. Femoral volume and length were 10% higher in the sedentary OVX animals compared with the trained (P < 0.05), indicating that the training had had a negative effect on the growth changes induced by ovariectomy. The fracture strength of the femoral shaft was reduced by 26% and 22% in the trained and sedentary OVX rats, respectively compared with the sham-operated group (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Exercise can provide protection against bone loss and prevent the decrease in mechanical strength of femoral neck in ovariectomized rats

The effect of treadmill exercise on bone loss in ovariectomized (OVX) rats was studied in two different sets of experiments. In the first experiment rats were either ovariectomized (n = 38) or sham operated (n = 18) at the age of 12 weeks. Half the OVX rats were trained twice a day for 30 minutes by running at 10 m/minute for 7 or 17 weeks. In the second experiment 40 female rats, aged 12 weeks, were divided into five groups (n = 8). One group of rats was sacrificed on day 0 for the baseline data. Other rats were sham operated or ovariectomized for 9 weeks. Half of both groups were trained using the same training program as in the first experiment. OVX reduced trabecular bone volume (TBV) in the distal femur to 42.7 and 48.3% in 8 and 18 weeks, respectively. Exercise opposed this effect significantly but could not prevent it totally. Exercise did not have any significant effect on sham-operated animals. OVX induced a 17.7 and 30.7% decrease in maximal failure load of femoral neck in 8 and 18 weeks, respectively. A corresponding decrease was also observed in the torque capacity of tibia. Exercise was able to prevent almost totally the decrease in bone strength of femoral neck, tibia, and humerus. In conclusion, our results suggest that the measurement of bone strength in aging female rat femoral neck can be used as a useful indicator of the deleterious effect of OVX in bone. These results further indicate that exercise can overcome a significant part of the decrease in trabecular bone volume and maintain the mechanical strength of femoral neck and tibial shaft in the OVX rats.

Effects of endurance exercise on bone histomorphometric parameters in intact and ovariectomized rats

Physical activity is important for maintenance of bone mass. The effects of exercise on bone histomorphometry were studied in 9-month-old intact (INT) and ovariectomized (OVX) rats. The rats were either kept sedentary (SED) or were exercised (EX) on a treadmill at 21 m/min for 1 h/day 5 days/week for 3 months. Bone resorption as well as formation parameters were significantly higher in OVX-SED than in INT-SED rats, indicating increased bone turnover in OVX rats. In OVX rats, lower osteoclast perimeter and number, lower labeled perimeter but higher mineral apposition rate (MAR) and bone formation rate (BFR) were associated with higher trabecular bone in OVX-EX compared with OVX-SED rats. In intact rats, trabecular bone mass and osteoclast number and perimeter were not affected by exercise. Labeled perimeter was slightly lower while MAR was higher and BFR was insignificantly higher in INT-EX than in INT-SED rats. Thus, exercise resulted in fewer resorption-formation sites, as indicated by lower labeled perimeter, but higher activity of individual osteoblasts, as indicated by higher MAR, both in estrogen-depleted and estrogen-replete states.

The effect of long-term exercise on vertebral and femoral bone mass, dimensions, and strength--assessed in a rat model

The rat model has previously been used to test the effect of ovariectomy and of PTH administration on vertebral bone mass, size, and biomechanical competence. In this study, we used the same "biomechanical rat model" to assess the effect of long-term exercise on vertebral bone mass and quality and also on femoral bone mass, dimensions, and strength. Sixty female Fischer rats were randomized into four groups. Two groups were exercised for 5 days a week on a treadmill with a running distance of 2 km per day. The exercise program was initiated at the age of 2 months. The two exercise groups were investigated after 4 and 10 months. Two sedentary groups (observed for 4 and 10 months) served as controls. At death, three lumbar vertebral bodies (L4-L6) and the left femur were obtained from each rat, and changes in bone mass (ash density, trabecular bone volume [BV/TV]), bone size, and biomechanical competence were assessed. The results revealed an age-related (4-10 months) increase in vertebral bone mass and strength. The additional effect of exercise on the vertebral bodies was an increase in cross-sectional area and bone biomechanical competence. In the femoral bone specimens, an age-related increase in bone mass, size, and strength was also disclosed, and while exercise by itself had no significant influence on biomechanical parameters it did reduce cortical-endosteal bone resorption. The study has demonstrated an anabolic effect of a light exercise regimen on both femoral cortical bone and vertebral bodies (mainly trabecular bone).(ABSTRACT TRUNCATED AT 250 WORDS)