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J Appl Physiol 104: 1594-1600, 2008. First published April 17, 2008; doi:10.1152/japplphysiol.01004.2007
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Jump exercise during remobilization restores integrity of the trabecular architecture after tail suspension in young rats

Y-I. Ju,1 T. Sone,2 T. Okamoto,3 and M. Fukunaga2

1Department of Health and Sports Sciences, Kawasaki University of Medical Welfare, Kurashiki; 2Department of Nuclear Medicine, Kawasaki Medical School, Kurashiki; 3Graduate School of Sport Sciences, Waseda University, Tokorozawa, Japan

Submitted 21 September 2007 ; accepted in final form 15 April 2008


   ABSTRACT
TOP
 ABSTRACT
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
Three-dimensional trabecular architecture was investigated in the femora of tail-suspended young growing rats, and the effects of jump exercise during remobilization were examined. Five-week-old male Wistar rats (n = 35) were randomly assigned to five body weight-matched groups: tail-suspended group (SUS; n = 7); sedentary control group for SUS (SCON; n = 7); spontaneous recovery group after tail suspension (S+RCON, n = 7); jump exercise group after tail suspension (S+RJUM; n = 7); and age-matched control group for S+RCON and S+RJUM without tail suspension and exercise (SCON+RCON; n = 7). Rats in SUS and SCON were killed immediately after tail suspension for 14 days. The jump exercise protocol consisted of 10 jumps/day, 5 days/wk, and jump height was 40 cm. Bone mineral density (BMD) of the femur and three-dimensional trabecular bone architecture at the distal femoral metaphysis were measured. Tail suspension induced a 13.6% decrease in total femoral BMD (P < 0.001) and marked deterioration of trabecular architecture. After 5 wk of free remobilization, femoral BMD, calf muscle weight, and body weight returned to age-matched control levels, but trabeculae remained thinner and less connected. On the other hand, S+RJUM rats showed significant increases in trabecular thickness, number, and connectivity compared with S+RCON rats (62.8, 31.6, and 24.7%, respectively; P < 0.05), and these parameters of trabecular architecture returned to the levels of SCON+RCON. These results indicate that suspension-induced trabecular deterioration persists after remobilization, but jump exercise during remobilization can restore the integrity of trabecular architecture and bone mass in the femur in young growing rats.

jump exercise; tail suspension (unloading); remobilization; trabecular architecture; microcomputed tomography

SKELETAL UNLOADING OR LOSS of normal weight bearing, as seen during space flight or prolonged bed rest, causes bone mass in humans (28, 52). Studies using rats have also demonstrated marked bone loss, impairment of bone mechanical properties and disruption of bone architectures following spaceflight (20), immobilization by tenotomy or sciatic neurectomy (36), or tail suspension (17).

The recovery potential of bone has been studied after spaceflight (45) and bed rest (29) in humans, and after immobilization (46) or tail suspension-induced bone loss (49) in animals. The time required to recover bone mass caused by mechanical unloading may be longer than the duration of unloading. Moreover, trabecular bone is more susceptible to changes in mechanical environment than cortical bone. Loss of trabecular bone in the proximal tibial metaphysis induced by skeletal unloading is apparently more pronounced and remains longer after reloading than that of cortical bone (44, 50). A previous study indicated that, although subsequent reloading for 14 days restored the reduced trabecular bone formation and suppressed the increased trabecular bone resorption, trabecular bone mass showed insufficient recovery during the reloading period after tail suspension (42). Even though subsequent normal weight bearing after a period of unloading results in increased bone formation to baseline levels, reconnecting trabecular bone architecture after initial disruption remains difficult. The development of countermeasures to prevent skeletal unloading-induced disorganization of bone architectures is of vital importance.

The recovery potential of bone after immobilization also depends on the age of the animal. In old rats, long-term disuse-induced bone loss is hardly restored after reloading (29, 34), whereas in young rats, bone can be recovered after various periods of immobilization (30, 31, 55). However, how exercise applied during a recovery period after mechanical unloading influences bone mass and architecture has not been clarified in detail. In particular, the effects of jump exercise on trabecular architecture in unloading-induced osteopenia has never been evaluated from a three-dimensional (3D) perspective. Weight-bearing exercise is known to be effective in increasing bone mass, and high-impact exercise, such as jumping, is considered particularly beneficial for bones (5, 22, 48). To the best of our knowledge, only one other study has evaluated the effects of physical exercise on restoration of bone architecture after tail suspension-induced osteopenia in young rats (4). They showed that the treadmill exercise during remobilization restored a normal trabecular network. However, that study was two dimensional (2D), and the 3D details of heterogeneous trabecular structures have not been clarified.

The strength of cancellous bone depends on the 3D trabecular architecture as well as the amount and quality of bone tissue. Thus the recovering capacity of 3D trabecular architecture would play an important role to restore the bone strength after immobilization. The present study investigated 3D trabecular architecture in the femur using tail-suspended rats as a hindlimb-unloading model and examined the effects of jump exercise during remobilization.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
Animal care.   The experiment protocol and all animal procedures were in compliance with the guidelines set forth in the Care and Use of Laboratory Animals in the Field of Physiological Sciences approved by the Council of the Physiological Society of Japan (http://www.soc.nii.ac.jp/psj/psj/doubutu.html). Male 4-wk-old Wistar rats (n = 35) were purchased from Clea Japan (Osaka, Japan) and individually housed in 35 x 35 x 35-cm metal-grill cages under standard laboratory conditions at a room temperature of 22 ± 1°C and a humidity of 60 ± 5% with a 12-h light-dark cycle (light cycle starting at 0800). Rats were fed standard laboratory animal chow (MF; Oriental Yeast, Chiba, Japan) containing 1.15% calcium and 0.88% phosphorus. After 1 wk of acclimation to the diet and new environment, rats were randomly assigned into five groups (n = 7 each): tail-suspended group (SUS); control group for SUS (SCON); spontaneous recovery group after tail suspension (S+RCON); jump exercise group after tail suspension (S+RJUM); and age-matched control group for S+RCON and S+RJUM without tail suspension and exercise (SCON+RCON). Food intake for theses groups of rats was monitored, and controls were pair-fed throughout the experiment. Access to water was unrestricted. Body weight and food intake were measured 3 times/wk. The groups of SUS and SCON rats were immediately killed by exsanguinations under pentobarbital sodium anesthesia (0.1 ml/100 g of body wt IP) after 14 days of tail suspension. Groups of S+RCON, S+RJUM, and SCON+RCON rats were killed 5 wk after the end of the experimental period (jump exercise protocol period). After death, the right hind limb muscles (gastrocnemius and soleus) of each rat were collected and immediately weighed. The right femur was excised from each rat and cleaned of soft tissue. Femoral length was measured using a digital caliper. The femur was stored at –80°C until required for further measurements.

Tail suspension.   The tail-suspension procedure was performed according to the recommendations of Morey-Holton and Globus (35), with slight modification. In brief, the tails were cleaned with 70% alcohol, removing all dead or dirty skin, then allowed to dry. Rats were not anesthetized. Traction tape was loosely wrapped around the tail in a helical pattern starting at 1 cm from the base of the tail. A strip of traction tape 1 cm wide was preattached to a metal connector, attached to two-thirds the length of the tail along the lateral sides, and then secured by two strips of filament tape. One strip of filament tape was placed around at the end of the body side of the traction tape, and a second strip was added about halfway up the tape. The filament tape was loosely applied to allow normal blood circulation but tight enough so that the traction tape would not peel from the tail. The metal connector was connected by a wire to a swivel mounted at the top of the cage, allowing free 360° rotation. Rats were maintained at an angle of ~30° from the cage floor, and thus the back feet of the rat did not touch the grid floor. Hind legs were adjusted by manual extension to ensure that the claws did not touch the floor. The forelimbs of rats maintained contact with the cage floor, allowing rats to move and freely access food and water. During the tail-suspension period, rats were carefully monitored several times a day to prevent restriction of tail growth and circulation and ensure adequate food and water intake, grooming behavior, urination, and defecation. The tape was also replaced every 3 days. Tail-suspended rats were maintained in this position for 14 days. Control rats were allowed to move unconstrained around the cages and were fed the average amount eaten by suspended rats daily.

Exercise protocol.   After removal from the tail suspension apparatus, rats rested for 24 h. The jumping exercise protocol was then implemented according to the method previously reported by Umemura et al. (48). Rats in the jump exercise groups were individually placed at the bottom of a special wooden box surrounded with boards. The height of this box can be adjusted. Rats were initially forced to jump by electric stimulus and to grasp the top of the board with the forelimbs and climb up the board. The rat was then returned to the floor of the cage to repeat the procedure. As rats became accustomed to the jump exercise, the electric stimulus was used less frequently. The jump exercise program comprised 10 jumps/day, 5 days/wk for 5 wk. Initial height of the box was 25 cm, and this was gradually increased to 40 cm during the first week. The time required for 10 jumps was ~1 min.

Bone mineral density measurements.   Bone mineral density (BMD) of the femur was measured by dual-energy X-ray absorptiometry using a QDR-2000 unit (Hologic, Waltham, MA) at small animal ultra-high resolution scan mode, starting from the distal end of the femur. For subregional analysis, the total femoral region was divided along the femoral long axis into seven equal regions, as reported previously (21): R1 (region including femoral head, neck, and greater trochanter), R2 (intertrochanter), R3 (proximal diaphysis), R4 (mid-diaphysis), R5 (distal diaphysis), R6 (distal metaphysis), and R7 (distal epiphysis).

Micro-CT scanning and 3D architectural parameters.   The bone microarchitecture of the right femur was evaluated using a micro-CT system (Ele Scan; Nittetsu Elex, Tokyo, Japan). This apparatus is based on fan-beam tomography and is able to function in multislice mode. An X-ray tube with a microfocus (spot size of 6 x 8 µm) was used and maximum resolution of 4 µm (pixel size) was attainable. Parameters selected for this study included source energy 30 kVp and 100 mA to obtain optimum contrast between bone and soft tissue. The sample area selected for scanning was positioned at a distance of 4–4.5 mm proximal to the distal femoral end, including the border between the distal metaphysis and growth plate. The distal femur was selected over the proximal femur because of the larger volume of cancellous bone available for 3D analysis in the distal femur. A total of 250 consecutive tomographic slices with a slice thickness of 14.1 µm (~3.5 mm) were acquired. Digital data were reconstructed to obtain CT images with a pixel size of 17.6 µm in 512 x 512 matrices.

After micro-CT scanning, the original image data were transferred to a workstation, and structural indexes were calculated using 3D image analysis software (TRI/3D-BON; Ratoc System Engineering, Tokyo, Japan). TRI/3D-BON builds 3D models from serial tomographic datasets for visualization and morphometric analysis (21). This software calculates 3D morphometric parameters of cancellous bone based on micro-CT scan datasets. The volume of interest was defined as the 180 slices above the most proximal portion of growth plate. The resulting gray-scale images were segmented using a 3 x 3 median filter to remove noise, and a fixed threshold of 120 (0–255 range) to extract the mineralized bone phase. The isolated small particles in marrow space and the isolated small holes in bone were removed using a cluster-labeling algorithm.

Cortical and trabecular bone were subsequently separated and structural indexes calculated. Bone surface area (BS), bone volume (BV), and total tissue volume (TV) were estimated using standard procedures (7, 32). Trabecular thickness (Tb.Th), trabecular number (Tb.N), and trabecular separation (Tb.Sp) were measured by distance-transform method, which is independent of an underlying model (13). Fractal dimension of trabecular bone was measured as a representative of complexity using a box-counting method (7) developed three dimensionally. Connectivity density (β1/TV) (8) and trabecular bone pattern factor (TBPf) (10) were calculated directly from segmented voxel representations. TBPf reflects a concave/convex structure of the trabecular bone surface and lower values imply a highly connected state among trabeculae (9). The parameter β1/TV also represents trabecular connectivity, indicating more directly the state of trabecular connections. Structural model index (SMI) was calculated according to the methods described by Hildebrand and Rüegsegger (14). SMI defined as a value between 0 and 3 is used to estimate rod-like and plate-like characteristic of trabecular structures. Degree of anisotropy (DA), reflecting trabecular orientation, was determined from the ratio between maximal and minimal radii of the mean intercept length ellipsoid (11).

Data analysis.   All statistical analyses were performed using SPSS software version 14.0 for Windows (SPSS, Chicago, IL). The significance of differences between values in SUS and SCON groups was determined using Student's t-test. Differences among treatment groups (S+RCON, S+RJUM, and SCON+RCON groups) were evaluated by one-way ANOVA followed by least significant difference post hoc testing. All data are expressed as means ± SD. Values of P < 0.05 were considered statistically significant.


   RESULTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
Body and muscle weights and femoral length.   Body weight and hind limb muscle weight, but not femoral length, were significantly lower in tail-suspended rats than in sedentary control rats (12%, 21%, and 0.5% lower in SUS compared with SCON, respectively) (Table 1). After 5 wk of free remobilization, body weight and hind limb muscle weight had recovered rapidly in the S+RCON group to the same level as age-matched control rat values. However, final body weight in the S+RJUM group was significantly lower compared with SCON+RCON and S+RCON groups (6.8% and 5.6% difference, respectively). Jump exercise did not affect either hind limb muscle weight or femoral length.


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  		Table 1. Physical parameters of the experimental rats

 
BMD in subregions of the femur.   The BMD with respect to anatomical location along the length of the femur are shown in Table 2. After 14 days of tail suspension, total and subregional BMD values of the femur were significantly lower compared with sedentary control rats (10–53% difference; P < 0.001). The BMD recovered with free mobilization at R2, R3, R5, and total femoral regions but not at R1, R4, R6, and R7 (4.1–6.5% difference; P < 0.05–0.01). Conversely, in the S+RJUM group, BMD in all regions had recovered to above the level of the S+RCON group after 5 wk of jump exercise (5.2–14% difference; P < 0.05–0.001). Moreover, total femoral, R5, and R6 BMD in the S+RJUM group were significantly higher even compared with the SCON+RCON group (4.3–6.9% difference; P < 0.05–0.01).


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  		Table 2. BMD in the subregions of femur measured by DXA

 
Microstructural properties.   Tail suspension induced a marked deterioration of trabecular architecture in the distal metaphysis of the femur (Table 3). After 5 wk of spontaneous recovery, trabecular BV, BS, BV/TV, Tb.N, β1/TV, and fractal dimension were significantly lower, whereas BS/BV, Tb.Sp, TBPf, and SMI were significantly higher in the S+RCON group compared with SCON+RCON group. No significant differences in Tb.Th and DA were observed between S+RCON and SCON+RCON groups. These changes were returned by jump exercise during the recovery period except for TV. DA was significantly higher in S+RJUN compared with S+RCON.


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  		Table 3. Trabecular bone parameters in distal femoral metaphysis

 
Figures 1 and 2 show typical features of 3D trabecular microstructure in the distal femoral metaphysis for a rat from each group. These images demonstrate that tail suspension elicited marked deterioration in trabecular architecture and that these changes recovered with jump exercise.


Figure 1
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  		Fig. 1. Typical three-dimensional (3D) images of the distal femoral metaphysis at day 14 in the sedentary control (SCON) group (A) and the tail-suspended (SUS) group (B), as visualized using micro-computer tomography (CT). Intact bone and isolated cancellous bone for calculating trabecular bone parameters are shown at top and bottom, respectively.

 

Figure 2
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  		Fig. 2. Typical 3D images of the distal femoral metaphysis at day 49 in the age-matched control group without tail suspension and exercise (SCON+RCON; A), the spontaneous recovery group after tail suspension (S+RCON; B), and the jump exercise group after tail suspension (S+RJUM; C), as visualized using micro-CT. Intact bone and isolated cancellous bone for calculating trabecular bone parameters are shown at top and bottom, respectively.

 

   DISCUSSION
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 
The goal of this study was to assess the ability of jump exercise to restore bone mass and trabecular bone structure to age-matched control levels after deterioration induced by tail suspension in young growing rats. The restoration reflects the ability to combat the disuse-induced deterioration as well as growth retardation of bone. Five weeks of spontaneous recovery after 2 wk of skeletal unloading by tail suspension restored total femoral bone density, whereas integrity of femoral trabecular architecture in young growing rats was not sufficiently recovered. However, subsequent jump exercise after tail suspension completely restored the reduced bone mass and microarchitectural deterioration of bone with a consequent increase in Tb.Th, Tb.N, and connectivity, and a decrease in rod-like structures. These results thus suggest that jump exercise applied during remobilization period allowed full recovery of the integrity of trabecular microarchitecture as well as overall bone mass at the femur in young growing rats.

Chronic reductions in mechanical loading, such as immobilization, bed rest, spinal cord injury, and exposure to microgravity, are well known to precipitate generalized skeletal loss, particularly in bones that bear weight under normal conditions. Conversely, mechanical loading from physical activity is known to play a key role in the development of bone mass in both humans and animals. In particular, among the various types of exercise regimens, high-impact training seems to be the most beneficial for the skeleton. However, previous exercise intervention studies on immobilization-induced osteopenia in rats have mostly used treadmill running exercise and have produced conflicting results (4, 24, 46). Several studies have reported that the strains created by running exercise might be below or a little over the minimum effective strain (3, 26). In addition, running exercise yielded different results depending on factors such as training intensity, duration, period, and frequency (41). On the other hand, jump exercise compared with running yielded greater increases in bone mass and strength because of the greater mechanical stress and higher strain rate (47). However, little is known about the effect of jump exercise in restoring trabecular bone architecture after tail suspension-induced osteopenia. To the best of our knowledge, this study is the first to use jump exercise to assess the recovery of trabecular bone architecture in a tail-suspended rat model.

To clarify the mechanisms underlying the loss of bone mass induced in microgravity environments, a number of in vivo and in vitro studies have been conducted during spaceflight. However, the availability of spaceflight experiments is extremely limited. Ground-based studies have thus been conducted to investigate the mechanisms of osteopenia induced by weightlessness. A hind limb elevation model of rat by tail suspension has frequently been used to simulate the microgravity environment during spaceflight. This model has also been well justified by previous studies as an appropriate model for the study of simulated bone changes induced by weightlessness (33, 54). In histomorphometric analyses of the proximal tibia isolated from 6-wk-old rats, 14 days of unloading reportedly results in a reduction in BV/TV by 50%, Tb.N by 50%, and Tb.Th by 25%, and an increase in Tb.Sp by 179% in the secondary spongiosa (2). These values are very similar in magnitude to data reported in the present study using 3D micro-CT analysis (–51%, –51%, –21%, and 58%, respectively). Our results imply that the decrease in cancellous bone induced by skeletal unloading is primarily due to trabecular disappearance (–51%) rather than by a thinning of trabeculae (–21%). This conclusion is supported by a previous histomorphometric study (4).

Most studies investigating recovery potential after skeletal unloading have not demonstrated complete restoration of bone morphology (42, 49). In the present study, although the results of dual-energy X-ray absorptiometry analysis indicated recovery in total femoral BMD in spontaneous recovery rats after 5 wk of remobilization without jump exercise, micro-CT analysis revealed that the microarchitecture of the distal femoral metaphysis had not completely recovered. Our results concur with the findings of a previous study (23), in which true trabecular disappearance could not be restored during remobilization. Sakata et al. (42) proposed two possibilities for the insufficient recovery of trabecular bone mass during reloading: that the reloading period was too short for sufficient recovery or that increased trabecular perforation due to rapid trabecular thinning caused deterioration of the trabecular bone packet and a decrease in possible sites of bone formation.

Several previous histomorphometric analyses have found that the increase in trabecular bone mass by mechanical exercise is primarily due to increased Tb.Th rather than to noticeable changes in numbers of trabeculae (16, 38). In the present study, jump exercise during the remobilization period induced a significant increase in Tb.N of 31% and Tb.Th of 63% when compared with the spontaneous recovery group, resulting in a total increase in cancellous bone mass. These results imply that the cancellous bone gain induced by jump exercise during remobilization is predominantly attributable to increases in Tb.Th with a slight increase in Tb.N. This result is in agreement with a previous study of the hind limbs of tail-suspended rats (4). Positive relationships between bone strength and parameters of trabecular architecture have been well demonstrated, and Tb.Th plays a particularly important role in bone strength (51). An increase in Tb.Th induced by jump exercise may thus have an intense positive effect on bone strength.

The loss of trabecular connectivity is known to be associated with a reduction in the physical strength of trabecular bone (43). In the present study, both TBPf and β1/TV indicated significant decreases in trabecular connectivity after tail suspension. In the distal femoral metaphysis of tail-suspended rats, after 5 wk of recovery without exercise, both TBPf and β1/TV had not fully recovered. Conversely, when jump exercise was applied during the recovery period, both TBPf and β1/TV returned to age-matched control rat values. Increases in trabecular connectivity are usually coupled with increases in bone strength (27). Moreover, some studies have shown that restoration of trabecular connectivity is important for strength recovery (18, 27). Changes in TBPf and β1/TV in the present study could thus have contributed to the beneficial effects of jump exercise on cancellous bone strength.

After 14-day tail suspension, SMI exhibited a significantly higher value compared with control rats, indicating a change in trabecular structure from plate-like to rod-like with tail suspension. These findings support the notion that disuse osteoporosis is associated with increased SMI, as found in neurectomized rats (19) and tail-suspended rats (6). Spontaneous recovery did not fully restore changes in the structural type of trabecular bone as shown by a significantly higher SMI compared with age-matched controls. Conversely, when jump exercise was applied during the recovery period, SMI recovered nearly to the level of age-matched control rats, suggesting a concomitant increase in mechanical strength.

Trabecular alignment is another important parameter contributing to the mechanical strength of bone (39). In the present study, DA, reflecting trabecular orientation, was unaffected by tail suspension. However, trabecular bone was oriented more heterotropically in jump-exercised rats than in age-matched control rats. In our previous study using running exercise, trabecular alignments remained unchanged after 10 wk of exercise in rats (21). These findings can be considered to represent quantitative verification of Wolff's trajectorial theory of trabecular alignment (53).

Changes in body weight and muscle mass (force) may play important roles in the regulation of bone mass. Exercise usually induces body weight loss in male rats, whereas muscle weight is often unchanged (40). In the present study, both body weight and hind limb muscle mass decreased by tail suspension and recovered after 5 wk of remobilization to the same level as in age-matched control rats. Conversely, jump exercise during the remobilization period induced weight loss compared with controls, suggesting a negative effect on bone mass. Nevertheless, final BV was greater in S+RJUM rats than in S+RCON rats. These data could indicate that the recovery of BV observed in jump-exercised rats is derived primarily from the exercise stress itself.

Although it is impressive that the jump training was able to restore trabecular architecture, at the same time it may have endangered the fragile trabecular structure weakened by disuse. The ground reaction force on the lower leg with a 40-cm jump in rats has been reported about five times of body weight (25). Thus jump training would cause a great mechanical stress on bone. Although in humans the jump training with the ground reaction force of 2.1–5.6 times of body weight effectively increased bone mass (12), its application to fragile bone should be further examined in the context of safety.

Several limitations of this study should be considered. First, we used young growing rats (5 wk old), because the effects of tail suspension in adult rats occur more slowly compared with young rats (1), and in humans and animals, growing subjects usually have greater potential for bone recovery after immobilization (37, 46). Therefore, although Umemura et al. (47) showed that the skeletal effects of jump training were at almost the same level among young (3 mo old) and adult rats (27 mo old), our results might differ quantitatively if adult rats were used in the tail-suspension model. Second, we did not measure braking force in cancellous bone per se at the distal femoral metaphysis. We interpreted the structural change in cancellous bone as being related to the increase in bone strength, since previous studies have demonstrated a positive relationship between bone strength and parameters such as Tb.Th, Tb.N, and connectivity. Finally, the rat is an established model for many aspects of human bone metabolism but displays some limitations in that cortical structure and bone-modeling patterns differ from those in human. Direct extrapolation of data from quadrupedal rats to bipedal humans is thus inappropriate. Nonetheless, the results obtained from the present study using 3D micro-CT analysis suggest the advantage of jump exercise in preventing the trabecular bone loss induced by immobilization and microgravity.

In summary, the results of 3D analysis in the present study demonstrated that suspension-induced trabecular deterioration persists after remobilization and jump exercise during the remobilization period could restore the integrity of trabecular architecture as well as bone mass at the femur in young growing rats.


   GRANTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
ACKNOWLEDGMENTS
 REFERENCES
 
This study was supported in part by Grant-in-Aid for Scientific Research (B) no. 18700566 from the Japan Society for the Promotion of Science and by Research Project Grant no. 18-605 from Kawasaki Medical School.


   ACKNOWLEDGMENTS
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
REFERENCES
 
We gratefully acknowledge Tatsushi Tomomistu, Yoshihisa Umemura, and Tsukasa Tobaru for technical assistance.


   FOOTNOTES
 

Address for reprint requests and other correspondence: T. Sone, Dept. of Nuclear Medicine, Kawasaki Medical School, 577 Matsushima, Kurashiki, Okayama 701-0192, Japan (e-mail: tsone{at}med.kawasaki-m.ac.jp)

The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.


   REFERENCES
TOP
 ABSTRACT
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 GRANTS
 ACKNOWLEDGMENTS
 REFERENCES
 

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