| Objective: Postmenopausal osteoporosis is a common disease in postmenopausal women. In this study, we take ovariectomized female rats as the model of postmenopausal osteoporosis. To explore the mechanism of moderate-intensity treadmill exercise on the loss of bone mass in ovariectomized rats.Methods: Sixty female SD rats were randomly divided into following three groups: sham-operation (Sham), ovariectomized (OVX) and ovariectomized exercised (EX, 18 m/minute, 45 min/day, 5 uphill, 4 times/week). All exercise training was conducted in the morning, feeding the rats in the same conditions. Weigh the body weight of rats and food intake every week. After formal training for 15 weeks, the rats in each group were randomly divided into subgroups, weighing the weight of rats in each group after ovariectomized for 16 and 32 weeks respectively; detected the the bone mineral density (BMD) and body composition in whole body and major parts of body, collected and weighed abdominal fat, uterus, the fat under femur, muscle and bone tissue. Bone mineral density (BMD) and bone mineral content (BMC) of isolated femur, tibia and L5 lumbar were detected by dual energy X-ray, and detect the femur bone biomechanics by the three-point bending method.Result: After ovariectomized for 16 weeks: (1) The body weight, Lee's, food intake, fat mass, fat content, abdominal fat and hip fat in OVX-16 group were significantly higher than Sham-16 group; the uterine weight, lean mass content, the relative weight of wet,ash and dry femur in both left and right and the levels of Ca,P in serum were significantly lower than Sham-16 group; Compared with OVX-16, fat mass, fat mass content, lean mass content, abdominal fat, fat under the femur, extensor digitorum longus weight, the relative weight of wet and dry femur in EX group were significantly different, but body weight, Lee's, uterine weight, the calcium and phosphorus content in serum have no significant difference. (2) Compared with Sham-16 group, BMD of the whole body,lumbar spine and femur,BMD and BMC of distal femur,BMD and BMC of the proximal and distal tibia in OVX-16 decreased significantly;After treadmill exercise training, BMD of the whole body,lumbar spine,BMD and BMC of the distal femur,BMD of proximal tibia,BMC of distal tibia in EX increased significantly; (3) Correlation analysis showed that, lean mass was significantly positively correlated with BMD of the whole body in Sham-16 group; Body weight, lean mass were significantly positively related to BMD of the whole body in OVX-16; abdominal fat was positively related to lumbar spine BMD in OVX-16; Body weight and lean mass were significantly positively related to BMD of the whole body in EX; Fat under left femur was significantly positively related to middle femur BMD in EX; Fat under right femur was significantly positively related to proximal and mid-BMD, abdominal fat and the proximal and distal femoral BMD has a significant positive correlation in EX. (4) Maximum load, elastic load, failure load, maximum stress, elastic stress, maximum strain, elastic strain in OVX-16 group was significantly lower than that of Sham-16 group; After treadmill exercise treatment, maximum load, elastic load, failure load, maximum deflection, maximum stress, elastic stress, maximum strain, elastic strain in EX were significantly higher than that of OVX-16 group.After ovariectomized for 32 weeks, compared with OVX-32 group: (1) Food intake was significantly increased; Body weight, Lee's, abdominal fat increased, but no significant difference in D-EX. (2) Although BMD of the whole body, lumbar spine and femur in D-EX is higher than OVX-32 group, but no significant difference; (3) Correlation analysis showed that, body weight had no significant related with BMD, lean mass was significantly positively correlated with BMD and femur BMD in Sham-32 group; Body weight and fat mass was significantly positively correlated with BMD and femoral BMD in OVX-32; body weight and BMD have a positive correlation with each other, fat mass was significantly positively related to the whole body, lumbar spine and femoral BMD, abdominal fat was positively correlated with lumbar spine BMD in D-EX group; (4) Maximum load, failure load, maximum stress, elastic stress in OVX-32 group were significantly lower than Sham-32 group, after detraining, elastic load, failure load, elastic stress in D-EX were significantly higher in OVX-32 group.Conclusion: Moderate-intensity treadmill exercise can: (1) reduce the fat mass, fat mass content in ovariectomized rats, increased lean mass content, optimize body composition; (2) slow the loss of bone mass in ovariectomized rats; (3 ) decrease the loss of both femur and tibial's inorganic mineral content in ovariectomized rats; (4) improve bone biomechanical properties of the femur in ovariectomized rats. But except bone biomechanical properties, the above effects are becoming weakened or disappeared due to detraining. (5) The level of calcium, phosphorus in serum in ovariectomized rats was significantly lower; the level of phosphorus in serum has no significant decrease. Effects of exercise on calcium and phosphorus in serum had no significant meaning.Correlation between BMD and body composition: (1) 16 weeks after ovariectomy, body weight is an important factor to bone mineral density in ovariectomized rats and lean body mass and bone mineral density is closely related to each other; (2) 32 weeks after ovariectomized, body weight, fat mass in ovariectomized rats are closely correlated with BMD. (3) Abdominal fat in ovariectomized rats is closely related with the lumbar spine bone mineral density, fat under femur is closely related to the proximal and middle femur BMD. |
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