Experimental Study On The Effect Of Immobilization On Expression Of Vitamin D Receptor In Bone And Exercising On Disuse Osteoporosis In Immature Rats

Objectives: To know of the effect of immobilization and remobilization on immature rat bone and explore the characteristics and pathogenesis of disuse osteoporosis of immature bone,and to supply some possible theories for knowing of ,preventing and treating disuse osteoporosis in children.Methods: The right hindlimbs of young rats aging 4 weeks and grown rats aging 12 months were immobilizated by limb-tail fixation for 2 and 4 weeks,and then the wet weight,gray weight,biomechanic properties of femurs,and bone mineral density of femurs and tibie,histomorphometric perameters were detected for evaluating the effect of immobilization on bone content, bone structure and bone strenth between growing rats and adult rats.Effect of low strenth exercise on bones of young rats immobilizated for 4 weeks was evaluated with the above parameters,too.The effect of immobilization on bone vitamin D receptors in the growing rats was evaluated by immunohistochemistry and image analysis. Results: The parameters of immobilizated limbs in the growing rats (wet weight,gray weight,biomechanic properties of femurs,and bone mineral density of femurs and tibie) were all lower than in age-macthed control goups with statisticdifferences ,but no statistic differences of the above parameters were found between the experimental groups and their age-macthed control goups in adult rats.Rare,small and broken bone trabeculae were found both in growing rats and adult rats after 2 and 4 weeks' immobilization,and statistic differences were also found respectively when comparing with their age-macthed control goups. Overexpression of vitamin D receptor in cellular plasm and nuclear membranes of osteoblasts in growing rats after immobilization was found. The above parameters in immobilizated limbs of growing rats were ameliorated or even recoveried to the levels of their age-macthed control goups by low strength exercises. Conclusions: It is a definite method to set up an animal model of disuse osteoporosis in young rats by leg-tail fixation; overexpression of Vitamin D receptors in growing bone under the condition of immobilization means that the disorder of vittamin D endocrine system may be related to pathogenesis of DOP;disuse osteoporosis is more easy to occur in growing rats than in adult rats with same immobilizations,but disuse osteoporosis in growing bones may be recoveried quickly by low strength exercises.