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[The effect of retinoic acid on induction of osteoporotic model rats and the possible mechanism].

OBJECTIVE
To observe the effect of retinoic acid on induction of osteoporotic model in rats and analyze the mechanism therein involved.


METHODS
SD rats were treated with retinoic acid 80 mg/(kg x d) by gastrogavage for 15 days to induce osteoporosis and were killed in batches at 0, 30 and 60 days after drug withdrawal. The levels of Ca, P, BGP, E2, IGF-1, AKP and TRAP in serum were assayed, the collagen and proteoglycan contents of bone and bone mineral density (BMD) were determined, and the morphological changes in cancellous and cortical bone and growth plate cartilage (GPC) of femurs from the experimental rats were observed.


RESULTS
After 15 days of induction by retinoic acid, the serum E2 and BGP contents of rats were obviously decreased, the activities of AKP and TRAP were significantly increased, and the levels of BMD were lowered. The masses of spongy bone and cortical bone of femurs from the rats were decreased, and the number of chondrocytes in GPC was reduced. At 30 days, after drug withdrawal, the masses of spongy bone and cortical bone of femurs from the osteoporotic model rats still showed reduction; the activities of AKP in serum were lower than those at 15 days after drug redrawal, but were still higher than those of normal group rats; the chondrocytes in GPC were increased, the serum BGP and Ca contents were increased. At 60 days, after drug withdrawal, only the masses of femoral spongy bone of the osteoporotic model rats continuously showed obvious reduction, the other indices, including BGP, E2, AKP, TRAP and the masses of cortical bone, showed no significant difference between the two groups.


CONCLUSION
The short-term effect of retinoic acid on induction of rat's osteoporotic model was noticeable, but the long-term effect was not so good, and the bone loss of spongy bone existed longer and was more obvious than that of cortical bone.