Abstract: objective :To investigate the effects of jumping stress stimulation on the parathyroid hormone( PTH )and molecules expression of OPG and RANKL related to bone metabolism in Rat’s Tibias,and to explore the molecular mechanism of bone destruction. Methods: 48 eight-week old SD rats were equally randomized into control group(C) ,jump group(J) and loading jump group(JL). After two weeks,8 rats were taken from three groups,marked as: C2,J2 and JL2 groups and after six weeks the rest taken and marked as:C6,J6 and JL6. J group participated in incremental load training,JL group gained 5% of body weight load whose training plan was the same with the J6 group and the C group was not treated. The serum PTH levels were measured by enzyme-linked immunosorbent assay(ELISA). Alkaline phosphatase (ALP) and anti-tartaric acid acidic phosphoric acid (StrACP) in serum were assayed by colorimetric method. One side tibia was made HE paraffin section,the other side was assayed the mRNA expression of IL-6,OPG and RANKL by RT-PCR. Results: (1) Compared with C6 and J6,collagen fibers of periost were disordered with a larger degree of damage to the cortical bone,the cavitys increases in JL6 group. (2) The serum ALP and StrACP levels in three jumping groups were significantly higher compared with those in control groups(p <0.05). The serum StrACP levels in JL6 and J6 groups were significantly higher compared with those in C6 groups(p<0.05). (3) Compared with the C2 group,the level of PTH was significantly lower in the J2 and JL2 groups(p<0.05). The serum PTH level in JL6 group was significantly lower compared with that in C6 and J6 groups(p<0.05). (4) The mRNA expression of OPG in JL6 and J6 groups were higher than in C6 (p <0.05),and it was the highest in J6 group. The mRNA expression of RANKL was significantly higher in JL6 group than in the C6 and J6 groups (p <0.01).Conclusions: Bone destruction characterized by higher bone turnover in rats’ tibias was severe after 6 weeks of loaded jump because of the increased expression of RANKL. The decreased level of PTH is not helpful for the heal of bone destruction.

Key words: jumping stress, PTH, OPG/RANKL