PTH1-34 Promoted Bone Mass Recovery in Rats with Reloading After Tail-suspension

OBJECTIVE To observe the changes of bone mass in tail-suspended and subsequent reloaded rats, as well as the effects and mechanism of PTH1-34 on these process. METHODS Twenty four 5 month old rats were divided into 4 groups:control(CL) group, tail suspension for 4 weeks(UL) group, tail suspension for 2 weeks and reloading for 2 weeks(UL+RL) group, tail suspension for 2 weeks and reloading plus PTH1-34 intervention for 2 weeks(UL+RL+PTH) group, 6 rats in each group. All rats were sacrificed 4 weeks later, left tibia was used for bone histomorphometry analysis, left femur was used for bone mineral density, and right tibia was assigned to biomechanical test, tibia were harvested for detecting expression levels of osteocalcin(OCN) by Western blotting and realtime PCR, respectively. The maximum load and elastic modulus of the right femur were analyzed by a three-point bending test. RESULTS Bone mineral density(BMD) in CL group was significantly higher than other three groups(P<0.05), UL+RL and UL+RL+PTH rats showed markedly higher values than UL rats(P<0.05), UL+RL+PTH rats showed markedly higher BMD than UL+RL rats(P<0.05). CL group showed markedly higher bone volume per total volume (BV/TV) values than those in the UL, UL+RL and UL+RL+PTH groups, UL+RL and UL+RL+PTH groups showed significantly higher BV/TV than that of UL group(P<0.05), UL+RL+PTH group showed markedly higher BV/TV than UL+RL group(P<0.05). Trabecular number in CL group was significantly higher than other three groups, UL+RL+PTH group showed markedly higher trabecular number than UL group(P<0.05); Trabecular separation in CL group was significantly lower than those in the UL, UL+RL and UL+RL+PTH groups(P<0.05), UL+RL and UL+RL+PTH groups showed significantly lower trabecular separation than that of UL group(P<0.05). UL group showed markedly lower maximal load compared to the other three groups, UL+RL group showed significantly lower maximal load than CL group(P<0.05). Rats in CL group showed markedly higher elastic modulus compared to other three groups(P<0.05); UL+RL+PTH group showed significantly higher elastic modulus than UL and UL+RL groups. Western blotting showed IOD of OCN in UL group was significantly lower than CL group and UL+RL+PTH group(P<0.05). No significant difference between any two groups was found of the mRNA expression level of OCN. CONCLUSION Two weeks of tail-suspension induced disuse of hindlimb caused bone loss, deterioration of biomechanical properties and reduction of OCN expression, which were partially restored after reloading and enhanced by PTH1-34 treatment.