Effects of Hindlimb Unloading on Bone Histomorphometry and Bone Mass in Rats.

Objective To study the effects of hindlimb unloading on bone histomorphometry, bone local growth factor,bone biomechanical properties and bone contents in rats. Method Male SD rats were arranged into free active control group (CON) and tail-suspended group (TS) with 9 rats in each group. The experiment lasted for 3 weeks. Bone histomorphometry, bone local growth factor, biomechanical properties and bone contents were measured before and after tail suspension. Result Structure of the trabecular bone was disorganized. Compared with CON, trabecular bone volume(%Tb.Ar), mean trabecular plate thickness(Tb.Th), osteoblast surface(Ob.S) were significantly reduced in TS. The eroded surface(Oc.N/BS) tended to be higher, though not significant at this stage of tail suspension; alkaline phosphatase (ALP) activity in the tibia were significantly reduced, but NO content in the femoral trunk was significantly decreased; bone biomechanical properties, bone mineral content(BMC), bone density(BD) and bone collagen density(BCD) in the femur were significantly reduced. Conclusion Hindlimb unloading may lead to regression of bone microstructure, change of bone local growth factor content, reduction of bone biomechanical properties and bone content.