Effect of Simvastatin on Bone Mass Recovery in Rats with Reloading after Tail-suspension. Zhou Pei-fei1, Hu Dong1, Zhang Yan2, Liu Hao2, Faming Tian3, Xing Lei2. 1Health Center of Xizhou Center, Xiangshan country, Ningbo, Zhejiang, 315722; 2 Affiliated Hospital of the North China University of Science and Techonology, Tangshan, Hebei, 063000; 3 Medical Research Center, North China University of Science and Techonology , Tangshan, Hebei, 063000) Abstract Objective: To observe the changes of bone mass in reloaded rats after tail-suspension, as well as the effect and mechanism of simvastatin on this process. Methods: Twenty-four 5-month old rats were divided into 4 groups of 6 animals in each group: Control (CL) group without tail-suspension, Unloaded (UL) group with tail-suspension for 6 weeks, other 12 rats were received tail-suspension for 3 weeks, then reloaded for subsequent 3 weeks (UL RL) or combined with simvastatin treatment (UL RL SIM) at a dosage of 10mg/kg/d. All rats were sacrificed 6 weeks later, left femur was used for bone mineral density, left tibia was used for bone histomorphometry analysis, and right femur and tibia were harvested for the biomechanical test and expression levels of Collagen type 1 by realtime PCR and Western blot, respectively. Results: 1. BMD of CL group is significantly higher than those of the other three group (P < 0.05), BMD of UL is also markedly lower than those in UL RL and UL RL SIM (P < 0.05). 2. Bone histomorphometry: BV/TV in CL group was significantly higher than those in the other 3 groups, UL RL and UL RL SIM groups showed significantly higher BV/TV than that of UL group (P < 0.05); Tb.Th is significantly higher in CL group in comparison with UL group; Tb.Sp in CL group was significantly lower than those in the other 3 groups (P < 0.05) , UL RL and UL RL SIM groups showed significantly lower Tb.Sp than that of UL group (P < 0.05); 3. Biomechanical test: the maximal load and elastic modulus in CL groups were significantly higher than those of the other three groups (P < 0.05); 4. Realtime PCR: No significant difference between any two groups of the mRNA expression level of ColⅠwas found. 5. Western blot: IOD of ColⅠin is significantly lower than CL group. Conslusions: Bone loss, deterioration of trabecular bone micro-architecture and biomechanical properties and reduction of Collagen typeⅠwere observe in tail-suspension rats, which were partially restored after reloading and were not enhanced when combined with simvastatin treatment.