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Objective: To observe the effects of different gravitational environments on release of prostaglandin E2 in rat calvarial osteoblasts induced by fluid shear stress (FSS) so that to investigate the influence of different gravity on mechanotransduction in osteoblasts. Methods: Osteoblasts were isolated from neonatal rat calvariae and then were set to three groups. Each was cultured in one gravitational environment:1G terrestrial gravitational environment (control), simulated weightlessness achieved by using clinostat and 3G gravitational environment achieved by using centrifuge for 60 h, then osteoblasts were treated with 0. 5 Pa or 1.5 Pa FSS in a flow chamber for 1 h. The release of PGE2 in osteoblasts was determined. Results: In 1G gravitational environment, the release of PGE2 was significantly increased along with the sustaining of FSS treatments (P＜0. 01), but there was no remarkable difference between the responses to 0. 5 Pa FSS and 1.5 Pa FSS (P＞0. 05). While in simulated weightlessness environment group, no detectable release of PGE2 was found with the treatment of 0. 5 Pa FSS (P＜0. 01), and the release of PGE2 was delayed and the amount of PGE2 production was remarkably decreased with 1.5 Pa FSS treatment as compared with that of 1G group (P＜0. 01). The responsiveness of osteoblasts cultured in 3G gravitational environment to FSS was similar to that of 1G group. Conclusion: These results indicate that in vitro the mechanotransduction in osteoblasts iss affected by stimulated weightlessness, whereas it is not altered in 3G gravitational environment.