['To investigate the inhibitory effect of salidroside (Sal) on pulmonary microvascular endothelial cell (HPMEC) apoptosis induced by simulated microgravity and its mechanism.', 'Human pulmonary microvascular endothelial cells cultured in vitro were divided into control group, clinorotation group and clinorotation+Sal pretreatment groups. Microgravity was simulated by clinorotation. The apoptotic rate of HPMECs was detected by flow cytometry using Annexin V-FITC staining, and the expressions of bcl-2, bax, and caspase-3 at the mRNA and protein levels were determined by real-time PCR and Western blotting, respectively.', 'A 72-h clinorotation significantly induced apoptosis in HPMECs. Real-time PCR results demonstrated a significantly lowered bcl-2 but increased bax and caspase-3 mRNA expressions in clinorotation group as compared with those in the control group. Western blotting showed that clinorotation inhibited the protein expressions of PI3K and p-AKT and increased caspase-3 protein expression. Salidroside significantly inhibited the cell apoptosis, reversed the expressions of Bcl-2 and Bax, and attenuated the decrease in the protein expression of PI3K and phosphorylation level of AKT. Salidroside also antagonized the activation of caspase-3.'] Does [ Salidroside inhibit clinorotation-induced apoptosis in pulmonary microvascular endothelial cells ]?