Abstract: Objective To explore the effect of Orexin A on the growth of human gastric cancer cell line SGC7901 and its mechanisms. Methods The SGC7901 cells were treated by Orexin A and SB408124 (an antagonist of Orexin A receptor subtype 1). The MTT assay was used to detect the growth inhibitory rates of Orexin A on human gastric cell SGC7901. The apoptosis was determined by Hoechst 33258 fluorochrome staining and flow cytometric analysis; and we used Western blot to detect the expressions of Bcl-2 Bax Cyt c and caspase-3. Results Orexin A can inhibit the growth of SGC7901 cells. This can be shown by a direct relationship between a longer time for cells to culture when given a higher dose of Orexin A. The strongest inhibitory rate was 65.32%±2.51%, when we used 1.0μmol/L Orexin A treat for 24h（P <0.01）; we can see many apoptotic cells that the nuclear condensation in Orexin A group，While cells that were pretreated with SB408124 showed the number of the native cell was decreased (P<0.05). After treated with Orexin A, the apoptosis rate was 59.52%±1.38%，but when we pretreated with SB408124, the apoptosis rate decrease to 38.96%±1.82%；the expressions of Bax Cyt c and caspase-3 protein were increased, but the expression of Bcl-2 was decreased（P <0.05）. As mentioned above, the inhibitory effects of Orexin A on SGC7901 cell were weakened by the pretreatment with SB408124. Conclusions Orexin A significantly inhibits the growth of SGC7901 cells through inducing cell apoptosis. Its molecular mechanism is associated with OX1R.

Key words: Orexin A, SGC7901 cell, SB408124, apoptosis