ObjectiveTo investigate the changes of peritoneal macrophages function of mice with gastric cancer in the CO2 pneumoperitoneum environment, as well as its effect on the peritoneal metastasis of gastric cancer. MethodsAn orthotopic implantation model of mouse forestomach cancer was established using the 615 mouse. The mice bearing tumors were randomly divided into five groups (n=30): anesthesia alone, laparotomy, and 2, 4, and 6 mm Hg CO2 insufflation groups. Peritoneal macrophages were collected from six mice in each group and cultured. The macrophage phagocytic function on neutral red and the levels of NO and TNF-α produced by macrophages were measured after 12, 24, 48, and 72 h of culture. The remaining mice were observed after two weeks for the rate of peritoneal metastasis of forestomach cancer cells and the total weight of implanted nodules. ResultsNo death and ascites were found and the difference of weight body was not significant in all mice (Pgt;0.05). The uptake of neutral red by peritoneal macrophages and the levels of NO and TNF-α secreted by peritoneal macrophages in the laparotomy group after 12 h of culture were all significantly higher than those in other four groups (Plt;0.05). The corresponding values in the 2, 4， and 6 mm Hg CO2 insufflation groups after 12 h were all significantly lower than those in the anesthesia alone group (Plt;0.05). Among three insufflation groups, the corresponding values in the 2 mm Hg after 12 h were significantly higher than those in the 4 and 6 mm Hg CO2 insufflation group, though the difference in the two latter was not significant (Pgt;0.05). The uptake of neutral red by peritoneal macrophages and the levels of NO and TNF-α secreted by peritoneal macrophages in the 6 mm Hg CO2 insufflation group after 24 h of culture were all significantly lower than those in other four groups (Plt;0.05), while the difference in the four groups was not significant (Pgt;0.05). The uptake of neutral red by peritoneal macrophages and the levels of NO and TNF-α secreted by peritoneal macrophages after 48 h and 72 h were not significantly different in the five groups (Pgt;0.05). The rate of peritoneal metastasis of mice was significantly lower in the 6 mm Hg insufflation CO2 group (75.0%, 15/20) than that in the anesthesia alone group (100%, 24/24), Plt;0.05, but higher than other three groups(Plt;0.05), which was not different in 2 mm Hg (47.8%, 11/23), 4 mm Hg insufflation group (45.45%, 10/22) and laparotomy group (50.0%, 10/20), Pgt;0.05. The total weight of implanted nodules of mouse forestomach cancer was (1.24±0.48) g, (1.02±0.38) g, (0.96±0.33) g, (0.93±0.45) g, and (1.18±0.37) g in the anesthesia alone group, the laparotomy group, and 2, 4, and 6 mm Hg CO2 insufflation group, and the difference was not significant (Pgt;0.05). ConclusionHigh pressure (6 mm Hg) CO2 pneumoperitoneum can constantly inhibit the phagocytosis and cytokine secretion functions of peritoneal macrophages in gastric cancer-bearing mice and promote peritoneal implantation of gastric cancer.