〔Abstract〕 Objective To explore the effects of phosphatidylinositol 3-kinase(PI3 K)/protein kinase B(Akt) signaling pathway on the expression of receptor for activated C kinase 1(RACK1) and ras-related C3 botulinum toxin substrate 1(rac1) in rat pulmonary microvascular endothelial cells(PMVEC) induced by lipopolysaccharide(LPS). Methods Cultured rat PMVEC in vitro were divided into different groups of LPS dose-dependent group, LPS time-dependent group, IGF-1 time-dependent group and LPS+LY294002 group. ① For LPS dose-dependent group, PMVEC were cultured with 0, 1, 5, 10 mg/L LPS for 12 h. ② For LPS time-dependent group, PMVEC were cultured with 10 mg/L LPS for 0, 3, 6, 8, 12, 24 h. ③ For IGF-1 time-dependent group, PMVEC were cultured with IGF-1 for 0, 3, 6, 8, 12, 24 h. ④ For LPS+LY294002 group, PMVEC were cultured with 100 ng/ml LY294002 for 1 h before the treatment of 10 mg/L LPS for an additional 12 h. In addition, blank, LPS and LY294002 groups were set as references. After intervention, the levels of RACK1, rac1 and p-Akt were detected with Western blot. Results ① In LPS dose-dependent group, the relative expression levels of RACK1, rac1 and p-Akt increased in a dose-dependent manner, and there were significant differences among the groups of RACK1(F=120.455,P<0.001), among the groups of rac1(F=165.813,P<0.001)and among the groups of p-Akt(F=309.346,P<0.05), respectively. ② In LPS time-dependent group, the relative expression levels of RACK1 and rac1 increased in a time-dependent manner, and there were significant differences among the groups of RACK1(F=454.034,P<0.001) and among the groups of rac1(F=423.630,P<0.001), respectively. The relative expression level of p-Akt raised at 3 h(0.460±0.089), peaked at 12 h(2.022±0.244), and it was still higher at 24 h(1.264±0.074) than 0 h(0.237±0.063). There were significant differences(F=137.726,P<0.001) among the groups of p-Akt expression. ③In IGF-1 time-dependent group, the relative expression levels of RACK1, rac1 and p-Akt increased in a time-dependent manner, and there were significant differences among the groups of RACK1(F=188.293,P<0.001), rac1(F=115.071,P<0.001) and p-Akt(F=60.175,P<0.001). ④ In LPS+ LY294002 intervention group, the expression of RACK1 was lower than that of the LPS group [(0.732±0.137)vs(1.498±0.167),P<0.001], the expression of rac1 was lower than that of the LPS group [(0.758±0.084)vs(1.384±0.170),P<0.001], the expression of p-Akt was lower than that of the LPS group [(0.492±0.148)vs(1.106±0.219),P<0.001]. Conclusions PI3 K/Akt signaling pathway participates in LPS-induced PMVEC injury by interfering with RACK1 and rac1 expression.