Objective:To investigate the inhibitory effect of Yifei Huoxue Granule (益肺活血颗粒,YFHXG) on the hypoxia-induced proliferation of rat pulmonary artery smooth muscle cells(PASMCs) and its mechanism of decreasing pulmonary arterial pressure.Methods:Twenty male Sprague-Dawley(SD) rats were randomly divided into four groups:saline,and 0.66,3.30 and 16.50 g/kg of YFHXG groups,the saline and different concentrations of YFHXG were given twice daily for 7 days,respectively.Serum-pharmacology method was used in the preparation of YFHXG serum.Tissue block anchorage was employed in the primary culture of rat PASMCs.The PASMCs were randomly divided into normoxia group,hypoxia group,and hypoxia+YFHXG group (0.66,3.30 and 16.50 g/kg doses of YFHXG-treated serum groups,exposed to hypoxic condition).PASMCs in normoxia and hypoxia group were cultured with saline serum,hypoxia+YFHXG groups were cultured with different concentrations of YFHXG serum.Cell viability was assessed with 3-(4,5-dimethylthiazol-2-yl)-2,5- diphenyltetrazolium bromide(MTT) assay.Cell cycle was analyzed using flow cytometry.In addition,hypoxia inducible factor-1-alpha(HIF-1α) protein expression was evaluated by immunocytochemistry analysis,the concentration of intracellular reactive oxygen species(ROS) and Ca~(2+) were determined by laser scanning confocal microscopy(LSCM).Results:MTT assay and flow cytometry showed that hypoxia could directly activate the proliferation of PASMCs,while YFHXG dose-dependently inhibited hypoxia-induced proliferation of rat PASMCs.Immunocytochemistry showed that hypoxia enhanced HIF-1αprotein expression,and LSCM showed that hypoxia significantly increased intracellular ROS and Ca~(2+),while YFHXG decreased the expression of HIF- 1αand attenuated the hypoxia-induced increase in intracellular concentration of ROS and Ca~(2+).Conclusions: YFHXG could inhibit hypoxia-induced proliferation of rat PASMCs,which may decrease pulmonary arterial pressure and vascular remodeling.The anti-hypoxia effect of YFHXG may be explained by its regulation of HIF-1α expression and of the levels of intracellular ROS and Ca~(2+). Objective: To investigate the inhibitory effect of Yifei Huoxue Granule on the hypoxia-induced proliferation of rat pulmonary artery smooth muscle cells (PASMCs) and its mechanism of decreased pulmonary arterial pressure. Methods: Twenty male Sprague- The saline and different concentrations of YFHXG were given twice twice daily for 7 days, respectively. Serum-pharmacology method was used in the preparation of YFHXG serum.Tissue block anchorage was employed in the primary culture of rat PASMCs.The PASMCs were differentiated into normoxia group, hypoxia group, and hypoxia + YFHXG group (0.66, 3.30 and 16.50 g / kg doses of YFHXG- treated serum groups exposed to hypoxic condition. PASMCs in normoxia and hypoxia groups were cultured with saline serum, hypoxia + YFHXG groups were cultured with different concentrations of YFHXG serum. Cell viability was assessed with 3- (4,5-dimethyl thiazol-2-yl) -2,5- diphenyltetrazolium bromide (MTT) assay. Cell cycle was analyzed using flow cytometry. In addition, hypoxia inducible factor- 1-alpha concentration of intracellular reactive oxygen species (ROS) and Ca ~ (2+) were determined by laser scanning confocal microscopy (LSCM). Results: MTT assay and flow cytometry showed that hypoxia could directly activate the proliferation of PASMCs, while YFHXG dose- dependently inhibited hypoxia-induced proliferation of rat PASMCs. Immunocytochemistry showed that hypoxia enhanced HIF-1αprotein expression, and LSCM showed that hypoxia- marked increased hypoxic intracellular ROS and Ca ~ (2 +), while YFHXG decreased the expression of HIF- 1αand attenuated the hypoxia-induced increase in intracellular concentration of ROS and Ca ~ (2 +). Conclusions: YFHXG could inhibit hypoxia-induced proliferation of rat PASMCs, which may decrease pulmonary arterial pressure and vascular remodeling. Th e anti-hypoxiaeffect of YFHXG may be explained by its regulation of HIF-1α expression and of the levels of intracellular ROS and Ca ~ (2+).