Abstract: Objective To investigate the protective effect of Astragalus saponins methyl glycoside on the apoptosis of alveolar epithelial cells induced by endoplasmic reticulum stress in rats with chronic obstructive pulmonary disease(COPD).Methods Sixty Sprague-Dawley(SD)rats were divided into a control group,a model control group,and low-,medium-and high-dose Astragalus saponins methyl glycoside groups randomly(12 rats in each group).Except for those in control group,all rats were exposed to cigarette smoke once a day continuously for 28 days following intratracheal instillation of lipopolysaccharide(LPS)at the first and 14th day of the treatment to establish COPD model.The apoptosis of alveolar epithelial cells was analyzed using terminal-deoxvnucleoitidvl transferase mediated nick end labeling(TUNEL).The aspartic acid specific cysteine proteinase 3(caspase-3)and aspartic acid specific cysteine protease-12(caspase-12)in lung tissues of the rats were detected using Western blot.Results Compared with that of the control group,the number of apoptotic cells in the model group increased significantly(173.13±19.20 vs.0.83±0.34 per microscopic field,P<0.01);while compared to that of the model control group,the number of apoptotic cells decreased significantly in high-,medium-,and low-dose Astragalus saponins methyl glycoside groups(149.23±8.95,118.77±9.47,and 78.87±9.59 per microscopic field)(all P<0.01).The expressions of caspase-3(0.847±0.103) and caspase-12(0.706±0.042) in the lung tissue of the rats of model control group increased significantly compared to that of the rats of the control group(all P<0.01);whereas compared to those of model control group,the expressions of caspase-3(0.412±0.057,0.508±0.084,and 0.714±0.061)and caspase-12(0.341±0.052,0.393±0.065,and 0.516±0.087) decreased significantly in the rats of high-,medium-,and low-dose Astragalus saponins methyl glycoside groups(all P<0.01).Conclusion Astragalus saponins methyl glycoside could alleviate apoptosis of alveolar epithelial cells induced by endoplasmic reticulum stress and the effect may be related to the downregulation of the expressions of caspase-3 and caspase-12 in lung tissue in rats.