要素市场扭曲和资源错配是生产率差异的重要来源。破除体制机制障碍,促进要素资源自由有序流动,有利于充分发挥市场配置资源的决定性作用,对助力中国经济高质量发展至关重要。本文在Hsieh and Klenow(2009)的基础上,以可变成本加成率为...要素市场扭曲和资源错配是生产率差异的重要来源。破除体制机制障碍,促进要素资源自由有序流动,有利于充分发挥市场配置资源的决定性作用,对助力中国经济高质量发展至关重要。本文在Hsieh and Klenow(2009)的基础上,以可变成本加成率为前提,提出了一种测算要素市场扭曲的新方法,并以中国加入世界贸易组织为准自然实验,系统评估了中间品贸易自由化对要素市场扭曲的影响方向和作用机制。研究发现:(1)中间品贸易自由化水平的提高显著降低了中国要素市场扭曲程度;(2)中间品贸易自由化对要素市场扭曲的改善作用在外商投资、直接进口、资本集中度低的企业中体现更为明显;(3)中间品关税削减幅度更大的地区(地级市),其要素市场扭曲下降更多;(4)降低企业进口要素价格,缓解企业融资约束可能是中间品贸易自由化影响要素市场扭曲的内在机制。本文研究强调了贸易自由化在降低要素市场扭曲、提高资源配置效率方面的重要作用,在当前要素市场化配置改革不断深化的背景下更具现实意义。展开更多
Background Cell transplantation for myocardial repair is limited by early cell death. Gene therapy with human growth hormone （hGH） has been shown to promote angiogensis and attenuate apoptosis in the experimental an...Background Cell transplantation for myocardial repair is limited by early cell death. Gene therapy with human growth hormone （hGH） has been shown to promote angiogensis and attenuate apoptosis in the experimental animal. This study was conducted to explore the effects of myoblast-based hGH gene therapy on heart function restoration and angiogenesis after myocardial infarction, and to compare the differences between myoblast-based hGH gene therapy and myoblast therapy.Methods Myoblasts were isolated from several SD rats, cultured, purified, and transfected with plasmid pLghGHSN and pLgGFPSN. Radioimmunoassay （RIA） was used to detect the expression of hGH in these myoblasts. SD rats underwent the ligation of the left anterior descending coronary artery so as to establish a heart ischemia model. Thirty surviving rats that underwent ligation were randomly divided into 3 equal groups 2 weeks after left coronary artery occlusion： pLghGHSN group received myoblast infected with hGH gene transplantation; pLgGFPSN group received myoblast infected with GFP gene transplantation; control group： received cultured medium only. Four weeks after the injection the surviving rat underwent evaluation of cardiac function by echocardiography. The rats were killed and ventricular samples were undergone immunohistochemistry with hematoxylin-eosin and factor Ⅷ. Cryosection was analyzed by fluorescence microscopy to examine the expression of green fluorescent protein. Reverse transcriptase-polymerase chain reaction （RT-PCR） was used to examine the mRNA expression of vascular endothelial growth factor （VEGF）, bax and Bcl-2. hGH expression in myocardium was examined by Western blot.Results Myoblast can be successfully isolated, cultured and transfected. The expression of hGH in transfected myoblast was demonstrated with RIA. Four weeks after therapy, the cardiac function was improved significantly in pLghGHSN group and pLgGFPSN group. Fractional shortening （FS） and ejection fraction （EF） in pLghGHSN group were elevated significantly compared with pLgGFPSN group and control group after therapy （FS： 36.9±5.3 vs 29.5±3.5, 21.8±2.9; EF： 56.9±4.3 vs 47.1±3.6, 38.4±4.8, P〈0.05）. Left ventricular end-diastolic dimension （LVEDD） and heart infracted size in pLghGHSN group were decreased significantly compared with pLgGFPSN group and control group after therapy （LVEDD： 5.9±0.3 vs 6.8±0.2, 8.6±0.3; heart infracted size： （34.5±4.2）% vs （40.0±3.9）%, （46.1±3.8）%, P〈0.05）; Green fluorescence was detected in cryosection of pLgGFPSN group. The capillary density of the pLgGFPSN group was significantly greater than those of the pLghGHSN group and control group （P〈0.05）. The mRNA expression of VEGF and Bcl-2/bax in pLghGHSN group was higher than in pLgGFPSN group or control group （P〈0.05）. The expression of hGH clene in myocardium tissue can be detected by Westem blot assay in pLghGHSN group.Conclusions Transplantation of heart cells transfected with hGH induced greater angiogenesis and effect of antiapoptosis than transplantation of cells transfected with GFP. Combined GH gene transfer and cell transplantation provided an effective strategy for improving postinfarction ventricular function.展开更多
文摘要素市场扭曲和资源错配是生产率差异的重要来源。破除体制机制障碍,促进要素资源自由有序流动,有利于充分发挥市场配置资源的决定性作用,对助力中国经济高质量发展至关重要。本文在Hsieh and Klenow(2009)的基础上,以可变成本加成率为前提,提出了一种测算要素市场扭曲的新方法,并以中国加入世界贸易组织为准自然实验,系统评估了中间品贸易自由化对要素市场扭曲的影响方向和作用机制。研究发现:(1)中间品贸易自由化水平的提高显著降低了中国要素市场扭曲程度;(2)中间品贸易自由化对要素市场扭曲的改善作用在外商投资、直接进口、资本集中度低的企业中体现更为明显;(3)中间品关税削减幅度更大的地区(地级市),其要素市场扭曲下降更多;(4)降低企业进口要素价格,缓解企业融资约束可能是中间品贸易自由化影响要素市场扭曲的内在机制。本文研究强调了贸易自由化在降低要素市场扭曲、提高资源配置效率方面的重要作用,在当前要素市场化配置改革不断深化的背景下更具现实意义。
基金This work was supported by a grant from the National Natural Science Foundation of China （No. 30470457）.
文摘Background Cell transplantation for myocardial repair is limited by early cell death. Gene therapy with human growth hormone （hGH） has been shown to promote angiogensis and attenuate apoptosis in the experimental animal. This study was conducted to explore the effects of myoblast-based hGH gene therapy on heart function restoration and angiogenesis after myocardial infarction, and to compare the differences between myoblast-based hGH gene therapy and myoblast therapy.Methods Myoblasts were isolated from several SD rats, cultured, purified, and transfected with plasmid pLghGHSN and pLgGFPSN. Radioimmunoassay （RIA） was used to detect the expression of hGH in these myoblasts. SD rats underwent the ligation of the left anterior descending coronary artery so as to establish a heart ischemia model. Thirty surviving rats that underwent ligation were randomly divided into 3 equal groups 2 weeks after left coronary artery occlusion： pLghGHSN group received myoblast infected with hGH gene transplantation; pLgGFPSN group received myoblast infected with GFP gene transplantation; control group： received cultured medium only. Four weeks after the injection the surviving rat underwent evaluation of cardiac function by echocardiography. The rats were killed and ventricular samples were undergone immunohistochemistry with hematoxylin-eosin and factor Ⅷ. Cryosection was analyzed by fluorescence microscopy to examine the expression of green fluorescent protein. Reverse transcriptase-polymerase chain reaction （RT-PCR） was used to examine the mRNA expression of vascular endothelial growth factor （VEGF）, bax and Bcl-2. hGH expression in myocardium was examined by Western blot.Results Myoblast can be successfully isolated, cultured and transfected. The expression of hGH in transfected myoblast was demonstrated with RIA. Four weeks after therapy, the cardiac function was improved significantly in pLghGHSN group and pLgGFPSN group. Fractional shortening （FS） and ejection fraction （EF） in pLghGHSN group were elevated significantly compared with pLgGFPSN group and control group after therapy （FS： 36.9±5.3 vs 29.5±3.5, 21.8±2.9; EF： 56.9±4.3 vs 47.1±3.6, 38.4±4.8, P〈0.05）. Left ventricular end-diastolic dimension （LVEDD） and heart infracted size in pLghGHSN group were decreased significantly compared with pLgGFPSN group and control group after therapy （LVEDD： 5.9±0.3 vs 6.8±0.2, 8.6±0.3; heart infracted size： （34.5±4.2）% vs （40.0±3.9）%, （46.1±3.8）%, P〈0.05）; Green fluorescence was detected in cryosection of pLgGFPSN group. The capillary density of the pLgGFPSN group was significantly greater than those of the pLghGHSN group and control group （P〈0.05）. The mRNA expression of VEGF and Bcl-2/bax in pLghGHSN group was higher than in pLgGFPSN group or control group （P〈0.05）. The expression of hGH clene in myocardium tissue can be detected by Westem blot assay in pLghGHSN group.Conclusions Transplantation of heart cells transfected with hGH induced greater angiogenesis and effect of antiapoptosis than transplantation of cells transfected with GFP. Combined GH gene transfer and cell transplantation provided an effective strategy for improving postinfarction ventricular function.
