| Object:To observe whether the myocardial protective effect of BNP which activatethe cGMP/PKG signaling pathway is associated with the activation of and ERK1/2protein kinase．Methods:84New Zealandwhite rabbits were randomly divided into sevengroups(n=12in each group):sham group,control group,BNP group,BNP+LY294002group (LY294002is phosphatidylinositol3-kinase inhibitor), LY294002group,BNP+PD98059group (PD98059is mitogen-activated protein kinase inhibitor) andPD98059group. Occlusion of the left circumflex artery for45min was followed by180min reperfusion. Rabbits of Sham group were opened chest without ligating theleft circumflex artery;rabbits of control group were infused with physiologicalsaline(0.lml/min) via vein5min before reperfusion; rabbits of BNP group wereinfused with BNP(0.01μg/kg/min) via vein5min before reperfusion; rabbits of BNP+LY294002group were infused with BNP(0.01μ g/kg/min) andLY294002(0.3mg/Kg) via vein5min before reperfusion; rabbits of LY294002groupwere infused with LY294002(0.3mg/Kg) via vein5min before reperfusion;rabbits ofBNP+PD98059group were infused with BNP(0.01μg/kg/min) and PD98059(0.3mg/Kg) via vein5min before reperfusion; rabbits of PD98059group were infusedwith PD98059(0.3mg/Kg) via vein5min before reperfusion.The heart rate and meanarterial blood pressure were recorded during the experiment ahead of ischemia,45minbefore ischemia,60min after reperfusion,120min after reperfusion and180min afterreperfusion;the changes of ECG and the incidence of arrhythmia were observedduring the experiment;At the end of experiment,6rabbit hearts were stained byEvan’s blue/TTC methods to test the area of infarction;Expression of P-Akt/Akt andP-ERK1/2/ERK1/2proteins was analyzed using western blot assay in the rest hearts. Results:1. Hemodynamics: There were no significant difference about HR andMABP at baseline among seven groups(p>0.05).Compared with the baseline, HR andMABP were significantly decreased during ischemia and reperfusion(I/R)period(p<0.05), HR and MABP remained relatively stable during the reperfusionperiod. There were no significant difference in the HR and MABP among sevengroups during the I/R period(p>0.05).2.Arrhythmia: Compared with the control group, the rate of arrhythmia was significantly reduced in BNP Group(p<0.003125). Compared with BNP group, therate of arrhythmia was significantly inceased in BNP+LY294002group, LY294002group, BNP+PD98059group and PD98059group(p<0.003125). Thedifference in arrhythmia between BNP+LY294002group and LY294002group was not statistically significant(p>0.003125). There were also no difference between BNP+PD98059group and PD98059group(p>0.003125).3.Myocardial infarct size:Myocardial infarction did not happen in sham group.Compared with the control group,myocardial infarct size were significantly smaller in BNP Group(p<0.05). Compared with BNP group, myocardial infarct sizewere significantly inceased in BNP+LY294002group, LY294002group, BNP+PD98059group and PD98059group(p<0.05).The difference in myocardial infarct size between BNP+LY294002group and LY294002group was not statistically significant(p>0.05). There were also no difference between BNP+PD98059group and PD98059group(p>0.05).4. The kinase phosphorylation ratio: Compared with the control group, the level of Akt and ERK1/2phosphorylation increased significantly in BNP group(P<0.05).Compared with BNP group, the level of Akt phosphorylation in BNP+LY294002group and the level of ERK1/2phosphorylation in BNP+PD98059group were significantly lower (P <0.05). The difference in Akt phosphorylation between BNP+LY294002group and LY294002group was not statistically significant(p>0.05). There were also no difference in ERK1/2phosphorylation between BNP+PD98059group and PD98059group(p>0.05). Conclusions:1. The activation of the cGMP/PKG signaling pathway by BNP havea protective effect on myocardial ischemia/reperfusion injury.2. The activation of the cGMP/PKG signaling pathway is associated with theactivation of RISK signaling pathway. Object:To observe that BNP activate cGMP/PKG signaling pathway has an impacton the open of mPTP and the phosphorylation of GSK-3β．Methods:48New Zealandwhite rabbits were randomly divided into fourgroups(n=12in each group):sham group,control group,BNP Group and BNP+KT5823group (KT5823is protein kinase G inhibitor). Occlusion of the leftcircumflex artery for45min was followed by180min reperfusion. Rabbits of Shamgroup were opened chest without ligating the left circumflex artery;rabbits of controlgroup were infused with physiological saline(0.lml/min) via vein5min beforereperfusion; rabbits of BNP group were infused with BNP(0.01μg/kg/min) via vein5min before reperfusion; rabbits of BNP+KT5823group were infused withBNP(0.01μg/kg/min) and LY294002(1mg/Kg) via vein5min before reperfusion.Theheart rate and mean arterial blood pressure were recorded during the experimentahead of ischemia,45min before ischemia,60min after reperfusion,120min afterreperfusion and180min after reperfusion;the changes of ECG and the incidence ofarrhythmia were observed during the experiment;At the end of experiment,6rabbithearts were stained by Evan’s blue/TTC methods to test the area ofinfarction;Expression of P-GSK-3β/GSK-3β and cytoplasmic cytochrome c/mitochondrial cytochrome c proteins was analyzed using western blot assay in therest hearts.Results:1. Hemodynamics: There were no significant difference about HR andMABP at baseline among four groups(p>0.05).Compared with the baseline, HR andMABP were significantly decreased during ischemia and reperfusion(I/R)period(p<0.05), HR and MABP remained relatively stable during the reperfusion period. There were no significant difference in the HR and MABP among four groupsduring the I/R period(p>0.05).2. Arrhythmia: Compared with the control group, the rate of arrhythmia wassignificantly reduced in BNP Group(p<0.0125). Compared with BNP group, the rateof arrhythmia was significantly inceased in BNP+KT5823group(p<0.0125).3. Myocardial infarct size:Myocardial infarction did not happen in shamgroup.Compared with the control group,myocardial infarct size were significantlysmaller in BNP Group(p<0.05). Compared with BNP group, myocardial infarct sizewere significantly inceased in BNP+KT5823group(p<0.05).4. The kinase phosphorylation ratio: Compared with the control group, the level of GSK-3β phosphorylation increased significantly and cytoplasm cytochromec/mitochondrial cytochrome c reduced significantly in BNP group(P <0.05).Compared with BNP group, the level of GSK-3β phosphorylation were significantly lower and cytoplasm cytochrome c/mitochondrial cytochrome c increased significantly in BNP+KT5823group (P <0.05).Conclusions:1. The myocardial protective effect of BNP which activate thecGMP/PKG signaling pathway is associated with inhibition of mPTP.2. The activation of the cGMP/PKG signaling pathway can promote the phosphorylation of GSK-3β. |
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