Effects Of Metformin On The Cardiac Function Mitochondrial Membrane Potential And AMPK In Endotoxemic Rats

1. Experimental background:Metformin is widely used in diabetes patients, but more and more research shows that metformin has protective effect to the heart function of patients who has myocardial infarction and myocardial ischemia reperfusion. But the influence of metformin to the heart function, mitochondrial membrane potential and AMPK activity of sepsis patients is still not clear.2. Expenment purpose:The purpose of this study was to investigate the effects of Metformin on the cardiac function,mitochondrial membrane potential and AMPK/P-AMPK activity in endotoxemic rats.3. Experimental methods:The rats were randomly divided into4groups:Sham, Sham treated with Metformin(Shame/M),LPS,LPS pretreated with Metformin (LPS/M).And the endotoxemia model is builded by injecting lipopolysaccaride (LPS) into caudal vein.While rats in Metformin treatment group (LPS/M) and Sham treated with Metformin group (Shame/M) were received a dose of200mg/kg metformin by intraperitoneal injection half an hour before LPS and physiological saline injection respectively. All experiment groups were subdivided into three subgroups (2,6and24 hour subgroup, n=6in each group).That is to say,rats in this study were sacrificed after measurements of heart function at2h,6h, or24h after tail intravenous administration,and cardiac muscle sampled,then we measured the mitochondrial membrane potential and the activity of AMPK/P-AMPK in each group.4. Results:4.1. Heart function:no cardiac function variables were detected when rat hearts were only treated by metformin at any one time. However, the marked drawdown of cardiac performance, such as LVSP and the maximum rate of rised left ventricular pressure, the maximum rate of decreased left ventricular pressure (±dP/dt max), in all LPS treated groups were observed comparing with those in control groups (sham groups). The levels of LVSP and±dP/dt max were dropped after2hours injection of LPS, got to the trough at6hour, then followed to rise again at24hour.(3913.242±104.094),(2006.383±126.316),(2550.230±29.886)VS(4372.429±171.692)(P<0.05);(-3337.051±125.594),(-1845.341±90.094),(-2394.306±115.501)VS(-3939.804±217.561)(P<0.05);(88.4514±2.926),(65.1198±4.794),(83.1238±4.220)VS(108.4990±5.546)(P<0.05).But in LPS/M group group, lower LVSP,+dp/dtmax levels were showed compairing with those in control group and M group,while significant increases in the recovery of LVSP and±dp/dt max were all observed comparing with those in LPS group at2,6,24hour separately.(4080.278+73.497),(2296.247+137.702),(3166.941+124.915) VS (4372.429±171.692)(P<0.05);(-3682.225±117.279),(-2196.585±100.571),(-2758.821±68.675) VS (-3939.804±217.561)(P<0.05);(96.4428±2.756)(74.4502±3.926)(82.3974±4.125) VS (108.4990±5.546)(P<0.05).4.2.Mitochondrial membrane potential measurement:mitochondrial membrane potential of LPS group decreased at three observation point(2h,6h,24h) compair with normal control group, and the levels of mitochondrial membrane potential got to the trough at6hour,then risen slightly at24h observation point(P<0.05). And the mitochondrial membrane potential both rise obviously at2h and6h time point in LPS/M group compaired with LPS group. There are no difference between LPS/M24h group and LPS24h group.4.3.Western blot:The activity of AMPK has no significant change at2h time point in each group(P>0.05),but the LPS group and LPS/M group has a increased activity of P-AMPK than normal control group (P<0.05),and the P-AMPK levels of LPS/M group is higher than LPS group;In6hours time point,AMPK has no significant change. And both the P-AMPK activity of LPS group and LPS/M group increased significantly compair with normal control group(P<0.05),beside the LPS/M group has a higher P-AMPK level than LPS group.No significant change of AMPK activity between each group in24h time point(P>0.05),and there are also significantly increased P-AMPK activity of LPS group and LPS/M group(P<0.05),and the P-AMPK activity of LPS/M group is higher than LPS group.5. Conclusion:5.1LPS can depress the cardiac function of SD rats, characterized by the reduced±p/dtmax and LVSP after injection of LPS. LPS/M group have a higher±dp/dtmax and LVSP than LPS group at the same observation point. Suggests that metformin could improve the cardiac function of endotoxemic rats.5.2Metformin can improve the mitochondrial membrane potential of endotoxemic rats.5.3Metformin can increase the activity of AMPK phosphorylation levels.