Beneficial Effect And Mechanism Of IMD1-53 On Cardiac Function After Septic Shock In Rats

Sepsis is a severe disease which would lead to the serious problems such as septic shock and mutiple organ dysfunction even death without immediate treatment, and it remains the major cause of mortality in the intensive care units. Cardiac dysfunction is the major cause of organ failure after sepsis, when accompanied by cardiac dysfunction after sepsis, the mortality rate is as high as 70%. So far there is no effective treatment for this complication.Intermedin(IMD), a family member of calcitonin gene-related peptide, has been confirmed that it can be degradated to IMD1-53 in vivo, the activity fragment of IMD. Previous research confirmed IMD1-53 had a protective effect on myocardium after ischemia reperfusion, and the protective effect was mainly related to its antioxidative effect and cell apoptosis inhibition effect. While whether IMD1-53 has protective effect on myocardial contractile function after septic shock, and the mechanisms, are not clear.So, using septic shock model of rat cardiac muscle and cardiac myocytes, we investigated the protective effects and the mechanism of IMD1-53 on myocardial contractile function after septic shock.The main research content:Experiments were divided into three parts:(1)with septic shock rats, isolated cardiac papillary muscle and cardiac myocytes, the beneficial effects of IMD1-53 on myocardial contractile function after septic shock were observed;(2)the protection mechanism of IMD1-53 on myocardial contraction after septic shock in calcium and calcium sensitivity pathway were observed in vivo and in vitro;(3)investigated whether IMD1-53 play overvall effect on septic shock rats via the cardiac contractile function protection.The main experimental methods:(1) Rat septic shock model was produced by cecal ligation and puncture(CLP);(2) The effects of IMD1-53 on cardiac contractile function were determined by observing the effects of IMD1-53 on cardiac papillary muscle and cardiac myocytes to isoprenaline;(3)The phosphorylation of troponin(Tn I) and Tn I, the expression of Rho kinase and large conductance Ca2+-activated K+ channel(BKCa) were measured by western blot;(4)BKCa channel current was measured by the patch clamp.The main results:PartⅠ: The protective effect of IMD1-53 on myocardial contractile function after septic shock1. Cardiac function was significantly impaired after septic shock. It appeared the cardiac output(CO), cardiac index(CI) and stroke index(SI) were significantly decreased; IMD1-53(0.5μg/kg, iv) could significantly improve the CO, CI and SI.2. The contractile response of septic shock rats on cardiac papillary muscle to isoprenaline was significantly decreased; after administration of IMD1-53, the contractile response was significantly improved.3. After septic shock, the myocardial contractility of myocardial cell to electrical stimulation(0.5Hz, 5ms) was significantly decreased; after administration of IMD1-53, the myocardial contractility of myocardial cell was significantly improved.These results indicated that IMD1-53 had the protective effect on myocardial contractile function after septic shock.PartⅡ: The protective mechanism of IMD1-53 on myocardial contractile function after septic shock1. The relationship between the protective effect of IMD1-53 on myocardial contraction and the expression of Rho kinase/Tn I phosphorylationThe results showed that after septic shock, the expression of Rho kinase was significantly decreased and the phosphorylation of Tn I was significantly increased; the contractile function of cardiac papillary muscle to isoprenaline was significantly decreased; IMD1-53 increased the expression of Rho kinase and decreased the phosphorylation of Tn I, and increased contractile function of cardiac papillary muscle; Rho kinase inhibitor Y27632(10-5mol/L) significantly antagonized the increased contractile function of cardiac papillary muscle induced by IMD1-53.2. The relationship between IMD1-53 protecting myocardial contractile function and BKCaThe expression of BKCa had no significant change after septic shock and IMD1-53 adminstration in vivo experiment. But in myocardial cell in vitro, the BKCa channel was obviously opened after LPS(100μg/ml) stimulation, the current of BKCa was significantly increased. IMD1-53 could decrease the increased the current of BKCa channel induced by LPS. Meanwhile, the opener agent of BKCa(NS1619, 300μmol/L) could inhibit IMD1-53 induced increased of myocardial constratile function in septic shock rats.PartⅢ:The overall protective effect of IMD1-53 on septic shock1. Effect of IMD1-53 on oxygen delivery, oxygen consumption, organ blood flow and blood gas after septic shockAfter septic shock, the oxygen delivery, oxygen consumption and the blood flow of liver, kidney and intestine were significantly decreased, IMD1-53(0.5μg/kg) could significantly improve these parameters, as compared with septic shock. Meanwhile IMD1-53(0.5μg/kg) could increase the Pa O2 and Sa O2 of septic shock rats.2. Effect of IMD1-53 on survival time and survival rate in septic shock ratsThe survival time and survival rate were significantly shortened after septic shock(5.1h±8.3h,0/16). IMD1-53(0.5μg/kg) could obviously prolong the survival time(25.8h±50.4h,19.6h±56.6h), and increase survival rate(5/16,4/16).Conclusion:1. IMD1-53 has good protective effect on cardiac contractile function in septic shock, and by this effect, plays overall protective effect on septic shock animals.2. The mechanism that IMD1-53 protects the myocardial contractile function is mainly related to Rho kinase/Tn I phosphorylation and BKCa ion channel. It realizes this effect mainly via increased of Rho kinase and Tn I phosphorylation, and inhibition of BKCa open.