Remote preconditioning provides myocardial protection against myocardial ischemia/reperfusion injury through downregulating the expression of calreticulin in rats

AIM: To evaluate the role of calreticulin (CRT) in myocardial protection of remote preconditioning against myocardial ischemia/reperfusion injury. METHODS: Thirty SD rats were randomly divided into 5 groups: ischemia reperfusion group (IR), ischemia preconditioning group (IP), remote preconditioning group Ⅰ (RPI), remote preconditioning group Ⅱ (RPII) and pseudo-operation group (PO). The ischemia/reperfusion model was established in vivo. Hemodynamic changes of heart function were observed. Serum cardiac troponin T (cTnT), superoxide dismutase (SOD), malondialdehyde (MDA) and the expression of calreticulin in myocardium were detected. RESULTS: Hemodynamic data, serum cTnT, DA, SOD and the expression of CRT in RPI and IR group were not statistically different (P>0.05). SOD level in IP and RPII group was higher than that in IR group (P<0.05). Accordingly, cTnT, MDA and the expression of CRT in these two groups were lower than those in IR group (P<0.05). CONCLUSION: Remote preconditioning may mimic the protective effect of ischemic preconditioning. Remote preconditioning attenuates myocardial ischemia/reperfusion injury in vivo possibly through down-regulation of CRT expression in rats.     

Effects of ischemic preconditioning on oxidative stress and mitochondrial function in young and old rat myocardium with ischemia/reperfusion

AIM: To study the protective effect of ischemia preconditioning (IPC) on ischemia/reperfusion (IR)-damaged myocardium in young and old rats. METHODS: Male Wistar rats aged at 3 months (young) and 20 months (old) were used to establish myocardial IPC model and IR model with the method of Langendorff heart perfusion. The rats were divided into young ischemia/reperfusion (YIR) group, young ischemic preconditioning (YPC) group, old ischemia/reperfusion (OIR) group and old ischemic preconditioning (OPC) group. Transmission electron microscopy was used to observe the ultrastructural changes of myocardial tissue and myocardial mitochondria. The myocardial infarction area was determined by TTC staining. The lactate dehydrogenase (LDH) content in coronary effluent fluid and the levels of superoxide dismutase (SOD) and malondialdehyde (MDA) in myocardial tissues were detected by the method of colorimetry. The levels of nitrated and carbonylated proteins in myocardial tissue were measured by ELISA. The myocardial cell apoptosis was analyzed by TUNEL assay. The mitochondrial respiratory function and mitochondrial permeability transition pore opening induced by calcium load were evaluated by oxygen electrode method. RESULTS: Compared with YIR group, the myocardial infarction area in YPC group was obviously smaller, SOD activity in myocardial tissues increased, LDH activity in coronary effluent fluid and the content of MDA decreased, and the levels of nitrated and carbonylated proteins in the cardiac tissues reduced. In YPC group, the mitochondrial membrane structure appeared intact, cristae of the mitochondria showed close arrangement, and the matrix was compressed under the electron microscope. Myocardial mitochondrial respiratory control rate, state Ⅲ oxygen consumption and the P/O ratio in YIR group all significantly increased, proton leak decreased, mitochondrial swelling induced by calcium distinctly reduced, and myocardial apoptosis rate declined. No significant difference of the above indexes between OIR group and OPC group was observed. Compared with YPC group, myocardial ultrastructural damage increased clearly, cardiac oxidative stress increased, mitochondrial respiratory function declined, and cell apoptosis and necrosis increased in OPC group. CONCLUSION: Ischemic preconditioning has protective effect against myocardial IR injury in young rat hearts, while old rat hearts were less sensitive to ischemic preconditioning, leading to bluntness of cardioprotection with IPC in aging hearts. This may be related to mitochondrial injury and severe cellular apoptosis caused by increase of cardiac oxidative stress levels in the aging ischemic preconditioning heart.     

Effects of adiponectin on expression of connexin 43 in rat myocardium during ischemia-reperfusion

AIM: To observe the effects of adiponectin(APN) on the expression of connexin 43 (Cx43) in rat myocardium during ischemia-induced arrhythmias. METHODS: The SD rats were randomly divided into 4 groups (n=12): sham operation group (SM group), ischemia and reperfusion group (I/R group), I/R+adiponectin(APN1) group: pre-ischemia with 3.5 μg/kg of APN; I/R+APN2 group: post-ischemia with 3.5 μg/kg of APN. The incidence of ventricular arrhythmias and ventricular arrhythmia score (VAS) were determined. The expression of Cx43 in the ischemic myocardium was studied by the techniques of immunohistochemistry and RT-PCR. The levels of malondialdehyde(MDA) and superoxide dismutase(SOD) were measured by the methods of xanthine oxidase and thiobarbituric acid. The expression of endothelial nitric oxide synthase (eNOS) at mRNA and protein levels was determined by RT-PCR and Western blotting,respectively.The morphological changes of the myocardial tissues were observed under electronic microscope. RESULTS: The VAS and concentration of MDA increased obviously and the activity of SOD was decreased in I/R group as compared with SM group (P<0.01). The expression of Cx43 was evidently decreased and the distribution of Cx43 in the myocardium was disturbed. The expression of eNOS at mRNA and protein levels was decreased in I/R group (P<0.05). The ultrastructure of ventricular myocardium was abnormal in I/R group. Compared with I/R group, APN obviously decreased the VAS caused by ischemia and reperfusion (P<0.01) no matter the drug was given before or after ischemia. APN increased the activity of SOD, inhibited the MDA content in serum, and resulted in normal distribution of Cx43 and increased the expression of Cx43 and eNOS. Compared with I/R group, the changes of heart ultrastructure attenuated greatly in APN group, but didn't recover to normal state. CONCLUSION: Adiponectin antagonizes the arrhythmias during myocardial ischemia and reperfusion via inhibiting oxidative stress and regulating Cx43.     

Effect of ischemic preconditioning on myoelectricity and the structure of myocardial gap junction during heart valve replacement surgery

AIM: To investigate the cardio-protective mechanism of ischemic preconditioning (IP) during heart valve replacement of the perspective of architectural changes of myocardial gap junction. METHODS: Fifty-four patients were prospectively randomized to receive or not ischemic preconditioning before cold cardioplegic arrest. The IP protocol in IP patients (n=22) consisted of a single 2-minute ischemia followed by 3-minute reperfusion just before aortic clamping and cold crystalloid cardioplegia for myocardial protection. The control group (n=32) received no ischemic preconditioning prior to cold cardioplegic arrest. The parameters including arrhythmias occurrence, Cx43 expression (immunohistochemistry SABC method) and myocardial structure and intercalated discs observed under electronic microscope were recorded before and after surgery in each group. RESULTS: In IP group, one case (4.55%) of ventricular arrhythmia (sporadic ventricular premature beat), 11 cases (50.00%) of supraventricular arrhythmia (atrial fibrillation, atrial flutter, supraventricular tachycardia, atrioventricular block) and 10 cases (45.50%) of ischemic ST-T changes were observed. In control group, there were 14 cases (43.75%) of ventricular arrhythmia (ventricular premature beat, tachycardia), 18 cases (56.25%) of supraventricular tachycardia and 28 cases (87.50%) of ischemic ST-T changes. No statistical difference in preoperative positive unit of Cx43 expression between the two groups was found (P>0.05). Postoperatively, the positive unit of Cx43 expression in IP group was 16.15±4.40, but the difference was not significant compared to the preoperative value (P>0.05). In control group, Cx43 expression was 11.92±1.26, significantly lower than that of the preoperative value (P<0.05). Cx43 expression between the two postoperative groups showed a significant difference (P<0.05). In control group, electronic microscopic observation revealed disrupted intercalated discs, with some partially or even totally ruptured and disintegrated. Enormous necrotic structural changes of myocardial fibers were also observed, including swelling, dissolution and disorganization of myofilaments and fibers, widening of the Z striae and disorganization. However in IP group, the intercalated discs appeared intact, continuous with normal myocardial structure. CONCLUSION: IP maintains normal expression of the myocardial junctional gap protein Cx43, which preserves a seamless intercellular gap junction and a normal myocardial electric conduction activity.     

Effects of glucagon-like peptide-1 on myocardial ischemia-reperfusion/hypoxia-reoxygenation injury in rats

AIM: To investigate the effects of glucagon-like peptide-1 (GLP-1) on myocardial ischemia-reperfusion (IR)/hypoxia-reoxygenation (HR) injury in rats. METHODS: Sprague-Dawley rats were randomly divided into 5 groups: sham group, IR group and IR+GLP-1 (0.03 nmol/L, 0.16 nmol/L and 0.30 nmol/L) groups. IR group and IR+GLP-1 group were subject to 30 min of ischemia and 3 h of reperfusion. The myocardial infarct size, the ultrastructural changes of the myocardial tissues, the apoptosis of the cardiomyocytes, the activity of superoxide dismutase (SOD) and the concentration of malondialdehyde (MDA) were detected. Primarily cultured cardiomyocytes were divided into 5 groups at random: control group, HR group and HR+GLP-1 (1 μmol/L, 5 μmol/L and 10 μmol/L) groups. The morphology and apoptosis of the cardiomyocytes were observed. The levels of lactate dehydrogenase (LDH),MDA,SOD,reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) in different groups were detected. RESULTS: Compared with IR group, the myocardial infarct size and cardiomyocyte apoptosis were remarkably reduced, mitochondrial ultrastructures were improved, the activity of SOD was increased and the concentration of MDA was decreased in IR+GLP-1 (0.03 nmol/L, 0.16 nmol/L and 0.30 nmol/L) groups. Compared with HR group, GLP-1 (1 μmol/L, 5 μmol/L and 10 μmol/L) preconditioning significantly decreased the myocardial injury, increased SOD activity, decreased MDA concentration and ROS production, and heightened MMP in a dose-dependent manner. CONCLUSION: GLP-1 protects cardiomyocytes from IR/HR injury, which may be partially due to the effects of anti-oxidative mechanism and the function of mitochondrial protection.     

Effects of Liqustrazin on respiratory enzymes in the myocardial mitochondria of the ischemia-reperfusion rats

AIM: To study the effects of Liquestrazin on succinic dehydrogenase (SDH) and cytochrome oxidase (CCO) in the myocardial mitochondria of the ischemia-reperfusion rats and its mechanism. METHODS:Model of myocardial ischemia-reperfusion injury was produced by coronary artery ligation . The rats were devided into sham operation control (SC), ischemia-reperfusion (IR) and ischemia-reperfusion protected with Liqustrazin (IR+L) group . Activity of SDH,CCO,SOD and GSH·PX and contents of malondialdehyde (MDA),Cyt aa₃,Cyt c and phospholipid(PL) were observed respectively . RESULTS: As compared with ischemia-reperfusion group (IR), IR+L group showed significantly increased activity of SDH, CCO,SOD and GSH·PX (P＜0.01) , MDA content decreased significantly , the contents of Cyt aa₃ , Cyt c and PL increased respectively . CONCLUSION : Liqustrazin has notable antagonistic effects on decrease in SDH and CCO activities in the myocardial mitochondria of the ischemia-reperfusion rats , which is due to its oxygen free radicals scavenging action and its anti-lipid peroxidation reaction.     

Effects of maternal limb ischemic preconditioning on structural and functional changes of mitochondria in fetal hippocampal neurons induced by intrauterine distress-reoxygenation in rats

AIM: To investigate the effects of maternal limb ischemic preconditioning (LIP) on the mitochondrial structures and functions of the hippocampal neurons induced by reoxygenation in the intrauterine distress fetal rats. METHODS: Pregnant rats (n=40) were randomly divided into 4 groups: sham (S) group, LIP group, fetal distress (FD) group and LIP+FD group. Intrauterine ischemia model was established through the experimental design. The ultrastructure of the mitochondria in CA1 area of the hippocampus was observed. The mitochondrial membrane potential and reactive oxygen species (ROS) were measured. The content of ATP and MDA in the hippocampus tissue was detected. The activity of Mn-SOD was observed. RESULTS: Compared with sham group, the ultrastructure of mitochondria in CA1 area of the hippocampus was damaged in FD group and LIP+FD group. The mitochondrial membrane potential, the content of ATP and the activity of Mn-SOD were decreased. However, the content of ROS and MDA was increased. Compared with FD group, the ultrastructure of mitochondria in CA1 area of the hippocampus was intact in LIP+FD group. Furthermore, the reduced mitochondrial membrane potential and ATP content were inhibited. The activity of Mn-SOD was increased, but the content of ROS and MDA was decreased in LIP+FD group. CONCLUSION: Limb ischemia preconditioning inhibits the damage the mitochondria of fetal hippocampal neurons induced by reoxygenation in the intrauterine distress fetal rats.     

Protective role of carnosine on cardiac dysfunction in type 1 diabetes mellitus rat model

AIM:To explore the effects of carnosine (CAR) on cardiac dysfunction in type 1 diabetic mellitus rats and the underlying mechanism. METHODS:The SD rats were randomly divided into 4 groups:control (C) group, control+carnosine (C+CAR) group, diabetes mellitus (DM) group and diabetes mellitus+carnosine (DM+CAR) group (n=10). The rats were sacrificed after 12 weeks. The cardiac function was assessed by ventricular cannulation. The activity of superoxide dismutase (SOD) and the content of malondialdehyde (MDA) were assessed by ELISA. The mRNA levels of tumor necrosis factor α(TNF-α), interleukin-1β(IL-1β) and IL-6 were measured by real-time PCR. The distribution of connexin 43 (Cx43) was examined by immunofluorescence. The protein levels of Cx43 and protein kinase C (PKC) were determined by Western blot. RESULTS:Compared with the C group, the left ventricular end diastolic pressure (LVEDP) was increased whereas the left ventricular pressure maximum rise/fall velocity (±dp/dt_max) was decreased in the DM group (P<0.01). The activity of SOD decreased while the MDA increased in the left ventricular tissues (P<0.01). The mRNA levels of TNF-α, IL-1β and IL-6 were increased (P<0.01). The Cx43 distribution was irregular. The protein levels of phosphorylated Cx43 and PKCε were elevated (P<0.01). Compared with the DM group, the cardiac function of LVEDP and ±dp/dt_max in DM+CAR group was ameliorated (P<0.01), with increased SOD activity and decreased MDA content (P<0.05). The mRNA levels of TNF-α, IL-1β and IL-6 were reduced (P<0.01). The Cx43 distribution was improved and the protein levels of phosphorylated Cx43 and PKCε were decreased (P<0.01). CONCLUSION:CAR treatment can improve the cardiac function by its anti-oxidative and anti-inflammation effects and suppression of Cx43 abnormalities through PKCε in DM rats.     

Role of apelin in rat myocardial ischemic preconditioning and ischemia/ reperfusion injury

AIM: To study the alteration and role of apelin in myocardial ischemic preconditioning and ischemia/reperfusion injury of rats.METHODS: Forty-five SD rats were randomly divided into three groups: ischemia/reperfusion group (IR),ischemia pre-conditioning group (IP) and sham operation group.ECG was continuously used to evaluate the score of arrhythmias.The protein levels of apelin-36 in myocardium and plasma were detected by radioimmunoassay.The expression of apelin was observed by immunohistochemistry.RESULTS: (1) The scores of arrhythmias in IP group (2.1±0.5) was only 58.3% of IR group (3.6±0.8) ( P<0.01).(2) The apelin-36 protein level of plasma and myocardium in IR group were respectively lower by 36.1% and 45.6% than those in SH group (P<0.01),and those in IP group were lower by 23.8% and 24.7% than those in SH group (P<0.01),but higher than those in IR group (18.9% and 38.5%,respectively,P<0.05).(3) The staining absorbance of apelin in IR,SH and IP group was (7.87±2.41),(22.53±2.54) and (14.23±2.15),respectively.There were significant differences between IR and SH (P<0.01) and between IP group and SH group (P<0.05).(4) The scores of arrhythmias in IP and IR were negatively correlated with the protein level of apelin-36 in myocardium (r= 0.847,P <0.01).CONCLUSION: The down-regulation of apelin-36 in the plasma and myocardium of rats indicates that apelin has an important role in myocardial ischemic preconditioning and ischemia/reperfusion injury.     

Effect of L-arginine on function and structure of mitochondria in ischemia-reperfusion myocardial cells in rabbits

AIM: To study the effect of L-arginine (L-Arg) on function and structure of mitochondria in ischemia-reperfusion (MRI) myocardial cells. METHODS: Thirty rabbits were randomly divided into three groups (n=10 in each), control group, MIR group and MIR+L-Arg group. The mitochondrial respiratory function, Ca²⁺ concentration ([Ca²⁺]m), malondialdehyde (MDA) content and superoxide dismutase (SOD) activity were determined. Meanwhile, the contents of adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), total adenylic acid number (TAN) and energy charge (EC) in the myocardial tissue were respectively measured. Moreover, the ultrastructure changes in myocardial mitochondria were observed during MIR. RESULTS: The mitochondrial respiratory control rate (RCR), velocity 3 (V₃), SOD, surface density (Sv) and specific surface (δ) in MIR+L-Arg group were higher than those in MIR group, velocity 4 (V₄), [Ca²⁺]m, MDA, volume density (Vv), horizental diameter (Hd) were lower than those in MIR group. ATP, ADP, TAN and EC levels of myocardial tissue were higher than those in MIR group. There was no significant difference between MIR+L-Arg and control group in V₃, V₄, SOD, MDA, Vv, Sv, δ, Nv, Vd, AMP and TNA. CONCLUSION: It is suggested that L-Arg improves the function and structure of mitochondria in myocardial cells in the reperfusion injury after myocardial ischemia by decreasing oxygen free radical level and Ca²⁺ overload in the mitochondria.     

Recent research advance in mitochondria Cx43 and its cardiovascular effects

Connexins are transmembrane proteins. The best-known function of connexins is to form gap junction channels. Cardiomyocytes predominantly express connexin 43 (Cx43). Recent studies show that Cx43 is not only present at the sarcolemma but is also detected in mitochondria of cardiomyocytes, at least in part in the inner mitochondrial membrane. Mitochondrial Cx43 plays a central role for triggering/mediating the cardioprotection by ischemic preconditioning (IPC), however the molecular mechanisms have not been elucidated in detail. The present article reviews the available evidence on the localization, the mechanism of transport, the phosphorylation status, the affecting factors and the physiological role of mitochondrial Cx43. These findings open a new field for investigating the previously unsuspected roles of Cx43 in mitochondria about their functions, regulation and molecular mechanisms involved in pathophysiology not only in myocardial ischaemia-reperfusion injury but also in other conditions in the cardiovascular system and beyond.     

Effects of urocortin-I preconditioning on myocardial mitochondrial respiratory function and enzyme activity in rats

ATM: To investigate the influence of urocortin-I (Ucn I) preconditioning on the myocardial mitochondrial respiratory function and enzyme activity in the rats with ischemia reperfusion, and to observe the changes of ATP content in the myocardial cells. METHODS: (1) The healthy male Sprague-Dawley rats were randomly divided into 4 groups:normal group (Nor group), ischemia reperfusion group (IR group), Ucn I preconditioning group (Ucn I group), 5-hydroxy acid (5-HD)+Ucn I group. Langendorff perfusion was used to establish the in vitro model of cardiac ischemia reperfusion. At the end of the balance (T₁), before ischemia (T₂) and at the end of the reperfusion (T₃) respectively, the myocardial mitochondria was extracted, the mitochondrial respiratory function and respiratory enzyme activity in each group were determined. (2) The method of MPA isolated heart perfusion was used to isolate myocardial cells of the adult rats. After cultured for 24 h, myocardial cells were divided into 4 groups:Nor group, hypoxia/reoxygenation group (I/R group), Ucn I group, 5-HD+Ucn I group. Hypoxia/reoxygenation model of myocardial cells was established. At the end of reoxygenation, the changes of myocardial ATP content were measured by high performance liquid chromatography.RESULTS: (1) Compared with T₁, T₂ time points, the respiratory function (state 3 respiratory rate, respiratory control rate) and NADH oxidase, succinate oxidase and cytochrome C oxidase activities at T₃ time point were significantly decreased (P<0.05) in all groups except Nor group. At T₃ time point, the myocardial mitochondrial respiratory function and respiratory enzyme activity in Ucn I group were superior to 5-HD+Ucn I group and IR group (P<0.05), but was inferior to Nor group (P<0.05). At T₃ time point, the respiratory function of myocardial mitochondria and respiratory enzyme activities (NADH oxidase, succinate oxidase) in 5-HD+Ucn I group were better than those in IR group (P<0.05), but no statistical difference of the cytochrome C oxidase activity between the 2 groups was observed. The respiratory function and 3 kinds of respiratory enzyme activities at T₁, T₂ time points had no statistical change. (2) At the end of the reoxygenation, the myocardial ATP content in Nor group was higher than that in other groups (P<0.01). The myocardial ATP contents in I/R group and 5-HD+Ucn I group were lower than that in Ucn I group (P<0.05). In additon, 5-HD+Ucn I group was higher ATP content compared with I/R group (P<0.05). CONCLUSION: Ucn I preconditioning attenuates the ischemia/reperfusion induced damages of myocardial mitochondrial respiratory function and respiratory enzyme activity, thus ensuring the myocardial ATP contents under the condition of hypoxia/reoxygenation.     

Effects of simvastatin on expression of Bcl-2 and Bax in myocardium of rats with renal ischemia-reperfusion injury

AIM: To observe the effect of simvastatin on myocardial tissue after renal ischemia-reperfusion injury and its mechanism. METHODS: A rat model of renal ischemia-reperfusion injury was prepared by clamping the bilateral renal arteries for 45 min. The rats (n=36) were randomly divided into sham operation group, renal ischemia-reperfusion (I/R) group and simvastatin group with 12 rats in each group. The content of serum creatinine (SCr), blood urea nitrogen (BUN) and myocardial tissue malondialdehyde (MDA), the myocardial activity of lactate dehydrogenase (LDH), creatine kinase (CK) and superoxide dismutase (SOD), and the myocardial protein expression of Bcl-2 and Bax were detected. RESULTS: Compared with sham operation group, the content of SCr, BUN and myocardial MDA, and the myocardial activity of LDH and CK in I/R group were significantly increased (P<0.05), and the activity of SOD was significantly decreased (P<0.05). Compared with I/R group, the content of SCr, BUN and myocardial MDA, and the myocardial activity of LDH and CK in simvastatin group were significantly decreased (P<0.05), while SOD activity was enhanced (P<0.05). The protein expression of Bcl-2 and Bax in sham operation group was less than that in I/R group (P<0.05), and the protein level of Bax in simvastatin group was significantly lower than that in I/R group (P<0.05), while the protein level of Bcl-2 was increased (P<0.05). CONCLUSION: Simvastatin has a protective effect on the myocardium of the rats with renal ischemia-reperfusion injury, and the protective mechanism may be related to the elimination of free radicals by simvastatin, increase in the protein expression of Bcl-2 and decrease in the protein expression of Bax.     

Oxygen free radical injury of myocardial mitochondria in the experimental type 2 diabetic rats

AIM: To study the mechanism of diabetic cardiomyopathy and abnormality of oxygen free radicals. METHODS: The contents of myocardial cytosolic cytochrome C, mitochondria cytochrome C, mitochondrial calcium, NO, MDA and the activity of SOD and NOS were determined in diabetic rats induced by STZ. The pathological changes were observed under transmission electron microscope. RESULTS: Compared to the normal and ganoderma group, the levels of mitochondrial NO, iNOS, MDA, calcium and plasma Cyt-C in rat myocardium were higher (P<0.05), while mitochondrial Cyt-C and SOD were lowered in model group (P<0.05). The bouncary indistinct, disorganization, a focal loss of muscular fibril, myocardium mitochondria swelling, pulmonary vascular endothelial cellular swelling and obstructed lumen of the capillary were also observed under transmission electronic microscope. CONCLUSION: The findings indicate that oxyradical and lipid peroxidation might be associated with the damage of myocardial mitochondria in NIDDM rats. Cyt-C and mitochondrial calcium is also involved in the process.     

Ischemic postconditioning reduces myocardial damage in rats suffering from limb ischemia-reperfusion

AIM: To investigate the protective effect of limb ischemic postconditioning on the myocardial damage in the rats suffering from limb ischemia-reperfusion (LIR). METHODS: Wistar rats were randomly divided into control group (C group), ischemia-reperfusion group (IR group) and ischemic post-conditioning group (IR+IPostC group). For conducting ischemic postconditioning, the rats in IR+IPostC group underwent 5 min of ischemia and 5 min of reperfusion on their hind limbs repeatedly after 4 h of ischemia, and then, 4 h of reperfusion was applied. The activity of superoxide dismutase (SOD), xanthine oxidase (XOD) and myeloperoxidase (MPO) was measured. The levels of malonaldehyde (MDA) in plasma and myocardial tissues, the levels of creatine kinase (CK), creatine kinase MB (CK-MB), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), α-hydroxybutyrate dehydrogenase (α-HBDH) and myocardial troponin I (cTnI) were also detected. The changes of ultrastructure in the myocardium were observed under electron microscope. RESULTS: Compared with C group,the levels of CK-MB, AST, LDH,α-HBDH and cTnI were all increased in IR and IR+IPostC groups. The levels of MDA and XOD also increased (P<0.05), but the activity of SOD decreased (P<0.05). However, compared with group IR, the levels of CK-MB, AST, LDH, α-HBDH and cTnI decreased (P<0.05) in IR+IPostC group.The levels of MDA and XOD also decreased (P<0.05), but the activity of SOD increased (P<0.05). Under electron microscope, the cardiac myofibrils arranged neatly, light and dark bands were clear, the mitochondrial cristae arranged closely and neatly, and the mitochondrial matrix densification was observed in C group. However, the cardiac fiber arrangement was disordered or disappeared, stromal edema was obvious, most or all mitochondrial cristae and membrane became fusion or disappeared, mitochondrial vacuolization and decrease in glycogen were obvious in IR group. In IR+IPostC group, the pathological changes mentioned above were attenuated somewhat than those in IR group. CONCLUSION: Ischemic postconditioning protects rat myocardium under limb ischemia-reperfusion.     

Protective effect of ischemic-preconditioning under the mild hypothermia against small intestine ischemia-reperfusion injury in rats

AIM: To investigate the protective effect of ischemic-preconditioning under the mild hypothermia against small intestine ischemia-reperfusion injury in rats and its mechanism. METHODS: Thirty-two rats were randomized into 4 groups (8 rats in each group): sham operated group (Sham), ischemia-reperfusion (I/R) group, ischemic-preconditioning (IP) group, mild hypothermia ischemic-preconditioning (MHIP) group. The wet/dry ratio, Ca²⁺-Mg²⁺-ATPase activity in intestine tissue, the malondialdehyde (MDA) content, activities of lactate dehydrogenase (LDH), superoxide dismutase (SOD) and total antioxdase (TAX) in blood were determined. Ultrastructure, Bcl-2 and Bax expression in intestinal mucosa tissue were also observed. RESULTS: After I/R, the intestinal tissue wet/dry ratio, the content of MDA, LDH activity, the optic density of Bcl-2 and Bax proteins were significantly higher in I/R group than those in sham group (P<0.01). The activities of Ca²⁺-Mg²⁺-ATPase, SOD, TAX were significantly lower in I/R group than those in sham group (P<0.01). The intestinal tissue wet/dry ratio, the content of MDA, LDH activity and the optic density of Bax protein were significantly lower in IP group than those in I/R group (P<0.01), and also lower in MHIP group than in IP group (P<0.05). The activities of Ca²⁺-Mg²⁺-ATPase, SOD, TAX and the optic density of Bcl-2 protein were significantly higher in IP group than in I/R group (P<0.01). CONCLUSION: MHIP can protect intestine against I/R injury in rats, which may be related to enhancing oxidation-resistance of intestine, inhibiting lipid peroxidation, upregulating the expression of Bcl-2 protein and downregulating the expression of Bax protein.     

Protective effect of rapid ischemic preconditioning against spinal cord ischemic injury in rabbits

AIM: To evaluate the protective effect of rapid phase of ischemic preconditioning against spinal cord ischemic injury in rabbits. METHODS: Thirty six male New Zealands white rabbits were randomly assigned to 3 groups (12 in each group): ischemia and reperfusion injury group (IR group), ischemic preconditioning + IR group (IPC+IR group) and sham operation group (sham). In IR group, spinal cord ischemia was induced by an infrarenal aorta clamping for 20 min; The rabbits in IPC+IR group underwent a 6 min ischemic preconditioning followed by 30 min of reperfusion before the 20 min clamping; The rabbits in sham group underwent the same procedures as the IR group except for infrarental aortic unclamping. Neurologic status was scored at 8, 12, 24 and 48 h after reperfusion. All animals were sacrificed at 48 h after reperfusion and the spinal cords (L_5-7) were removed for histopathologic study and determination of the activity of Na⁺, K⁺-ATPase. RESULTS: The neurologic function scores in sham group and IPC+IR group at each observation interval were higher than those in IR group (P＜0.01). Compared to IR group, there were more normal neurons in anterior horn of spinal cord in sham group and IPC+IR group (P＜0.01); the activity of Na⁺, K⁺-ATPase in sham group and IPC+IR group were higher than those in IR group (P＜0.01). CONCLUSION: The rapid phase of ischemic preconditioning has a protective effect against spinal cord ischemic injury in rabbits, and this neuroprotection may be related to the maintenance of Na⁺, K⁺-ATPase activity.     

Effect of ischemic preconditioning on myocardial Bcl-2 expression and mitochondrial structure during heart valve replacement surgery

AIM: To investigate the effect of ischemic preconditioning (IP) on myocardial Bcl-2 expression and mitochondrial structure during heart valve replacement surgery under cardiopulmonary bypass. METHODS: Fifty-four patients were prospectively randomized to receive or not ischemic preconditioning (IP) before cold cardioplegic arrest. Ischemic preconditioning in the IP patients (n=22) was induced by a single 2-min ischemia followed by 3-min reperfusion just before aortic clamping and cold crystalloid cardioplegia for myocardial protection. The control group (n=32) received no ischemic preconditioning before cold cardioplegic arrest. The levels of ejection fraction (EF), fractional shortening(FS) and stroke volume (SV) in both groups were measured and compared. troponin T (c-TnT) level, Bcl-2 protein expression and microscopic changes of myocardial mitochondrial structure were recorded for each group before and after surgery. RESULTS: The level of EF, FS and SV in IP group was higher than those in control group (P<0.05). No significant difference in preoperative c-TnT levels between two groups was observed. The level of c-TnT in IP group was lower than that in control group and with a declining trend over time of 6 h, 24 h, 48 h, 72 h and 5 d after surgery, respectively. The preoperative positive unit of Bcl-2 expression between two groups showed no statistical difference (P> 0.05). Postoperatively, the positive unit of Bcl-2 expression in IP group was 19.85±5.88, significantly increased as compared to the preoperative value (P<0.05). In control group, the positive unit of Bcl-2 expression was 14.17±3.39, showed no statistically significant difference to the preoperative value (P>0.05). Postoperative Bcl-2 expression between two groups showed a significant difference (P<0.05). In the control group, microscopic observation revealed swollen mitochondrion, with a hardly visible or disrupted membrane for some mitochondrion; mitochondrial crista were obviously dissolved and loose with a large number of vacuoles formation. However in IP group, myocardial mitochondrion appeared with intact membrane, concentrated mitochondrial cristae with high electron density and no vacuoles formation was observed. CONCLUSION: IP may up-regulate the expression of myocardial anti-apoptotic protein Bcl-2 to protect the mitochondrion, thus protecting cardiocytes and cardiac functions.     

Effects of Tongxinluo on connexin 43 remodeling and ventricular arrhythmia after myocardial infarction in rats

AIM: To determine the effects of Tongxinluo(TXL) on connexin 43(Cx43) remodeling and ventricular arrhythmia(VA) after myocardial infarction(MI) in rats. METHODS: Male SD rats were randomly divided into sham-operated(sham) group(n=25) and operation group(n=75). The left anterior descending(LAD) was ligated in operated group, while the rats in sham group only underwent pericardiotomy. The rats in operation group which survived for 3 d after operation were randomly assigned to TXL group and MI group. The rats in TXL group was administrated with TXL(2 g·kg^-1·d^-1, intragastric administration) for 4 weeks, while normal saline was applied to the rats in sham group and MI group. The levels of interleukin-1β(IL-1β) and endothelin-1(ET-1) in the tissue from the border zone were measured by ELISA after treatment. The distribution and the mRNA and protein expression of Cx43 were detected by immunohistochemical staining, RT-PCR and Western blotting, respectively. The burst pacing was used to induce ventricular arrhythmia(VA). RESULTS: Compared with sham group, the levels of IL-1β and ET-1 and the incidence of VA were significantly increased, while the mRNA and protein expression of Cx43 was markedly reduced with irregular distribution in MI group(P<0.05). Compared with MI group, the levels of IL-1β and ET-1 and the incidence of VA were significantly reduced, while the expression of Cx43 at mRNA and protein levels was markedly increased with augmented linear distribution in the myocardial cell intercalated disc in TXL group(P<0.05). CONCLUSION: TXL reduces the incidence of VA after MI via inhibiting the Cx43 remodeling.     

Effects of cardiac contractility modulation on ventricular electrical remodeling in rabbits with chronic heart failure

AIM: To investigate the effects of cardiac contractility modulation (CCM) on ventricular electrical remodeling in a rabbit model of chronic heart failure. METHODS: The rabbits were divided into sham group, heart failure(HF) group and HF+ CCM group. The rabbit model of chronic heart failure was established by ligating the ascending aortic root. Then electrical stimulations during the absolute refractory period were delivered lasting 6 h everyday for 4 weeks in rabbits of HF+ CCM group. The QTc and ventricular effective refrective period (VERP) were recorded. The protein and mRNA levels of Kv1.4, Kv4.3 and connexin 43 (Cx43) were determined by Western blot and RT-qPCR. RESULTS: Compared with sham group, QTc were significantly prolonged in HF rabbits at week 12 (P<0.05). CCM therapy shortened QTc of rabbits with heart failure at week 16 (P<0.05). Compared with sham group, VERP significantly increased in HF group and HF+ CCM group, while CCM therapy shortened VERP of rabbits with heart failure at week 16 (P<0.05). Compared with sham group, the mRNA and protein levels of Kv1.4, Kv4.3 and Cx43 were decreased in HF group and HF+ CCM group (P<0.05). However, CCM therapy restored the mRNA and protein levels of Kv1.4, Kv4.3 and Cx43 of rabbits with heart failure (P<0.05). CONCLUSION: CCM suppresses ventricular electrical remodeling in heart failure and the underlying mechanism may be associated with increasing Kv1.4, Kv4.3 and Cx43 expression.