N-acetylcysteine restores isoflurane-induced preconditioning against myocardial infarction during hyperglycemia

BACKGROUND: Hyperglycemia generates reactive oxygen species and prevents isoflurane-induced preconditioning. The authors tested the hypothesis that scavenging reactive oxygen species with N-acetylcysteine will restore protection against myocardial infarction produced by isoflurane in vivo. METHODS: Barbiturate-anesthetized dogs (n = 45) were instrumented for measurement of systemic hemodynamics. Myocardial infarct size and coronary collateral blood flow were measured with triphenyltetrazolium staining and radioactive microspheres, respectively. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Dogs were randomly assigned to receive an infusion of 0.9% saline or 15% dextrose in water to increase blood glucose concentrations to 600 mg/dl (hyperglycemia) in the absence or presence of isoflurane (1.0 minimum alveolar concentration) with or without pretreatment with N-acetylcysteine (150 mg/kg i.v.) in six experimental groups. Isoflurane was discontinued, and blood glucose concentrations were allowed to return to baseline values before left anterior descending coronary artery occlusion. RESULTS: Myocardial infarct size was 27 +/- 2% (n = 8) of the left ventricular area at risk in control experiments. Isoflurane significantly (P < 0.05) decreased infarct size (13 +/- 2%; n = 7). Hyperglycemia alone did not alter infarct size (29 +/- 3%; n = 7) but abolished the protective effect of isoflurane (25 +/- 2%; n = 8). N-Acetylcysteine alone did not affect infarct size (28 +/- 2%; n = 8) but restored isoflurane-induced cardioprotection during hyperglycemia (10 +/- 1%; n = 7). CONCLUSIONS: Acute hyperglycemia abolishes reductions in myocardial infarct size produced by isoflurane, but N-acetylcysteine restores these beneficial effects. The results suggest that excessive quantities of reactive oxygen species generated during hyperglycemia impair isoflurane-induced preconditioning in dogs.     

Mechanisms of isoflurane-induced myocardial preconditioning in rabbits

BACKGROUND: Isoflurane has cardioprotective effects that mimic the ischemic preconditioning phenomenon. Because adenosine triphosphate-sensitive potassium channels and adenosine receptors are implicated in ischemic preconditioning, the authors wanted to determine whether the preconditioning effect of isoflurane is mediated through these pathways. METHODS: Myocardial infarct size was measured in seven groups of propofol-anesthetized rabbits, each subjected to 30 min of anterolateral coronary occlusion followed by 3 h of reperfusion. Groups differed only in the pretreatments given, and controls received no pretreatment. An ischemia-preconditioned group was pretreated with 5 min of coronary occlusion and 15 min of reperfusion. An isoflurane-preconditioned group was pretreated with 15 min end-tidal isoflurane, 1.1%, and then 15 min of washout. An isoflurane-plus-glyburide group was administered 0.33 mg/kg glyburide intravenously before isoflurane pretreatment. An isoflurane plus 8-(p-sulfophenyl)-theophylline (SPT) group received 7.5 mg/kg SPT intravenously before isoflurane. Additional groups were administered identical doses of glyburide or SPT, but they were not pretreated with isoflurane. Infarct size and area at risk were defined by staining. Data were analyzed by analysis of variance or covariance. RESULTS: Infarct size, expressed as a percentage of the area at risk (IS:AR) was 30.2+/-11% (SD) in controls. Ischemic preconditioning and isoflurane preexposure reduced myocardial infarct size significantly, to 8.3+/-5% and 13.4+/-8.2% (P<0.05), respectively. Both glyburide and SPT pretreatment eliminated the preconditioning-like effect of isoflurane (IS:AR = 30.0+/-9.1% and 29.2+/-12.6%, respectively; P = not significant). Neither glyburide nor SPF alone increased infarct size (IS:AR = 33.9+/-7.6% and 31.8+/-12.7%, respectively; P = not significant). CONCLUSIONS: Glyburide and SPT abolished the preconditioning-like effects of isoflurane but did not increase infarct size when administered in the absence of isoflurane. Isoflurane-induced preconditioning and ischemia-induced preconditioning share similar mechanisms, which include activation of adenosine triphosphate-sensitive potassium channels and adenosine receptors.     

Colchicine inhibits isoflurane-induced preconditioning

BACKGROUND: When administered before prolonged myocardial ischemia and reperfusion, isoflurane exerts potent cardioprotective effects similar to those inferred by ischemic preconditioning. To determine whether an intact cytoskeleton is critically important in isoflurane-induced preconditioning, the authors used a rabbit model in which isoflurane-induced myocardial preconditioning decreases myocardial infarct size (IS) substantially. In this model, the authors tested whether the microtubule depolymerizing agent, colchicine, would inhibit isoflurane-induced myocardial preconditioning. METHODS: Myocardial IS was measured in four groups of propofol-anesthetized rabbits, each subjected to 30 min of anterolateral coronary occlusion followed by 3 h of reperfusion. Groups differed only in the pretreatments given, and only the control group received no pretreatment. An isoflurane-preconditioned group was pretreated with 15 min of end-tidal isoflurane, 1.1%, and then 15 min of washout. An isoflurane-plus-colchicine group was administered 2 mg/kg colchicine intravenously before isoflurane pretreatment. A colchicine-control group was administered 2 mg/kg colchicine but no isoflurane pretreatment. Myocardial IS and area at risk (AR) were defined by staining. Data were analyzed by analysis of variance or covariance. RESULTS: Infarct size, expressed as a percentage of AR (IS:AR) was 33.6%+/-8.8% (SD) in the control group. Isoflurane preexposure reduced myocardial IS:AR significantly, to 11.8%+/-9.1%. Colchicine pretreatment eliminated the preconditioning-like effect of isoflurane (IS:AR = 32.6%+/-8.7%). Colchicine alone did not alter IS (IS:AR = 27.6%+/-7.1%; P = not significant). CONCLUSIONS: Colchicine abolished the preconditioning effect of isoflurane but did not increase IS when administered alone. An intact microtubular cytoskeleton is critically important in the process of volatile anesthetic-induced preconditioning.     

Desflurane-induced preconditioning against myocardial infarction is mediated by nitric oxide

BACKGROUND: Volatile anesthetics induce myocardial preconditioning through a signal transduction pathway that is remarkably similar to that observed during ischemic preconditioning. Nitric oxide-dependent signaling plays an important role in anesthetic and ischemic preconditioning. Therefore, the authors tested the hypothesis that desflurane-induced preconditioning is mediated by nitric oxide. METHODS: Barbiturate-anesthetized rabbits were instrumented for measurement of hemodynamics. All rabbits were subjected to 30-min coronary artery occlusion followed by 3 h of reperfusion. Myocardial infarct size was assessed with triphenyltetrazolium chloride staining. Myocardial nitric oxide synthase activity was assessed with a [H]L-arginine-conversion assay. Rabbits were randomized to five separate experimental groups. They received 0.0 or 1.0 minimum alveolar concentration desflurane for 30 min, which was discontinued 30 min before ischemia in the absence or presence of the nitric oxide synthase inhibitor N-nitro-L-arginine (L-NA). L-NA was given either 20 min before or 10 min after desflurane administration, respectively. Data are mean +/- SEM. RESULTS: Infarct size was 56 +/- 8% in control experiments. Desflurane significantly (P < 0.05) reduced infarct size to 35 +/- 4%. Preconditioning by desflurane was totally blocked by administration of L-NA either during or after desflurane inhalation (58 +/- 4 and 59 +/- 9%, respectively). L-NA alone had no effect on infarct size (56 +/- 7%). Nitric oxide synthase activity was significantly (P < 0.05) increased by desflurane. CONCLUSION: The results demonstrate that desflurane-induced preconditioning markedly reduced myocardial infarct size. This beneficial effect was blocked by the nitric oxide synthase inhibitor L-NA either during or after desflurane-administration. These data suggest that early desflurane-induced preconditioning is mediated by nitric oxide.     

Inhibition of glycogen synthase kinase enhances isoflurane-induced protection against myocardial infarction during early reperfusion in vivo

Inhibition of glycogen synthase kinase (GSK)-beta protects against ischemia-reperfusion injury. Brief exposure to isoflurane before and during early reperfusion after coronary artery occlusion also protects against infarction. Whether GSK-beta mediates this action is unknown. We tested the hypothesis that GSK inhibition enhances isoflurane-induced postconditioning. Rabbits (n = 88; 6 to 7 per group) subjected to a 30-min coronary occlusion followed by 3 h reperfusion received saline, isoflurane (0.5 or 1.0 minimum alveolar concentration [MAC]) administered for 3 min before and 2 min after reperfusion, the selective GSK inhibitor SB216763 (SB21; 0.2 or 0.6 mg/kg), or 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Other groups of rabbits pretreated with phosphatidylinositol-3 kinase (PI3K) inhibitor wortmannin (0.6 mg/kg), 70-kDa ribosomal protein s6 kinase (p70s6K) inhibitor rapamycin (0.25 mg/kg), or mitochondrial permeability transition pore (mPTP) opener atractyloside (5 mg/kg) received 0.6 mg/kg SB21 or 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Additional groups received the mPTP inhibitor, cyclosporin A (5 mg/kg), plus 0.2 mg/kg SB21 with or without atractyloside pretreatment. Isoflurane (1.0 but not 0.5 MAC) and SB21 (0.6 but not 0.2 mg/kg) reduced (P < 0.05) infarct size (21% +/- 5%, 44% +/- 7%, 23% +/- 4%, and 46% +/- 2%, respectively, of left ventricular area at risk, mean+/- sd; triphenyltetrazolium staining) as compared with control (42% +/- 6%). Isoflurane (0.5 MAC) plus 0.2 mg/kg SB21 and cyclosporin A plus 0.2 mg/kg SB21 produced similar degrees of protection (24% +/- 4% and 27% +/- 6%, respectively). Atractyloside but not wortmannin or rapamycin abolished protection produced by 0.6 mg/kg SB21 and 0.5 MAC isoflurane plus 0.2 mg/kg SB21. Thus, GSK inhibition enhances isoflurane-induced protection against infarction during early reperfusion via a mPTP-dependent mechanism.     

Isoflurane does not produce a second window of preconditioning against myocardial infarction in vivo

The administration of a volatile anesthetic shortly before a prolonged ischemic episode exerts protective effects against myocardial infarction similar to those of ischemic preconditioning. A second window of preconditioning (SWOP) against myocardial infarction can also be elicited by brief episodes of ischemia when this occurs 24 h before prolonged coronary artery occlusion. Whether remote exposure to a volatile anesthetic also causes delayed myocardial protection is unknown. We tested the hypothesis that the administration of isoflurane 24 h before ischemia produces a SWOP against infarction. Barbiturate-anesthetized dogs (n = 25) were instrumented for measurement of hemodynamics, including aortic and left ventricular (LV) pressures and LV +dP/dt(max), and subjected to a 60-min left anterior descending coronary artery occlusion followed by 3 h of reperfusion. Myocardial infarct size and coronary collateral blood flow were assessed with triphenyltetrazolium chloride staining and radioactive microspheres, respectively. Two groups of dogs received 1.0 minimum alveolar anesthetic concentration isoflurane for 30 min or 6 h that was discontinued 30 min (acute) or 24 h (delayed) before ischemia and reperfusion, respectively. A control group of dogs did not receive isoflurane. Infarct size was 27% +/- 3% of the LV area at risk in the absence of pretreatment with isoflurane. Acute, but not remote, administration of isoflurane reduced infarct size (12% +/- 1% and 31% +/- 3%, respectively). No differences in hemodynamics or transmural myocardial perfusion during or after occlusion were observed between groups. The results indicate that isoflurane does not produce a SWOP when administered 24 h before prolonged myocardial ischemia in vivo. IMPLICATIONS: Isoflurane mimics the beneficial effects of ischemic preconditioning by protecting myocardium against infarction when it is administered shortly before a prolonged ischemic episode. However, unlike ischemic preconditioning, isoflurane does not produce a second window of protection 24 h after administration in dogs.     

Morphine enhances isoflurane-induced postconditioning against myocardial infarction: the role of phosphatidylinositol-3-kinase and opioid receptors in rabbits

Isoflurane reduces myocardial infarct size during early reperfusion by activating phosphatidylinositol-3-kinase (PI3K) signaling. We tested the hypothesis that this cardioprotection against reperfusion injury is enhanced by morphine and that a decrease in apoptosis plays a role in preservation of myocardial viability. Rabbits (n = 108) instrumented for hemodynamic measurement and subjected to a 30-min coronary occlusion followed by 3 h reperfusion received 0.9% saline, the selective PI3K inhibitor wortmannin (0.6 mg/kg), or the nonselective opioid antagonist naloxone (6 mg/kg) before coronary occlusion in the presence or absence of isoflurane (0.5 or 1.0 MAC), morphine (0.05 or 0.1 mg/kg), or their combination administered for 3 min before and 2 min after reperfusion. Infarct size was determined using triphenyltetrazolium staining and apoptosis assessed using cytochrome c translocation and Terminal Deoxynucleotidyl Transferase-Mediated dUTP Nick End Labeling (TUNEL) staining of left ventricular myocardium in situ. Isoflurane (1.0 but not 0.5 MAC) and morphine (0.1 but not 0.05 mg/kg) reduced (P < 0.05) infarct size (mean +/- sd 21% +/- 4%, 44% +/- 6%, 19% +/- 4%, and 41% +/- 6% of left ventricular area at risk, respectively) as compared with control (41% +/- 4%). The combination of 0.5 MAC isoflurane and 0.05 mg/kg morphine also decreased infarct size (18% +/- 9%). Wortmannin and naloxone alone did not affect infarct size but blocked the protection produced by isoflurane, morphine, and their combination. Isoflurane and morphine reduced cytochrome c translocation and TUNEL staining. The results indicate that morphine enhances isoflurane-induced postconditioning by activating PI3K and opioid receptors in vivo. A reduction in apoptotic cell death contributes to preservation of myocardial integrity during postconditioning by isoflurane. IMPLICATIONS: The results of this study indicate that morphine enhances isoflurane-induced postconditioning by activating phosphatidylinositol-3-kinase and opioid receptors in vivo. A reduction in apoptotic cell death contributes to preservation of myocardial integrity during postconditioning by isoflurane and morphine.     

诱导型一氧化氮合酶在异氟醚延迟相预处理心肌保护中的作用

目的研究诱导型一氧化氮合酶(iNOS)在异氟醚延迟相预处理心肌保护中的作用。方法新西兰白兔36只随机分成五组:异氟醚预处理组(n=9),异氟醚持续吸入2h;1400Wa组(n=6),给予选择性iNOS阻滞药1400W;1400Wb组(n=6),于缺血-再灌注前30min给予1400W;异氟醚 1400W组(n=6),给予异氟醚持续吸入2h,在缺血-再灌注前30min给予1400W;对照组(n=9),给予生理盐水。各组建立心肌局部缺血-再灌注模型。监测缺血-再灌注期间血流动力学参数,测定心肌梗死范围,检测iNOS基因水平表达和蛋白表达。结果异氟醚预处理组[(23.98±2.65)%]和对照组[(42.14±3.06)%]相比明显减少心肌缺血-再灌注后心肌梗死范围(P<0.01),异氟醚 1400W组[(42.12%±2.60)%]和异氟醚预处理组相比,1400W可以取消异氟醚的减少心肌梗死范围的作用(P<0.01)。iNOS在基因水平和蛋白表达水平均增加。结论异氟醚延迟相预处理具有抗心肌缺血-再灌注损伤的作用,而且这种作用是由iNOS所介导。     

术中预缺血对猪骨骼肌保护作用的实验研究

目的　研究术中预缺血对骨骼肌缺血坏死的保护作用及相关的肌肉代谢变化。方法　１０ 只猪背阔肌瓣在４ｈ 缺血前先进行３ 个循环１０ ｍｉｎ 的术中预缺血,４８ｈ 后用染色法记录肌肉成活率,于肌肉缺血前、缺血后２ ,４ｈ 和再灌流１５ｈ 分别作肌肉活检。结果　４ｈ 缺血后的肌瓣,术中预缺血组成活率高出对照组４４ ％ ,肌肉活检三磷酸腺苷（ Ａ Ｔ Ｐ） 增加和乳酸降低（ Ｐ＜ ００５） 。结论　术中预缺血可增加骨骼肌对缺血坏死的保护作用,这与肌肉中能量代谢的减低相关。     

Hypocapnia prevents the decrease in regional cerebral metabolism during isoflurane-induced hypotension

In neurologic surgery, induced hypotension is often used while the patient is hypocapnic. We investigated, by tissue biopsy methods and scintillation counting, the regional cerebral glucose utilization (rCMRglc) and blood flow (rCBF) in rats subjected to hypocapnia alone and in combination with hypotension. Anesthesia was maintained with 1.0% isoflurane in nitrous oxide/oxygen. Seven rats were maintained at PaCO2 of 40 mm Hg, six rats were ventilated to PaCO2 of 20 mm Hg, and six animals to PaCO2 of 20 mm Hg in combination with arterial hypotension of 50 mm Hg induced by isoflurane 2.5-3.5%. During hypocapnia, rCMRglc tended to increase in all regions, but the increase was statistically insignificant; rCBF was reduced uniformly by 40%. During combined hypocapnia/hypotension, rCMRglc was unaltered when compared to hypocapnia; compared to normocapnia, increases were seen in hippocampus and cerebellum. During hypocapnia/hypotension, rCBF was unaltered in cortical areas, while increases were seen in all subcortical areas compared to hypocapnia. Regional values of the ratio of rCBF/rCMRglc indicated that during hypocapnia and hypotension induced by isoflurane in nitrous oxide/oxygen, the individual brain areas were perfused according to their metabolic needs. It is suggested that hypocapnia may prevent the decrease in rCMRglc, which is usually observed during deep isoflurane anesthesia.     

术中预缺血对猪骨骼肌保护作用的实验研究

目的研究术中预缺血对骨骼肌缺血坏死的保护作用及相关的肌肉代谢变化。方法 10只猪背阔肌瓣在4h 缺血前先进行3个循环10min 的术中预缺血,48h 后用染色法记录肌肉成活率,于肌肉缺血前、缺血后2,4h 和再灌流1.5h 分别作肌肉活检。结果 4h 缺血后的肌瓣,术中预缺血组成活率高出对照组44％,肌肉活检三磷酸腺苷(ATP)增加和乳酸降低(P<0.05)。结论术中预缺血可增加骨骼肌对缺血坏死的保护作用,这与肌肉中能量代谢的减低相关。     

术中预缺血对猪骨骼肌保护作用的实验研究

OBJECTIVE: The aim of this study was to investigate metabolism of ischemic muscle and the efficacy of acute ischemic preconditioning for protection of skeletal muscles against infarction. METHODS: The efficacy of preconditioning was tested by subjecting pig latissimus dorsi muscle to 3 cycles of ischemia reperfusion, each for 10 min, before 4 h of global ischemia. Infarction was assessed at 48 h reperfusion using nitroblue tetrazolium dye. Muscle biopsies were taken from the latissimus dorsi before ischemia, at the end of 2 and 4 h of ischemia and 1.5 h of reperfusion. RESULTS: Preconditioning reduced the total infarct size by 44% in the latissimus dorsi. The muscle contents of ATP were maintained higher and the lactate lower (P < 0.05) in the preconditioned than in the non-preconditioned muscle at the end of 2 h, 4 h of ischemia and 1.5 h of reperfusion. CONCLUSION: Preconditioning of pig skeletal muscle is associated with a lower energy metabolism during sustained ischemia. At the present time, it is not known if this energy sparing effect is a major mechanism of ischemia preconditioning against infarction in the skeletal muscle.