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Meeting Abstracts  |   November 1999
Sevoflurane Reduces Myocardial Infarct Size and Decreases the Time Threshold for Ischemic Preconditioning in Dogs 
Author Affiliations & Notes
  • Wolfgang G. Toller, M.D., D.E.A.A.
    *
  • Judy R. Kersten, M.D.
  • Paul S. Pagel, M.D., Ph.D.
  • Douglas A. Hettrick, Ph.D.
  • David C. Warltier, M.D., Ph.D.
    §
  • *Research Fellow, Department of Anesthesiology. †Associate Professor, Department of Anesthesiology. ‡Assistant Professor, Department of Anesthesiology. §Professor, Departments of Anesthesiology, Pharmacology and Toxicology, and Medicine; and Vice Chairman, Research of Anesthesiology.
Article Information
Meeting Abstracts   |   November 1999
Sevoflurane Reduces Myocardial Infarct Size and Decreases the Time Threshold for Ischemic Preconditioning in Dogs 
Anesthesiology 11 1999, Vol.91, 1437. doi:
Anesthesiology 11 1999, Vol.91, 1437. doi:
PRECONDITIONING with single or multiple episodes of brief ischemia and reperfusion renders myocardium temporarily resistant to subsequent prolonged ischemia. 1 The precise underlying mechanism(s) of ischemic preconditioning (IPC) has been the focus of intense investigation. Accumulating evidence indicates that adenosine triphosphate–sensitive potassium (KATP) channels, 2,3 adenosine A1receptors, 4 and protein kinase C 5–7 are involved in IPC signal transduction. Notably, a threshold 8 level of the ischemic stimulus must be present for IPC to occur, and combination of two independent subthreshold stimuli may exert protective effects. 9 Recent evidence also suggests that KATPchannels and A1receptors modulate an acute memory phase characterized by increased tolerance to a subsequent prolonged coronary artery occlusion after a brief ischemic episode. 10 
Previous investigations from this 11–14 and other laboratories 15,16 have demonstrated that volatile anesthetics, including isoflurane and halothane, exert cardioprotective effects during ischemia and reperfusion. The mechanisms for anesthetic-induced myocardial protection are similar to those observed during IPC and are mediated by KATPchannels, 13 A1receptors, 14 and protein kinase C. 15 Like IPC, isoflurane has also been shown to produce an acute memory phase with a duration of at least 30 min. 13 Whether the new volatile anesthetic sevoflurane exerts similar protective effects during myocardial ischemia and reperfusion is unknown. The present study tested the hypothesis that sevoflurane reduces experimental myocardial infarct size by activation of KATPchannels. Additionally, it is unknown whether volatile anesthetics affect the time threshold for IPC, allowing a stimulus of shorter duration to provide cardioprotection. KATPchannel activation has been shown to decrease this time threshold. 9 Thus, the present investigation also tested the hypothesis that sevoflurane reduces the time threshold of IPC in vivo  .
Methods and Materials 
All experimental procedures and protocols used in this investigation were reviewed and approved by the Animal Care and Use Committee of the Medical College of Wisconsin. All procedures were in conformity with the Guiding Principles in the Care and Use of Animals  17 of the American Physiologic Society and were performed in accordance with the Guide for the Care and Use of Laboratory Animals  . 18 
General Preparation 
The experimental methods have been previously described in detail. 12 Briefly, mongrel dogs of either sex (26 ± 1 kg; mean ± SEM) were fasted overnight, anesthetized with sodium barbital (200 mg/kg) and sodium pentobarbital (15 mg/kg), and ventilated with an air and oxygen mixture (fraction of inspired oxygen = 0.25) after tracheal intubation. Tidal volume and respiratory rate were adjusted to maintain arterial blood gas tensions within a physiologic range (p  H, 7.39–7.44; carbon dioxide partial pressure, 28–35 mmHg; oxygen partial pressure, 140–210 mmHg). After calibration, a dual pressure transducer–tipped catheter was inserted into the aorta and left ventricle (LV)via  the left carotid artery to measure aortic and LV pressures, respectively. The maximum rate of increase of LV pressure (+dP/dtmax) was obtained by electronic differentiation of the LV pressure waveform. The femoral vein and artery were cannulated for fluid administration and for the withdrawal of reference blood flow samples used in the calculation of regional myocardial blood flow, respectively. A thoracotomy was performed at the left fifth intercostal space. A heparin-filled catheter was inserted into the left atrial appendage for administration of radioactive microspheres. A 1.0-cm segment of the left anterior descending (LAD) coronary artery was dissected immediately distal to the first diagonal branch, and a silk ligature was positioned around the vessel to permit episodic coronary artery occlusion. Regional myocardial perfusion was measured in the ischemic (LAD) and normally (left circumflex coronary artery) perfused regions using the radioactive microsphere technique. 12 Myocardial infarct size was determined with triphenyltetrazolium chloride staining at the completion of each experiment. 19 End-tidal concentrations of sevoflurane were measured at the tip of the endotracheal tube by an infrared anesthetic gas analyzer that was calibrated with known standards before and during experimentation. The canine minimum alveolar concentration (MAC) value of sevoflurane used in the present investigation was 2.36%. 20 Hemodynamic data were continuously monitored throughout the experiment, recorded with a polygraph, and digitized using a computer interfaced with an analog-to-digital converter.
Experimental Protocol 
The experimental design used in the present investigation is illustrated in figure 1. Dogs were randomly assigned to one of seven experimental groups. All dogs underwent a 60-min LAD occlusion followed by 3 h of reperfusion. Ninety minutes after completion of the surgical preparation and in four groups of experiments, dogs received either intravenous drug vehicle (50% polyethylene glycol and 50% ethyl alcohol) or the KATPchannel antagonist glyburide (0.1 mg/kg infusion over 10 min) in the presence and absence of a 30-min administration of 1 MAC end-tidal concentration sevoflurane. These experiments were designed to test the hypothesis that sevoflurane reduces myocardial infarct size by KATPchannel activation. To determine whether the use of sevoflurane is associated with an acute memory phase, another group of dogs was pretreated with 1 MAC sevoflurane for 30 min, which was then discontinued 30 min before the prolonged LAD occlusion. Finally, to test the hypothesis that sevoflurane reduces the time threshold of IPC, two additional groups of dogs were subjected to a brief (2-min) LAD occlusion 1 h before the prolonged LAD occlusion with or without a subsequent 30-min exposure to 1 MAC sevoflurane and 30 min of memory.
Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
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Statistical Analysis 
Statistical analysis of data within and between groups was performed with multiple analysis of variance for repeated measures followed by application of the Student t  test with Duncan's correction for multiplicity. Linear regression analysis was performed to determine the relationship between transmural collateral blood flow and infarct size expressed as a percentage of the area at risk for infarction. Changes within and between groups were considered statistically significant at P  < 0.05. All data are expressed as mean ± SEM.
Results 
Seventy-five dogs were instrumented to provide 58 successful experiments. Sixteen dogs were excluded from analysis because transmural collateral blood flow exceeded 0.2 ml · min−1· g−1in the ischemic zone during LAD occlusion (two control, five sevoflurane alone, four sevoflurane and glyburide, two sevoflurane with memory, two IPC alone, and one IPC and sevoflurane). One dog in the group that received sevoflurane with memory was excluded because intractable ventricular fibrillation occurred during LAD occlusion.
Systemic Hemodynamics 
There were no differences in systemic hemodynamics during baseline conditions between experimental groups (tables 1–7). Sevoflurane alone significantly (P  < 0.05) decreased heart rate, mean arterial and LV systolic pressures, rate–pressure product, and LV +dP/dtmax(table 2). Glyburide produced no hemodynamic effects (table 3), and there were no hemodynamic differences in glyburide- compared with vehicle-pretreated control dogs. Sevoflurane produced similar hemodynamic effects in the presence (table 4) or absence (table 2) of glyburide. When sevoflurane was discontinued 30 min before prolonged LAD occlusion in acute memory phase experiments, heart rate and rate–pressure product remained decreased during the following 30-min memory period compared with baseline values (table 5). A 2-min IPC briefly reduced LV systolic pressure and increased end-diastolic pressure but did not alter heart rate, mean arterial pressure, and rate–pressure product (table 6). Sevoflurane produced similar effects in the presence (table 7) or absence (table 5) of a preceding IPC stimulus. Prolonged LAD occlusion caused immediate and sustained increases in LV end-diastolic pressure and decreases in +dP/dtmaxin all groups. There were no differences in hemodynamics during coronary artery occlusion between groups. No differences in heart rate, mean arterial pressure, and rate–pressure product were observed between groups during reperfusion after the 1-h LAD occlusion.
Table 1. Systemic Hemodynamics in Control Dogs 
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Table 1. Systemic Hemodynamics in Control Dogs 
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Table 2. Systemic Hemodynamics in Dogs Receiving Sevoflurane 
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Table 2. Systemic Hemodynamics in Dogs Receiving Sevoflurane 
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Table 3. Systemic Hemodynamics in Dogs Receiving Glyburide 
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Table 3. Systemic Hemodynamics in Dogs Receiving Glyburide 
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Table 4. Systemic Hemodynamics in Dogs Receiving Sevoflurane and Glyburide 
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Table 4. Systemic Hemodynamics in Dogs Receiving Sevoflurane and Glyburide 
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Table 5. Systemic Hemodynamics in Dogs Receiving Sevoflurane with Memory 
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Table 5. Systemic Hemodynamics in Dogs Receiving Sevoflurane with Memory 
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Table 6. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning with Memory 
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Table 6. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning with Memory 
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Table 7. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning and Sevoflurane with Memory 
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Table 7. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning and Sevoflurane with Memory 
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Regional Myocardial Perfusion 
Transmural myocardial blood flow in the ischemic (LAD) and normal (left circumflex coronary artery) regions is summarized in table 8. LAD occlusion caused equivalent decreases in transmural perfusion to the ischemic (LAD) zone in each group, and there were no differences in collateral blood flow between groups. Blood flow to the LAD region increased 1 h after final reperfusion in all groups.
Table 8. Transmural Myocardial Blood Flow (ml · min−1· g−1) in the Ischemic (LAD) and Normal (LCCA) Regions 
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Table 8. Transmural Myocardial Blood Flow (ml · min−1· g−1) in the Ischemic (LAD) and Normal (LCCA) Regions 
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Myocardial Infarct Size 
Sevoflurane administered until immediately before coronary artery occlusion significantly reduced myocardial infarct size to 13 ± 2% of the area at risk compared with control experiments (23 ± 1%;fig. 2). Although glyburide alone had no effect on infarct size (23 ± 2%), the protective effects of sevoflurane were abolished by pretreatment with glyburide (21 ± 3%). Discontinuation of sevoflurane 30 min before the LAD occlusion (sevoflurane with memory) or a 2-min preconditioning stimulus did not produce cardioprotection (21 ± 4% and 24 ± 2%, respectively;fig. 3). In contrast, combined sevoflurane pretreatment and a 2-min period of IPC together after 30 min of memory caused significant reductions in myocardial infarct size (9 ± 2%;figs. 3 and 4). The relationship between infarct size and transmural collateral blood flow during threshold of IPC experiments is shown in figure 4. IPC and sevoflurane followed by 30 min of memory reduced the extent of myocardial infarction at any given level of collateral blood flow and shifted the regression relation downward as compared with unprotected dogs (control, sevoflurane with memory, and IPC groups). The area at risk for myocardial infarction was similar between groups (control, 41 ± 2; sevoflurane, 40 ± 2; glyburide, 40 ± 2; sevoflurane plus glyburide, 46 ± 2; sevoflurane plus memory, 44 ± 2; IPC, 44 ± 2; IPC plus sevoflurane plus memory, 45 ± 1% of the LV).
Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
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Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
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Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
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Discussion 
Substantial experimental evidence suggests that KATPchannels play an important role in mediating the protective effects of IPC. 21–23 Activation of these channels by pharmacologic agents mimics IPC 24 and reduces the time threshold necessary to produce IPC in dogs. 9 Consistent with this hypothesis, the KATPchannel antagonist glyburide 21,22 abolishes IPC. Volatile anesthetics 13,15,16 have been shown to reduce ischemia–reperfusion injury by activating KATPchannels and to produce an acute memory phase, 13 characteristics that are also distinctive of IPC. The present results indicate that sevoflurane causes anesthetic-induced preconditioning, 16 reducing myocardial infarct size by a KATPchannel–mediated mechanism. The present findings confirm and extend our previous results with isoflurane 13,25 and support the contention that KATPchannel activation may represent an end-effector of a signal transduction pathway responsible for anesthetic-induced preconditioning. Further in vitro  investigation is required to clarify whether sevoflurane or other volatile anesthetics directly stimulate KATPchannels, 26 alter the ATP sensitivity of such channels, 27 or trigger a signaling cascade that indirectly leads to KATPchannel activation.
Ischemic preconditioning with a 2-min LAD occlusion was not sufficient to reduce myocardial infarct size in the present investigation. These data confirm the majority of previous findings indicating that a threshold stimulus > 3 min is generally required for IPC to occur. Miura et al.  28 demonstrated no protective effects of 2-min IPC in anesthetized rabbits. A similar lack of protection was shown for preconditioning periods of 2.5 and 3 min but not 5 min in dogs. 9,24,29 In contrast, Ovize et al.  30 demonstrated that a 2.5-min coronary artery occlusion reduced infarct size in dogs subjected to 60-min coronary artery occlusion and reperfusion; however, a substantially smaller area at risk for infarction (20% of the LV) was present in this study 30 compared with the present study and other investigations. 9,24,29 
The present investigation is the first to examine whether a volatile anesthetic is capable of lowering the time threshold for IPC. Neither the 2-min LAD occlusion alone nor administration of sevoflurane followed by a 30-min memory period afforded protection against infarction, but the combination of brief LAD occlusion and remote sevoflurane exposure caused a dramatic reduction of infarct size (9 ± 2% of the area at risk for infarction). Previous studies have demonstrated that although two individual subthreshold stimuli are insufficient to produce preconditioning when administered separately, their combination often provides a full protective effect. The KATPchannel opener bimakalim, 9 dipyridamole, 28 allosteric enhancement of A1receptor activity, 29 and activation of bradykinin B2receptors 31 have been shown to lower the time threshold required for IPC. Because the protective effects of volatile anesthetics have also been attributed to KATPchannels 12,27 and A1receptors, 14,15 these agents may have the capability to enhance a subthreshold stimulus and produce IPC as well.
Despite convincing evidence for synergistic actions of various stimuli of IPC, the precise underlying mechanisms remain unclear. Yao and Gross 9 demonstrated the capability of enhanced activation of KATPchannels to sensitize the myocardium and lower the threshold for ischemia necessary to produce IPC. Miura et al.  28 and Auchampach and Gross 32 suggested that elevation of interstitial adenosine concentrations may enhance the effect of IPC. It is unknown if sevoflurane increased interstitial concentrations of adenosine in the present investigation. We have previously shown that isoflurane decreases interstitial adenosine concentration and blunts the increase in adenosine that occurs during a brief period of coronary artery occlusion. 14 Despite decreases in interstitial adenosine concentrations during isoflurane, the cardioprotective effects of this anesthetic were attenuated by an A1receptor antagonist. 14 Similarly to isoflurane, sevoflurane may have activated KATPchannels or A1receptors and thereby enhanced the insufficient stimulus of a 2-min LAD occlusion to produce IPC in the present investigation.
Discontinuation of sevoflurane 30 min before the prolonged LAD occlusion produced no subsequent protective effects, indicating that this volatile anesthetic does not cause an acute memory period. This finding contrasts with our previous results with isoflurane, where persistent cardioprotective actions were observed when this volatile agent was discontinued 30 min before the prolonged LAD occlusion. 13 The cellular mechanisms responsible for the induction and maintenance of the acute memory period of IPC and isoflurane anesthesia are not completely understood; however, evidence suggests that pharmacologic activation of both KATPchannels and A1receptors is required for the acute memory phase of IPC to occur. 10,33 We have shown that isoflurane-induced cardioprotection is mediated through both KATPchannels 12,13,25 and A1receptors. 14 Thus, isoflurane may contribute to a memory period by mechanisms similar to those observed during memory and IPC. Memory associated with isoflurane anesthesia may have also required the persistent presence of residual amounts of this agent in the myocardium that continued to open KATPchannels for at least 30 min after discontinuation. However, systemic hemodynamics returned to baseline values, and end-tidal isoflurane concentrations were undetectable 30 min after discontinuation of this agent. 13 Nevertheless, it remains possible that the substantially lower blood-gas solubility of sevoflurane may have resulted in less residual drug in the myocardium than isoflurane after a 30 min washout period and may partially account for the absence of memory after exposure to sevoflurane.
The mechanism or extent of KATPchannel opening may be different between volatile agents. As discussed previously, volatile anesthetics may directly activate KATPchannels or trigger a series of intracellular events leading to KATPchannel opening as the final common pathway. However, the direct effects of volatile anesthetics on KATPchannel opening using patch clamp methodology are as yet unclear, 26,27 and whether isoflurane and sevoflurane produce differential actions on intracellular signal transduction pathways, leading to KATPactivation, has yet to be examined. Sustained activity of protein kinase C may contribute to maintenance of the memory of IPC 29 and may be observed during ischemia and reperfusion injury. Both isoflurane-34 and halothane-induced 15 myocardial protection may also be causally linked to enhanced protein kinase C activity to varying degrees. However, whether sevoflurane activates protein kinase C is unknown.
The present findings must be interpreted within the constraints of several possible limitations. Sevoflurane-induced decreases in heart rate and myocardial contractility during ischemia may have produced favorable alterations in myocardial oxygen supply–demand relations, thereby contributing to a reduction in infarct size. However, halothane has been shown to exert protective effects even during mechanical arrest produced by cardioplegia, 35 indicating that preferential alterations in myocardial metabolism are not solely responsible for the antiischemic actions of this anesthetic. Glyburide also blocked the cardioprotection afforded by sevoflurane without affecting the hemodynamic actions of this anesthetic. Nevertheless, coronary venous oxygen tension was not measured and myocardial oxygen consumption was not determined in the present investigation, and favorable changes in myocardial metabolism during administration of sevoflurane cannot be completely excluded. We have recently shown that sevoflurane selectively dilates coronary collateral vessels independent of KATPchannels in a canine model of enhanced collateral development. 36 Such a preferential increase in coronary collateral blood flow may have contributed to sevoflurane-mediated protection in the present investigation. However, transmural collateral perfusion during LAD occlusion was similar between experimental groups conducted in the present investigation in dogs with relatively poor coronary collateral vasculature, indicating that sevoflurane-induced coronary collateral dilation was not responsible for the beneficial effects of this agent on infarct size. Furthermore, sevoflurane reduced the threshold of IPC at any given level of collateral blood flow. Interpretation of the present findings should also be qualified because only a single end-tidal concentration of sevoflurane was used, and the possibility that higher sevoflurane concentrations may have produced more pronounced reductions in infarct size or a memory response also cannot be excluded. Finally, we were unable to specifically evaluate the role of sarcolemmal versus  mitochondrial KATPchannels to mediate sevoflurane-induced cardioprotection because glyburide is a nonselective antagonist of these channels. 37,38 It has been suggested that mitochondrial KATPchannels may be primarily responsible for the protective effects of IPC 39; however, the relative contribution of mitochondrial versus  sarcolemmal KATPchannels during anesthetic-induced cardioprotection is currently unknown.
In summary, the present results indicate that sevoflurane reduces experimental myocardial infarct size by activating KATPchannels. Discontinuation of sevoflurane 30 min before a prolonged coronary artery occlusion affords no inherent myocardial protection but reduces the time required for a brief ischemic stimulus to exert cardioprotective effects.
The authors thank Todd Schmeling and David Schwabe for technical assistance, and Drs. Werner F. List and Helfried Metzler (Department of Anesthesiology and Intensive Care Medicine, University of Graz, Austria) for their gracious support.
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Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
Fig. 1. Schematic illustration of the experimental protocol used to study the role of adenosine triphosphate–sensitive potassium (KATP) channels in sevoflurane (SEV)-induced decreases in myocardial infarct size and the ability of sevoflurane to reduce the time threshold required for ischemic preconditioning (IPC) to occur. All dogs were subjected to 60 min of left anterior descending (LAD) coronary artery occlusion and 180 min of reperfusion. Dogs received vehicle (Control) or glyburide (GLB; 0.1 mg/kg intravenously) in the presence or absence of 1 minimum alveolar concentration (MAC) SEV before LAD occlusion. Additional dogs received 1 MAC sevoflurane that was discontinued 30 min before the LAD occlusion without IPC (SEV+MEM), and two other groups of dogs were subjected to a 2-min period of IPC 1 h before the prolonged LAD occlusion with or without a subsequent 30-min administration of 1 MAC SEV with memory. Regional myocardial blood flow (radioactive microspheres) was measured before, during, and 60 min after the LAD occlusion. 
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Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
Fig. 2. Histograms depicting myocardial infarct size as a percentage of area at risk in control (CON) dogs or those that received glyburide (GLB) in the presence and absence of 1 minimum alveolar concentration (MAC) sevoflurane (SEV). *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from GLB alone;§Significantly (  P  < 0.05) different from SEV plus GLB. 
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Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
Fig. 3. The extent of myocardial infarction as a percentage of area at risk was similar in control (CON) dogs and those that received either a 2-min ischemic preconditioning (IPC) period alone or 1 minimum alveolar concentration (MAC) of sevoflurane (SEV) with 30 min of memory (MEM). In contrast, SEV with memory and IPC together (IPC+SEV+MEM) produced significant reductions in myocardial infarct size. *Significantly (  P  < 0.05) different from CON;†Significantly (  P  < 0.05) different from IPC;§Significantly (  P  < 0.05) different from SEV plus MEM. 
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Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
Fig. 4. Relationship between myocardial infarct size and transmural collateral blood flow in dogs without evidence of cardioprotection (  open squares  , control [CON];  open triangles  , sevoflurane with memory [SEV+MEM];  open circles  , 2-min period of ischemic preconditioning [IPC]) and in dogs in which sevoflurane reduced the threshold of IPC (IPC+SEV+MEM;  closed circles  ). The combination of IPC and sevoflurane with memory significantly (  P  < 0.05) shifted the regression line (  dashed  ) downward (indicating cardioprotection) in comparison to the unprotected groups (  solid line  ). 
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Table 1. Systemic Hemodynamics in Control Dogs 
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Table 1. Systemic Hemodynamics in Control Dogs 
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Table 2. Systemic Hemodynamics in Dogs Receiving Sevoflurane 
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Table 2. Systemic Hemodynamics in Dogs Receiving Sevoflurane 
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Table 3. Systemic Hemodynamics in Dogs Receiving Glyburide 
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Table 3. Systemic Hemodynamics in Dogs Receiving Glyburide 
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Table 4. Systemic Hemodynamics in Dogs Receiving Sevoflurane and Glyburide 
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Table 4. Systemic Hemodynamics in Dogs Receiving Sevoflurane and Glyburide 
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Table 5. Systemic Hemodynamics in Dogs Receiving Sevoflurane with Memory 
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Table 5. Systemic Hemodynamics in Dogs Receiving Sevoflurane with Memory 
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Table 6. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning with Memory 
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Table 6. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning with Memory 
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Table 7. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning and Sevoflurane with Memory 
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Table 7. Systemic Hemodynamics in Dogs Receiving Ischemic Preconditioning and Sevoflurane with Memory 
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Table 8. Transmural Myocardial Blood Flow (ml · min−1· g−1) in the Ischemic (LAD) and Normal (LCCA) Regions 
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Table 8. Transmural Myocardial Blood Flow (ml · min−1· g−1) in the Ischemic (LAD) and Normal (LCCA) Regions 
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