1. Antioxidant Defenses and Isoflurane Delayed Preconditioning Against Myocardial Stunning George J. Crystal, PhD, Gautam Malik, MD, Sung-Ho Yoon, MD, Juaquin B. Gonzalez, MD, Song-Jung Kim, PhD Department of Anesthesiology and Section of Cardiology, Advocate Illinois Masonic Medical Center, Chicago, IL 60657 and Departments of Anesthesiology and of Physiology and Biophysics, University of Illinois College of Medicine, Chicago, IL 60612 Background Conclusions Abstract Methods References Results 1.ISOPC and IPC had comparable, powerful delayed antistunning effects in the heart of the conscious dog. 2.These effects were associated with an increased activity of Mn SOD, thus providing evidence for a role for increased endogenous antioxidant defenses. Further studies are required to determine whether there is a causal relationship between the increase in myocardial antioxidant activity and the delayed antistunning effects of ISOPC and IPC. 1. Kim al. Anesthesiology 2008:A538 2. Bolli. Circulation 1990;82:723-738 3. Cowan et al. J Mol Cell Cardiol 1992;24:423-433 Our previous study demonstrated that isoflurane can produce delayed preconditioning (ISOPC) against myocardial stunning in the conscious dog. 1 This effect was powerful and comparable to that caused by ischemic preconditioning (IPC). 1 Because reactive oxygen species make an important contribution to the pathogenesis of myocardial stunning 2 and because previous studies have indicated that an exposure to oxidative stress can induce antioxidant enzymes in a variety of tissues, including the myocardium, 3 we tested the hypothesis that an increased activity of the antioxidant proteins, Cu-Zn SOD, Mn SOD, and catalase, plays a role in the delayed protection against myocardial stunning produced by ISOPC and IPC. 1. Eleven dogs were divided into two groups: Group 1, isoflurane induced preconditioning (ISOPC, n = 6). Group 2, ischemic preconditioning (IPC, n = 5). 2. Animals were chronically instrumented to measure CBF, global LV function, and regional wall thickening (WT) (Figure 1). 3. Arterial and coronary sinus samples were obtained to calculate myocardial oxygen consumption (MVO 2 ). 4. ISOPC was induced by inhaling 1 MAC isoflurane for 1 hr. IPC was induced by a 10-min coronary artery occlusion (CAO). 24 hr after either ISOPC or IPC, CAO was produced and the recovery of WT during reperfusion was assessed over time., The recovery of WT following the initial CAO in Group 2 served, as control response for both ISOPC and IPC. 5. Myocardial expression and activity of Cu-Zn SOD, Mn SOD, and catalase were measured by Western blotting and spectrophotometric techniques, respectively. Figure 1. A schematic diagram of chronic instrumentation. Introduction: Our previous study demonstrated that isoflurane can produce delayed preconditioning (ISOPC) against myocardial stunning in the conscious dog. 1 This effect was powerful and comparable to that caused by ischemic preconditioning (IPC). 1 Because reactive oxygen species make an important contribution to the pathogenesis of myocardial stunning, 2 we tested the hypothesis that an increased activity of the antioxidant proteins, Cu-Zn superoxide dismutase (SOD), Mn SOD, and catalase, plays a role in the delayed protection against myocardial stunning produced by ISOPC and IPC. Methods: Eleven mongrel dogs were chronically instrumented to measure coronary blood flow and myocardial wall thickening (WT). In group 1 (n=6), dogs inhaled 1 MAC ISO (1.4 % in O 2 ) for 60 min, after which time they were allowed to recover for 24 hrs during full reperfusion and studied in the conscious state. A 10-min coronary artery occlusion (CAO) was induced and the recovery of WT was monitored for 24 hrs. In group 2 (n=5), dogs underwent IPC, induced by a 10-min CAO; 24 hrs later they were subjected to another 10-min CAO. The recovery of WT following the initial CAO served as control response for both ISOPC and IPC. Myocardial protein expression and activity of Cu-Zn SOD, Mn SOD, and catalase were measured by western blotting and spectrophotometry, respectively. Findings in ISOPC (group 1) and IPC (group 2) were compared to those in normal region of group 2. Results: A 10-min CAO caused akinesis under all conditions. WT remained depressed (-25±4%) after three hours reperfusion in absence of either ISOPC or IPC (1st CAO; control response); 24 hrs of reperfusion were required for complete recovery. In contrast, only three hours reperfusion were required for complete recovery of WT following either ISOPC or IPC. Neither ISOPC nor IPC affected myocardial expression of Cu-Zn SOD, Mn SOD, or catalase. However, ISOPC and IPC both increased activity of Mn SOD by +36% and +73%, respectively; values for Cu-Zn SOD and catalase activity were unaffected. Conclusion: The powerful, delayed antistunning effects of ISOPC and IPC were associated with an increased activity of Mn SOD, thus providing evidence for a role for increased endogenous antioxidant defenses in these effects. Further studies are required to determine whether there is a causal relationship between the increase in myocardial antioxidant activity and these delayed preconditioning effects on myocardial stunning. Figure 2. A comparison of wall thickening (WT) changes during reperfusion following 1 st 10-min coronary artery occlusion (1 st CAO) i.e., without preconditioning, and following isoflurane preconditioning (ISOPC) or ischemic preconditioning (IPC). The results indicate that ISOPC and IPC caused comparable, more rapid recovery of WT during reperfusion. Figure 3. Western blotting of Cu-Zn SOD, Mn SOD, and catalase in normal (N), ischemic preconditioned (IPC), and isoflurane preconditioned (ISOPC) myocardium. There was no change in the expression of the antioxidant proteins during either ISOPC or IPC.