Mechanism of Preconditioning by Isoflurane in Rabbits: A Direct Role for Reactive Oxygen Species
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Lippincott Williams & Wilkins, Inc.
LARGE quantities of reactive oxygen species (ROS) released during reperfusion after coronary artery occlusion damage proteins responsible for intracellular homeostasis, produce tissue injury, 1–3 depress contractile function, and increase myocardial infarct size. In contrast, small quantities of ROS may exert beneficial effects during ischemia and reperfusion when released before a prolonged ischemic event. 4 ROS derived from mitochondria during a brief ischemic episode produce preconditioning. 5,6 Free radical scavengers administered during ischemic preconditioning (IPC) markedly attenuate the protective effect of the preconditioning stimulus on infarct size. 5,7 These data suggest that IPC is mediated in part by small quantities of ROS released during preconditioning. Volatile anesthetics protect myocardium against infarction through a signal transduction pathway that includes adenosine type 1 receptors, 8–10 protein kinase C, 9,11 inhibitory guanine regulatory proteins, 12 and mitochondrial and sarcolemmal adenosine triphosphate-regulated potassium (KATP) channels. 13–16 A recent investigation by Müllenheim et al . provides compelling evidence that ROS also mediate myocardial protection produced by volatile anesthetics. 17 We sought to confirm and extend these important results by examining the hypothesis that ROS scavengers inhibit isoflurane-induced protection against irreversible ischemic injury. We further tested the hypothesis that isoflurane directly generates ROS in rabbit ventricular myocardium in vivo using a confocal microscopic technique combined with the superoxide anion-specific fluorescent probe dihydroethidium.