Sevoflurane Exposure Generates Superoxide but Leads to Decreased Superoxide During Ischemia and Reperfusion in Isolated Hearts Leo G. Kevin, FCARCSI*, Enis Novalija, MD*†, Matthias L. Riess, MD*†, Amadou K. S. Camara, PhD*, Samhita S. Rhodes*‡, and David F. Stowe, MD, PhD*†‡§ Anesthesiology Research Laboratories, Departments of *Anesthesiology and †Physiology, and §Cardiovascular Research Center, The Medical College of Wisconsin, Milwaukee, Wisconsin; ‡Department of Biomedical Engineering, Marquette University, Milwaukee, Wisconsin; and Research Service, Veterans Affairs Medical Center, Milwaukee, Wisconsin Reactive oxygen species (ROS) are largely responsible for cardiac injury consequent to ischemia and reperfu- sion, but, paradoxically, there is evidence suggesting that anesthetics induce preconditioning (APC) by gen- erating ROS. We hypothesized that sevoflurane gener- ates the ROS superoxide (O 2 · - ), that APC attenuates O 2 · - formation during ischemia, and that this attenua- tion is reversed by bracketing APC with the O 2 · - scav- enger manganese (III) tetrakis (4-benzoic acid) porphy- rin chloride (MnTBAP) or the putative mitochondrial adenosine triphosphate-sensitive potassium (mK ATP ) channel blocker 5-hydroxydecanoate (5-HD). O 2 · - was measured continuously in guinea pig hearts by us- ing dihydroethidium. Sevoflurane was administered alone (APC), with MnTBAP, or with 5-HD before 30 min of ischemia and 120 min of reperfusion. Control hearts underwent no pretreatment. Sevoflurane di- rectly increased O 2 · - ; this was blocked by MnTBAP but not by 5-HD. O 2 · - increased during ischemia and during reperfusion. These increases in O 2 · - were at- tenuated in the APC group, but this was prevented by MnTBAP or 5-HD. We conclude that sevoflurane di- rectly induces O 2 · - formation but that O 2 · - formation is decreased during subsequent ischemia and reperfu- sion. The former effect appears independent of mK ATP channels, but not the latter. Our study indicates that APC is initiated by ROS that in turn cause mK ATP chan- nel opening. Although there appears to be a paradoxi- cal role for ROS in triggering and mediating APC, a pos- sible mechanism is offered. (Anesth Analg 2003;96:949 –55) A nesthetic preconditioning (APC) describes the phenomenon whereby brief exposure of the heart to a volatile anesthetic induces a state of protection against the effects of ischemia/reperfusion injury (1–5). This protection is manifested by de- creased myocardial stunning, decreased arrhythmias, and decreased infarction after ischemia/reperfusion. There is indirect evidence that anesthetics cause the release of reactive oxygen species (ROS) to trigger APC, because the protective effects of APC were abol- ished when ROS scavengers were given during anes- thetic exposure (2,3). In addition, a reduction in ROS formation appears to mediate, at least in part, the reduced tissue injury during ischemia and reperfusion because APC attenuated the release of oxidation prod- ucts during reperfusion (3). There is now evidence that significant ROS formation occurs during ischemia before reperfusion (6 – 8). The mitochondrial electron transport chain is believed to be the principle source of ROS during ischemia in cardiac cells (7) and may also be the source of the postulated ROS formation during anesthetic exposure, because an- esthetics are known to alter several indices of electron transport chain function (4,9,10). We have recently shown in intact hearts that APC leads to more normal- ized nicotinamide-adenine dinucleotide (NADH) (4) and attenuated mitochondrial Ca 2+ loading (5) during isch- emia and that APC leads to reduced ROS release from intact hearts (3) and to less ROS formation in isolated mitochondria during reperfusion (11). These findings suggest that improved mitochondrial bioenergetics dur- ing ischemia or reperfusion is a feature of APC and is likely to underlie the global functional and structural Supported in part by National Institutes of Health Grants HL- 58691 and GM-8204-06, by American Heart Association Grant 0360042Z, and by the Department of Veterans Affairs. Accepted for publication November 27, 2002. Address correspondence and reprint requests to David F. Stowe, MD, PhD, M4280, 8701 Watertown Plank Rd., Medical College of Wisconsin, Milwaukee, WI 53226. Address e-mail to dfstowe@ mcw.edu. DOI: 10.1213/01.ANE.0000052515.25465.35 ©2003 by the International Anesthesia Research Society 0003-2999/03 Anesth Analg 2003;96:949–55 949