Isoflurane Preconditions Myocardium Against Infarction via Activation of Inhibitory Guanine Nucleotide Binding Proteins

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Abstract
Background: Isoflurane-induced myocardial protection during ischemia is mediated by adenosine triphosphate-regulated potassium (KATP) channels; however, the intracellular signal transduction cascade responsible for this process has been incompletely evaluated. The authors tested the hypothesis that isoflurane reduces myocardial infarct size through a Gi protein-mediated process. Methods: Forty-eight hours after pretreatment with vehicle (0.9% saline) or the Gi protein inhibitor pertussis toxin (10 microg/kg intravenously), barbiturate-anesthetized dogs (n = 43) were instrumented for measurement of aortic and left ventricular pressures and maximum rate of increase of left ventricular pressure. All dogs were subjected to a 60-min left anterior descending coronary artery occlusion followed by 3-h reperfusion. In four separate groups, vehicle- or pertussis toxin-pretreated dogs were studied with or without administration of 1 minimum alveolar concentration isoflurane. In two additional groups, dogs received the direct KATP channel agonist nicorandil (100 microg/kg bolus and 10 microg x kg-1 x min-1 intravenous infusion) in the presence or absence of pertussis toxin pretreatment. Myocardial perfusion and infarct size were measured with radioactive microspheres and triphenyltetrazolium staining, respectively. Results: Isoflurane significantly (P < 0.05) decreased infarct size to 7 +/- 2% of the area at risk compared with control experiments (26 +/- 2%). Pertussis toxin pretreatment alone had no effects on myocardial infarct size (31 +/- 4%) but blocked the beneficial effects of isoflurane (21 +/- 3%). Nicorandil decreased infarct size (11 +/- 2%), but, in contrast to isoflurane, this effect was independent of pertussis toxin pretreatment (11 +/- 1%). Conclusion: Isoflurane reduces myocardial infarct size by a Gi protein-mediated mechanism in vivo.