Flumazenil mimics whereas midazolam abolishes ischemic preconditioning in a rabbit heart model of ischemia-reperfusion

Background: The goal of the current study was to assess the effects of flumazenil, a benzodiazepine receptor antagonist, in limiting infarct size and in reducing hydroxyl free radical production. Methods: After intravenous salicylate (100 mg/kg) administration, rabbits were subjected to 40 min of regional myocardial ischemia and 2 h of reperfusion. In one group, flumazenil (0.05 mg/kg) and, in another, midazolam (0.05 mg/kg) was administered 15 min before 40 min of ischemia. Ischemic preconditioning (IP) was elicited by 5 min of ischemia followed by 10 min of reperfusion (before the 40-min ischemia period). In two other groups, midazolam was added to flumazenil and IP. Infarct size was determined using triphenyl tetrazolium chloride staining. The authors quantified the hydroxyl-mediated conversion of salicylate to its 2,3- and 2,5-dihydroxybenzoate derivatives during reperfusion by high-performance liquid chromatography coupled with electrochemical detection. Results are expressed as mean +/- SEM. Results: Flumazenil, like IP, significantly decreased infarct size (23 +/- 4 and 22 +/- 5%, respectively, vs. 57 6% in control group; P < 0.01). Midazolam inhibited the effects of flumazenil and IP. Flumazenil and IP significantly limited the increase in the normalized concentrations of 2,3- and 2,5-dihydrox-ybenzoic acids. With midazolam, however, the increase was comparable to that of the control group. 5-Hydroxydecanoate, a selective mitochondrial adenosine triphosphate-sensitive K+ channel blocker, given with flumazenil, abolished the protection obtained with the latter. Conclusions: Flumazenil mimics preconditioning to decrease infarct size and hydroxyl radical production during reperfusion. Midazolam, however, abolishes these effects. Blockade of benzodiazepine receptors is upstream to the mitochondrial adenosine triphosphate-sensitive K+ channels in the preconditioning cascade.