Mechanisms by which Epoxyeicosatrienoic Acids (EETs) Elicit Cardioprotection in Rat Hearts

摘要

Cytochrome P450 (CYP) epoxygenases and their arachidonic acid (AA) metabolites, the epoxyeicosatrienoic acids (EETs), have been shown to produce reductions in infarct size in canine myocardium following ischemia/reperfusion injury via opening of either the sarcolemmal KATP (sarc KATP) or mitochondrial KATP (mito KATP) channel. In the present study, we subjected intact rat hearts to 30 minutes of left coronary artery occlusion and 2 hours of reperfusion followed by tetrazolium staining to determine infarct size as a percent of the area at risk (IS/AAR,%). The results demonstrate that the two major regioisomers of the CYP epoxygenase pathway, 11,12-EET (2.5 mg/kg, iv) and 14,15-EET (2.5 mg/kg, iv) significantly reduced myocardial infarct size (IS/AAR,%) in rats as compared with control (41.9±2.3%, 40.9±1.2% vs. 61.5±1.6%, respectively), whereas, a third regioisomer, 8,9-EET (2.5 mg/kg,iv) had no effect (55.2±1.4). The protective effect of pretreatment with 11,12-and 14,15-EET was completely abolished (61.9±0.7%, 58.6±3.1%, HMR; 63.3±1.2%, 63.2±2.5%, 5-HD) in the presence of the selective sarc KATP channel antagonist, HMR 1098 (6 mg/kg, iv) or the selective mito KATP channel antagonist, 5-HD (10 mg/kg, iv) given 10 minutes after 11,12- or 14,15-EET administration but 5 minutes prior to index ischemia. Furthermore, concommitant pretreatment with 11,12- or 14,15-EET in combination with the free radical scavenger, 2-mercaptopropionyl glycine (2-MPG), at a dose (20 mg/kg,iv) that had no effect on IS/AAR (57.7±1.3%), completely abolished the cardioprotective effect of 11,12 and 14,15- EET (58.2±1.6%, 61.4±1.0%), respectively. These data suggest that part of the cardioprotective effects of EETs in rat hearts against infarction is the result of an initial burst of reactive oxygen species (ROS) and subsequent activation of both the sarc KATP and mito KATP channel.