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Infarct size and nitric oxide synthase in murine myocardium
M S Sumeray1, D D Rees, D M Yellon
1The Hatter Institute, Department of Academic and Clinical Cardiology, University College Hospital, Grafton Way, London, WC1E 6DB, UK.
Abstract:
Controversy surrounds the involvement of nitric oxide (NO) in myocardial ischaemia-reperfusion injury and the balance between deleterious and beneficial effects. NO synthase (NOS) is expressed constitutively as two isoforms: endothelial (eNOS) and neuronal (nNOS). Knockout mice lacking the gene for either eNOS (eNOS KO) or nNOS (nNOS KO), were compared with wild-types (WT) during a protocol of global ischaemia-reperfusion injury. Thirty-six mouse hearts (12 from each group) were isolated and the aorta cannulated for Langendorff perfusion with modified Krebs solution at constant pressure. An apical suture connected the left ventricle to a force transducer via a light weight coupling rod. Following stabilization hearts were subjected to 30 min of global ischaemia at 37 degrees C. During 30 min reperfusion, the recovery of baseline force-rate product (F%) was recorded. Hearts were then stained with tetrazolium, frozen, sliced, and fixed with formalin. Slices were compressed between plexiglas plates, and a magnified video image digitized to allow planimetry for infarct size (as percentage of ventricular volume I/R). Although recovery of contractile function did not differ between groups, eNOS KOs suffered significantly larger infarcts than WT or nNOS KOs (41 v 33 and 30% respectively, P<0.05 for both comparisons). A protective role for eNOS against global ischaemia-reperfusion injury has been demonstrated for the first time in murine myocardium. This may have important clinical implications for future pharmacotherapy to enhance myocardial protection.
Insights
Endothelial nitric oxide synthase (eNOS) protects the heart from injury after reperfusion. Mice lacking eNOS experienced larger infarcts, suggesting a protective role for eNOS in myocardial ischemia-reperfusion injury.
Area of Science:
- Cardiovascular Research
- Molecular Cardiology
- Ischemia-Reperfusion Injury
Background:
- The role of nitric oxide (NO) in myocardial ischemia-reperfusion (I/R) injury is debated, with potential for both harmful and beneficial effects.
- Nitric oxide synthase (NOS) exists as two constitutive isoforms: endothelial (eNOS) and neuronal (nNOS).
Purpose of the Study:
- To investigate the distinct roles of eNOS and nNOS in myocardial I/R injury using knockout mouse models.
- To determine the protective or detrimental effects of eNOS and nNOS during cardiac I/R.
Main Methods:
- Comparison of wild-type (WT), eNOS knockout (eNOS KO), and nNOS knockout (nNOS KO) mouse hearts subjected to 30 minutes of global ischemia and 30 minutes of reperfusion.
- Langendorff perfusion system used to assess recovery of contractile function (force-rate product) and infarct size (planimetry).
Main Results:
- Recovery of contractile function did not significantly differ between WT, eNOS KO, and nNOS KO groups.
- eNOS KO hearts exhibited significantly larger infarct sizes (41%) compared to WT (33%) and nNOS KO (30%) hearts (P<0.05).
Conclusions:
- Endothelial nitric oxide synthase (eNOS) plays a protective role against myocardial ischemia-reperfusion injury in murine models.
- These findings suggest potential clinical implications for pharmacotherapies targeting eNOS to enhance myocardial protection.