Abstract 16190: In vivo Myocardial Ischemia-Reperfusion Alters Endothelial Nitric Oxide Synthase (eNOS) Function Secondary to Endogenous Tetrahydrobiopterin (BH4) Depletion
eNOS activity is regulated by the cofactor tetrahydrobiopterin (BH4) and reduced BH4 availability in disease may lead to impaired eNOS activity and increased superoxide generation. It is reported that myocardial BH4 levels are decreased after myocardial ischemia-reperfusion injury (IRI); however, the extent to which alterations in endogenous BH4 availability might play a crucial role in modulating myocardial salvage following in vivo IR remains unclear. Therefore, to address the role of BH4 and eNOS in myocardial IRI, rats were subjected to 60-min in vivo left coronary artery occlusion and varying periods (10-min, 20-min, 24-hr) of reperfusion with or without preischemic BH4 supplementation (1 mg/kg, iv, n=8). Myocardial BH4 content, eNOS protein levels, and NOS activity were determined in the area at risk (AAR) and nonischemic (NI) area of left ventricle (LV). Myocardial infarct size was measured 24-hr after reperfusion. In untreated rats, 60-min regional ischemia drastically reduced LV BH4 content in AAR (39%) compared to NI area and it remained lower during early reperfusion (34% for 10-min and 47% for 20-min) followed by recovery at 24-hr reperfusion (100%). peNOS- S1177 level and NOS activity were also significantly reduced during ischemia and/or early reperfusion, but, recovered at 24-hr reperfusion. BH4 supplementation markedly increased baseline BH4 levels in both AAR and NI area (11-fold and 10-fold). Importantly, compared to untreated groups, BH4 levels were identical in the AAR and NI area during ischemia (7-fold in AAR and 2-fold in NI) and early reperfusion (6-fold in AAR, 1.6-fold in NI for 10-min and 3-fold in AAR, 1.2-fold in NI for 20-min), and they were significantly higher than those in untreated AAR. While BH4 treatment preserved peNOS- S1177 expression in the AAR during I/R, the decrease in total eNOS was delayed compared to untreated rats (20- vs. 10-min reperfusion). BH4 supplementation significantly reduced myocardial infarct size compared to untreated group (31±2% vs. 61±1%, P<0.001, n=8/group). Thus, these findings provide direct evidence that in vivo I/R induces eNOS dysfunction secondary to BH4 depletion and preischemic BH4 treatment prevents eNOS dysfunction and improves postischemic myocardial salvage.
- © 2010 by American Heart Association, Inc.