Submitted on March 29, 2006
Accepted on January 16, 2007
Evidence for Enhanced eNOS Function in Coronary Microvessels during the Second Window of Protection
Song-Jung Kim1*, Xiaoping Zhang2, Xiaobin Xu3, Alice Chen4, Joaquin B Gonzalez4, Sharat Koul5, Kalpana Vijayan5, George J. Crystal6, Stephen F. Vatner7, and Thomas H. Hintze3
1 Physiology and Biophysics, UIC-College of Medicine, Chicago, Illinois, United States
2 Cell and Molecular Medicine, UMDNJ, Newark, New Jersey, United States
3 Physiology, New York Medical College, Valhalla, New York, United States
4 Cardiology, AIMMC, Chicago, Illinois, United States
5 Cardiology, AIMMC, Chicago, Illinois, United States; Chicago, Illinois, United States
6 Dept. of Anesthesiology, University of Illinois College of Medicine, Chicago, Illinois, United States
7 Cell Biology and Molecular Medicine, University of Medicine and Dentistry of New Jersey, New Jersey Medical School, Newark, New Jersey, United States
* To whom correspondence should be addressed. E-mail: kimso{at}uic.edu.
NO derived from endothelial NOS (eNOS) has been identified as a trigger for the second window of protection (SWOP), but its role as a mediator during the SWOP is a matter of debate. Eighteen mongrel dogs were chronically instrumented to measure left ventricular function, coronary blood flow, and wall thickening. Myocardial preconditioning was induced by 10 min coronary artery occlusion. Following 24 hrs of reperfusion (during the SWOP), the hearts were excised. Coronary microvessels were isolated and incubated in presence of (1) the endothelium-dependent agonists, carbachol and bradykinin, (2) the calcium ionophore, A23187, and (3) the ACE inhibitors, enalaprilat and ramiprilat. Nitrite, a metabolite of NO, was measured. Under baseline conditions, nitrite production in microvessels from SWOP was 30% higher than that from Normal (96±4 vs. 74±3 pmol/mg, p<0.01, respectively). Nitrite production in response to carbachol, bradykinin, and A23187 was also enhanced in microvessels from SWOP (p<0.05). These enhanced responses were abolished by L-NAME or the endothelial receptor-specific antagonists, atropine and HOE-140. The level of eNOS protein in the SWOP myocardium was 2-fold higher than that in the non-SWOP myocardium. Nitrite production in response to the ACE inhibitors was greater in microvessels from SWOP. These effects were blocked by L-NAME, HOE-140, or DCIC (which inhibits kinin formation). We found that a brief ischemic episode induced delayed, enhanced NO production in coronary microvessels and an upregulation of eNOS protein. These findings suggest that eNOS is a mediator during the SWOP. The ability of ACE inhibitors to enhance NO release during the SWOP points to an additional clinical application for these drugs.
