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,
,
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* From the Department of Anesthesiology, and
Section of Cardiology, Advocate Illinois Masonic Medical Center; and the
Departments of Anesthesiology and of Physiology and
Biophysics, University of Illinois College of Medicine, Chicago, Illinois, USA.
Address correspondence to: Dr. George J. Crystal, Department of Anesthesiology, Advocate Illinois Masonic Medical Center, 836 West Wellington Avenue, Chicago, IL 60657 USA. Phone: 773-296-5375; Fax: 312-296-5362; E-mail: gcrystal{at}uic.edu
Introduction: It is well known that hemoglobin is a scavenger of nitric oxide (NO). The present study used a canine model to test the hypothesis that acute normovolemic hemodilution (ANH) affects NO-mediated coronary vasodilation.
Methods: Studies were performed in 18 open-chest, anesthetized dogs. In Series 1, the contribution of endogenous NO to coronary vasodilatation during ANH with 5% dextran-40 (reduction in hematocrit by 50%) was assessed. This was accomplished by comparing myocardial blood flow (MBF; radioactive microspheres) in the left anterior descending (LAD) region, which was treated with the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), to that in the circumflex (control) region. In Series 2, the LAD was perfused via a controlled-pressure extracorporeal system with coronary blood flow (CBF) measured with an ultrasonic, transit-time flow transducer. The dose-dependent increases in CBF caused by acetylcholine (ACh), which releases endogenous NO from the vascular endothelium, and sodium nitroprusside (SNP), which provides exogenous NO, were compared before and during ANH.
Results: Acute normovolemic hemodilution caused similar (approximately twofold) increases in MBF (P < 0.01) in the absence and presence of L-NAME, and it did not affect the dose-related increases in CBF caused by ACh and SNP.
Conclusions: Series 1: under baseline conditions, hemoglobin in red blood cells does not limit the coronary vasodilatation resulting from tonic release of NO; NO does not mediate coronary vasodilation during ANH. Series 2: ANH does not influence the coronary vasodilating effects of increased levels of NO, whether due to endogenous release (ACh) or infusion of an NO donor (SNP).
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