Coronary Nitric Oxide Production in Response to Exercise and Endothelium-Dependent Agonists

Background—Endothelium-derived nitric oxide (NO) contributes to epicardial coronary artery vasodilation during exercise. However, blockade of NO production does not impair the increase in coronary blood flow (CBF) during exercise, suggesting that NO is not obligatory for exercise-induced coronary resistance vessel dilation. In contrast, the increases in CBF produced by endothelium-dependent agonists are decreased after NO blockade. Consequently, this study was performed to determine whether the increase in coronary NO production in response to agonists is greater than that which occurs during exercise. Methods and Results—We measured the oxidation products of NO (nitrate+nitrite=NOx) in aortic and coronary sinus plasma using chemiluminescence to assess NOx production across the coronary circulation in chronically instrumented dogs during a 3-stage treadmill exercise protocol and in response to intracoronary administration of the endothelium-dependent agonists acetylcholine (37.5 μg/min) and bradykinin (3....