Nitric oxide inhibition impairs blood flow during exercise in hearts with a collateral-dependent myocardial region
Abstract
We sought to determine the importance of nitric oxide (NO) production in maintaining coronary blood flow during exercise in hearts with collateral-dependent myocardium. Coronary collateral vessels demonstrate endothelium-mediated NO-dependent vasodilation in response to agonists such as acetylcholine. However, the contribution of endogenous NO production to maintaining vasodilation of coronary collateral vessels during exercise has not been previously studied. Collateral vessel growth was induced in 13 chronically instrumented dogs by intermittent 2-min occlusions, followed by permanent occlusion of the left anterior descending coronary artery (LAD). One week after permanent LAD occlusion, myocardial blood flow was measured with microspheres during rest and treadmill exercise at 6.4 km/h at a 15% grade. Measurements were then repeated after blockade of NO production with N-nitro-L-arginine (LNNA) (20 mg/kg body weight intravenously). LNNA caused a 62 +/- 4% (mean +/- SEM) inhibition of the coronary vasodilation produced by acetylcholine. During rest conditions, LNNA caused a slight decrease in blood flow to the collateral region (p = NS), with no change in normal zone blood flow. During exercise, LNNA caused a decrease in mean ...Continue Reading
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