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Objective— Coronary flow is closely correlated to the myocardial metabolic demand. We tested the hypothesis that hydrogen peroxide (H2 O2 ) derived from beating hearts mediates metabolic coronary microvascular dilation.Methods and Results— We used a bioassay method in which an isolated microvessel is placed on a beating heart to detect myocardium-derived vasoactive mediators. A rabbit coronary arterial microvessel (detector vessel [DV], n=25) was pressurized and placed on a canine beating heart. After intrinsic tone of DV had developed, we observed DV at rest (heart rate, 120 bpm) and during tachypacing (heart rate, 240 bpm) using an intravital microscope equipped with a floating objective. The tachypacing produced DV dilation by 8.2% (P &lt;0.01 versus baseline), and the dilation was abolished by cell-impermeable catalase (a H2 O2 scavenger, 500 U/mL). We performed myocardial biopsy at rest and tachypacing. The biopsy specimens were loaded with 2′,7′-dichlorodihydrofluorescein diacetate (10 μmol/L) to visualize H2 O2, and observed with confocal microscopy. Dichlorofluorescein fluorescence was diffusely identified in the myocardium and the tachypacing increased the fluorescence intensity (P &lt;0.01). Exogenous H2 O2 caused vasodilation of arterial microvessels in vitro in a concentration-dependent manner that was abolished by catalase.Conclusions— H2 O2 derived from the beating heart mediates tachypacing-induced metabolic coronary vasodilation in vivo.

Hydrogen Peroxide Derived From Beating Heart Mediates Coronary Microvascular Dilation During Tachycardia