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We hypothesized that the endogenous coronary vasodilator adenosine may reduce infarct size by progressively increasing reflow in a preparation of coronary occlusion-reperfusion. After 90 min of proximal left anterior descending artery occlusion, 20 dogs were randomized to blood reperfusion with (n = 10) or without (n = 10) adenosine into the proximal left anterior descending vessel at 3.75 mg/min for 60 min after reperfusion. Regional myocardial blood flow was determined serially with microspheres and regional ventricular function was assessed by a computerized radial shortening method. At 24 hr, the area at risk was defined in vivo with monastral blue dye and area of necrosis was determined after incubation of left ventricular slices in triphenyltetrazolium chloride. Hemodynamic variables were similar in the two groups during the experimental protocol. Infarct size was significantly reduced in treated animals, both when expressed as a percentage of the area at risk (9.9 2.8% vs 40.9 + 6.6%, p < .001) and as a percentage of the left ventricle (4.6 ± 1.3% vs 18.0 ± 3.4%, p = .002). This was associated with significant improvement in radial shortening in the ischemic zone 24 hr after reperfusion (10. 1 ± 2.5 vs -2.8 + 2.2%, p < .01). Regional myocardial blood flow was significantly increased in endocardial and epicardial regions from the lateral ischemic zone 1 hr after reperfusion in adenosine-treated animals. Light microscopy demonstrated decreased neutrophil infiltration in the ischemic zone and electron microscopy showed relative preservation of endothelial structure in the subendocardium with reduced neutrophil and red cell stagnation ofcapillaries in the treated group. These findings suggest that intracoronary administration of adenosine after reperfusion significantly reduces infarct size and improves regional ventricular function in the ischemic zone in the canine preparation.

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