CHOLINERGIC AND ALPHA-ADRENERGIC CORONARY CONSTRICTION WITH INCREASING ISCHEMIA-REPERFUSION INJURY

Ischemia-reperfusion-induced injury of the coronary vasculature could result in an attenuated vasodilator or increased vasoconstrictor tone that might impact on myocardial recovery and viability. In 30 open-chest dogs the left circumflex coronary artery was occluded for 15 or 60 min and then reperfused, and responses to intracoronary acetylcholine, the alpha(1)-adrenergic agonist methoxamine, and the alpha(2)-adrenergic agonist BHT-933 (n = 10 each) were measured. In the experiments with 60 min of occlusion, triphenyltetrazolium chloride (TTC) staining was used to distinguish reversibly (TTC+) and irreversibly (TTC-) injured myocardium. After 15 min of occlusion, the vasodilator response to acetylcholine was not altered but was significantly reduced in TTC+ subendocardium and midmyocardium after 60 min of occlusion and was further reduced in TTC-subendocardium, midmyocardium, and also in subepicardium. The vasoconstrictor responses to methoxamine and BHT-933 were not altered after 15 or 60 min of occlusion in both TTC+ and TTC- myocardium. Posterior wall thickening was not affected by acetylcholine, methoxamine, or BHT-933. Thus, in reversibly injured myocardium after 15 min of occlusion, cholinergic and alpha-adrenergic coronary vasomotor responses are unchanged. With increasing duration of ischemia, reversibly and even more so irreversibly injured reperfused myocardium are characterized by an impaired cholinergic coronary vasodilation but not an enhanced alpha-adrenergic coronary vasoconstriction.