A pathogenetic role of .OH in myocardial stunning has been inferred from the protective effects of .OH scavengers and iron chelators. However, conclusive demonstration of the .OH radical hypothesis of myocardial stunning requires direct verification of three major, but still unproven, assumptions: (1) .OH is produced in the stunned myocardium in vivo; (2) antioxidant therapy inhibits .OH production; and (3) such inhibition results in enhanced recovery of contractility (ie, .OH is necessary for the development of myocardial stunning). Since phenylalanine (Phe) reacts with .OH to form the hydroxylated products ortho-, meta-, and para-tyrosines (o-, m-, and p-tyr), we used aromatic hydroxylation of Phe to detect .OH formation in the stunned myocardium. Open-chest dogs undergoing a 15-minute coronary occlusion followed by reperfusion received an intravenous infusion of Phe (54.3 mg/kg for 11.5 minutes beginning 90 seconds before reperfusion); these animals were given either no antioxidant therapy (group I, n ...
Recent studies suggest that the hydroxyl radical (.OH) plays a pathogenetic role in postischemic ventricular dysfunction (myocardial stunning). This concept, however, is predicated exclusively on results obtained in anesthetized open-chest preparations, which are subject to the confounding influence of many unphysiological conditions and in which both myocardial stunning and free radical generation are greatly exaggerated. The lack of supporting evidence in more physiological animal models represents a major limitation of the .OH hypothesis of stunning. Furthermore, concern has been raised that myocardial stunning may be a period of rest necessary for full recovery, so that attenuation of the early phase of stunning by antioxidant therapy may have subsequent detrimental effects on the resting function and/or on the return of myocardial contractile reserve. To address these issues, in phase 1 of this study conscious unsedated dogs undergoing a 15-minute coronary artery occlusion received an intravenous...
BACKGROUNDMounting evidence suggests a protective effect of exogenous adenosine in myocardial ischemia and reperfusion. We tested the hypothesis that augmentation of endogenous adenosine levels, achieved by inhibiting adenosine catabolism and washout, is beneficial in postischemic myocardial dysfunction (stunning).METHODS AND RESULTSIn phase I of the study, open-chest dogs undergoing a 15-minute coronary artery occlusion and 4 hours of reperfusion received an intracoronary infusion of either saline (controls, n = 23) or 6-(4-nitrobenzyl)-mercapto: purine ribonucleoside (NBMPR, a selective nucleoside transport inhibitor) combined with erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA, a potent adenosine deaminase inhibitor) (EHNA + NBMPR, n = 15) starting 15 minutes before coronary occlusion and ending 15 minutes after the initiation of reflow. Regional myocardial function (assessed as systolic wall thickening) was similar in control and treated groups at baseline and during ischemia. After reperfusion, however...
We studied the effects of a thrombolytic agent (t-PA) and a thromboxane synthetase inhibitor (CGS-13080) in a model of myocardial ischemia and reperfusion. Occlusion of the left anterior descending coronary artery for 2 hours followed by 4 hours of reperfusion in anesthetized cats results in a large washout of creatine kinase into the blood (32 +/- 7 IU/mg protein) and an area of necrotic tissue comprising 52 +/- 5% of the area at risk and 9 +/- 0.6% of the left ventricle. Intravenous administration of t-PA (500 IU/kg.min) for 30 minutes alone at reperfusion or infusion of CGS-13080 (500 micrograms/kg.hr) had no effect on washout of creatine kinase or extent of necrotic tissue development. Administration of the same doses of both t-PA and CGS-13080 together markedly attenuated creatine kinase release to 10 +/- 2 IU/mg protein (p less than 0.01) and reduced the area of necrotic tissue to 9 +/- 2% of the area at risk and only 1.3 +/- 0.3% of the left ventricle (p less than 0.001). No significant sustained e...
