Protection of Myocardial Function and Coronary Vasculature by Streptokinase

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Abstract
Coronary artery reperfusion established by thrombolytic agents early in the evolution of an acute myocardial infarction is known to result in the salvage of otherwise jeopardized heart muscle. Recently, experimental evidence has suggested that reactive products of oxygen are formed as a result of reperfusion and can increase the amount of myocardial tissue that becomes irreversibly damaged. The purpose of the present study was to determine if the thrombolytic agent, streptokinase, could serve to scavenge reactive species of oxygen, thereby protecting the myocardium by a mechanism independent of its ability to lyse an occlusive thrombus. Rabbit isolated hearts were perfused at a constant rate with Krebs-Henseleit buffer (25 ml/min, 31°C, pH 7.4) using a modified Langendorff method. Changes in the permeability of the coronary vascular bed were determined with ‘“1-labeled albumin added to the perfusion buffer. An intraventricular fluid-filled latex balloon connected to a pressure transducer maintained the left ventricle in an isovolumic state and was used to detect changes in myocardial contractility throughout the study protocol. Electrolysis of the oxygenated Krebs-Henseleit perfusion buffer with a 20 mA direct current for 2 min, delivered with a stainless-steel anode (proximal) and a platinum cathode (distal), resulted in the generation of reactive products of oxygen. Perfusion of the isolated heart with buffer containing the products of electrolysis resulted in an increase in mean coronary artery perfusion pressure, from 48 ± 3 to 121 ±6 mm Hg [mean ± SEM (n = 17)]. and an increase in the left ventricular end-diastolic pressure, from 10 ± 1 to 54 ± 6 mm Hg. The addition of streptokinase (150 U/ml) or heparin (20 U/ml) to the perfusion medium attenuated the observed increase in coronary artery perfusion pressure from 42 ± 3 to 73 ± 9 mm Hg (n = 9) or from 43 ± 2 to 98 ± 9 mm Hg (n = 9), respectively. In addition, streptokinase prevented the increase in the left ventricular end-diastolic pressure (11 ± I to 36 ± 5 mm Hg, n = 9) and preserved left ventricular function as determined by the pressure-volume relationship. Myocardial accumulation of l25I-la-beled albumin after exposure of the heart to the reactive products of oxygen was attenuated by the addition of streptokinase or heparin to the buffer solution. The data suggest that streptokinase and, to a lesser extent, heparin may preserve myocardial and coronary vascular function by scavenging reactive oxygen species.