Myocardial dysfunction and norepinephrine release in the isolated rat heart injured by electrolysis-induced oxygen free radicals

Abstract

In the present investigation, we used electrolysis as a source of oxygen free radicals to test their possible role in norepinephrine release, as well as in the mechanism of cellular injury, cardiac dysfunction and arrhythmias. In the isolated rat heart perfused under constant pressure, according to the Langendorff technique, electrolysis of the Krebs-Henseleit solution (10 mA d.c. current for 1 min) produced myocardial irreversible dysfunction within 5 min. Fifteen minutes after electrolysis, significant falls in the left ventricular pressure (from 87.5 ± 6.8 to 33.7 ± 5.2 mmHg), dP dt max (from 1230 ± 90 to 375 ± 59 mmHg/s), heart rate (from 287 ± 18 to 119 ± 13.5 beats/min) and coronary flow (from 14.8 ± 9 to 3·4 ± 1.7 ml/min) were observed, along with an increase in left ventricular end diastolic pressure from 10 to 50 ± 3.5 mmHg ( n = 8, P < 0.01). AV conduction block and/or sinus bradycardia were noted in all preparations. An increase in norepinephrine washout from 298.5 ± 84 at baseline to 610 ± 110 pg/min/g 5 min after electrolysis was measured ( n = 8, P < 0.05) and a 44.8 ± 9·2% and 35 ± 7.5% reduction, respectively in right and left ventricular tissue norepinephrine content was also found at 30 min ( n = 5, P < 0.05). Pretretment of the hearts 10 min before electrolysis and throughout the experimental period by superoxide dismutase (SOD; 100 U/ml), catalase (150 U/ml), a combination of SOD + catalase or mannitol (50 m m) partially blocked the deleterious effect of free radicals and permitted a functional recovery of 50 to 60%, mannitol being the more potent protective agent. Furthermore, these scavengers also significantly reduced norepinephrine washout. Thus, it appears that electrolysis-generated free radicals may injure sympathetic neuronal as well as myocardial membranes, hence induce norepinephrine release, rhythm disturbances and cardiac dysfunction.