Failure of brief ischemic episodes to protect against myocardial dysfunction caused by ischemia and reperfusion in isolated rat hearts.

Brief periods of ischemia have been suggested to protect against myocardial injury caused by a subsequent episode of prolonged ischemia and reperfusion. However, the protective effects of brief ischemic periods against myocardial dysfunction after prolonged myocardial ischemia are controversial. To examine whether the protective effects of brief ischemic episodes relate to the extent of prior ischemic events, isolated rat hearts were subjected to either no preischemia (group A); one 5-minute episode of preischemia and 10 minutes of reperfusion (group B); or two 1-minute episodes of ischemia, each followed by 5 minutes of reperfusion (group C). All hearts were then subjected to 15 minutes of total ischemia and 10 minutes of reperfusion. In group A, after 10 min of reperfusion coronary perfusion pressure (CPP) was 31% +/- 10% (mean +/- SEM) higher than the control value, peak force of cardiac contraction (FCC) was 64% +/- 5% lower, and heart rate was 18% +/- 3% lower. In group B, CPP increased 26% +/- 6%, FCC fell 58% +/- 7%, and heart rate decreased 22% +/- 8% (group B vs group A, P value not significant) after ischemia and reperfusion. In group C, CPP increased 23% +/- 7%, FCC decreased 57% +/- 8%, and heart rate fell 8% +/- 4% on reperfusion (group C vs groups A and B, P value not significant). Creatine kinase (CK) was measured in the hearts from different groups and was found to be similar. Release of the adenosine triphosphate (ATP) metabolites hypoxanthine, inosine, and adenosine was also not different in the coronary effluents of the three groups of hearts.(ABSTRACT TRUNCATED AT 250 WORDS)