Differences in plasma β-endorphin and bradykinin levels between patients with painless or with painful myocardial ischemia

Abstract

To verify whether plasma β-endorphin and bradykinin affects the pathophysiology of myocardial ischemia and the perception of cardiac pain, 35 patients with coronary artery disease were subjected to treadmill testing and 48-hour Holter ECG monitoring to measure their pain thresholds. Patients were divided into two groups during exercise testing: group 1 (N = 19) who had ST segment depression, and group 2 (N = 16), who had chest pain. Both groups were then compared with 12 age-matched control subjects. Pain thresholds were measured after Holter ECG monitoring, and blood samples were drawn before and immediately after exercise. No statistical differences were noted between groups 1 and 2 with regard to the severity of myocardial ischemia as assessed by ST segment depression or exercise tolerance time. The frequency of the episodes of silent myocardial ischemia in group 1 was found to be significantly ( p < 0.05) higher than that in group 2. The duration of the episodes of silent myocardial ischemia in group 1 was 41.9 minutes (range 3 to 343 minutes), which was significantly ( p < 0.05) longer than that in group 2 (11.5 minutes; range 0 to 74). The pain threshold in group 1 was a statistically ( p < 0.05) higher value than that in group 2. Although the resting plasma β-endorphin level in group 1 was not statistically significantly different from values in either group 2 or the control group, during exercise the plasma β-endorphin levels in both group 1 and the control group were significantly ( p < 0.05) elevated in comparison with their resting levels. The resting plasma bradykinin level in group 2, on the other hand, was significantly ( p < 0.01) higher than those values in group 1 and the control group. Similarly during exercise the plasma bradykinin level increased in all three groups, but after exercise this increase was sustained only in group 2. These results suggest that plasma β-endorphin and bradykinin appear to possess factors that influence the perception of anginal pain.