Reexamination of the roles of beta-endorphin and cardiac autonomic function in exercise-induced silent myocardial ischemia

Abstract

Background: Anginal pain perception has been reported to be modulated by endogenous opiates, or peripherally as a result of neuropathy. However, whether these factors can contribute to the mechanisms of silent myocardial ischemia remains unclear. Methods: Based on the results of previous exercise testing, a total of 140 patients (39 diabetic and 101 nondiabetic) with exercise-induced myocardial ischemia were divided into the following four groups: 19 diabetics with silent myocardial ischemia; 49 nondiabetics with silent myocardial ischemia; 20 diabetics with anginal symptoms; and 52 nondiabetics with anginal symptoms. All patients underwent treadmill exercise testing and 24-hour ambulatory electrocardiographic recording plasma beta- endorphin levels and tactile thresholds were measured before and during exercise. With regard to the ambulatory electrocardiographic recording, the mean of the standard deviations (SDNNIDX) of all normal sinus RR intervals during successive 5-minute recording periods over 24 hours was analyzed and considered as an index of the autonomic function. Results: The plasma beta- endorphin level during exercise was significantly greater in nondiabetic patients with silent myocardial ischemia than in diabetics with silent myocardial ischemia and in nondiabetics with anginal symptoms. The SDNNIDX mean was significantly less in diabetics with silent myocardial ischemia than in diabetics with anginal symptoms; in nondiabetics with anginal symptoms; and in nondiabetics with silent myocardial ischemia. Conclusions: We confirm that elevated beta-endorphin levels are associated with silent myocardial ischemia in nondiabetic patients and that abnormalities in autonomic function seen in diabetes are associated with the silent form of myocardial ischemia.