Role of adenosine and opioid-receptor mechanisms for pain in patients with silent myocardial ischemia or angina pectoris: a double-blind, placebo-controlled study.

UNLABELLED: Patients with silent myocardial ischemia have similar prognosis but fewer primary care and emergency care visits than patients with angina pectoris. Silent myocardial ischemia has been associated with an increased pain threshold because of an increased endogenous opioid receptor activity. In this double-blind, placebo-controlled study, we tested whether patients with silent myocardial ischemia would have less sensitivity to the ischemic pain messenger adenosine compared with angina pectoris patients and healthy controls. In addition, we tested whether this effect might be due to an increased opioid receptor activity.

MATERIALS AND METHODS: Thirteen male patients with silent myocardial ischemia (mean age 58 +/- 10 years with BMI 25 +/- 3) were compared with 10 male patients with angina pectoris (mean age 57 +/- 9 years with BMI 29 +/- 5). Healthy volunteers (mean age 52 +/- 7 years with BMI 25 +/- 3, n = 10), acted as controls. Increasing doses of adenosine were injected rapidly into an antebrachial vein in a double-blind, randomized order. Central chest pain was provoked and quantified using psychophysical methods. The procedure was repeated after an injection of 0.4 mg of the non-selective opioid antagonist, naloxone.

RESULTS: Patients with silent myocardial ischemia exhibited higher pain threshold than patients with angina pectoris and healthy volunteers. After naloxone, healthy volunteers and patients with angina pectoris tended to have more pain than patients with silent myocardial ischemia.

CONCLUSION: In conclusion, patients with silent myocardial ischemia had a decreased sensitivity to adenosine-provoked chest pain compared with patients with angina pectoris. The decreased pain sensitivity was not related to opioid receptor activity.