Free radical scavenging properties of beta-adrenoceptor blockers are not relevant for cardioprotection in isolated rabbit hearts

Several beta-adrenoceptor-blocking agents have been shown to possess free radical scavenging properties. Therefore, the direct cardioprotective properties of propranolol or pindolol were investigated in comparison to superoxide dismutase (SOD). We used isolated rabbit hearts paced at a constant rate (Langendorff, constant pressure: 70 cm H2O, Tyrode solution, Ca2+ 1.8 mmol/l). Acute regional myocardial ischemia (MI) was induced by left coronary artery branch occlusion and quantitated from epicardial NADH-fluorescence photography. Propranolol (10(-8) mol/l), pindolol (10(-6) mol/l) or SOD (48 I.U./ml) had no significant influence on left ventricular pressure, pressure-rate product or global coronary flow (p > 0.05). Whereas epicardial NADH-fluorescence area after repetitive coronary occlusions was significantly diminished by SOD-treatment (-25%) (p < 0.05), MI size was not significantly affected by either propranolol or pindolol (p > 0.05). Conclusion: Oxygen-derived free radicals contribute to tissue injury during myocardial ischemia, and propranolol or pindolol do not possess free radical scavenging properties relevant for cardioprotection in a repetitive coronary occlusion model in isolated rabbit hearts.