Protection by beta-blocking agents against free radical-mediated sarcolemmal lipid peroxidation.

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Abstract
The effects of beta-blocking and class I antiarrhythmic agents on free radical-mediated sarcolemmal lipid peroxidation were examined. Highly purified canine myocytic sarcolemmal membranes were pretreated with 10-800 microM of selected beta-blocking (propranolol, pindolol, metoprolol, atenolol, or sotalol) and class I (quinidine, lidocaine, procainamide, or diphenylhydantoin) antiarrhythmic agents at 37 degrees C for 10 minutes. Subsequently, a superoxide radical (derived from dihydroxyfumarate) driven, Fe3+-ADP catalyzed free radical generating system was added and incubated for up to 45 minutes. Lipid peroxidation of sarcolemma was determined by malondialdehyde formation. Pretreatment of the membranes with the five beta-blockers resulted in various degrees (20-95%) of inhibition of sarcolemmal peroxidation in a concentration- and time-dependent manner. All the class I agents were less effective (less than 20% inhibition). The order of potency of the beta-blockers was propranolol greater than pindolol greater than metoprolol greater than atenolol greater than sotalol and appeared to relate to their degree of lipophilicity. Propranolol, the most potent agent, achieved half-maximal inhibition of peroxidation at about 100 microM and achieved significance (p less than 0.01) at 20 microM. At pH 6.0, the efficacy of pindolol, metoprolol, atenolol, and sotalol diminished by 30-50% compared to pH 7.2, but the potency of propranolol remained unchanged. Since increased free radical production may occur during myocardial ischemia/reperfusion injury, the above findings suggest that the lipophilic beta-blockers may provide additional antiperoxidative protection of ischemic tissue.