An enzyme mechanism in explanation of pain in angina pectoris.

The effect of catecholamines, represented by epinephrine and norepinephrine, on the activity of phospholipase A2 from bee venom was studied. It was shown that the hydrolysis of l-alpha-lecithin to lysolecithin and a fatty acid was considerably activated by preincubation of the lecithin with the biogenic amine. On the other hand, addition of nitroglycerin or propranolol to the enzyme solution considerably curtailed activation by the catecholamines. The pharmacological effect of the split products of l-alpha-lecithin, free fatty acids (FFA), and lysolecithin in the nascent state on the myocardial cell membrane might be more plausible than the commonly accepted theory that the FFA derive from lipolysis of remote fat deposits. Certain arrhythmias and ion imbalances might be caused by catecholamine activation of phospholipase A2. Of great pharmacological interest is the observation that this activation is inhibited by a beta-adrenergic blocking agent without the presence of cyclic adenosine monophosphate as a messenger. The reaction may serve as a model for the study of the pharmacological influence of nitroglycerin and propranolol on angina pectoris.