title: Cardiac electrophysiologic effects of quinidine and propranolol isomers in anesthetized dogs: concentration-response relationships.
abstract: Electrophysiological properties of quinidine and the two isomers of propranolol were compared in pentobarbital-anesthetized dogs using His bundle recordings and programmed stimulation in order to differentiate the effects resulting from beta-blockade from those related to nonspecific membrane-stabilizing effects. Quinidine in the plasma concentration range of 2.7-20 microM/liter resulted in concentration-dependent increases in atrionodal and His-Purkinje system conduction times and in the atrial effective refractory period. Quinidine did not produce any significant concentration-dependent change in atrioventricular (AV) nodal and ventricular refractory periods, sinus node automaticity, or QTc interval duration. Propranolol isomers in concentration range of 0.03-0.85 microM/liter produced a concentration-dependent increase in atrionodal conduction time but exerted no significant effect on His-Purkinje conduction time, QTc duration, or ventricular refractory period. Both isomers increased the atrial effective refractory period, but with slopes of concentration-response regression lines which were significantly different from those of quinidine. Only l-propranolol produced concentration-dependent increases in AV nodal refractory period, Wenckebach cycle length, and sinus node recovery time. These results suggest that the electrophysiological effects of propranolol isomers are related to beta-blockade and are significantly different from those resulting from the membrane-stabilizing effect of quinidine.
mesh_terms: D000758:Anesthesia; D000818:Animals; D001283:Atrioventricular Node / Q000187:drug effects; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects* / Q000502:physiology; D006339:Heart Rate / Q000187:drug effects; D008297:Male; D011433:Propranolol / Q000494:pharmacology*; D011802:Quinidine / Q000494:pharmacology*; D012032:Refractory Period, Electrophysiological / Q000187:drug effects; D013237:Stereoisomerism
chemical_list: D011433:Propranolol; D011802:Quinidine