Antiarrhythmic Effect And Mechanism Of The Boxwood Alkali A Study Of The Ring

CPB-A 1-4 mg/kg ( 1/100-1/25 LD₅₀) iv produced therapeutic and prophylactic effects which were found to de dose-dependent on experimental atrial and ventricular arrhythmias induced by BaCl₂ , aconitine, chloroform, adrenaline, ouabain and CaCl₂-Ach. It elevated the ventricular fibrillation thresholds (VFT) elicited by electrical stimulation,and reduced the incidences of ventricular arrhythmias after coronary artery occlusion and reperfusion in rats. Given at equitoxic doses, the antagonistic effects of CPB-A against ouabain-induced ventricular tachycardia and ischemia-elicited ventricular ectopic were more pronounced than those of CVB—D and Amio. The therapeutic index (LD₅₀/ED₅₀) and LD₁/ED,, of CPB—A were 1.8 and 4.2 times that of CVB-D respectively, and greater than that of Amio as well. Reserpine and vagotomy exerted no effects on the elevation of VFT and the increase in ouabain dosage for vertricular arrhythmias induced by CPB-A. Pithing of the spinal cord also did not prevent CPB-A from increasing doses of ouabain-induced arrhythmias. The statistical differences in heart rate (HR) and blood pressure (BP) between CPB-A, CVB-D or Amio and control were not found in guinea pigs. To sum up, CPB-A showed marked effectiveness against atrial and ventricular arrhythmias, which would not bear upon the autonomic nervous system, HR and BP. As Compared with CVB-D or Amio, CPB-A was likely a more potent and less toxic antiarrhythmic agent.