ANTIARRHYTHMIC ACTIVITY OF DEXTRO- AND LEVO-ISOMERS OF 5-METHYL-8-(2-HYDROXY-3-T-BUTYLAMINO-PROPOXY) COUMARIN HYDROCHLORIDE (BUCUMOLOL), A β-ADRENERGIC BLOCKING AGENT, ON ACONITINE-INDUCED ATRIAL AND OUABAIN-INDUCED VENTRICULAR ARRHYTHMIAS IN DOGS

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-The β-blocking, antiarrhythmic, and local anesthetic effects of the racemic mixture and optical isomers of bucumolol, 5-methyl-8-(2-hydroxy-3-t-butylamino-propoxy) coumarin hydrochloride, were studied in dogs, guinea-pigs and frogs. In blocking the positive chronotropic response to isoproterenol, the levo-isomer of bucumolol was about 40 times more potent in dogs, and 270 times in guinea-pigs than its dextro-isomer and twice as effective in both species as the racemic mixture. In frog sciatic nerves bucumolol was 1/10-1115 as potent in local anesthetic action as propranolol on a weight basis. Dextro- and levo-isomers and racemic bucumolol neither elevated electrical threshold for propagated impulses nor prolonged the effective refractory period of the dog right atrium. The levo-isomer and racemic bucumolol were capable of suppressing aconitine-induced atrial arrhythmia, while the dextro-isomer was less effective Both isomers and racemic bucumolol were capable of reversing ventricular arrhythmia caused by ouabain, but the effective dose of the levo-isomer was significantly less than that of the dextro-isomer. The results suggest that both specific β-blocking activity and non-specific membrane action of bucumolol suppressed experimental arrhythmias in dogs produced by aconitine and ouabain.
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