Experimental Study of Practolol on Cardiac Arrhythmias

ABSTRACT

Recently several adrenergic beta receptor blocking agents such as dichloroisoprenaline, pronethalol, INPEA, H13/57, propranolol, sotalol, tolamolol, practolol and butoxamine were reported. It has been postulated for some time that there are two subgroups of beta receptors cardiac receptors (beta 1-eceptor) and peripheral receptors (beta 2-receptor) responsible for vasodilatation and broncholdilatation. More recently, the cardioselective beta blockers have been developed; for example, practolol, and talamolol. Rabbits were anesthetized by the peritoneal injection of urethane 1 gm/kg and observed for 30 minutes. Arrhythmias were produced with lanatocide-C and norepinephrine through the ear vein of the anesthetized rabbits. Arrhythmias such as premature ventricular contraction and ventricular tachycardia were present within 7 minutes to 20 minutes after the injection of lanatocide-C 0.9mg, and within 15 seconds to 2 minutes after the injection of norepinephrine 150ug. Propranolol or practolol were injected before and after the production of the arrhythmias and so Lead II of the electrocardiogram was obtained from nedle electrodes inserted into the skin. Practolol was compared with propranolol on the changes of the heart rates and the arrhytmias produced by the injection of norepinephrine and lanatocide-C. The intravenous injection of propranolol and practolol reduced the heart rate but practolol reduced much lesser than propranolol. All of arrhythmias produced by lanatocide-C in anesthetzedrabbits were not abolished by practolol, but it blocked and prevented the development of arrhythmias in anesthetized rabbits on the administration of norepinephrine.