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EFFECTS OF TIPRENOLOL, PRACTOLOL AND PROPRANOLOL ON EXPERIMENTAL VENTRICULAR TACHYARRHYTHMIAS

1 Low doses of tiprenolol (0.01–0.02 mg/kg) and propranolol (0.05 mg/kg) abolished the ventricular arrhythmias produced by the intravenous injection of adrenaline in anaesthetized dogs respired with halo thane. 2 Larger doses of tiprenolol (2.0–4.0 mg/kg) restored sinus rhythm in four of five dogs with ventricular tachycardia produced by toxic doses of ouabain. Propranolol (2.0–4.0 mg/kg) had the same effect in each of four dogs. 3 Both tiprenolol (4.0–8.0 mg/kg) and propranolol (4.0 mg/kg) increased the frequency of sinus beats and reduced the ventricular rate in dogs with ventricular tachycardia 20–44 h after ligation of a coronary artery. 4 Practolol (0.5–16.0 mg/kg) did not reduce the ventricular rate or increase the frequency of sinus beats in dogs with ventricular tachycardia after ligation of a coronary artery. 5 In dogs with ouabain‐induced ventricular tachycardia mean arterial pressure was reduced after the administration of tiprenolol (0.5–8.0 mg/kg) or propranolol (4.0–8.0 mg/kg). Depression of sinus and atrioventricular nodal function, and of intraventricular conduction developed in some of the dogs given tiprenolol (4–8 mg/kg) or propranolol (8.0 mg/kg). 6 The administration of tiprenolol (1.0–8.0 mg/kg) or propranolol (4.0–8.0 mg/kg) depressed the arterial pressure and caused the deaths of some dogs in which a coronary artery had been ligated. Such deaths did not occur in the group which had been given toxic doses of ouabain.