Comparison of cardiac effects of timolol and propranolol.
The cardiac effects of the beta-adrenergic blocking agent, timolol, were compared to those of propranolol after intravenous administration in 6 healthy male subjects. The effects of timolol and propranolol on maximal exercise-induced tachycardia were measured. Timolol was about ten times as potent as propranolol in antagonizing exercise-induced tachycardia. Dose-response curves to intravenous infusions of isoproterenol were obtained after three doses of each beta-antagonist. Changes in myocardial contractility were assessed by cardiac systolic time intervals and were compared to the simultaneous changes in heart rate elicited by isoproterenol. For the 6 subjects, the mean potency ratios of timolol to propranolol as an antagonist of the chronotropic and inotropic effects of isoproterenol were 13.8 (+/-0.8) and 12.7 (+/-1.0), respectively. Neither timolol nor propranolol acted more selectively on beta-receptors affecting heart rate than on those influencing contractility.
D000328:Adult; D002986:Clinical Trials as Topic; D004305:Dose-Response Relationship, Drug; D005080:Exercise Test; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects; D011412:Propanolamines / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology*; D013830:Thiadiazoles / Q000494:pharmacology; D013997:Time Factors
D011412:Propanolamines; D013830:Thiadiazoles; D011433:Propranolol; D007545:Isoproterenol