Comparison of the effects of atenolol and practolol on exercise tachycardia in normal subjects.

The relationship between cumulative doses of practolol and atenolol and resultant decreases in exercise tachycardia has been examined in 4 healthy volunteers. Continuous intravenous infusions of practolol (0.4 mg/kg), atenolol (0.12 mg/kg) and saline were administered between 7 and 12 minutes of bicycle exercise. The mean (+/- S.E.M.) heart rate (HR) at 7 min. for practolol (133 +/- 5.1) and atenolol (132 +/- 2.8) were significantly (p less than .01) reduced to 115 +/- 2.3 and 104 +/- 2.9 beats/min. respectively. The pre-infusion HR in the saline study (132 +/- 1.2) was unchanged (133 +/- 4.6) at 12 min. The relationship between the log cumulative dose of each drug and the per cent fall in HR/min was linear for each subject. The log dose-response curve (mean of 4 subjects) for practolol (y = 9.6x + 18.1) was more horizontal than for atenolol (y = 18.4x + 38.6).