Studies of cardioselectivity and partial agonist activity in beta-adrenoceptor blockade comparing effects on heart rate and peak expiratory flow rate during exercise.
1 The effects of beta-adrenoceptor antagonists given in single doses by oral or intravenous routes were examined in two double-blind controlled studies performed in healthy volunteers. Heart rate and peak expiratory flow rate (PEFR) were measured at rest and during standardized exercise. 2 Propranolol 80 mg and metoprolol 100 mg orally tended to reduce, and propranolol and metoprolol 0.2 mg/kg intravenously did reduce the physiological increase in PEFR during exercise; oxprenolol 80 mg orally and 0.2 mg/kg intravenously did not. Practolol 200 mg orally reduced this increase, but practolol 1 mg/kg intravenously did not. 3 In a third study of similar design, pindolol 0.05 mg/kg intravenously did not affect exercise-induced increase in PEFR. 4 Heart rate during exercise was reduced to a comparable extent at different times by all the active treatments. 5 Oxprenolol and pindolol share with practolol the property of partial agonist activity, which might contribute to their apparent lack of effect on airways resistance. A further possibility is that alpha-adrenoceptor blockade helps to maintain exercise-induced increase in PEFR.