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.