Comparison of the bronchodilator and cardiovascular actions of salbutamol, isoprenaline and orciprenaline in guinea‐pigs and dogs

Abstract

1 Bronchodilator and cardiovascular actions of salbutamol and isoprenaline have been compared in guinea-pigs and dogs. Orciprenaline was also included in some experiments. 2 All three drugs antagonized acetylcholine-induced increases in pulmonary resistance. In addition they increased heart rate and decreased arterial blood pressure. 3 Compared with isoprenaline, salbutamol has relatively stronger actions on bronchial and vascular β-adrenoceptors than on cardiac β-adrenoceptors, on which its action is very weak. In contrast, orciprenaline has similar potencies on β-adrenoceptors in these three tissues. 4 The positive chronotropic potency of intravenously or orally administered salbutamol was increased in conscious dogs. These heart rate responses to salbutamol were probably mainly reflex in origin. 5 Salbutamol and orciprenaline were both longer acting than isoprenaline. 6 The results support the idea of two distinct groups of β-adrenoceptors. Salbutamol differentiates between bronchial and vascular β₂-adrenoceptors on the one hand and cardiac β₁-adrenoceptors on the other. Isoprenaline and orciprenaline do not differentiate between β₁- and β₂-adrenoceptors.