Comparative study of six -adrenoceptive antagonists on airway resistance and heart rate in the guinea-pig.

1. The effects of six beta-adrenoceptive antagonists [(+/-)-propranolol, (+)-propranolol, (+/-)-sotalol, (+/-)-practolol, (+/-)-pindolol and (+/-)-procinolol] were studied on airway resistance and heart rate in guinea-pigs and dose-response curves constructed.2. All beta-adrenoceptive antagonists decreased heart rate and increased airway resistance. A significant correlation was found between the increase in airway resistance and the degree of bradycardia induced by all drugs except practolol. The orders of activity of the six drugs in inducing significant variations of the two parameters were respectively, for airway resistance: (+/-)-procinolol>(+/-)-pindolol>(+/-)-propranolol>(+/-)-sotalol>(+)-propranolol>(+/-)-practolol, and for heart rate: (+/-)-pindolol>(+/-)-procinolol>(+/-)-propranolol>(+/-)-sotalol>(+)-propranolol>(+/-)-practolol.3. (+/-)-Sotalol, (+/-)-pindolol and (+/-)-procinolol-induced changes in airway resistance and heart rate reached plateau values, which were not modified by increasing the dose. Since sotalol and procinolol have only very weak partial agonist and cardiac depressant properties, it appears that these changes can mainly be accounted for by the suppression of sympathetic tone. It is probable that this is also the case with pindolol.4. On the other hand, (+/-)-propranolol and (+)-propranolol induced dose-related changes in airway resistance and heart rate. Thus, a direct and non-specific effect of both drugs on the bronchial muscle, similar to that observed on the heart appears to be implicated, together with sympathetic tone suppression in these variations.5. (+/-)-Practolol-induced effects on airway resistance and heart rate were different from those observed with the five other beta-adrenoceptive antagonists.