Beta-blockers in bronchial asthma: effect of propranolol and pindolol on large and small airways.

In 11 asthmatic subjects the relative magnitude and the site of airway bronchoconstriction were compared after the oral administration of 40 mg of propranolol and 2.5 mg of pindolol and the magnitude and site of bronchodilation produced by 0.5 mg subcutaneous terbutaline were tested after pretreatment with propranolol and pindolol. Specific airway conductance (sGaw) and peak expiratory flow rate (PEFR), both believed to reflect changes in large airways, and capacity isoflow (Ciso-v) and delta Vmax50, both believed to reflect changes in small airways, were determined before and after administration of placebo, pindolol, and propranolol. Treatments were given double blind and in random order. After the administration of propranolol we noted a significant bronchoconstrictive effect in the large airways (mean values of PEFR and sGaw, expressed as percentages of control values, decreased by 87.4% +/- 13.2% and 43.3% +/- 8.9%) and in the small airways (mean value of Ciso-v increased by 20.6% +/- 4.7% and that of delta Vmax50 decreased by 50% +/- 11.9% of control). By contrast, pindolol produced no significant effect on sGaw or PEFR but the tests of small airway function showed significant bronchoconstriction (mean values of Ciso-v increased by 12.9% +/- 2.6% and those of delta Vmax50 decreased by 47.2% +/- 9.2%). This action makes pindolol potentially dangerous in asthmatic patients. The bronchodilator action of terbutaline on large airways is diminished after the use of both propranolol and pindolol.