Time course of the bronchial response to salbutamol after placebo, betaxolol and propranolol.

The effects on specific airway conductance (sGaw) of placebo, betaxolol and propranolol following the inhalation of salbutamol were studied in 8 healthy volunteers by whole body plethysmography. Each subject received placebo and single oral doses of betaxolol 40 mg and 80 mg, and propranolol 160 mg, and 320 mg. sGaw was measured before dosing and after 2 h, just before salbutamol was inhaled. It was then measured again after 15 min and 0.5, 1, 2, 3, 4 and 6 h. sGaw 2 h after the beta-blockers did not differ from the value whilst on placebo. The peak response to salbutamol after placebo and both doses of betaxolol was almost identical, whereas it was significantly reduced after propranolol. The AUC of the response to salbutamol over 6 h showed a reduction of 11% after betaxolol and of 19% after propranolol (p less than 0.01 between beta-blockers). The results indicate that, after betaxolol and in contrast to propranolol, a proportion of the bronchial beta 2-receptor population remains available to a beta 2-agonist.