Evidence for a dual effect by beta-adrenoceptor antagonists on post-exercise airway calibre

The effect of selectivity of beta-adrenoceptor antagonists on resting and post-exercise airway calibre in normal subjects was studied. Eight normal subjects were given atenolol 50 mg, propranolol 80 mg and placebo orally, in random order, double-blind. Specific airways conductance and flow-volume curves (partial and complete) were recorded before, 2 hours after drug administration and after exercise. Neither beta-adrenoceptor antagonist had a measurable effect on lung function tests at rest. The post-exercise increase in flow rates measured from partial flow volume curves was inhibited by propranolol but not by the beta-1-selective adrenoceptor antagonist atenolol, whereas both drugs caused a decrease in specific airways conductance after exercise. Beta-adrenoceptor antagonists may have a dual effect on airway calibre. Firstly, a direct effect on the beta-2 receptors in airway smooth muscle may occur. Secondly, beta-adrenoceptor blockade may, in the large airways, inhibit vagal pre-junctional beta-1 receptors which normally inhibit acetylcholine release at the nerve ending, thereby permitting vagally-induced airway narrowing.