Rapid reversibility of the allergen-induced pulmonary late-phase reaction by an intravenous beta 2-agonist

This studywas performed to determine the degree to which₂-adrenergic receptor agonistscan reverse the allergen-induced late reduction in lungfunction. On two occasions, seven asthmatic subjects wereadministered terbutaline or its vehicle by intravenous infusion 7 hafter inhaled allergen, at which point the forced expiratory volume in1 s was 57% of baseline. On another occasion, terbutaline was infusedat baseline to determine maximal attainable bronchodilation. Afterallergen challenge, terbutaline rapidly improved lung function. At theend of terbutaline infusion, the forced expiratory volume in 1 sreached 100 ± 1.3% of baseline and 84.2 ± 4.3% of maximalattainable value, but the bronchodilating effect of the -agonist didnot plateau. The values for forced vital capacity were 102 ± 1.3%of baseline and 95.1 ± 3% of maximal attainablevalue. The kinetics of the terbutaline effect, when it wasinfused at baseline, were similar to those in the late phase. Becausethe late-phase reduction in lung function is rapidly reversible by₂-adrenergic agonists, weconclude that it is caused mainly by bronchial smooth muscle spasm.