REVERSIBILITY OF THE ALLERGEN-INDUCED PULMONARY LATE-PHASE REACTION BY AN INTRAVENOUS BETA(2)-AGONIST

This study was performed to determine the degree to which beta(2)-adre nergic receptor agonists can reverse the allergen-induced late reducti on in lung function. On two occasions, seven asthmatic subjects were a dministered terbutaline or its vehicle by intravenous infusion 7 h aft er inhaled allergen, at which point the forced expiratory volume in 1 s was 57% of baseline. On another occasion, terbutaline was infused at baseline to determine maximal attainable bronchodilation. After aller gen challenge, terbutaline rapidly improved lung function. At the end of terbutaline infusion, the forced expiratory volume in 1 s reached 1 00 +/- 1.3% of baseline and 84.2 +/- 4.3% of maximal attainable value, but the bronchodilating effect of the beta-agonist did not plateau. T he values for forced vital capacity were 102 +/- 1.3% of baseline and 95.1 +/- 3% maximal attainable value. The kinetics of the terbutaline effect, when it was infused at baseline, were similar to those in the late phase. Because the late-phase reduction in lung function is rapid ly reversible by beta(2)-adrenergic agonists, we conclude that it is c aused mainly by bronchial smooth muscle spasm.