Rapid reversibility of the allergen-induced pulmonary late-phase reaction by an intravenous β2-agonist

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Abstract
This study was performed to determine the degree to which β2-adrenergic receptor agonists can reverse the allergen-induced late reduction in lung function. On two occasions, seven asthmatic subjects were administered terbutaline or its vehicle by intravenous infusion 7 h after 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 allergen challenge, terbutaline rapidly improved lung function. At the end of terbutaline infusion, the forced expiratory volume in 1 s reached 100 ± 1.3% of baseline and 84.2 ± 4.3% of maximal attainable value, but the bronchodilating effect of the β-agonist did not plateau. The values for forced vital capacity were 102 ± 1.3% of baseline and 95.1 ± 3% of 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 rapidly reversible by β2-adrenergic agonists, we conclude that it is caused mainly by bronchial smooth muscle spasm.

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