FACTORS THAT CONTRIBUTE TO INHIBITION OF METHACHOLINE-INDUCED BRONCHOCONSTRICTION

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Abstract
To evaluate the factors that contribute to inhibition of airways reactivity, we compared the effect of inhaled isoproterenol, 125 .mu.g, on the response to metacholine-induced bronchoconstriction in 10 normal and 10 asthmatic subjects. We measured in each subject baseline lung function, response to inhaled bronchodilator, dose of bronchodilator causing 50% maximal response, and degree of airways reactivity to inhalation of metacholine before and after isoproterenol. In asthmatics, but not normal subjects, inhalation of isoproterenol led to significant inhibition of metacholine-induced bronchospasm. In asthmatics, the greater the airways reactivity to methacholine the greater the inhibition by isoproterenol (p < 0.05). In both groups, there was significant correlation between baseline lung function and level of airways reactivity. In neither normal subjects nor asthmatics did the maximal bronchodilator response to isoproterenol inhalation correlate with inhibition of airways reactivity. Studies evaluating inhibition of airways reactivity should take into account the population tested, baseline lung function, and baseline level of airways reactivity.

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