Significant changes in nonspecific bronchial responsiveness after isolated immediate bronchospecific reactions caused by isocyanates but not after a late reaction caused by plicatic acid

Abstract

Although late bronchospastic reactions after exposure to antigenic and sensitizing agents usually significantly alter bronchial responsiveness to histamine or methacholine, presumably by causing bronchial inflammation, isolated immediate bronchospastic reactions do not induce such changes. We studied three subjects who demonstrated different patterns of reaction. The first individual was diagnosed as having occupational asthma to red cedar. This was confirmed by specific inhalation challenges that resulted in late bronchospastic reaction. No significant changes in the provocative concentration of histamine causing a 20% fall in FEV 1 (PC 20) were found 1 day after this reaction. Two weeks later, serial assessments (five and six, respectively) of PC 20 histamine were recorded on control days and up to 48 hours after exposure to plicatic acid, which caused a late bronchospastic reaction with a maximum fall of 37% in FEV 1. No significant changes in PC 20 were found; the maximum variations on control days were 0.36 to 0.74 mg/ml, and on active days, from 0.37 to 0.59 mg/ml. By contrast, two other subjects, who demonstrated isolated immediate reactions after exposure to diphenylmethane diisocyanate, had significant changes in PC 20 histamine and methacholine, in one subject from 3.1 mg/ml to 0.6 mg/ml 8 hours after exposure, and in the other subject, from 61.0 to 7.4 mg/ml 7 hours after exposure, with recovery during the next few days. These examples demonstrate that the pattern of nonspecific bronchial responsiveness after immediate and late bronchospastic reactions can be different from what has previously been described. Immediate bronchospastic reactions may lead to bronchial hyperresponsiveness, whereas late asthmatic reactions do not always induce changes in bronchial responsiveness. This suggests that changes in bronchial responsiveness and late asthmatic reactions after specific inhalation challenges might be initiated by different mechanisms, which are, however, often related.