Histamine Dose-Response Relationships in Normal and Asthmatic Subjects

We examined the effects of pharmacologic antagonists on the bronchial response to inhaled histamine in 11 normal and 11 asthmatic subjects. We constructed cumulative log dose-response curves and determined the steepest slope and the provocative dose of histamine (PD35) needed to cause a 35% fall in specific airway conductance (SGaw). The slope was positively related to starting SGaw in both groups. Starting SGaw and slope were approximately 2-fold lower in asthmatics. After inhaling salbutamol (200 μg) and atropine (4 mg), there was an increase in starting SGaw and slope of the histamine response by approximately 1.5-fold in normal subjects and 2-fold in asthmatics, the relationship between starting SGaw and slope being preserved. Chlorpheniramine (4 mg) had little effect on starting SGaw and slope. Atropine, salbutamol, and chlorpheniramine increased PD35 by approximately 4-fold in normal subjects and 6-fold in asthmatics. After bronchodilatation with atropine or salbutamol, mean starting SGaw, slope, an...