Pharmacodynamic aspects of chlorpheniramine-induced bronchodilatation.

In 12 asthmatic (A) and ten normal (N) subjects, we measured the effect of inhaled saline solution, acetylcholine, histamine (H), and chlorpheniramine (CP) on specific airway conductance and forced exploratory flows. We found that CP dilated the bronchi in six asthmatic patients and one normal subject by acting on bronchial H1 receptor. This action is also modulated by the abnormal functions of this receptor-transducer, explaining why CO exerts a tonic effect only in subjects with H hyperresponsiveness. Furthermore, as shown by CO and CP + H responses, bronchial histamine seems to be present primarily in large airways and in relatively small amounts. We also found that bronchial H, the abnormal H1 receptor-transducer, and the bronchial caliber are regulated independently of each other. Consequently, this limits the therapy with H1 blockers in asthma.