Further studies on the mechanism of human histamine-induced asthma: the effect of an aerosolized H1 receptor antagonist (diphenhydramine).

This study was designed to better define the mechanism of histamine-induced bronchoconstriction in humans by pharmacologic manipulation of the postulated bronchial histamine receptor sites. Histamine challenges were performed on a heterogeneous group of adult asthmatic subjects. The cumulative units of histamine required for induction of a sustained 20% or greater decrease in FEV1 from baseline were determined. The effect of pretreatment with an aerosolized H1 receptor antagonist, diphenhydramine hydrochloride, was then studied. Analysis of the data showed that the administration of an H1 receptor antagonist prior to histamine challenge significantly blocked the bronchial response to histamine (p less than 0.005). This effect was considered to be due to specific competitive antagonism at the H1 receptor site and suggests the presence of H1 receptors in human bronchial mucosa.