Effect of inhaled H1 and H2 receptor antagonists in normal and asthmatic subjects

Abstract

The effects on airflow resistance of an inhaled H1 receptor antagonist, clemastine, and an H2 receptor antagonist, cimetidine, have been investigated in normal and asthmatic subjects. No significant changes in specific conductance (sGaw) were seen in 6 normal subjects. In 8 asthmatic subjects a significant increase in forced expiratory volume in 1 sec (FEV1) occurred at 60 min (<0.02), 90 min (<0.02), and 120 min (<0.05) after the inhalation of clemastine, whereas inhaled cimetidine had no effect on airflow resistance. Clemastine and cimetidine were tested on histamine-induced bronchoconstriction in 8 normal and 8 asthmatic subjects. Clemastine significantly reduced the fall in sGaw in normal subjects and the fall in FEV1 in asthmatic subjects, whereas cimetidine had no protective effect. Clemastine and ipratropium bromide were tested on methacholine-induced bronchoconstriction in 8 normal subjects. Ipratropium bromide, but not clemastine, significantly reduced the fall in sGaw after methacholine. These results suggest that in normal and asthmatic subjects histamine-induced bronchoconstriction is mediated predominantly via H1 rather than H2 receptors in the airways.