Histamine receptors in the lung.

The availability of specific histamine receptor antagonists has provided evidence that human airways have both H1 and H2 receptors. H1 receptors, which mediate bronchoconstriction, predominate. H1 receptor antagonism can produce significant bronchodilatation in some asthmatics, block bronchoconstriction induced by antigen and histamine inhalation challenge, and have some protective effect against exercise and aspirin-induced bronchoconstriction. H2 receptors mediate bronchodilatation, but this effect is relatively weak in man. The role of classic antihistamines (H1 receptor antagonists) in the treatment of asthma has not been established. Since factors that precipitate asthma are quite varied, these agents may provide benefit in select patients. The availability of new, nonsedating H1 receptor antagonists show some promise in this regard. Future studies may more precisely define their use in asthma therapy.