Histamine increases lung permeability by an H2-receptor mechanism.

The effect of specific H1 and H2 receptor antagonists on bronchial reactivity and increase in lung epithelial permeability in response to inhaled histamine was measured in 5 non-smoking men (age range 24-36 years). Inhaled histamine produced a short-lived but consistent increase in permeability to 99Tc-diethylenetriamine penta-acetate. An H1-receptor antagonist, terfenadine (60 mg), protected against the bronchoconstrictor effect but had no significant influence on the increase in permeability. The H2-receptor antagonist ranitidine (150 mg) significantly reduced the permeability response without having an effect on bronchial reactivity. These results demonstrate that the bronchoconstrictor effect of histamine is mediated by H1 receptors and permeability increase is mediated by H2 receptors. H2-receptor mediated increase in lung epithelial permeability may be important clinically.