Inhibitory Effects of Histamine H₁ Receptor Blocking Drugs on Metabolic Activations of Neutrophils

Abstract

Inhibitory effects of various histamine receptor-blocking agents including antiallergic agents on metabolic activations of neutrophils were examined by measuring leukotrienes (C₄, D₄ and E₄) formation, arachidonic acid release and superoxide generation. The stimulation of neutrophils by calcium ionophore (A23187) causes the production of leukotrienes concomitantly with the release of arachidonic acid from the cells and these were effectively diminished with a variety of antihistaminic agents. Almost all the histamine H₁ receptor-blocking drugs studied here showed as inhibitors of the metabolic activations of neutrophils, although the degree was dependent on the drug concentrations. The order of potency of the inhibitory effects on the arachidonic acid release were : homochlorcyclizine, clemastine, and azelastine (IC₅₀<20μM) > oxatomide (IC₅₀<60μM) and diphenylpyraline >triprolidine, meclizine, diphenhydramine (IC₅₀>100μM). The superoxide generation from neutrophils activated by phorbol 12-myristate 13-acetate was also effectively inhibited by these agents, but generally lower concentrations were required to obtain the same degrees of effects. These results indicated that some of the histamine H₁ receptor-blocking drugs, such as clemastine and homochlorcyclizine, may act as inhibitors of formation of leukotrienes at the locus of inflammation.