Effect of azelastine on activation and release stages of allergic histamine secretion in rabbit basophils

In this study the effect of azelastine on the activation (antigen-dependent, Ca(2+)-dependent, Stage I) and release (antigen-independent, Ca(2+)-dependent, Stage II) phases of allergen-induced histamine secretion in rabbit mixed leukocytes (basophils) was investigated. Azelastine (5 microM, 10-min) and diltiazem (5 microM: a Ca2+ antagonist, 10 min) inhibited ragweed extract-induced histamine secretion during the Stage II (release) phase. Theophylline (100 microM), a phosphodiesterase inhibitor, added immediately before antigen challenge, inhibited allergic histamine secretion during the Stage I (activation) phase. The data obtained in this study suggest that diltiazem and azelastine act on the Ca(2+)-dependent and antigen-independent phase (Stage II) of allergic histamine secretion in rabbit basophils.