Beyond the histamine receptor: effect of antihistamines on mast cells

Many antihistamines exhibit inhibition of mediator release from mast cells and basophils, in in vitro studies in addition to H-1 antagonism. The under lying mechanism is unclear but is unrelated to H-1-receptor antagonism. Cli nical studies of antihistamins in antigen challenge and seasonal allergy de monstrate reduction of mast cell mediators in nasal lavage. It is not known what mechanism(s) underly these observations, although the concentrations required in in vitro studies suggests that a direct effect on mast cells is unlikely. Furthermore, the therapeutic contribution of this effect is diff icult to assess because of concomitant clinically significant H-1 antagonis m. This and other potential anti-allergic effects may enhance the therapeut ic benefit of antihistamines and long-term studies are underway to explore this possibility.