Clonidine inhibits IgE-mediated and IgE-independent in vitro histamine release from human basophil leukocytes

Clonidine, a common antihypertensive agent, was recently shown to inhibit antigen-induced wheal and flare reactions, as well as allergen-evoked bronchoconstriction in allergic patients. In this study we investigated the in vitro anti-allergic properties of clonidine. This alpha 2 adrenoceptor agonist inhibited, in a dose-dependent fashion, basophil histamine secretion elicited by anti-IgE and f-met peptide; it also blocked, though to a lesser extent, the calcium ionophore A23187-induced histamine release. H2 receptor stimulation seems to be responsible for the reduction in histamine release observed, since it can be antagonized by cimetidine, but not by alpha 1, alpha 2 and H1 blockers.