Comparison of the effects of clonidine and guanfacine on the histamine liberation from human mast cells and basophils and on the human bronchial smooth muscle activity.

The inhibitory effects of clonidine and guanfacine on antigen-induced histamine release from human basophils and mast cells and on bronchial muscle tension were compared. Clonidine, but not guanfacine inhibited the antigen-induced histamine release from human basophils and mast cell preparations. This effect of clonidine was prevented by an H2-antagonist, cimetidine. Clonidine and guanfacine, like norepinephrine, inhibited the twitch contraction of electrically stimulated human segmental bronchi by stimulation of alpha 2-adrenoceptors. Clonidine and guanfacine had no effects on the basal bronchial muscle tone, but in very high concentrations they could reduce a carbacholine-induced bronchial tone. It is suggested that the inhibitory effects of clonidine on allergic reactions and on exicitatory nerve transmission in human airways may be useful in the treatment of asthmatic patients.