Effect of the H1 antihistamine chlorpheniramine maleate on histamine-induced symptoms in the human conjunctiva. Indirect evidence for nervous H1 receptors.

Earlier studies have shown that intranasal chlorpheniramine (0.77%) can inhibit histamine-induced tickling, sneezing, and hypersecretion by a local effect on nerve fibres. The aim of the present study was to examine whether this solution had local anaesthetic of parasympatholytic properties. If neither of these properties are present it suggests that the anti-pruritic effects of the solution are caused by inhibition of H1 receptors, which in turn is indirect evidence for the presence of H1 receptors on nerve fibers. In a double-blind design 15 normal subjects were provoked with histamine in the eye after pretreatment with chlorpheniramine or with a local anaesthetic, oxybuprocain. Both drugs inhibited itching, but the H1 antihistamine was significantly more effective than the local anaesthetic (P less than 0.01). Corneal sensitivity was measured by an esthesiometer, and pupil difference was used as a measure for atropine activity. Chlorpheniramine had neither a local anaesthetic nor a parasympatholytic effect. This study has therefore strengthened the hypothesis that there are nervous H1 receptors in the mucous membranes of the eye and airways and has extended its application in animals to also include man.