Attenuation of Axon Reflexes to Compound 48/80 after Repeated Iontophoresis of Compound 48/80 in Skin of the Human Forearm

The aim of this study was to determine whether the iontophoretic administration of the mast cell degranulator compound 48/80 influences axon reflex vasodilatation in the skin of the human forearm. In stage 1, compound 48/80 was administered by iontophoresis to a circular site in the forearm of 9 healthy men and 8 healthy women on four occasions spread over 24 h. Two control sites were also prepared by passing the iontophoretic current through 0.9% saline. Large wheals initially developed at the compound 48/80 site in 8 of the males and in 2 of the females, but wheals were minimal in all subjects by the fourth administration. In stage 2, compound 48/80 iontophoresis provoked substantial flaring at the first control site, whereas saline iontophoresis induced only minor flaring at the second control site, indicating that compound 48/80 induced axon reflex vasodilatation. However, prior treatment with compound 48/80 inhibited flaring to compound 48/80 in subjects who initially developed wheals, consistent with mast cell degranulation. In stage 3, flaring after iontophoresis of histamine was investigated at the site of compound 48/80 pretreatment and at the second control site in 12 subjects. Flaring was impaired only slightly in 6 subjects who initially developed wheals to compound 48/80. The persistence of flaring indicates that repeated administrations of compound 48/80 did not abolish neurogenic inflammation. Transcutaneous iontophoresis of compound 48/80 may be an attractive alternative to intradermal injection in studies that aim at clarifying the function of mast cells in healthy and diseased skin.