Mast cell mediators other than histamine induce pruritus in atopic dermatitis patients: a dermal microdialysis study

While histamine is the crucial mediator of pruritus in type 1 allergic reac tions, its role in atopic dermatitis (AD) is unclear. In this study, the ro le of mast cell mediators in protein extravasation and pruritus was evaluat ed using intradermal microdialysis. The microdialysis capillaries were used to apply the mast cell degranulating substance compound 48/80 (C48/80; 0.0 5%) or histamine (0.01%) and also to deliver H1-blockers (cetirizine, 200 m u g mL(-1)) in nine AD patients and nine controls, Large pore size membrane s (3000 kDa) enabled simultaneous analysis of protein extravasation. Itch s ensation was measured psychophysically and weal and flare reaction were eva luated planimetrically. Protein extravasation induced by histamine and C48/ 80 was significantly reduced in AD patients. Blockade of H1-receptors by ce tirizine significantly reduced C48/80-induced protein extravasation in AD p atients and controls to an identical level. C48/80-induced pruritus was abo lished by cetirizine in controls, whereas pruritus in AD patients was uncha nged after H1 blockade. We conclude that mast cell mediators others than hi stamine are involved in C48/80-induced pruritus in AD patients. Whether the reduced capacity of AD patients to induce protein extravasation is of path ophysiological relevance for pruritus remains to be established.