Nitric oxide participates in prick test and irritant patch test reactions in human skin

The aim of this study was to investigate the involvement of nitric oxide (NO) in the modulation of immediate and delayed immunological and nonimmunological reactions in human skin. The NO donor nitroglycerin, 0.1 microgram, and the NO synthase inhibitor, NG-nitro-L-arginine (L-NAME), 0.1 microgram, were injected intracutaneously prior to provocation tests. The following provocation tests were carried out: 8 patients with pollen allergy to birch were provoked by a prick test with the allergen and the volume of the weals was measured; 20 patients with allergy to nickel were provoked with nickel sulfate epicutaneously; and 26 healthy volunteers were provoked with tuberculin (causing delayed immunologic reaction), benzalkonium chloride (irritant contact dermatitis), UV radiation or benzoic acid (nonimmunological contact urticaria). The test reactions were evaluated by planimetry. L-NAME inhibited irritant contact dermatitis (P = 0.020) but augmented immediate immunological reactions (prick test) (P = 0.016). The other test reactions remained unchanged. Nitroglycerin did not affect any of the reactions significantly. The results suggest that NO is involved in immediate immunological reactions and irritant contact dermatitis.