Endogenous nitric oxide modifies antigen-induced microvascular leakage in sensitized guinea pig airways

To examine the role of endogenous nitric oxide in allergic airway inflammation, we investigated the effect of a nitric oxide synthase inhibitor, N omega-nitro-L-arginine methyl ester (L-NAME), on antigen-induced airway microvascular leakage in actively senstitized guinea pigs by using Evans blue dye. Three weeks after sensitization with obalbumin (10 mu g), the tracheas were cannulated, and lungs were artifically ventilated. Animals were pretreated with atropine and propranolol (both 1 mg/kg, intravenously) to avoid neural modification. Ovalbumin inhalation (3 mg/ml, 1 minute) challenge caused significant microvascular leakage in all airway portions, which was significantly suppressed in a dose-dependent manner by pretreatment with intravenous injection of L-NAME (1 and 10 mg/kg) but not with the inactive enantiomer D-NAME (10 mg/kg). This inhibition by L-NAME was significantly reversed by co-administration of L-arginine (100 mg/kg, intravenously). Pretreatment with a vasoconstrictor, phenylephrine (20 mu g/kg, intravenously), had no inhibitory effects on antigen-induced airway microvascular leakage despite increasing systemic blood pressure. Inhalation of representative mast cell-derived mediators, histamine (2 mg/ml, 1 minute) or leukotriene D-4 (5 mu g/ml, 1 minute), produced significant microvascular leakage in all airways. L-NAME (10 mg/kg, intravenously) partially but significantly inhibited leukotriene D-4-induced leakage, whereas histamine-induced leakage was not affected. These results suggest that endogenous nitric oxide acts to increase airway microvascular leakage after airway allergic reaction.