Decreased pulmonary and tracheal smooth muscle expression and activity of type 1 nitric oxide synthase (nNOS) after ovalbumin immunization and multiple aerosol challenge in guinea pigs

Pharmacological evidence supports a role of a transient decreased endogenou s nitric oxide (NO) synthesis in ovalbumin (OVA)-induced early airway hyper responsiveness in guinea pigs. However, no data are available regarding the expression and activity of the constitutive NO synthases (cNOS; NOS1 and N OS3, nNOS and eNOS, respectively) in this model. Therefore, we evaluated cN OS activity (conversion of L-[H-3]arginine to L-[H-3]citrulline in the pres ence of Ca2+ and calmodulin), nitrate and nitrite (NQx) concentration (modi fied Griess method), and NOS1 and NOS3 protein expression (Western blot) in lung homogenates and in the tracheal smooth muscle from OVA-immunized and multiple aerosol-challenged guinea pigs (six challenges, once daily). The e xpression and activity of the inducible NOS isoform (NOS2), the levels of e xhaled NO, and the in vivo airway reactivity were also determined. Constitu tive NOS activity and NO, concentration were significantly lower 6 h after the last OVA challenge as compared with saline exposure, being similar at 2 4 h. Expression of NOS1 paralleled cNOS activity, which was reduced 6, but not 24 h after OVA challenge. The decrease in NOS1 expression was accompani ed by a significant decrease in the amounts of exhaled NO and by a maximal airway hyperresponsiveness to histamine. The levels of NOS3 were not modifi ed at the two time points evaluated, and no NOS2 expression and activity we re found at any time point. Similar modifications were observed in the trac heal smooth muscle. We conclude that OVA stimulation in immunized guinea pi gs induced a transient reduction in NOS1 protein expression and activity in the respiratory system, which probably participates in airway hyperrespons iveness.