INDUCTION OF CALCIUM-INDEPENDENT NITRIC-OXIDE SYNTHASE BY ALLERGEN CHALLENGE IN SENSITIZED RAT LUNG IN-VIVO

There is some evidence that nitric oxide synthase (NOS) is induced in the lungs of patients with allergic asthma, but the mechanism of this is not understood. The aim of the present study was to investigate whe ther the levels of NOS in rat lung could be altered by exposure of the animals to aerosols of allergen (ovalbumin). Brown-Norway rats were a ctively sensitized to ovalbumin, raising a mixed IgE/IgG antibody resp onse. The levels of total and calcium-independent NOS in lung tissue h omogenates were elevated at 6 h and 24 h after allergen exposure in se nsitized rats but not in unsensitized rats. The induction was not due to contaminating lipopolysaccharide in the challenge solution. The all ergen-induced increase in calcium-independent lung NOS was inhibited b y pretreatment of the animals with the corticosteroid betamethasone (3 mg kg(-1) i.p., 1 h prior to and 6 h after allergen). These results s how that allergen challenge induces calcium-independent NOS in the lun gs of sensitized rats, a process inhibited by an anti-inflammatory cor ticosteroid.