Plasma and bronchoalveolar fluid concentrations of nitric oxide and localization of nitric oxide synthesis in the lungs of horses with summer pasture-associated obstructive pulmonary disease

Objective-To determine concentrations of nitric oxide (NO) in plasma and br onchoalveolar lavage fluid (BALF) and localize nitric oxide synthesis in th e lungs of horses with summer pasture-associated obstructive pulmonary dise ase (SPAOPD). Animals-7 adult horses with SPAOPD and 6 clinically normal adult horses. Procedure-Severity of SPAOPD was determined by use of clinical scores, chan ge In intrapleural pressure (Delta Ppl) during tidal breathing, cytologic a nalysis of BALF and histologic evaluation of lung specimens obtained during necropsy. Nitric oxide concentrations in plasma, BALF, and epithelial lini ng fluid (ELF) were determined by use of a chemiluminescent method. Inducib le nitric oxide synthase (iNOS) and nitrotyrosine (NT) were localized in fo rmalin-fixed lung speck mens by use of immunohistochemical staining, and ni cotinamide adenine dinucleotide phosphate diaphorase (NADPHd) activity was localized in cryopreserved specimens by use of histochemical staining. Results-Plasma concentration of NO in affected horses was slightly but not significantly greater than concentration in nonaffected horses. Nitric oxid e concentrations in BALF or ELF did not differ between groups. Immunoreacti vity of NOS in bronchial epithelial cells of 3 of 5 lung lobes was greater in horses with SPAOPD, compared with nonaffected horses. However, staining for NT and NADPHd activity did not differ between groups. Conclusions and Clinical Relevance-Expression of NOS was greater in bronchi al epithelial cells of horses with SPAOPD, compared with nonaffected horses , suggesting that NO may play a role in amplifying the inflammatory process in the airways of horses with this disease.