Peptidase inhibitors reverse steroid-induced suppression of neutrophil adhesion in rat tracheal blood vessels.

Exposure of the tracheal mucosa of rats to capsaicin evokes neurogenic inflammation, one manifestation of which is the adherence of neutrophils to the endothelium of venules. In the present experiments, with the use of aerosolized capsaicin, we determined whether this neutrophil adhesion is inhibited by dexamethasone and whether the effect of dexamethasone can be reversed by inhibiting endopeptidase 24.11 (neutral endopeptidase, NEP) and kininase II (angiotensin-converting enzyme, ACE), which degrade the neuropeptides that mediate neurogenic inflammation. Adult male pathogen-free F344 rats were treated for 2 days with dexamethasone or with vehicle (controls) and were then exposed for 2 min to aerosolized capsaicin. Neutrophils adhering to the endothelium of venules in tracheal whole mounts were stained histochemically for myeloperoxidase and then counted. Sites of increased vascular permeability were localized with Monastral blue. In the control rats, aerosolized capsaicin (10(-8)-10(-3) M) increased in a concentration-dependent fashion the number of adherent neutrophils and the amount of Monastral blue labeling of blood vessels. Dexamethasone in doses of 0.5, 1, 2, or 4 mg.kg-1.day-1 reduced by 49 63, 80, and 93%, respectively, the number of adherent neutrophils in capsaicin-exposed rats and caused similar reductions in the amount of Monastral blue labeling. When given alone, neither phosphoramidon, an inhibitor of NEP, nor captopril, an inhibitor of ACE, completely reversed this effect of dexamethasone, but when the two drugs were administered together, adherent neutrophils were as numerous in the dexamethasone-pretreated rats (112 +/- 9 neutrophils/mm2) as in controls (109 +/- 10 neutrophils/mm2). The amount of Monastral blue labeling was also similar in these two groups.(ABSTRACT TRUNCATED AT 250 WORDS)