Inhibition of eosinophil chemotaxis by chronic blockade of nitric oxide biosynthesis

Abstract

The effect of chronic N ω-nitro- l-arginine methyl ester ( l-NAME) treatment on the in vivo eosinophil migration induced by bradykinin, platelet-activating factor (PAF), lipopolysaccharide and carrageenin has been investigated in the rat using the pleurisy model. The in vitro (microchemotaxis chamber) eosinophil migration induced by N-formyl-methionyl-leucyl-phenylalanine (fMLP), PAF and zymosan-activated serum was also evaluated in the rat. The eosinophils were obtained from the peritoneal cavity of male Wistar rats and isolated on a discontinuous metrizamide gradient. Chronic inhibition of nitric oxide biosynthesis was achieved by adding l-NAME to the drinking water to give an intake of approximately 75 μmol/rat/day for 4 weeks. Rats treated chronically with l-NAME developed a significant level of hypertension (163 ± 4.8 mmHg; P < 0.01) compared with animals which received either the same dose of the inactive enantiomer d-NAME (124 ± 3.2 mmHg) or tap water alone (119 ± 1.6 mmHg). The intrapleural injection of bradykinin (50 μg), PAF (1 μg), lipopolysaccharide (0.25 μg) and carrageenin (125 μg) into untreated rats in vivo induced a significant level of eosinophil migration by 24 h post-injection. This migration was markedly reduced in l-NAME-treated rats. Eosinophils obtained from untreated rats showed a significant level of migration in vitro in response to fMLP (5 × 10 −8 M), PAF (10 −8 M) and zymosan-activated serum (27 μl). In contrast, the migration induced by these chemotactic agents was markedly reduced in cells isolated from animals treated chronically with l-NAME. l-Arginine (5.5 mM), but not d-arginine (5.5 mM), restored the ability of eosinophils from l-NAME-treated animals to migrate in response to fMLP. Our results indicate that nitric oxide plays a major role in the in vivo and ex vivo migration of eosinophils.