PHARMACOLOGICAL AND IMMUNOHISTOCHEMICAL EVIDENCE FOR A FUNCTIONAL NITRIC-OXIDE SYNTHASE SYSTEM IN RAT PERITONEAL EOSINOPHILS

Eosinophil migration in vivo is markedly attenuated in rats treated ch ronically with the NO synthase (NOS) inhibitor NW-nitro-L-arginine met hyl ester (L-NAME). In this study, we investigated the existence of a NOS system in eosinophils. Our results demonstrated that rat peritonea l eosinophils strongly express both type LI (30.2 +/- 11.6% of counted cells) and type IU (24.7 +/- 7.4% of counted cells) NOS, as detected by immunohistochemistry using affinity purified mouse mAbs. Eosinophil migration in vitro was evaluated by using 48-well microchemotaxis cha mbers and the chemotactic agents used were N-formyl-methionyl-leucyl-p henylalanine (fMLP, 5 x 10(-8) M) and leukotriene B-4 (LTB4, 10(-8) M) . L-NAME (but not D-NAME) significantly inhibited the eosinophil migra tion induced by both fMLP (54% reduction for 1.0 mM; P < 0.05) and LTB 4 (61% reduction for 1.0 mM; P < 0.05). In addition, the type II NOS i nhibitor 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine and the type I/I I NOS inhibitor 1-(2-trifluoromethylphenyl) imidazole also markedly (P < 0.05) attenuated fMLP- (52% and 38% reduction for 1.0 mM, respectiv ely) and LTB4- (52% and 51% reduction for 1.0 mM, respectively) induce d migration. The inhibition of eosinophil migration by L-NAME was mimi cked by the soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3,-a] quinoxalin-1-one (0.01 and 0.1 mM) and reversed by either sod ium nitroprusside (0.1 mM) or dibutyryl cyclic GMP (1 mM). We conclude that eosinophils do express NO synthase(s) and that nitric oxide play s an essential role in eosinophil locomotion by acting through a cycli c GMP transduction mechanism.