Functional importance of neuronal nitric oxide synthase in the endotheliumof rat basilar arteries

The function of the neuronal isoform of nitric oxide synthase (nNOS) was st udied by comparing the effects of the specific nNOS blocker 7-nitro indazol e monosodium salt (7-NINA) with that of the general NOS inhibitor N-G-nitro -L-arginine (L-NA) in isolated rat basilar artel ies (BAs). 7-NINA had no s ignificant effect on the resting tone of the vessels, while both L-NA and 1 H-[1,2,4]oxadiazolo[4,3-n]quinoxalin-1-one (ODQ), a selective inhibitor of the soluble guanylyl cyclase, induced contraction. The relaxant effect of b radykinin was attenuated in the presence of L-NA but was not changed by 7-N INA. In contrast, 7-NINA markedly reduced the acetylcholine induced, endoth elium-dependent relaxation. These results demonstrate that nNOS contributes significantly to the relaxant effect of acetylcholine, indicating the func tional importance of this isoenzyme in the cerebrovascular endothelium. (C) 2000 Elsevier Science B.V. All rights reserved.