Neuronal NOS-dependent dilation to flow in coronary arteries of male eNOS-KO mice.

Flow-induced dilation was examined in isolated coronary arteries of endothelial nitric oxide (NO) synthase knockout mice (eNOS-KO) and wild-type (WT) mice. The basal tone of arteries (percentage of passive diameter) was significantly greater in eNOS-KO than in WT mice; their flow-induced dilations, however, were similar. Endothelial removal eliminated the dilations in vessels of both strains of mice. In arteries of WT mice, N(omega)-nitro-L-arginine methyl ester (L-NAME) (10(-4) M) or indomethacin (10(-5) M) alone, inhibited flow-induced dilation by approximately 50%, whereas their simultaneous administration abolished the responses. In arteries of eNOS-KO mice, flow-induced dilation was inhibited by approximately 40% with L-NAME. The residual portion (60%) of the response was eliminated by the additional administration of indomethacin. 7-Nitroindazole (10(-4) M) attenuated flow-induced dilation by approximately 40% in arteries of eNOS-KO mice, but did not affect responses in those of WT mice. 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (3 x 10(-5) M) inhibited the L-NAME/7-nitroindazole-sensitive portion of the responses in arteries of eNOS-KO mice. Immunohistochemical evidence confirms the presence of neuronal NOS (nNOS) in the arterial endothelium of eNOS-KO mice. In conclusion, nNOS-derived NO, via activation of cGMP, together with prostaglandins, maintains flow-induced dilation in coronary arteries of male eNOS-KO mice.