EDHF mediates flow-induced dilation in skeletal muscle arterioles of female eNOS-KO mice

Vasodilation to increases in flow was studied in isolated gracilis muscle arterioles of female endothelial nitric oxide synthase (eNOS) knockout (KO) and female wild-type (WT) mice. Dilation to flow (0-10 mul/min) was similar in the two groups, yet calculated wall shear stress was significantly greater in arterioles of eNOS-KO than in arterioles of WT mice. Indomethacin, which inhibited flow-induced dilation in vessels of WT mice by similar to 40%, did not affect the responses of eNOS-KO mice, whereas miconazole and 6-(2-proparglyoxyphenyl) hexanoic acid (PPOH) abolished the responses. Basal release of epoxyeicosatrienonic acids from arterioles was inhibited by PPOH. Iberiotoxin eliminated flow-induced dilation in arterioles of eNOS-KO mice but had no effect on arterioles of WT mice. In WT mice, neither N-omega-nitro-L-arginine methyl ester nor miconazole alone affected flow-induced dilation. Combination of both inhibitors inhibited the responses by similar to 50%. 1H-[1,2,4]oxadiazolo[4,3-a] quinoxalin-1-one (ODQ) alone inhibited flow-induced dilation by similar to 49%. ODQ + indomethacin eliminated the responses. Thus, in arterioles of female WT mice, nitric oxide and prostaglandins mediate flow-induced dilation. When eNOS is inhibited, endothelium-derived hyperpolarizing factor substitutes for nitric oxide. In female eNOS-KO mice, metabolites of cytochrome P-450, via activation of large-conductance Ca2+-activated K+ channels of smooth muscle, mediate entirely the arteriolar dilation to flow.