An endothelium-derived hyperpolarizing factor distinct from NO and prostacyclin is a major endothelium-dependent vasodilator in resistance vessels ofwild-type and endothelial NO synthase knockout mice

In addition to nitric oxide (NO) and prostacyclin (PGl(2)) the endothelium generates the endothelium-derived hyperpolarizing factor (EDHF). We set out to determine whether an EDHF-like response can be detected in wild-type (W T) and endothelial NO synthase knockout mice (eNOS -/-) mice. Vasodilator r esponses to endothelium-dependent agonists were determined in vivo and in v itro. In vivo, bradykinin induced a pronounced, dose-dependent decrease in mean arterial pressure (MAP) which did not differ between WT and eNOS -/- m ice and was unaffected by treatment with N-omega-nitro-L-arginine methyl es ter and diclofenac. In the saline-perfuse hindlimb of WT and eNOS -/- mice, marked N-omega-nitro-L-arginine (L-NA, 300 mu mol/liter)- and diclofenac-i nsensitive vasodilations in response to both bradykinin and acetylcholine ( ACh) were observed, which were more pronounced than the agonistinduced vaso dilation in the hindlimb of WT in the absence of L-NA. This endothelium-dep endent, NO/PGl(2)-independent vasodilatation was sensitive to KCl (40 mM) a nd to the combination of apamin and charybdotoxin. Cap junction inhibitors (18 alpha-glycyrrhetinic acid, octanol, heptanol) and CB-1 cannabinoid-rece ptor agonists (Delta 9-tetrahydrocannabinol, HU210) impaired EDHF-mediated vasodilation, whereas inhibition of cytochrome P450 enzymes, soluble guanyl yl cyclase, or adenosine receptors had no effect on EDHF-mediated responses . These results demonstrate that in murine resistance vessels the predomina nt agonist-induced endothelium-dependent vasodilation in vivo and in vitro is not mediated by NO, PGl(2), or a cytochrome P450 metabolite, but by an E DHF-like principle that requires functional gap junctions.