An Endothelium-Derived Hyperpolarizing Factor Distinct from NO and Prostacyclin Is a Major Endothelium-Dependent Vasodilator in Resistance Vessels of Wild-Type and Endothelial NO Synthase Knockout Mice

In addition to nitric oxide (NO) and prostacyclin (PGI2), 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 (WT) and endothelial NO synthase knockout mice (eNOS -/-) mice. Vasodilator responses to endothelum-dependent agonists were determined in vivo and in vitro. In vivo, bradykinin induced a pronounced, dose-dependent decrease in mean arterial pressure (MAP) which did not differ between WT and eNOS -/- mice and was unaffected by treatment with Nω-nitro-L-arginine methyl ester and diclofenac. In the saline-perfused hindlimb of WT and eNOS -/- mice, marked Nω-nitro-L-arginine (L-NA, 300 μ mol/liter)- and diclofenac-insensitive vasodilations in response to both bradykinin and acetylcholine (ACh) were observed, which were more pronounced than the agonist-induced vasodilation in the hindlimb of WT in the absence of L-NA. This endothelium-dependent, NO/PGI2-independent vasodilatation was sensitive to KCl(40 mM) and to the combination of apamin and charybdotoxin. Gap junction inhibitors (18α -glycyrrhetinic acid, octanol, heptanol) and CB-1 cannabinoid-receptor agonists (Δ9-tetrahydrocannabinol, HU210) impaired EDHF-mediated vasodilation, whereas inhibition of cytochrome P450 enzymes, soluble guanylyl cyclase, or adenosine receptors had no effect on EDHF-mediated responses. These results demonstrate that in murine resistance vessels the predominant agonist-induced endothelium-dependent vasodilation in vivo and in vitro is not mediated by NO, PGI2, or a cytochrome P450 metabolite, but by an EDHF-like principle that requires functional gap junctions.