Objective - Epoxyeicosatrienoic acids (EETs) serve as endothelial-derived hyperpolarizing factors (EDHF), but may also affect vascular function by other mechanisms. We identified a novel interaction between EETs and endothelial NO release using soluble epoxide hydrolase (sEH) -/- and +/+ mice.

Methods and Results - EDHF responses to acetylcholine (ACh) in pressurized isolated mesenteric arteries were neither affected by the sEH inhibitor, N-adamantyl-N'-dodecylurea (ADU), nor by sEH gene deletion. However, the EDHF responses were abolished by catalase and by apamin/charybdotoxin (ChTx), but not by iberiotoxin, nor by the cytochrome P450 inhibitor PPOH. All four EETs (order of potency: 8,9-EET>14,15-EET~5,6-EET>11,12-EET) and all four dihydroxy derivatives (14,15-DHET~8,9-DHET~11,12-DHET>5,6-DHET) produced dose-dependent vasodilation. Endothelial removal or L-NAME blocked 8,9-EET and 14,15-DHET-dependent dilations. The effects of apamin/ChTx were minimal. 8,9-EET and 14,15-DHET induced NO production in endothelial cells. ADU (100 mg/ml in drinking water) lowered blood pressure in angiotensin II-infused hypertension, but not in L-NAME-induced hypertension. Blood pressure and EDHF responses were similar in L-NAME-treated sEH +/+ and -/- mice. Vasorelaxation by ACh in the presence of L-NAME was equipotent between sEH +/+ and -/- arteries of L-NAME treated animals. Catalase 1000 U/ml inhibited this EDHF response.

Conclusions - Our data indicate that the EDHF response in mice is caused by hydrogen peroxide, but not by P450 eicosanoids. Moreover, P450 eicosanoids are vasodilatory, largely through their ability to activate endothelial NO synthase (eNOS) and NO release.