14,15-epoxyeicosa-5(Z)-enoic acid -: A selective epoxyeicosatrienoic acid antagonist that inhibits endothelium-dependent hyperpolarization and relaxation in coronary arteries

Endothelium-dependent hyperpolarization and relaxation of vascular smooth muscle are mediated by endothelium-derived hyperpolarizing factors (EDHFs). EDHF candidates include cytochrome P-450 metabolites of arachidonic acid, K+. hydrogen peroxide, or electrical coupling through gap junctions. In bovine coronary arteries, epoxyeicosatrienoic acids (EETs) appear to function as EDHFs. A 14,15-EET analogue, 14,15-epoxyeicosa-5(Z)-enoic acid (14,15-EEZE) was synthesized and identified as an EET-specific antagonist. In bovine coronary arterial rings preconstricted with U46619, 14,15-EET, 11, 12-EET, 8,9-EET, and 5,6-EET induced concentration-related relaxations. Preincubation of the arterial rings with 14,15-EEZE (10 mumol/L) inhibited the relaxations to 14,15-EET, I 1,12-EET, 8,9-EET, and 5,6-EET but was most effective in inhibiting 14,15-EET-itiduced relaxations, 14,15-EEZE also inhibited indomethacin-resistant relaxations to methacholine and arachidonic acid and indomethacin-resistant and L-nitroarginine-resistant relaxations to bradykinin. It did not alter relaxation responses to sodium nitropusside, iloprost, or the K-channel activators (NS1619 and bimakalim). Additionally, in small bovine corollary arteries pretreated with indomethacin and L-nitroarginine and preconstricted with U46619. 14,15-EEZE (3 mumol/L) inhibited bradykinin (10 nmol/L)-induced smooth muscle hyperpolarizations and relaxations. In rat renal microsomes. 14, 15-EEZE ( 10 mumol/L) did not decrease EET synthesis and did not alter 20-hydroxyeicosatetraenoic acid synthesis. This analogue acts as all EET antagonist by inhibiting the following: (1) EET-induced relaxations, (2) the EDHF component of methacholine-induced. bradykinin-induced, and arachidonic acid-induced relaxations. and (3) the smooth muscle hyperpolarization response to bradykinin. Thus, a distinct molecular structure is required for EET activity, and alteration of this structure modifies agonist and antagonist activity. These findings support a role of EETs as EDHFs.