Abstract
Epoxy- and dihydroxy-eicosatrienoic acids (EETs and DHETs) are vasoactive cytochrome P450 metabolites of arachidonic acid. Interestingly, however, the mechanism(s) by which EETs/DHETs mediate smooth muscle relaxation remains unclear. In contrast to previous reports, where dilation was purportedly large-conductance Ca2+-activated K+ (BKCa) and/or transient receptor potential cation channel, subfamily V, member 4 (TRPV4) channel-mediated, 14,15-EET-induced vasodilation [reversal of contractile tone established with the thromboxane receptor (TP) agonist 15-hydroxy-11α,9α-(epoxymethano)prosta-5,13-dienoic acid (U-46619)] was unaltered in BKCa and TRPV4 knockout mouse isolated aortae compared with wild-type controls, indicating a significant BKCa/TRPV4-resistant mechanism. Whereas all EET and DHET regioisomers reversed U-46619 contraction in rat aortae and mouse mesenteric resistance arteries, these eicosanoids failed to alter phenylephrine-induced contraction, suggesting that they mediated dilation via a “TP-selective” mechanism. Competitive TP antagonism was also observed in nonvascular tissue, including rat fundus and tertiary bronchus, indicating that the effect is not specific to blood vessels. Such effects were TP-selective because 14,15-EET failed to inhibit “non-TP” prostanoid receptor-mediated function in multiple cell/tissue-based assays (Kb > 10 μM). In accordance, 14,15-EET inhibited specific [3H]7-(3-((2-((phenylamino)carbonyl)hydrazino)-methyl)-7-oxabicyclo(2.2.1)hept-2-yl)-5-heptenoic acid (SQ-29548) binding to human recombinant TP receptor, with a Ki value of 3.2 μM, and it showed weaker affinity for non-TP prostanoid receptors, including DP, FP, EP1–4, and IP receptors (Ki values of 6.1, 5.3, 42.6, 19.7, 13.2, 20.2, and >25 μM, respectively) and no appreciable affinity (Ki values >10 μM) for a diverse array of pharmacologically distinct receptors, including the leukotriene receptors Cys-LT1/2 and BLT1. As such, EETs/DHETs represent a unique class of “endogenous” G protein-coupled receptor competitive antagonists, inducing vasodilation via direct TP inhibition. Thus, EETs/DHETs represent novel autoregulatory agents, directly modulating the actions of cyclooxygenase-derived eicosanoids following arachidonic acid mobilization.
Footnotes
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.108.145102.
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ABBREVIATIONS: COX, cyclooxygenase; P450, cytochrome P450; EET, epoxyeicosatrienoic acid; DHET, dihydroxyeicosatrienoic acid; sEH, soluble epoxide hydrolase; EDHF, endothelium-derived hyperpolarizing factor; BKCa, large-conductance, calcium-activated potassium channel; TRPV4, transient receptor potential cation channel, subfamily V, member 4; GPCR, G protein-coupled receptor; TP, thromboxane receptor; EP, prostaglandin E receptor; U-46619, 15-hydroxy-11α,9α-(epoxymethano)prosta-5,13-dienoic acid; IP, prostacyclin receptor; SQ-29548, [3H]7-(3-((2-((phenylamino)carbonyl)hydrazino)methyl)-7-oxabicyclo(2.2.1)hept-2-yl)-5-heptenoic acid; DP, prostaglandin D receptor; BW245C, 3-((2-cyclohexyl-2-hydroxyethylidene)amino)-2,5-dioxo-4-imidazolidineheptanoic acid; BWA868C, 4-Imidazolidineheptanoic acid, 3-((2-cyclohexyl-2-hydroxyethyl)amino)-2,5-dioxo-1-(phenylmethyl)-3-benzyl-5-(6-carboxyhexyl)-1-(2-cyclohexyl-2-hydroxyethylamino)hydantoin; Cys-LT1, leukotriene D4 receptor; Cys-LT2, leukotriene C4 receptor; FP, prostaglandin F receptor; BLT1, leukotriene B4 receptor; 5-HT, 5-hydoxytryptamine (serotonin); PG, prostaglandin; AH6809, 6-isopropoxy-9-oxoxanthene-2-carboxylic acid; SC-51322, 8-chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid, 2-[3[2-(furanylmethyl)thio]1-oxopropyl]hydrazine; AL 8810, 9,15-dihydroxy-11-fluoro-15-(2-indanyl)-16,17,18,19,20-pentanor-5,13-prostadienoic acid; CAY10441, (4,5-dihydro-1H-imidazol-2-yl)-[4-(4-isopropoxybenzyl)phenyl]amine; ANOVA, analysis of variance.
- Received August 20, 2008.
- Accepted September 30, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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