E poxyeicosatrienoic acids (EETs) are products of epoxygenation of arachidonic acid. They participate in cardiovascular regulation via vasodilator and natriuretic effects. Research on their actions used urine or plasma measurements of their 4 active regioisomers (5,8,11,and 14, and their relatively inactive derivatives, the dihydroxyeicosatrienoic acids [DHETs]. The latter are produced by enzymatic (soluble epoxide hydrolase [sEH]) or nonenzymatic (eg, pH, oxidative stress) degradation.Previous studies in animals suggested that urine and plasma EETs may reflect 2 distinct pools with different functions. The volume of distribution of intravenous radiolabeled 14,15-EET in dogs approximates their plasma volume, and no radioactivity can be detected in their urine.1 Plasma EET responses to regulatory PPARα (peroxisome proliferatoractivated receptor α) ligands in mice run parallel to Cyp2c epoxygenase expression and EET biosynthesis in the liver. These studies suggest that plasma EETs reflect a systemic, not a renal pool. Conversely, increased renal EET content produced by dopamine agonists in mice is not associated with changes in plasma EETs,3 indicating that the renal EET pool might be better reflected by urine measurements. Our first aim was to assess whether these putative pools could be uncovered by studying clinical and biochemical correlates of urine and plasma EETs in normal volunteers; that is, normotensive, saltresistant (SR) subjects, during salt loading and depletion.EETs may play a role in salt sensitivity of blood pressure (BP). Salt stimulates renal microsomal biosynthesis of EETs in normal Sprague Dawley 4 and Dahl-R rats, 5 whereas this response is absent in the salt-sensitive (SS) Dahl-S strain, leading to hypertension with reduced renal expression of the epoxygenase CYP2C23 and urine excretion of EETs. 5 In SR rats, the epoxygenase inhibitor clotrimazole decreases urinary EETs and reproduces SS hypertension.5 Cyp4a10 knockout mice, which have reduced renal epoxygenase (Cyp2c44) activity, 6 and the Cyp2c44 knockout, 7 have diminished urine EETs and amiloride-sensitive hypertension. This is associated with decreased inactivating threonine phosphorylation of γENaC (epithelial sodium channel), 7 which is reversible by the PPARα ligands that stimulate epoxygenases.6 Our second aim was to investigate whether SS subjects exhibit differences in urine or plasma EETs levels or in their responses to changes in salt balance or in their clinical or biochemical correlates compared with SR. To avoid confounding effects of established hypertension, we performed these studies in normotensive volunteers.Abstract-We measured epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids (DHETs) in 21 normotensive subjects classified as salt resistant (13) or salt sensitive (8) with an inpatient protocol of salt loading (460 mEq Na + /24 hours, HiNa) and depletion (10 mEq Na + /24 hours+furosemide 40 mg×3, LoNa). No urine EETs were detected; hence, enzyme linked innumosorbent assay 14,15-DHETs (dihydroxyeicosatrie...