Role of epoxyeicosatrienoic acids in renal functional response to inhibition of NO production in the rat

Abstract

Nitric oxide (NO) inhibits hemoproteins, including cytochrome (CYP) 2C, the gene responsible for the production of epoxyeicosatrienoic acids (EETs). EETs and NO are produced in the kidney, and both regulate renal vascular tone and Na+ transport. However, the role of EETs in NO-mediated renal function is not known. This study tested the hypothesis that NO tonically regulates the renal production of EETs, thereby impacting renal vasomotor tone and electrolyte balance. LPS (10 mg/kg iv) inhibited microsomal conversion of 14C-labeled arachidonic acid to EETs and reduced mean arterial blood pressure (MABP; Δ = 63 ± 5 mmHg). Nitro-l-arginine methyl ester (l-NAME, 10 mg/kg), an inhibitor of NO synthase, increased MABP (Δ = 26 ± 6 mmHg), reduced cortical (CBF) and medullary (MBF) blood flow (Δ = -0.86 ± 0.15 and -0.34 ± 0.09 V, respectively) and glomerular filtration rate (GFR; from 0.82 ± 0.16 to 0.32 ± 0.10 ml·g kidney-1·min-1), and increased Na+ excretion (UNaV, from 0.16 ± 0.04 to 0.30 ± 0.06 μmol·g kidney-1·min-1). 2-(2-Propynyloxy)-benzenehexanoic acid (PPOH), a suicide substrate inhibitor of EET production, did not affect the l-NAME-induced increase in MABP but attenuated the effects of l-NAME on CBF (31 ± 7%, P < 0.05%), GFR (44 ± 6%, P < 0.05), and UNaV (78 ± 7%, P < 0.05). Miconazole (1.3 mg·kg-1·h-1), a heme inhibitor of epoxygenase enzymes, produced effects similar to those of PPOH. Renal intraarterial infusion of 5,6-, 8,9-, 11,12-, and 14,15-EET (1-10 ng/min) elicited dose-dependent reductions in CBF and GFR accompanied by regioisomeric changes in MBF, UNaV, and urine flow rate. In addition, 11,12-EET dose dependently restored the PPOH blunting the effects of l-NAME on CBF, MBF, and GFR. We conclude that NO tonically regulates epoxygenase activity and that EETs are renal vaosoconstrictors in vivo and contribute, at least in part, to the renal functional responses following inhibition of NO production.