Inhibition of 20-HETE Production Contributes to the Vascular Responses to Nitric Oxide

Abstract

Nitric oxide (NO) inhibits a variety of heme-containing enzymes, including NO synthase and cytochrome P4501A1 and 2B1. The present study examined whether NO inhibits the production of 20-hydroxyeicosatetraenoic acid (20-HETE) by cytochrome P4504A enzymes and whether blockade of the production of this substance contributes to the vascular effects of NO. Sodium nitroprusside (SNP; 10 −5 , 10 −4 , and 10 −3 mol/L) reduced the production of 20-HETE by renal microsomes incubated with arachidonic acid to 71±5%, 29±4%, and 4±2% of control, respectively (n=5). Similar results were obtained with the use of 1-propanamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazino) (n=3). To determine whether inhibition of 20-HETE contributes to the vasodilatory effects of NO, the effects of dibromo-dodecenyl-methylsulfimide (DDMS), a selective inhibitor of the formation of 20-HETE, on the response to SNP (10 −7 to 10 −3 mol/L) were examined in rat renal arterioles preconstricted with phenylephrine (n=5). SNP increased vascular diameter in a concentration-dependent manner to 82±4% of control. After DDMS (25 μmol/L), SNP (10 −3 mol/L) increased vascular diameter by only 17±3%. The effects of DDMS on the mean arterial pressure (MAP) and renal blood flow (RBF) responses to infusion of an NO donor and a synthase inhibitor were also examined in thiobutabarbital-anesthetized, Sprague-Dawley rats. Infusion of MAHMA NONOate at 1, 3, 5, and 10 nmol/min reduced MAP by 16±2, 30±3, 40±5, and 48±5 mm Hg and lowered renal vascular resistance (RVR) by 15±3%, 26±2%, 30±3%, and 34±4% of control. After DDMS (10 mg/kg, n=7 rats), the MAP and RVR responses to 1-hexamine, 6-(2-hydroxy-1-methyl-2-nitrohydrazino) N -methyl (MAHMA NONOate) averaged only 20% of those seen during control. In other experiments, MAP increased by 32±4% and RBF fell to 56±5% of control after administration of N -nitro- l -arginine (L-NArg) (10 mg/kg IV). After DDMS (10 mg/kg, n=7 rats), MAP increased by only 19±4% and RBF fell by only 7±4% after L-NArg. These results indicate that NO inhibits cytochrome P4504A enzymes and that inhibition of the production of 20-HETE contributes to the vasodilatory effects of NO.