Identification of 13-Hydroxy-14,15-epoxyeicosatrienoic Acid as an Acid-stable Endothelium-derived Hyperpolarizing Factor in Rabbit Arteries

Patients with essential hypertension have abnormal endothelium-dependent vasodilation. Because the endothelium exerts its action on the vascular smooth muscle through the release of several substances, it is important to identify which of these factors is involved in the abnormal response of hypertensive arteries. To investigate the role of endothelium-derived nitric oxide in this abnormality, we studied the vascular effect of the arginine analogue NG-monomethyl-L-arginine, an inhibitor of the endothelial synthesis of nitric oxide, under baseline conditions and during infusion of acetylcholine, an endothelium-dependent vasodilator, and sodium nitroprusside, a direct smooth muscle dilator. The study included 11 hypertensive patients (seven men; age, 46.5 +/- 9 years) and 10 normal control subjects (seven men; age, 45.7 +/- 7 years). Drugs were infused into the brachial artery, and the response of the forearm vasculature was measured by strain-gauge plethysmography. Basal blood flow was similar in normal control subjects and hypertensive patients (2.97 +/- 0.7 versus 2.86 +/- 1.1 mL.min-1.100 mL-1, respectively). NG-monomethyl-L-arginine produced a significantly greater decrease in blood flow in control subjects than in patients (1.08 +/- 0.6 versus 0.32 +/- 0.4 mL.min-1.100 mL-1; p < 0.004). The vasodilator response to acetylcholine was reduced in patients compared with control subjects (maximum flow, 8.2 +/- 4 versus 16.4 +/- 8 mL.min-1.100 mL-1; p < 0.001). NG-monomethyl-L-arginine blunted the vasodilator response to acetylcholine in control subjects (maximum flow decreased from 16.4 +/- 8 to 7.01 +/- 3 mL.min-1.100 mL-1; p < 0.004); however, the arginine analogue did not significantly alter the response to acetylcholine in hypertensive patients (maximum flow, 8.2 +/- 4 versus 8.01 +/- 5 mL.min-1.100 mL-1). NG-monomethyl-L-arginine did not modify the vasodilator response to sodium nitroprusside in either control subjects or patients. These findings indicate that patients with essential hypertension have a defect in the endothelium-derived nitric oxide system that may at least partly account for both the increased vascular resistance under basal conditions and the impaired response to endothelium-dependent vasodilators.

The mechanism by which neutrophils [polymorphonuclear leukocyte (PMNs)] are stimulated to move across epithelial barriers at mucosal surfaces has been basically unknown in biology. IL-8 has been shown to stimulate PMNs to leave the bloodstream at a local site of mucosal inflammation, but the chemical gradient used by PMNs to move between adjacent epithelial cells and traverse the tight junction at the apical neck of these mucosal barriers has eluded identification. Our studies not only identify this factor, previously termed pathogen-elicited epithelial chemoattractant, as the eicosanoid hepoxilin A(3) (hepA(3)) but also demonstrate that it is a key factor promoting the final step in PMN recruitment to sites of mucosal inflammation. We show that hepA(3) is synthesized by epithelial cells and secreted from their apical surface in response to conditions that stimulate inflammatory events. Our data further establish that hepA(3) acts to draw PMNs, via the establishment of a gradient across the epithelial tight junction complex. The functional significance of hepA(3) to target PMNs to the lumen of the gut at sites of inflammation was demonstrated by the finding that disruption of the 12-lipoxygenase pathway (required for hepA(3) production) could dramatically reduce PMN-mediated tissue trauma, demonstrating that hepA(3) is a key regulator of mucosal inflammation.

1. Experiments were designed to determine whether endothelium-dependent relaxing factor(s) released by acetylcholine from the canine femoral artery influences the membrane potential of coronary arterial smooth muscle. 2. The membrane potential was recorded in small canine coronary arteries (internal diameter less than or equal to 500 micron; without endothelium) by means of intracellular microelectrodes. The organ bath also contained a strip of left descending coronary artery without endothelium in which isometric force was measured to bioassay relaxing factor(s) as well as segments of femoral artery with endothelium, which served as the source of endothelium-derived relaxing factor(s). 3. Acetylcholine induced endothelium-dependent, transient hyperpolarizations and relaxations that were not affected by indomethacin. 4. Inhibition of the sodium-potassium pump by ouabain or potassium-free solution did not inhibit the relaxation to acetylcholine but prevented the corresponding hyperpolarization. 5. Activation of the sodium-potassium pump of the smooth muscle cells by readmission of potassium ions after incubation in potassium-free solution caused relaxation and marked hyperpolarization. 6. These results suggest that endothelium-derived relaxing factor(s) induces hyperpolarization of vascular smooth muscle of the canine coronary artery, possibly by activation of sodium-potassium pumping, but that this effect on the cell membrane may only partially explain endothelium-dependent relaxations evoked by acetylcholine.