Endothelium-dependent Hyperpolarizing Factor Research Articles

Inhibition of endothelium-dependent vascular relaxation by lysophosphatidylcholine: impact of lysophosphatidylcholine on mechanisms involving endothelium-derived nitric oxide and endothelium derived hyperpolarizing factor.

Hyperlipidemia has been associated with an increase in the incidence of atherosclerosis. The oxidation of low density lipoprotein (LDL) plays an important role in the initiation and progression of atherosclerosis, one of its effects being the inhibition of endothelium dependent relaxation (EDR). The elevated level of lysophosphatidylcholine (LPC) in oxidatively modified LDL has been shown to be a biochemical factor responsible for the impairment of EDR in vascular ring preparations. Several endothelium-derived modulators are thought to control vascular responsiveness. The present work examined whether acetylcholine (ACh)-induced EDR in rat aorta (pre-contracted with phenylephrine, PE) involved both endothelium-derived nitric oxide (EDNO) and endothelium-dependent hyperpolarizing factor (EDHF) and whether LPC inhibited either of these selectively. Indomethacin (10(-5) M), had no significant effect on EDR, indicating that products of cyclooxygenase, including prostacyclin, are not involved. Treatment with either N(W)-nitro-L-arginine methyl ester (L-NAME, 6.8 microM) to inhibit the production of EDNO or with elevated K+ (15 mM), to block the hyperpolarizing effect of EDHF impaired EDR considerably (each of these shifting the inhibitory dose-response relationship to ACh by almost one log unit); in muscles treated with both of these agents EDR was completely inhibited. In each of L-NAME- and K-treated muscles, the addition of LPC (20 microM) further impaired EDR. LPC did not independently raise the tone of resting- or PE-contracted aorta. We conclude that the inhibition of EDR of rat aorta by LPC involves the actions of both EDNO and EDHF.

Attenuation of endothelium-dependent hyperpolarizing factor by bacterial lipopolysaccharides

Endothelium-dependent hyperpolarizing factor (EDHF) is an important contributor to agonist-induced vascular dilation. Recent studies suggest that bacterial lipopolysaccharides attenuate endothelium-dependent dilation. Whether or not this effect is mediated through inhibition of EDHF is not known. We studied the in vitro influence of Escherichia coli lipopolysaccharides on endothelium-dependent smooth muscle dilation and hyperpolarization in porcine coronary arteries. Endothelium-intact porcine coronary arterial rings were examined after 20 h of incubation with either saline or E. coli lipopolysaccharides (100 μg/ml). Endothelium-dependent dilation elicited by increasing concentrations of bradykinin was significantly attenuated by lipopolysaccharides. Baseline values of smooth muscle membrane potential were not influenced by lipopolysaccharides. However, lipopolysaccharides significantly attenuated bradykinin-induced smooth muscle membrane hyperpolarization. Our results suggest that attenuation of EDHF is an important mechanism through which lipopolysaccharides influence vascular dilation in severe sepsis.

Conducted arteriolar dilations persist in the presence of nitroarginine.

At least two mechanisms of arterial dilations are induced by the application of muscarinic agonists. One is caused by nitric oxide, and the second is the result of the release of an endothelium-dependent hyperpolarizing factor (EDHF) that has yet to be clearly defined. This study was performed to determine whether two modes of dilation also are present in the microcirculation. Arterioles (38 microns maximal diameter) in the cheek pouch of anesthetized hamsters were stimulated with the micropipette application of a muscarinic-receptor agonist (methacholine 10(-4) M; MCh). A single microapplication of MCh (5 s) caused dilation at the tip of the pipette, as well as a dilation remote from the site of application. Two modes of muscarinic receptor-induced dilation were suggested within arterioles because nitroarginine (10(-6)-10(-3) M) significantly decreased the local dilation from control of 14 +/- 1.8 microns to 5 +/- 0.9 microns in the presence of 10(-4) M nitroarginine, without significantly affecting the conducted response (control, 4.7 +/- 0.8 microns; with 10(-4) M nitroarginine, 3.1 +/- 0.5 microns). Therefore, in hamster check-pouch arterioles there are two modes of dilation caused by muscarinic agonists, and they are mediated by different mechanisms: one is nitric oxide and the other is consistent with a hyperpolarizing factor.

Effects of calcium dobesilate on the synthesis of endothelium-dependent relaxing factors in rabbit isolated aorta.

1. Some cardiovascular disturbances which occur in diabetics are a consequence of alterations in vascular contractility as well as in endothelium-dependent relaxation. 2. Calcium dobesilate (DOBE) is a drug used in diabetic retinopathy and its mechanism of action is not yet understood. 3. The aim of this study was to investigate the effects of DOBE on synthesis and release of endothelium-dependent relaxing factor (EDRF) and endothelium-dependent hyperpolarizing factor (EDHF) in rabbit isolated aorta. 4. Endothelium-dependent relaxation induced by acetylcholine (ACh) (10(-8)-(10(-5) M) increased in the presence of DOBE 10(-5) M only when vascular endothelium was kept intact. 5. NG-nitro-L-arginine methyl ester (L-NAME; 10(-8)-10(-4) M progressively decreased the enhancing effect of DOBE on endothelium-dependent relaxation whereas it was progressively increased by L-Arg. 6. DOBE 10(-5) M increased in a non-significant manner endothelium-dependent relaxation induced by ACh when the arteries were incubated with both L-NAME 10(-4) M and indomethacin 10(-5) M. 7. DOBE (10(-6) M and 10(-5) M) was able to scavenge superoxide anion radicals generated by the hypoxanthine/xanthine oxidase reaction. 8. These results provide evidence that DOBE is able to affect the vascular disorders associated with diabetes mellitus since it enhances the synthesis of endothelium-dependent relaxing factors.

Thimerosal hyperpolarizes arterial smooth muscles in an endothelium-dependent manner

Thimerosal activates the production of endothelium-derived relaxing factor (EDRF). I examined whether thimerosal also causes the release of an endothelium-dependent hyperpolarizing factor (EDHF). Thimerosal caused an endothelium-dependent hyperpolarization of smooth muscle. This effect is unlikely to be caused by the property of thimerosal to inhibit the acyl-coenzyme A: lysolecithin acyltransferase (LAT) since neither arachidonic acid nor lysolecithin hyperpolarized the muscles. I conclude that thimerosal is not a pure activator of EDRF (nitric oxide) production, but that it also releases a distinct EDHF.