Nitric oxide is the mediator of both endothelium-dependent relaxation and hyperpolarization of the rabbit carotid artery

Abstract

It is controversial whether the endothelial cell release of nitric oxide (NO) or a different factor(s) accounts for endothelium-dependent hyperpolarization, because in many arteries endothelium-dependent relaxation and hyperpolarization resists inhibitors of NO synthase. The contribution of NO to acetylcholine-induced endotheliumdependent hyperpolarization and relaxation of the rabbit carotid artery was determined by measuring NO with electrochemical and chemiluminescence techniques. In the presence of phenylephrine to depolarize and contract the smooth muscle cells, acetylcholine caused concentration-dependent hyperpolarization and relaxation which were closely correlated to the release of NO. N -nitro-L-arginine methyl ester (30 M) partially reduced the release of NO and caused a similar reduction in smooth muscle cell relaxation and hyperpolarization. To determine if the residual responses were mediated by another endothelium-derived mediator or NO released despite treatment with N -nitro-L-arginine methyl ester, N -nitro-L-arginine (300 M) was added. The combined inhibitors further reduced, but did not eliminate, NO release, smooth muscle relaxation, and hyperpolarization. Hyperpolarization and relaxation to acetylcholine remained closely correlated with the release of NO in the presence of the inhibitors. In addition, the NO donor, SIN-1, caused hyperpolarization and relaxation which correlated with the concentrations of NO that it released. These studies indicate that (i) the release of NO by acetylcholine is only partially inhibited by these inhibitors of NO synthase when used even at high concentrations, and (ii) NO rather than another factor accounts fully for endothelium-dependent responses of the rabbit carotid artery.Nitric oxide (NO) is now accepted to be the major mediator of endothelium-dependent, arterial smooth muscle relaxation (1). However, whether or not NO accounts for endotheliumdependent hyperpolarization is controversial (2, 3). Authentic NO and NO donors hyperpolarize vascular smooth muscle cells (4); however, in some studies, concentrations of NO that were too high to be considered physiological were required, or the hyperpolarization observed was smaller than that caused by an endothelial cell agonist (2, 3). In addition, in many in vitro and in vivo studies of human and animal arteries, endotheliumdependent relaxation, vasodilatation, and hyperpolarization persist in the presence of L-arginine analogues that are inhibitors of NO synthase (NOS) (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20). This has led to the supposition that factors other than NO are important mediators of endothelium-dependent responses including hyperpolarization (2, 3). Cytochrome P450 metabolites of arachidonic acid (21,22), and carbon monoxide (23) have been proposed as alternative mediators. Neither the release from the endothelium of sufficient quantities of these mediators to account for the responses has been measured, nor has NO release been measured directly to exclude its contributio...

P 2u Receptor–Mediated Release of Endothelium-Derived Relaxing Factor/Nitric Oxide and Endothelium-Derived Hyperpolarizing Factor From Cerebrovascular Endothelium in Rats

“…7 This issue was critical in light of a recent publication indicating that endothelial EDRF/NO may be difficult to block. 15 The present study conclusively demonstrates that (1) EDRF/NO was blocked, for all practical purposes, and (2) a relaxing factor other than EDRF/NO was involved in the UTP-mediated dilation. This conclusion is based on 3 findings.…”

“…This issue is critical in light of a recent publication indicating that endothelial EDRF/NO may be difficult to block. 15 (2) Is it distinct from prostacyclin or another cyclooxygenase metabolite? We have previously determined that the dilation did not involve a cyclooxygenase metabolite, 7 and therefore we will not further address this issue in the present studies.…”

cAMP facilitates EDHF-type relaxations in conduit arteries by enhancing electrotonic conduction via gap junctions

“…This amplifying effect of IBMX was not dependent on dynamic increases in cAMP accumulation as this phophodiesterase inhibitor induced similar sustained Ϸ2-fold elevations in the cAMP content of rings both with and without intact endothelium, and 8-bromo-cAMP, a cell permeant analog of cAMP, also potentiated and prolonged mechanical responses to ACh. Direct measurement of cGMP levels confirmed that blockade of NO synthesis was essentially complete under the experimental conditions used and that IBMX, which inhibits hydrolysis of both cGMP and cAMP (23), did not potentiate the EDHF-type relaxant response to ACh by amplifying the biochemical consequences of residual NO activity (24).…”

Endothelial mediators of 17ß-estradiol-induced coronary vasodilation in the isolated rat heart

“…The contribution of each of these factors to endothelium-dependent vasodilation varies across vascular beds and also according to what agent is used to stimulate the endothelium. In general, the endothelium predominantly releases NO in large arteries (28) such as carotid arteries (29), while the contribution of EDHF is more important in smaller resistance arteries (30) such as the mesenteric arteries (31), and arterioles (32). The involvement of prostanoid (mainly prostacyclin) in the regulation of vascular tone has not been widely reported and is often overlooked due to experimental designs in which cyclooxygenase blockers were present since the onset of experimentation.…”