Nitric oxide regulates the expression of vasoconstrictors and growth factors by vascular endothelium under both normoxia and hypoxia.

Abstract

The mechanisms by which hypoxia causes vasoconstriction in vivo are not known. Accumulating evidence implicates the endothelium as a key regulator of vascular tone. Hypoxia induces the expression and secretion of endothelin-1 (ET-1), a potent vasoconstrictor in cultured human endothelial cells. We report here that nitric oxide (NO), an endothelial-derived relaxing factor, modifies this induction of ET-1. Whereas low oxygen tension (Po2 = 20-30 Torr) increases ET-1 expression four-to eightfold above that seen at normal oxygen tension (Po2 = 150 Torr), sodium nitroprusside, which releases NO, suppresses this effect. This inhibition of hypoxia-induced ET-1 expression occurs within the first hour of exposure of cells to sodium nitroprusside. Moreover, when the endogenous constitutive levels of NO made by endothelial cells are suppressed using N-w-nitro-L-arginine, a potent competitive inhibitor of NO synthase, the baseline levels of ET-1 produced in normoxic environments are increased three-to fourfold. The effects of hypoxia and the NO synthase inhibitor on ET-1 expression are additive. The regulation of ET-1 production by NO appears to be at the level of transcription. Similar effects of NO were observed on the expression of the PDGF-B chain gene. PDGF-B expression was suppressed by NO in a hypoxic environment and induced by N-w-nitro-L-arginine in both normoxic and hypoxic environments. These findings suggest that in addition to its role as a vasodilator, NO may also influence vascular tone via the regulated reciprocal production ofET-1 and PDGF-B in the vasculature. (J. Clin. Invest. 1993. 92:99-104.) Key words: hypoxianitric oxide * endothelin * umbilical vein * platelet-derived growth factor-B Introduction Endothelial cells serve a key role in the local regulation ofblood vessel tone via the release of vasoactive agents controlling smooth muscle cell proliferation and contractility. They are known to release both vasoconstrictors such as endothelin-1 (ET-1) 1 ( 1 ) and PDGF (2) and vasodilators such as endothelial-derived nitric oxide (NO) (3) in response to local and circulating factors. In fact, the presence of an intact endothelium

Novel guanylyl cyclase inhibitor, ODQ reveals role of nitric oxide, but not of cyclic GMP in endothelin‐1 secretion

“…This conclusion is strengthened by the fact that control compounds (spermine and glutathione) did not affect ET-1 secretion and produced no measurable NO. Interestingly, a similar conclusion was reached recently using L-NNA [12], although this inhibitor cannot differentiate between a regulatory effect mediated by decreasing endogenous NO as opposed to cyclic GMP levels. Given the present evidence, in their study L-NNA probably reduced ET-1 levels by lowering endogenous NO production and not via reduced cyclic GMP levels.…”

“…The reasons for the inconsistent effect of nitric oxide synthase inhibition on basal ET-1 secretion rates are not clear. The inhibition of basal ET-I secretion reported by Kourembanas et al [12] following 24 h of incubation with L-NNA (2.5 mM) was not consistently observed in the present and a previous study [17] using cultured cells, nor in several other ones using native endothelial cells [9] and whole blood vessels [8]. The reasons may include differences in incubation time (24 h in [12] vs. 3-6 h in the other studies), quality of cells (6th to tenth passage [12] vs one passage or native cells), and different levels of [Ca2+]i which we have recently shown to affect basal ET-1 secretion rates [20].…”

“…L-NNA, an inhibitor of NO synthase [12]. These authors interpreted their data as evidence for an active inhibitory role of NO, rather than cyclic GMP in ET-1 secretion.…”

“…To determine if cyclic GMP or NO, or both mediate(s) the suppression of ET-1 production, cyclic GMP production must be inhibited selectively, while leaving NO unaffected. This has been attempted with methylene blue [7,8,12], but cannot be achieved with this dye since it inhibits both guanylyl cyclase and NO synthase, as we have shown recently [14]. The other tool used in the above studies, inhibition of NO synthase by L-arginine derivatives, will reduce both endogenous NO and cyclic GMP levels, thus making it impossible to differentiate between the two putative mediators.…”

Vascular Endothelin-1 Gene Expression and Synthesis and Effect on Renal Type I Collagen Synthesis and Nephroangiosclerosis During Nitric Oxide Synthase Inhibition in Rats

“…Several recent studies suggest that activation of endothelin (ET) is associated with a deficiency of the NO pathway. 5,6 The pathophysiological relevance of such an NO/ET imbalance in the renal angiosclerotic process has still to be demonstrated. ET-1 has mitogenic properties and the ability to regulate extracellular matrix synthesis by vascular smooth muscle cells (VSMCs) in vitro.…”