Role of endothelial nitric oxide in pulmonary and systemic arteries during hypoxia (original) (raw)
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American Journal of Physiology-Heart and Circulatory Physiology, 1999
The present study was aimed at examining the role of nitric oxide (NO) in the hypoxic contraction of isolated small pulmonary arteries (SPA) in the rat. Animals were treated with either saline (sham experiments) or Escherichia coli lipolysaccharide [LPS, to obtain expression of the inducible NO synthase (iNOS) in the lung] and killed 4 h later. SPA (300- to 600-μm outer diameter) were mounted as rings in organ chambers for the recording of isometric tension, precontracted with PGF2α, and exposed to either severe (bath [Formula: see text] 8 ± 3 mmHg) or milder (21 ± 3 mmHg) hypoxia. In SPA from sham-treated rats, contractions elicited by severe hypoxia were completely suppressed by either endothelium removal or preincubation with an NOS inhibitor [ N G-nitro-l-arginine methyl ester (l-NAME), 10−3 M]. In SPA from LPS-treated rats, contractions elicited by severe hypoxia occurred irrespective of the presence or absence of endothelium and were largely suppressed by l-NAME. The milder hy...
On the Mechanism by Which Vascular Endothelial Cells Regulate Their Oxygen Consumption
Proceedings of The National Academy of Sciences, 1999
Two enzymes, soluble guanylyl cyclase and cytochrome c oxidase, have been shown to be exquisitely sensitive to nitric oxide (NO) at low physiological concentrations. Activation of the soluble guanylyl cyclase by endogenous NO and the consequent increase in the second messenger cyclic GMP are now known to control a variety of biological functions. Cytochrome c oxidase, the terminal enzyme of the mitochondrial respiratory chain, is inhibited by NO. However, it is not clear whether NO produced by the constitutive NO synthase interacts with cytochrome c oxidase, nor is it known what the biological consequences of such an interaction might be. We now show that NO generated by vascular endothelial cells under basal and stimulated conditions modulates the respiration of these cells in response to acute changes in oxygen concentration. This action occurs at the cytochrome c oxidase and depends on inf lux of calcium. Thus, NO plays a physiological role in adjusting the capacity of this enzyme to use oxygen, allowing endothelial cells to adapt to acute changes in their environment.
Biphasic modulation of vascular nitric oxide catabolism by oxygen
American Journal of Physiology-Heart and Circulatory Physiology, 2004
Endothelium-derived nitric oxide (NO) plays an important role in the regulation of vascular tone. Lack of NO bioavailability can result in cardiovascular disease. NO bioavailability is determined by its rates of generation and catabolism; however, it is not known how the NO catabolism rate is regulated in the vascular wall under normoxic, hypoxic, and anaerobic conditions. To investigate NO catabolism under different oxygen concentrations, studies of NO and O2consumption by the isolated rat aorta were performed using electrochemical sensors. Under normoxic conditions, the rate of NO consumption in solution was enhanced in the presence of the rat aorta. Under hypoxic conditions, NO consumption decreased in parallel with the O2concentration. Like the inhibition of mitochondrial respiration by NO, the inhibitory effects of NO on aortic O2consumption increased as O2concentration decreased. Under anaerobic conditions, however, a paradoxical reacceleration of NO consumption occurred. This...
Regulation of Oxygen Distribution in Tissues by Endothelial Nitric Oxide
Circulation Research, 2009
Nitric oxide (NO) decreases cellular oxygen (O 2 ) consumption by competitively inhibiting cytochrome c oxidase. Here, we show that endogenously released endothelial NO, either basal or stimulated, can modulate O 2 consumption both throughout the thickness of conductance vessels and in the microcirculation. Furthermore, we have shown that such modulation regulates O 2 distribution to the surrounding tissues. We have demonstrated these effects by measuring O 2 consumption in blood vessels in a hypoxic chamber and O 2 distribution in the microcirculation using the fluorescent oxygen-probe Ru(phen) 3 2+ . Removal of NO by physical or pharmacological means, or in eNOS −/− mice, abolishes this regulatory mechanism. Our results indicate that, in addition to its well-known effect on the regulation of vascular tone, endothelial NO plays a major role in facilitating the distribution of O 2 , an action which is crucial for the adaptation of tissues, including the vessel wall itself, to hypoxi...
British Journal of Pharmacology, 2003
1 Chronic hypoxia (CH) increases lung tissue expression of all types of nitric oxide synthase (NOS) in the rat. However, it remains unknown whether CH-induced changes in functional and histological NOS distributions are correlated in rat small pulmonary arteries. 2 We measured the effects of NOS inhibitors on the internal diameters (ID) of muscular (MPA) and elastic (EPA) pulmonary arteries (100 -700 mm ID) using an X-ray television system on anaesthetized rats. We also conducted NOS immunohistochemical localization on the same vessels. 3 Nonselective NOS inhibitors induced ID reductions in almost all MPA of CH rats (mean reduction, 3673%), as compared to B60% of control rat MPA (mean, 1072%). The inhibitors reduced the ID of almost all EPA with similar mean values (B26%) in both CH and control rats. On the other hand, inducible NOS (iNOS)-selective inhibitors caused ID reductions in B60% of CH rat MPA (mean, 1573%), but did so in only B20% of control rat MPA (mean, 272%). This inhibition caused only a small reduction (mean, B4%) in both CH and control rat EPA. A neuronal NOSselective inhibitor had no effect. 4 The percentage of endothelial NOS (eNOS)-positive vessels was B96% in both MPA and EPA from CH rats, whereas it was 51 and 91% in control MPA and EPA, respectively. The percentage for iNOS was B60% in both MPA and EPA from CH rats, but was only B8% in both arteries from control rats. 5 The data indicate that in CH rats, both functional and histological upregulation of eNOS extensively occurs within MPA. iNOS protein increases sporadically among parallel-arranged branches in both MPA and EPA, but its vasodilatory effect is predominantly observed in MPA. Such NOS upregulation may serve to attenuate hypoxic vasoconstriction, which occurs primarily in MPA and inhibit the progress of pulmonary hypertension.
Antioxidants & Redox Signaling, 2008
Nitric oxide (NO) affects two key aspects of O 2 supply and demand: It regulates vascular tone and blood flow by activating soluble guanylate cyclase (sGC) in the vascular smooth muscle, and it controls mitochondrial O 2 consumption by inhibiting cytochrome c oxidase. However, significant gaps exist in our quantitative understanding of the regulation of NO production in the vascular region. Large apparent discrepancies exist among the published reports that have analyzed the various pathways in terms of the perivascular NO concentration, the efficacy of NO in causing vasodilation (EC 50 ), its efficacy in tissue respiration (IC 50 ), and the paracrine and endocrine NO release. In this study, we review the NO literature, analyzing NO levels on various scales, identifying and analyzing the discrepancies in the reported data, and proposing hypotheses that can potentially reconcile these discrepancies. Resolving these issues is highly relevant to improving our understanding of vascular biology and to developing pharmaceutical agents that target NO pathways, such as vasodilating drugs.
British Journal of Pharmacology, 2001
1 Inhaled nitric oxide (iNO) is widely used in the treatment of pulmonary hypertension while inhaled NO donors have been suggested as an alternative therapy. The dierential susceptibility to inactivation by oxidative stress and oxyhaemoglobin of NO and two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetyl-penicillamine (SNAP) were analysed in isolated endothelium-denuded pulmonary arteries from 2-week-old piglets stimulated with U46619. 2 NO, SNAP and SNP relaxed the arteries (pIC 30 =7.73+0.12, 7.26+0.17 and 6.43+0.13, respectively) but NO was not detected electrochemically in the bath after the addition of SNP and only at concentrations at which SNAP produced more than 50% relaxation. 3 The sGC inhibitor ODQ (10 76 M) or the sarcoplasmic Ca 2+ -ATPase thapsigargin (2610 76 M) markedly inhibited the relaxation induced by NO, SNAP and SNP. 4 Addition of oxyhaemoglobin (3610 77 M) or diethyldithiocarbamate (1 mM) markedly inhibited NO-(pIC 30 =6.88+0.07 and 6.92+0.18, respectively), weakly inhibited SNAP-and had no eect on SNP-induced relaxation. Xanthine oxidase (5 mu ml 71 ) plus hypoxanthine (10 74 M) markedly inhibited NO-(pIC 30 =6.96+0.12) but not SNAP-or SNP-induced relaxation. 5 Superoxide dismutase (SOD), MnCl 2 , diphenileneiodonium and exposing the luminal surface of the rings outwards (inversion) potentiated the relaxant responses of NO (pIC 30 =8.52+0. 16, 8.23+0.11, 8.01+0.11 and 8.20+0.10, respectively). However, SOD did not modify the NO detected by the electrode and had no eect on SNAP-or SNP-induced relaxation. 6 Therefore, the kinetics and local distribution of NO release of NO donors in¯uence the susceptibility to the scavenging eects of oxyhaemoglobin and superoxide.
Circulation, 2007
Background-Nitric oxide (NO) activates soluble guanylate cyclase (sGC), a heterodimer composed of ␣and -subunits, to produce cGMP. NO reduces pulmonary vascular remodeling, but the role of sGC in vascular responses to acute and chronic hypoxia remains incompletely elucidated. We therefore studied pulmonary vascular responses to acute and chronic hypoxia in wild-type (WT) mice and mice with a nonfunctional ␣1-subunit (sGC␣1 Ϫ/Ϫ ). Methods and Results-sGC␣1 Ϫ/Ϫ mice had significantly reduced lung sGC activity and vasodilator-stimulated phosphoprotein phosphorylation. Right ventricular systolic pressure did not differ between genotypes at baseline and increased similarly in WT (22Ϯ2 to 34Ϯ2 mm Hg) and sGC␣1 Ϫ/Ϫ (23Ϯ2 to 34Ϯ1 mm Hg) mice in response to acute hypoxia. Inhaled NO (40 ppm) blunted the increase in right ventricular systolic pressure in WT mice (22Ϯ2 to 24Ϯ2 mm Hg, PϽ0.01 versus hypoxia without NO) but not in sGC␣1 Ϫ/Ϫ mice (22Ϯ1 to 33Ϯ1 mm Hg) and was accompanied by a significant rise in lung cGMP content only in WT mice. In contrast, the NO-donor sodium nitroprusside (1.5 mg/kg) decreased systemic blood pressure similarly in awake WT and sGC␣1 Ϫ/Ϫ mice as measured by telemetry (Ϫ37Ϯ2 versus Ϫ42Ϯ4 mm Hg). After 3 weeks of hypoxia, the increases in right ventricular systolic pressure, right ventricular hypertrophy, and muscularization of intra-acinar pulmonary vessels were 43%, 135%, and 46% greater, respectively, in sGC␣1 Ϫ/Ϫ than in WT mice (PϽ0.01). Increased remodeling in sGC␣1 Ϫ/Ϫ mice was associated with an increased frequency of 5Ј-bromo-deoxyuridine-positive vessels after 1 and 3 weeks (PϽ0.01 versus WT).
Oxygen Mediates Vascular Smooth Muscle Relaxation in Hypoxia
PLoS ONE, 2013
The activation of soluble guanylate cyclase (sGC) by nitric oxide (NO) and other ligands has been extensively investigated for many years. In the present study we considered the effect of molecular oxygen (O 2 ) on sGC both as a direct ligand and its affect on other ligands by measuring cyclic guanosine monophosphate (cGMP) production, as an index of activity, as well as investigating smooth muscle relaxation under hypoxic conditions. Our isolated enzyme studies confirm the function of sGC is impaired under hypoxic conditions and produces cGMP in the presence of O 2 , importantly in the absence of NO. We also show that while O 2 could partially affect the magnitude of sGC stimulation by NO when the latter was present in excess, activation by the NO independent, haem-dependent sGC stimulator 3-(59-hydroxymethyl-29-furyl)-1-benzylindazole (YC-1) was unaffected. Our in vitro investigation of smooth muscle relaxation confirmed that O 2 alone in the form of a buffer bolus (equilibrated at 95% O 2 /5% CO 2 ) had the ability to dilate vessels under hypoxic conditions and that this was dependent upon sGC and independent of eNOS. Our studies confirm that O 2 can be a direct and important mediator of vasodilation through an increase in cGMP production. In the wider context, these observations are key to understanding the relative roles of O 2 versus NO-induced sGC activation.
Diminished NO release in chronic hypoxic human endothelial cells
American Journal of Physiology-Heart and Circulatory Physiology, 2007
The present study addressed whether chronic hypoxia is associated with reduced nitric oxide (NO) release due to decreased activation of endothelial NO synthase (eNOS). Primary cultures of endothelial cells from human umbilical veins (HUVECs) were used and exposed to different oxygen levels for 24 h, after which NO release, intracellular calcium, and eNOS activity and phosphorylation were measured after 24 h. Direct measurements using a NO microsensor showed that in contrast to 1-h exposure to 5% and 1% oxygen (acute hypoxia), histamine-evoked (10 μM) NO release from endothelial cells exposed to 5% and 1% oxygen for 24 h (chronic hypoxia) was reduced by, respectively, 58% and 40%. Furthermore, chronic hypoxia also lowered the amount and activity of eNOS enzyme. The decrease in activity could be accounted for by reduced intracellular calcium and altered eNOS phosphorylation. eNOS Ser1177and eNOS Thr495phosphorylations were reduced and increased, respectively, consistent with lowered e...