Nitric oxide production in the hypoxic lung (original) (raw)
Related papers
Reduced Hypoxic Pulmonary Vascular Remodeling by Nitric Oxide From the Endothelium
Hypertension, 2001
We examined whether overproduction of endogenous nitric oxide (NO) can prevent hypoxia-induced pulmonary hypertension and vascular remodeling by using endothelial NO-overexpressing (eNOS-Tg) mice. Male eNOS-Tg mice and their littermates (wild-type, WT) were maintained in normoxic or 10% hypoxic condition for 3 weeks. In normoxia, eNOS protein levels, Ca 2ϩ -dependent NOS activity, and cGMP levels in the lung of eNOS-Tg mice were higher than those of WT mice. Activity of eNOS and cGMP production in the lung did not change significantly by hypoxic exposure in either genotype. Chronic hypoxia did not induce iNOS expression nor increase its activity in either genotype. Plasma and lung endothelin-1 levels were increased by chronic hypoxia, but these levels were not significantly different between the 2 genotypes. In hemodynamic analysis, right ventricular systolic pressure (RVSP) in eNOS-Tg mice was similar to that in WT mice in normoxia. Chronic hypoxia increased RVSP and induced right ventricular hypertrophy in both genotypes; however, the degrees of these increases were significantly smaller in eNOS-Tg mice. Histological examination revealed that hypoxic mice showed medial wall thickening in pulmonary arteries. However, the increase of the wall thickening in small arteries (diameter Ͻ80 m) by chronic hypoxia was inhibited in eNOS-Tg mice. Furthermore, muscularization of small arterioles was significantly attenuated in eNOS-Tg mice. Thus, we demonstrated directly that overproduction of eNOS-derived NO can inhibit not only the increase in RVSP associated with pulmonary hypertension but also remodeling of the pulmonary vasculature and right ventricular hypertrophy induced by chronic hypoxia. (Hypertension. 2001;37:322-327.)
Variable expression of endothelial NO synthase in three forms of rat pulmonary hypertension
American Journal of …, 1999
Endothelial nitric oxide (NO) synthase (eNOS) mRNA and protein and NO production are increased in hypoxia-induced hypertensive rat lungs, but it is uncertain whether eNOS gene expression and activity are increased in other forms of rat pulmonary hypertension. To investigate these questions, we measured eNOS mRNA and protein, eNOS immunohistochemical localization, perfusate NO product levels, and NO-mediated suppression of resting vascular tone in chronically hypoxic (3-4 wk at barometric pressure of 410 mmHg), monocrotaline-treated (4 wk after 60 mg/kg), and fawn-hooded (6-9 mo old) rats. eNOS mRNA levels (Northern blot) were greater in hypoxic and monocrotaline-treated lungs (130 and 125% of control lungs, respectively; P Ͻ 0.05) but not in fawn-hooded lungs. Western blotting indicated that eNOS protein levels increased to 300 Ϯ 46% of control levels in hypoxic lungs (P Ͻ 0.05) but were decreased by 50 Ϯ 5 and 60 Ϯ 11%, respectively, in monocrotaline-treated and fawn-hooded lungs (P Ͻ 0.05). Immunostaining showed prominent eNOS expression in small neomuscularized arterioles in all groups, whereas perfusate NO product levels increased in chronically hypoxic lungs (3.4 Ϯ 1.4 µM; P Ͻ 0.05) but not in either monocrotaline-treated (0.7 Ϯ 0.3 µM) or fawn-hooded (0.45 Ϯ 0.1 µM) lungs vs. normotensive lungs (0.12 Ϯ 0.07 µM). All hypertensive lungs had increased baseline perfusion pressure in response to nitro-L-arginine but not to the inducible NOS inhibitor aminoguanidine. These results indicate that even though NO activity suppresses resting vascular tone in pulmonary hypertension, there are differences among the groups regarding eNOS gene expression and NO production. A better understanding of eNOS gene expression and activity in these models may provide insights into the regulation of this vasodilator system in various forms of human pulmonary hypertension.
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.
The Chinese journal of physiology, 2006
Hyperoxia may affect lung physiology in different ways. We investigated the effect of hyperoxia on the protein expression of endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS), nitric oxide (NO) production, and hypoxic pulmonary vasoconstriction (HPV) in rat lung. Twenty-four male rats were divided into hyperoxic and normoxic groups. Hyperoxic rats were placed in > 90% F1O2 for 60 h prior to experiments. After baseline in vitro analysis, the rats underwent isolated, perfused lung experiments. Two consecutive hypoxic challenges (10 min each) were administered with the administration of a non-specific NOS inhibitor, N-nitro-L-arginine methyl ester (L-NAME), in between. We measured intravascular NO production, pulmonary arterial pressure, and protein expression of eNOS and iNOS by immunohistochemistry. We found that hyperoxia rats exhibited increased baseline NO production (P < 0.001) and blunted HPV response (P < 0.001) during hypoxic challeng...
Journal of Clinical Investigation, 1998
Chronic hypoxia induces pulmonary hypertension and right ventricular (RV) hypertrophy. Nitric oxide (NO) has been proposed to modulate the pulmonary vascular response to hypoxia. We investigated the effects of congenital deficiency of endothelial NO synthase (NOS3) on the pulmonary vascular responses to breathing 11% oxygen for 3-6 wk. After 3 wk of hypoxia, RV systolic pressure was greater in NOS3-deficient than in wild-type mice (35 Ϯ 2 vs 28 Ϯ 1 mmHg, x Ϯ SE, P Ͻ 0.001). Pulmonary artery pressure (P PA ) and incremental total pulmonary vascular resistance (R PI ) were greater in NOS3-deficient than in wild-type mice (P PA 22 Ϯ 1 vs 19 Ϯ 1 mmHg, P Ͻ 0.05 and R PI 92 Ϯ 11 vs 55 Ϯ 5 mmHg·min·gram·ml Ϫ 1 , P Ͻ 0.05). Morphometry revealed that the proportion of muscularized small pulmonary vessels was almost fourfold greater in NOS3-deficient mice than in wild-type mice. After 6 wk of hypoxia, the increase of RV free wall thickness, measured by transesophageal echocardiography, and of RV weight/body weight ratio were more marked in NOS3-deficient mice than in wildtype mice (RV wall thickness 0.67 Ϯ 0.05 vs 0.48 Ϯ 0.02 mm, P Ͻ 0.01 and RV weight/body weight ratio 2.1 Ϯ 0.2 vs 1.6 Ϯ 0.1 mg·gram Ϫ 1 , P Ͻ 0.05). RV hypertrophy produced by chronic hypoxia was prevented by breathing 20 parts per million NO in both genotypes of mice. These results suggest that congenital NOS3 deficiency enhances hypoxic pulmonary vascular remodeling and hypertension, and RV hypertrophy, and that NO production by NOS3 is vital to counterbalance pulmonary vasoconstriction caused by chronic hypoxic stress. (
American Journal of Physiology-lung Cellular and Molecular Physiology, 1998
Recent studies have characterized a rebound pulmonary vasoconstriction with abrupt withdrawal of inhaled nitric oxide (NO) during therapy for pulmonary hypertension, suggesting that inhaled NO may downregulate basal NO production. However, the exact mechanism of this rebound pulmonary hypertension remains unclear. The objectives of these studies were to determine the effect of NO exposure on endothelial NO synthase (eNOS) gene expression, enzyme activity, and posttranslational modification in cultured pulmonary arterial endothelial cells. Sodium nitroprusside (SNP) treatment had no effect on eNOS mRNA or protein levels but did produce a significant decrease in enzyme activity. Furthermore, although SNP treatment induced protein kinase C (PKC)-dependent eNOS phosphorylation, blockade of PKC activity did not protect against the effects of SNP. When the xanthine oxidase inhibitor allopurinol or the superoxide scavenger 4,5-dihydroxy-1-benzene-disulfonic acid were coincubated with SNP, the inhibitory effects on eNOS activity could be partially alleviated. Also, the levels of superoxide were found to be elevated 4.5-fold when cultured pulmonary arterial endothelial cells were exposed to the NO donor spermine/NO. This suggests that NO can stimulate xanthine oxidase to cause an increase in cellular superoxide generation. A reaction between NO and superoxide would produce peroxynitrite, which could then react with the eNOS protein, resulting in enzyme inactivation. This mechanism may explain, at least in part, how NO produces NOS inhibition in vivo and may delineate, in part, the mechanism of rebound pulmonary hypertension after withdrawal of inhaled NO.
Role of endothelial nitric oxide in pulmonary and systemic arteries during hypoxia
Nitric Oxide, 2014
Our aim was to investigate the role played by endothelial nitric oxide (NO) during acute vascular response to hypoxia, as a modulator of both vascular tone (through guanylate cyclase (sGC) activation) and mitochondrial O 2 consumption (through competitive inhibition of cytochrome-c-oxydase (CcO)). Organ bath experiments were performed and O 2 consumption (Clark electrode) was determined in isolated aorta, mesenteric and pulmonary arteries of rats and eNOS-knockout mice. All pre-contracted vessels exhibited a triphasic hypoxic response consisting of an initial transient contraction (not observed in vessels from eNOS-knockout mice) followed by relaxation and subsequent sustained contraction. Removal of the endothelium, inhibition of eNOS (by L-NNA) and inhibition of sGC (by ODQ) abolished the initial contraction without altering the other two phases. The initial hypoxic contraction was observed in the presence of L-NNA+NO-donors. L-NNA and ODQ increases O 2 consumption in hypoxic vessels and increases the arterial tone in normoxia but not in hypoxia. When L-NNA+mitochondrial inhibitors (cyanide, rotenone or myxothiazol) were added, the increase in tone was similar in normoxic and hypoxic vessels, which suggests that inhibition of the binding of NO to reduced CcO restored the action of NO on sGC. CONCLUSION: A complex equilibrium is established between NO, sGC and CcO in vessels in function of the concentration of O 2 : as O 2 falls, NO inhibition of mitochondrial O 2 consumption increases and activation of sGC decreases, thus promoting a rapid increase in tone in both pulmonary and systemic vessels, which is followed by the triggering of NOindependent vasodilator/vasoconstrictor mechanisms.