Effect of inhibitors of nitric oxide release and action on vascular tone in isolated lungs of pig, sheep, dog and man

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Reactive Oxygen and Nitrogen Species in the Development of Pulmonary Hypertension

Pulmonary arterial hypertension (PAH) is a progressive disease of the lung vasculature that involves the loss of endothelial function together with inappropriate smooth muscle cell growth, inflammation, and fibrosis. These changes underlie a progressive remodeling of blood vessels that alters flow and increases pulmonary blood pressure. Elevated pressures in the pulmonary artery imparts a chronic stress on the right ventricle which undergoes compensatory hypertrophy but eventually fails. How PAH develops remains incompletely understood and evidence for the altered production of reactive oxygen and nitrogen species (ROS, RNS respectively) in the pulmonary circulation has been well documented. There are many different types of ROS and RNS, multiple sources, and collective actions and interactions. This review summarizes past and current knowledge of the sources of ROS and RNS and how they may contribute to the loss of endothelial function and changes in smooth muscle proliferation in the pulmonary circulation.

Measurement of exhaled nitric oxide concentration in patients with obstructive sleep apnea: A meta-analysis

BACKGROUND

Exhaled nitric oxide (eNO) has been proposed as a noninvasive measure of airway inflammation. However, its value in patients with obstructive sleep apnea (OSA) is still controversial. The authors aim to assess the difference in eNO levels between patients with OSA and controls by a meta-analysis.

METHODS

A systematic search was performed in the PubMed, EMBASE, the Cochrane Library, and MEDLINE databases to collect relevant studies published from 1996 to 2016. Eligible studies that reported eNO levels in patients with OSA were included. STATA (version 12.0) was used for data analysis.

RESULTS

Two hundred eighty-four studies were reviewed for inclusion, with 16 studies pooled for analysis (16 studies for fractional exhaled nitric oxide [FENO], 5 for alveolar nitric oxide [CANO], and 4 for the maximum airway wall flux of nitric oxide [J'awNO]). The FENO levels were significantly higher in patients with OSA compared with that in the control groups (6.32 ppb, 95% confidence interval [CI] 4.46-8.33, P < 0.001). Furthermore, FENO was significantly increased (4.00 ppb, 95% CI 1.74-6.27, P = 0.001) after overnight sleep in patients with OSA, but not in healthy controls. Additionally, long-term continuous positive airway pressure (CPAP) therapy reduced FENO levels (-5.82 ppb, 95% CI -9.6 to -2.01, P < 0.001). However, the CANO (-0.01 ppb, 95% CI -1.66 to 1.64, P = 0.989) and J'awNO levels (220.32 pl/s, 95% CI -49.31 to 489.94, P = 0.109) were not significantly different between the OSA groups and non-OSA groups.

CONCLUSION

The results of the meta-analysis suggest that OSA is significantly associated with airway inflammation and elevated FENO levels can be modified by long-term CPAP therapy. J'awNO and CANO levels were not significantly different between the OSA groups and control groups.

Extracellular Vesicles in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by the progression of irreversible airflow limitation and is a leading cause of morbidity and mortality worldwide. Although several crucial mechanisms of COPD pathogenesis have been studied, the precise mechanism remains unknown. Extracellular vesicles (EVs), including exosomes, microvesicles, and apoptotic bodies, are released from almost all cell types and are recognized as novel cell–cell communication tools. They have been shown to carry and transfer a wide variety of molecules, such as microRNAs, messenger RNAs, and proteins, which are involved in physiological functions and the pathology of various diseases. Recently, EVs have attracted considerable attention in pulmonary research. In this review, we summarize the recent findings of EV-mediated COPD pathogenesis. We also discuss the potential clinical usefulness of EVs as biomarkers and therapeutic agents for the treatment of COPD.

Pulmonary vasculature in COPD: The silent component

Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction that results from an inflammatory process affecting the airways and lung parenchyma. Despite major abnormalities taking place in bronchial and alveolar structures, changes in pulmonary vessels also represent an important component of the disease. Alterations in vessel structure are highly prevalent and abnormalities in their function impair gas exchange and may result in pulmonary hypertension (PH), an important complication of the disease associated with reduced survival and worse clinical course. The prevalence of PH is high in COPD, particularly in advanced stages, although it remains of mild to moderate severity in the majority of cases. Endothelial dysfunction, with imbalance between vasodilator/vasoconstrictive mediators, is a key determinant of changes taking place in pulmonary vasculature in COPD. Cigarette smoke products may perturb endothelial cells and play a critical role in initiating vascular changes. The concurrence of inflammation, hypoxia and emphysema further contributes to vascular damage and to the development of PH. The use of drugs that target endothelium-dependent signalling pathways, currently employed in pulmonary arterial hypertension, is discouraged in COPD due to the lack of efficacy observed in randomized clinical trials and because there is compelling evidence indicating that these drugs may worsen pulmonary gas exchange. The subgroup of patients with severe PH should be ideally managed in centres with expertise in both PH and chronic lung diseases because alterations of pulmonary vasculature might resemble those observed in pulmonary arterial hypertension. Because this condition entails poor prognosis, it warrants specialist treatment.

Peripheral circulation

Blood flow (BF) increases with increasing exercise intensity in skeletal, respiratory, and cardiac muscle. In humans during maximal exercise intensities, 85% to 90% of total cardiac output is distributed to skeletal and cardiac muscle. During exercise BF increases modestly and heterogeneously to brain and decreases in gastrointestinal, reproductive, and renal tissues and shows little to no change in skin. If the duration of exercise is sufficient to increase body/core temperature, skin BF is also increased in humans. Because blood pressure changes little during exercise, changes in distribution of BF with incremental exercise result from changes in vascular conductance. These changes in distribution of BF throughout the body contribute to decreases in mixed venous oxygen content, serve to supply adequate oxygen to the active skeletal muscles, and support metabolism of other tissues while maintaining homeostasis. This review discusses the response of the peripheral circulation of humans to acute and chronic dynamic exercise and mechanisms responsible for these responses. This is accomplished in the context of leading the reader on a tour through the peripheral circulation during dynamic exercise. During this tour, we consider what is known about how each vascular bed controls BF during exercise and how these control mechanisms are modified by chronic physical activity/exercise training. The tour ends by comparing responses of the systemic circulation to those of the pulmonary circulation relative to the effects of exercise on the regional distribution of BF and mechanisms responsible for control of resistance/conductance in the systemic and pulmonary circulations.

Hemoglobin infusion does not alter murine pulmonary vascular tone

Plasma hemoglobin (Hb) scavenges endothelium-derived nitric oxide (NO), producing systemic and pulmonary vasoconstriction in many species. We hypothesized that i.v. administration of murine cell-free Hb would produce pulmonary vasoconstriction and enhance hypoxic pulmonary vasoconstriction (HPV) in mice. To assess the impact of plasma Hb on basal pulmonary vascular tone in anesthetized mice we measured left lung pulmonary vascular resistance (LPVRI) before and after infusion of Hb at thoracotomy. To confirm the findings obtained at thoracotomy, measurements of right ventricular systolic pressure (RVSP) and systemic arterial pressure (SAP) were obtained in closed-chest wild-type mice. To elucidate whether pretreatment with Hb augments HPV we assessed the increase in LPVRI before and during regional lung hypoxia produced by left mainstem bronchial occlusion (LMBO) in wild-type mice pretreated with Hb. Infusion of Hb increased SAP but did not change pulmonary arterial pressure (PAP), left lung pulmonary arterial flow (QLPA) or LPVRI in either wild-type or diabetic mice with endothelial dysfunction. Scavenging of NO by plasma Hb did not alter HPV in wild-type mice. Inhibition of NO synthase with l-NAME did not change the basal LPVRI, but augmented HPV during LMBO. Our data suggest that scavenging of NO by plasma Hb does not alter pulmonary vascular tone in mice. Therefore, generation of NO in the pulmonary circulation is unlikely to be responsible for the low basal pulmonary vascular tone of mice.

Effects of hypercapnia and NO synthase inhibition in sustained hypoxic pulmonary vasoconstriction

Background

Acute respiratory disorders may lead to sustained alveolar hypoxia with hypercapnia resulting in impaired pulmonary gas exchange. Hypoxic pulmonary vasoconstriction (HPV) optimizes gas exchange during local acute (0-30 min), as well as sustained (> 30 min) hypoxia by matching blood perfusion to alveolar ventilation. Hypercapnia with acidosis improves pulmonary gas exchange in repetitive conditions of acute hypoxia by potentiating HPV and preventing pulmonary endothelial dysfunction. This study investigated, if the beneficial effects of hypercapnia with acidosis are preserved during sustained hypoxia as it occurs, e.g in permissive hypercapnic ventilation in intensive care units. Furthermore, the effects of NO synthase inhibitors under such conditions were examined.

Method

We employed isolated perfused and ventilated rabbit lungs to determine the influence of hypercapnia with or without acidosis (pH corrected with sodium bicarbonate), and inhibitors of endothelial as well as inducible NO synthase on acute or sustained HPV (180 min) and endothelial permeability.

Results

In hypercapnic acidosis, HPV was intensified in sustained hypoxia, in contrast to hypercapnia without acidosis when HPV was amplified during both phases. L-N^G-Nitroarginine (L-NNA), a non-selective NO synthase inhibitor, enhanced acute as well as sustained HPV under all conditions, however, the amplification of sustained HPV induced by hypercapnia with or without acidosis compared to normocapnia disappeared. In contrast 1400 W, a selective inhibitor of inducible NO synthase (iNOS), decreased HPV in normocapnia and hypercapnia without acidosis at late time points of sustained HPV and selectively reversed the amplification of sustained HPV during hypercapnia without acidosis. Hypoxic hypercapnia without acidosis increased capillary filtration coefficient (Kfc). This increase disappeared after administration of 1400 W.

Conclusion

Hypercapnia with and without acidosis increased HPV during conditions of sustained hypoxia. The increase of sustained HPV and endothelial permeability in hypoxic hypercapnia without acidosis was iNOS dependent.

Nitrative stress in inflammatory lung diseases

Since the discovery of nitric oxide (NO), an intracellular signal transmitter, the role of NO has been investigated in various organs. In the respiratory system, NO derived from the constitutive type of NO synthase (cNOS, NOS1, NOS3) induces bronchodilation and pulmonary vasodilatation to maintain homeostasis. In contrast, the roles of excessive NO derived from the inducible type of NOS (iNOS, NOS2) in airway and lung inflammation in inflammatory lung diseases including bronchial asthma and chronic obstructive pulmonary disease (COPD) are controversial. In these inflammatory lung diseases, excessive nitrosative stress has also been observed. In asthma, some reports have shown that nitrosative stress causes airway inflammation, airway hyperresponsiveness, and airway remodeling, which are the features of asthma, whereas others have demonstrated the anti-inflammatory role of NO derived from NOS2. In the case of refractory asthma, more nitrosative stress has been reported to be observed in such airways compared with that in well-controlled asthmatics. In COPD, reactive nitrogen species (RNS), which are NO and NO-related molecules including nitrogen dioxide and peroxynitrite, cause lung inflammation, oxidative stress, activation of matrix metalloproteinase, and inactivation of antiprotease, which are involved in the pathophysiology of the disease. In the present paper, we review the physiological and pathophysiological effects of NO and NO-related molecules in the respiratory system and in inflammatory lung diseases.

Deficiency of lung antioxidants in idiopathic pulmonary arterial hypertension

Idiopathic pulmonary arterial hypertension (IPAH) is associated with lower levels of the pulmonary vasodilator nitric oxide (NO) and its biochemical reaction products (nitrite [NO(2) (-)], nitrate [NO(3) (-)]), in part, due to the reduction in pulmonary endothelial NO synthesis. However, NO levels are also determined by consumptive reactions, such as with superoxide to form peroxynitrite, which subsequently may generate stable products of nitrotyrosine (Tyr-NO(2)) and/or NO(3) (-). In this context, superoxide dismutase (SOD) preserves NO in vivo by scavenging superoxide and preventing the consumptive reactions. Here, we hypothesized that reactive oxygen species (ROS) consumption of NO may contribute to the low NO level and development of pulmonary hypertension. To test this, nitrotyrosine and antioxidants glutathione (GSH), glutathione peroxidase (GPx), catalase, and SOD were evaluated in IPAH patients and healthy controls. SOD and GPx activities were decreased in IPAH lungs (all p < 0.05), while catalase and GSH activities were similar among the groups (all p > 0.2). SOD activity was directly related to exhaled NO (eNO) (R(2)= 0.72, p= 0.002), and inversely related to bronchoalveolar lavage (BAL) NO(3) (-) (R(2)=-0.73, p= 0.04). Pulmonary artery pressure (PAP) could be predicted by a regression model incorporating SOD, GPx, and NO(3) values (R(2)= 0.96, p= 0.01). These findings suggest that SOD and GPx are associated with alterations in NO and PAP in IPAH.

L-Arginine promotes angiogenesis in the chronically hypoxic lung: a novel mechanism ameliorating pulmonary hypertension

Chronic alveolar hypoxia, whether due to residence at high altitude or lung disease, leads to a sustained increase in pulmonary vascular resistance and pulmonary hypertension (PH). Strategies that augment endogenous nitric oxide production or activity, including l-arginine supplementation, attenuate the development of PH. This action has been attributed to inhibition of vessel wall remodeling, thus preventing structural narrowing of the vascular lumen. However, more recent evidence suggests that structural changes are not responsible for the elevated vascular resistance observed in chronic hypoxic PH, calling into question the previous explanation for the action of l-arginine. We examined the effect of dietary l-arginine supplementation on pulmonary vasoconstriction, structurally determined maximum vascular lumen diameter, and vessel length in rats during 2 wk of exposure to hypoxia. l-Arginine attenuated the development of hypoxic PH by preventing increased arteriolar resistance. It did not alter mean maximal vascular lumen diameter, nor did it augment nitric oxide-mediated vasodilatation, in chronically hypoxic lungs. However, the total length of vessels within the gas exchange region of the hypoxic lungs was significantly increased after l-arginine supplementation. These findings suggest that dietary l-arginine ameliorated hypoxic PH, but not by an effect on the structurally determined lumen diameter of pulmonary blood vessels. l-Arginine enhanced angiogenesis in the hypoxic pulmonary circulation, which may attenuate hypoxic PH by producing new parallel vascular pathways through the lung.

Pulmonary vascular involvement in COPD

Alterations in pulmonary vessel structure and function are highly prevalent in patients with COPD. Vascular abnormalities impair gas exchange and may result in pulmonary hypertension, which is one of the principal factors associated with reduced survival in COPD patients. Changes in pulmonary circulation have been identified at initial disease stages, providing new insight into their pathogenesis. Endothelial cell damage and dysfunction produced by the effects of cigarette smoke products or inflammatory elements is now considered to be the primary alteration that initiates the sequence of events resulting in pulmonary hypertension. Cellular and molecular mechanisms involved in this process are being extensively investigated. Progress in the understanding of the pathobiology of pulmonary hypertension associated with COPD may provide the basis for a new therapeutic approach addressed to correct the imbalance between endothelium-derived vasoactive agents. The safety and efficacy of endothelium-targeted therapy in COPD-associated pulmonary hypertension warrants further investigation in randomized clinical trials.

Nitric-oxide-mediated zinc release contributes to hypoxic regulation of pulmonary vascular tone

The metal binding protein metallothionein (MT) is a target for nitric oxide (NO), causing release of bound zinc that affects myogenic reflex in systemic resistance vessels. Here, we investigate a role for NO-induced zinc release in pulmonary vasoregulation. We show that acute hypoxia causes reversible constriction of intraacinar arteries (<50 microm/L) in isolated perfused mouse lung (IPL). We further demonstrate that isolated pulmonary (but not aortic) endothelial cells constrict in hypoxia. Hypoxia also causes NO-dependent increases in labile zinc in mouse lung endothelial cells and endothelium of IPL. The latter observation is dependent on MT because it is not apparent in IPL of MT(-/-) mice. Data from NO-sensitive fluorescence resonance energy transfer-based reporters support hypoxia-induced NO production in pulmonary endothelium. Furthermore, hypoxic constriction is blunted in IPL of MT(-/-) mice and in wild-type mice, or rats, treated with the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)-ethylenediamine (TPEN), suggesting a role for chelatable zinc in modulating HPV. Finally, the NO donor DETAnonoate causes further vasoconstriction in hypoxic IPL in which NO vasodilatory pathways are inhibited. Collectively, these data suggest that zinc thiolate signaling is a component of the effects of acute hypoxia-mediated NO biosynthesis and that this pathway may contribute to constriction in the pulmonary vasculature.

Control of pulmonary vascular tone during exercise in health and pulmonary hypertension

Despite the importance of the pulmonary circulation as a determinant of exercise capacity in health and disease, studies into the regulation of pulmonary vascular tone in the healthy lung during exercise are scarce. This review describes the current knowledge of the role of various endogenous vasoactive mechanisms in the control of pulmonary vascular tone at rest and during exercise. Recent studies demonstrate an important role for endothelial factors (NO and endothelin) and neurohumoral factors (noradrenaline, acetylcholine). Moreover, there is evidence that natriuretic peptides, reactive oxygen species and phosphodiesterase activity can influence resting pulmonary vascular tone, but their role in the control of pulmonary vascular tone during exercise remains to be determined. K-channels are purported end-effectors in control of pulmonary vascular tone. However, K(ATP) channels do not contribute to regulation of pulmonary vascular tone, while the role of K(V) and K(Ca) channels at rest and during exercise remains to be determined. Pulmonary hypertension is associated with alterations in pulmonary vascular function and structure, resulting in blunted pulmonary vasodilatation during exercise and impaired exercise capacity. Although there is a paucity of studies pertaining to the regulation of pulmonary vascular tone during exercise in idiopathic pulmonary hypertension, the few studies that have been performed in models of pulmonary hypertension secondary to left ventricular dysfunction suggest altered control of pulmonary vascular tone during exercise. Since the increased pulmonary vascular tone during exercise limits exercise capacity, future studies are needed to investigate the vasomotor mechanisms that are responsible for the blunted exercise-induced pulmonary vasodilatation in pulmonary hypertension.

Oxidative and nitrative stress in bronchial asthma

There has been a marked increase in the global prevalence, morbidity, and mortality of asthma, and its associated economic burden has also grown over the last 40 years. Approximately 300 million people worldwide currently have asthma, and its prevalence increases by 50% every decade. Airway inflammation is the most proximate cause of the recurrent episodes of airflow limitation in asthma. Recent research has revealed that numerous biologically active proinflammatory mediators are responsible for the pathogenesis of asthma. Among these mediators, there is increasing evidence that endogenous or exogenous reactive oxygen species (ROS) and reactive nitrogen species (RNS) are responsible for the airway inflammation of asthma. Many reports have shown that there is an excessive production of ROS and RNS in the airways of asthmatic individuals compared with healthy subjects. Excessively produced ROS and RNS have been reported to lead to airway inflammation, airway hyper-responsiveness, airway microvascular hyperpermeability, tissue injury, and remodeling in animal models and human studies. Although human lungs have a potent antioxidant system, excessive oxidative and nitrative stress leads to an imbalance of oxidants/antioxidants. This review describes the rapidly accruing data linking oxidative and nitrative events to the pathogenesis of bronchial asthma.

Alveolar-derived exhaled nitric oxide is reduced in obstructive sleep apnea syndrome

BACKGROUND

Obstructive sleep apnea syndrome (OSAS) is associated with cardiovascular diseases, in particular systemic arterial hypertension. We postulated that intermittent nocturnal hypoxia in OSAS may be associated to decreased fractional exhaled nitric oxide (FENO) levels from distal airspaces.

METHODS

Multiple flow rate measurements have been used to fractionate nitric oxide (NO) from alveolar and bronchial sources in 34 patients with OSAS, in 29 healthy control subjects, and in 8 hypertensive non-OSAS patients. The effect of 2 days of treatment with nasal continuous positive airway pressure (nCPAP) on FENO was examined in 18 patients with severe OSAS.

RESULTS

We found that the mean [+/- SE] concentrations of exhaled NO at a rate of 50 mL/s was 21.8 +/- 1.9 parts per billion (ppb) in patients with OSAS, 25.1 +/- 3.3 ppb in healthy control subjects, and 15.4 +/- 1.7 ppb in hypertensive control patients. The mean fractional alveolar NO concentration (CANO) in OSAS patients was significantly lower than that in control subjects (2.96 +/- 0.48 vs 5.35 +/- 0.83 ppb, respectively; p < 0.05). In addition, CANO values were significantly lower in OSAS patients with systemic hypertension compared to those in normotensive OSAS patients and hypertensive patients without OSAS. The mean values of CANO significantly improved after nCPAP therapy (2.67 +/- 0.41 to 4.69 +/- 0.74 nL/L, respectively; p = 0.01).

CONCLUSIONS

These findings suggest that alveolar FENO, and not bronchial FENO, is impaired in patients with OSAS and that this impairment is associated with an increased risk of hypertension. NO production within the alveolar space is modified by treatment with nCPAP.

Red blood cells and hemoglobin in hypoxic pulmonary vasoconstriction

Nitric oxide (NO) plays an important role in the modulation of hypoxic pulmonary vasoconstriction; in turn, red blood cells (RBCs) augment HPV by hemoglobin-mediated oxidation and inactivation of NO. In addition, scavenging of reactive oxygen species by RBCs may play a role in augmentation of HPV. NO delivery and/or production by RBCs does not appear to be important in the control of pulmonary vasomotor tone. This review will discuss regulation of HPV by RBCs with an emphasis on hemoglobin-NO interactions. In addition, the review will discuss how biologic (S-nitrosation) or pharmacologic (cross-linking) modification of hemoglobin may affect pulmonary circulatory-hemoglobin interactions.

The role of nitric oxide in regulation of the cardiovascular system in reptiles

The roles that nitric oxide (NO) plays in the cardiovascular system of reptiles are reviewed, with particular emphasis on its effects on central vascular blood flows in the systemic and pulmonary circulations. New data is presented that describes the effects on hemodynamic variables in varanid lizards of exogenously administered NO via the nitric oxide donor sodium nitroprusside (SNP) and inhibition of nitric oxide synthase (NOS) by l-nitroarginine methyl ester (l-NAME). Furthermore, preliminary data on the effects of SNP on hemodynamic variables in the tegu lizard are presented. The findings are compared with previously published data from our laboratory on three other species of reptiles: pythons (), rattlesnakes () and turtles (). These five species of reptiles possess different combinations of division of the heart and structural complexity of the lungs. Comparison of their responses to NO donors and NOS inhibitors may reveal whether the potential contribution of NO to vascular tone correlates with pulmonary complexity and/or with blood pressure. All existing studies on reptiles have clearly established a potential role for NO in regulating vascular tone in the systemic circulation and NO may be important for maintaining basal systemic vascular tone in varanid lizards, pythons and turtles, through a continuous release of NO. In contrast, the pulmonary circulation is less responsive to NO donors or NOS inhibitors, and it was only in pythons and varanid lizards that the lungs responded to SNP. Both species have a functionally separated heart, so it is possible that NO may exert a larger role in species with low pulmonary blood pressures, irrespective of lung complexity.

Role of endogenous nitric oxide in endotoxin-induced alteration of hypoxic pulmonary vasoconstriction in mice

Pulmonary vasoconstriction in response to alveolar hypoxia (HPV) is frequently impaired in patients with sepsis or acute respiratory distress syndrome or in animal models of endotoxemia. Pulmonary vasodilation due to overproduction of nitric oxide (NO) by NO synthase 2 (NOS2) may be responsible for this impaired HPV after administration of endotoxin (LPS). We investigated the effects of acute nonspecific (N(G)-nitro-L-arginine methyl ester, L-NAME) and NOS2-specific [L-N6-(1-iminoethyl)lysine, L-NIL] NOS inhibition and congenital deficiency of NOS2 on impaired HPV during endotoxemia. The pulmonary vasoconstrictor response and pulmonary vascular pressure-flow (P-Q) relationship during normoxia and hypoxia were studied in isolated, perfused, and ventilated lungs from LPS-pretreated and untreated wild-type and NOS2-deficient mice with and without L-NAME or L-NIL added to the perfusate. Compared with lungs from untreated mice, lungs from LPS-challenged wild-type mice constricted less in response to hypoxia (69 +/- 17 vs. 3 +/- 7%, respectively, P < 0.001). Perfusion with L-NAME or L-NIL restored this blunted HPV response only in part. In contrast, LPS administration did not impair the vasoconstrictor response to hypoxia in NOS2-deficient mice. Analysis of the pulmonary vascular P-Q relationship suggested that the HPV response may consist of different components that are specifically NOS isoform modulated in untreated and LPS-treated mice. These results demonstrate in a murine model of endotoxemia that NOS2-derived NO production is critical for LPS-mediated development of impaired HPV. Furthermore, impaired HPV during endotoxemia may be at least in part mediated by mechanisms other than simply pulmonary vasodilation by NOS2-derived NO overproduction.

The role of nitric oxide in the regulation of the systemic and pulmonary vasculature of the rattlesnake, Crotalus durissus terrificus

The functional role of nitric oxide (NO) was investigated in the systemic and pulmonary circulations of the South American rattlesnake, Crotalus durissus terrificus. Bolus, intra-arterial injections of the NO donor, sodium nitroprusside (SNP) caused a significant systemic vasodilatation resulting in a reduction in systemic resistance (Rsys). This response was accompanied by a significant decrease in systemic pressure and a rise in systemic blood flow. Pulmonary resistance (Rpul) remained constant while pulmonary pressure (Ppul) and pulmonary blood flow (Qpul) decreased. Injection of L-Arginine (L-Arg) produced a similar response to SNP in the systemic circulation, inducing an immediate systemic vasodilatation, while Rpul was unaffected. Blockade of NO synthesis via the nitric oxide synthase inhibitor, L-NAME, did not affect haemodynamic variables in the systemic circulation, indicating a small contribution of NO to the basal regulation of systemic vascular resistance. Similarly, Rpul and Qpul remained unchanged, although there was a significant rise in Ppul. Via injection of SNP, this study clearly demonstrates that NO causes a systemic vasodilatation in the rattlesnake, indicating that NO may contribute in the regulation of systemic vascular resistance. In contrast, the pulmonary vasculature seems far less responsive to NO.

Correlation of exhaled breath temperature with bronchial blood flow in asthma

In asthma elevated rates of exhaled breath temperature changes (Δe°T) and bronchial blood flow (Q_aw) may be due to increased vascularity of the airway mucosa as a result of inflammation.

We investigated the relationship of Δe°T with Q_aw and airway inflammation as assessed by exhaled nitric oxide (NO). We also studied the anti-inflammatory and vasoactive effects of inhaled corticosteroid and β₂-agonist.

Δe°T was confirmed to be elevated (7.27 ± 0.6 Δ°C/s) in 19 asthmatic subjects (mean age ± SEM, 40 ± 6 yr; 6 male, FEV₁ 74 ± 6 % predicted) compared to 16 normal volunteers (4.23 ± 0.41 Δ°C/s, p < 0.01) (30 ± 2 yr) and was significantly increased after salbutamol inhalation in normal subjects (7.8 ± 0.6 Δ°C/ s, p < 0.05) but not in asthmatic patients. Q_aw, measured using an acetylene dilution method was also elevated in patients with asthma compared to normal subjects (49.47 ± 2.06 and 31.56 ± 1.6 μl/ml/min p < 0.01) and correlated with exhaled NO (r = 0.57, p < 0.05) and Δe°T (r = 0.525, p < 0.05). In asthma patients, Q_aw was reduced 30 minutes after the inhalation of budesonide 400 μg (21.0 ± 2.3 μl/ml/min, p < 0.05) but was not affected by salbutamol.

Δe°T correlates with Q_aw and exhaled NO in asthmatic patients and therefore may reflect airway inflammation, as confirmed by the rapid response to steroids.

Decreased whole body endogenous nitric oxide production in patients with primary pulmonary hypertension

Impaired pulmonary release of nitric oxide (NO) is one of the characteristic phenotypic changes of vascular cells in pulmonary hypertension. The aim of this study was to determine nitric oxide synthase (NOS)-dependent whole body NO production in patients with primary pulmonary hypertension. NOS-dependent whole body NO production was assessed by giving an intravenous infusion of L-[(15)N](2)-arginine (50 micromol/min for 30 min) and measuring isotopic urinary enrichment of (15)N-nitrite and (15)N-nitrate. Four female patients with no signs of infection were recruited and compared with 6 age-matched control subjects. Mean 12-hour excretion of (15)N-nitrite and (15)N-nitrate in the total urine over 36 h was smaller in patients than in control subjects (57.2 +/- 27.6 vs. 229.1 +/- 65.2 nmol/mmol creatinine, p < 0.01, Mann-Whitney U test, respectively). Neither mean 12-hour excretion of (14)N-nitrite and (14)N-nitrate (51.6 +/- 10.0 vs. 72.4 +/- 10.0 micromol/mmol creatinine, p = 0.3) nor glomerular filtration rates (84.5 +/- 15.8 vs. 129.7 +/- 16.0 ml/min, p = 0.1) were different between patients and control subjects. Our results suggest that either basal NOS-dependent whole body NO production is impaired or excess NO metabolism occurs in patients with primary pulmonary hypertension.

Angiotensin II stimulates nitric oxide production in pulmonary artery endothelium via the type 2 receptor

We previously reported that angiotensin II stimulates an increase in nitric oxide production in pulmonary artery endothelial cells. The aims of this study were to determine which receptor subtype mediates the angiotensin II-dependent increase in nitric oxide production and to investigate the roles of the angiotensin type 1 and type 2 receptors in modulating angiotensin II-dependent vasoconstriction in pulmonary arteries. Pulmonary artery endothelial cells express both angiotensin II type 1 and type 2 receptors as assessed by RT-PCR, Western blot analysis, and flow cytometry. Treatment of the endothelial cells with PD-123319, a type 2 receptor antagonist, prevented the angiotensin II-dependent increase in nitric oxide synthase mRNA, protein levels, and nitric oxide production. In contrast, the type 1 receptor antagonist losartan enhanced nitric oxide synthase mRNA levels, protein expression, and nitric oxide production. Pretreatment of the endothelial cells with either PD-123319 or an anti-angiotensin II antibody prevented this losartan enhancement of nitric oxide production. Angiotensin II-dependent enhanced hypoxic contractions in pulmonary arteries were blocked by the type 1 receptor antagonist candesartan; however, PD-123319 enhanced hypoxic contractions in angiotensin II-treated endothelium-intact vessels. These data demonstrate that angiotensin II stimulates an increase in nitric oxide synthase mRNA, protein expression, and nitric oxide production via the type 2 receptor, whereas signaling via the type 1 receptor negatively regulates nitric oxide production in the pulmonary endothelium. This endothelial, type 2 receptor-dependent increase in nitric oxide may serve to counterbalance the angiotensin II-dependent vasoconstriction in smooth muscle cells, ultimately regulating pulmonary vascular tone.

Impaired NO signaling in small pulmonary arteries of chronically hypoxic newborn piglets

We performed studies to determine whether chronic hypoxia impairs nitric oxide (NO) signaling in resistance level pulmonary arteries (PAs) of newborn piglets. Piglets were maintained in room air (control) or hypoxia (11% O2) for either 3 (shorter exposure) or 10 (longer exposure) days. Responses of PAs to a nonselective NO synthase (NOS) antagonist, Nω-nitro-l-arginine methylester (l-NAME), a NOS-2-selective antagonist, aminoguanidine, and 7-nitroindazole, a NOS-1-selective antagonist, were measured. Levels of NOS isoforms and of two proteins involved in NOS signaling, heat shock protein (HSP) 90 and caveolin-1, were assessed in PA homogenates. PAs from all groups constricted to l-NAME but not to aminoguanidine or 7-nitroindazole. The magnitude of constriction to l-NAME was similar for PAs from control and hypoxic piglets of the shorter exposure period but was diminished for PAs from hypoxic compared with control piglets of the longer exposure period. NOS-3, HSP90, and caveolin-1 levels were similar in hypoxic and control PAs. These findings indicate that NOS-3, but not-NOS 2 or NOS-1, is involved with basal NO production in PAs from both control and hypoxic piglets. After 10 days of hypoxia, NO function is impaired in PAs despite preserved levels of NOS-3, HSP90, and caveolin-1. The development of NOS-3 dysfunction in resistance level PAs may contribute to the progression of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

Changes in functional and histological distributions of nitric oxide synthase caused by chronic hypoxia in rat small pulmonary arteries

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 micro m 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, 36+/-3%), as compared to approximately 60% of control rat MPA (mean, 10+/-2%). The inhibitors reduced the ID of almost all EPA with similar mean values (approximately 26%) in both CH and control rats. On the other hand, inducible NOS (iNOS)-selective inhibitors caused ID reductions in approximately 60% of CH rat MPA (mean, 15+/-3%), but did so in only approximately 20% of control rat MPA (mean, 2+/-2%). This inhibition caused only a small reduction (mean, approximately 4%) in both CH and control rat EPA. A neuronal NOS-selective inhibitor had no effect. 4. The percentage of endothelial NOS (eNOS)-positive vessels was approximately 96% 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 approximately 60% in both MPA and EPA from CH rats, but was only approximately 8% 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.

Endogenous NO does not regulate baseline pulmonary pressure, but reduces acute pulmonary hypertension in dogs

It has remained unclear whether endogenous production of nitric oxide (NO) plays an important role in the regulation of physiologically normal pulmonary pressures. Severe alveolar hypoxia is accompanied by decreased pulmonary NO production, which could contribute to the development of hypoxic pulmonary hypertension. On the other hand, pharmacological NO inhibition further augments this hypertensive response.

AIMS

The aims of the present study were to test: (a) whether NO contributes importantly in the maintenance of baseline pulmonary pressure; and (b) to which degree NO is involved in the pulmonary haemodynamic adjustments to alveolar hypoxia.

METHODS

In anaesthetized dogs (n=37), the systemic and pulmonary haemodynamic effects of the NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME, 20 mg kg(-1)) and substrate, L-arginine (200-500 mg kg(-1)), were determined at baseline and during alveolar hypoxia. Constant blood flows were accomplished by biventricular bypass, and systemic normoxaemia was maintained by extracorporeal oxygenation.

RESULTS

The primary findings were: (a) L-NAME failed to increase baseline mean pulmonary arterial pressure (10.1 +/- 0.7 vs. 10.5 +/- 0.5 mmHg, P=ns), despite effective NO synthase inhibition as evidenced by robust increases in systemic arterial pressures; (b) L-NAME augmented the pulmonary hypertensive response to alveolar hypoxia (10.2 +/- 0.7 to 19.5 +/- 1.7 with L-NAME vs. 9.9 +/- 1.1 to 15.5 +/- 1.0 mmHg without L-NAME, P<0.05); and (c) L-arginine failed to decrease baseline or elevated pulmonary pressures. Instead, prolonged L-arginine caused increases in pulmonary pressure.

CONCLUSION

These findings suggest that NO plays no significant role in the tonic physiological control of pulmonary pressure, but endogenous NO becomes an important vasodilatory modulator during elevated pulmonary pressure.

Basal and nitroglycerin-induced exhaled nitric oxide before and after cardiac surgery with cardiopulmonary bypass

BACKGROUND

Exhaled nitric oxide (NO) may reflect NO production and consumption but the pulmonary origin of NO in exhaled gas is not clear. There are also conflicting data on exhaled NO after cardiopulmonary bypass (CPB). Because intravenous nitrovasodilators increase exhaled NO by conversion to NO in the lung, we measured basal and nitroglycerin (GTN)-induced exhaled NO in patients having low-risk coronary artery bypass graft (CABG) operations using routine CPB. We reasoned that GTN-induced exhaled NO would be a primarily vascular mechanism, which would contrast with the airway epithelial origin of basal exhaled NO, and that they might be differentially influenced by CPB.

METHODS

Breath-to-breath concentrations of gas phase NO were measured in 12 CABG patients before and 1, 3 and 6 h after CPB. After the baseline measurements, three increasing doses of 1, 2 and 3 micro g kg(-1) intravenous GTN were given by a central venous catheter and exhaled NO and haemodynamic responses were recorded.

RESULTS

Intravenous administration of 1, 2 and 3 micro g kg(-1) doses of GTN produced a dose-dependent increase in exhaled NO and a reduction in systemic blood pressure. Baseline exhaled NO remained unchanged. Exhaled NO but not blood pressure responses were reduced 1 and 3 h after CPB.

CONCLUSIONS

The capacity of the lungs to increase exhaled NO in response to intravenous GTN is reduced after CPB, suggesting microvascular injury and/or atelectasis after routine open-heart surgery.

Effect of L-arginine or nitroglycerine during deep hypothermic circulatory arrest in neonatal lambs

BACKGROUND

The role of nitric oxide (NO) in ischemia-reperfusion injury remains controversial. This study evaluated the effects of L-arginine (NO precursor) or nitroglycerine (NO donor) on cardiac and lung function after deep hypothermic circulatory arrest in neonatal lambs.

METHOD

Three groups of anesthetized lambs underwent cardiopulmonary bypass, deep hypothermic circulatory arrest (120 minutes at 18 degrees C), and rewarming (40 minutes). During reperfusion, L-arginine (5 mg/kg per minute), nitroglycerine (2 microg/kg per minute), or saline (control group) was infused for 100 minutes. All animals were separated from cardiopulmonary bypass and observed for 3 additional hours. Preload recruitable stroke work, cardiac index, pulmonary vascular resistance, alveolar-arterial oxygen difference, and lung compliance plasma nitrate/nitrite levels (NO metabolites) were measured before and after cardiopulmonary bypass. Malondialdehyde in heart tissue and lung tissue was measured 3 hours after cardiopulmonary bypass.

RESULTS

Recovery of preload recruitable stroke work and cardiac index were significantly higher in the L-arginine and nitroglycerine groups than in the control group (p < 0.05). Pulmonary vascular resistance was significantly lower in the L-arginine and nitroglycerine groups than in the control group (p < 0.05). Levels of NO metabolites and issue malondialdehyde did not differ among groups.

CONCLUSIONS

L-arginine and nitroglycerine improved recovery of left ventricular function and reduced pulmonary vascular resistance after deep hypothermic circulatory arrest. The mechanism of beneficial action could involve increased NO levels, but we did not find higher levels of NO metabolites compared with controls. Tissue malondialdehyde levels were not affected by L-arginine or nitroglycerine. These results show that, at these dosage levels, provision of substrate for NO production or provision of an NO donor were beneficial to the recovery of myocardial and pulmonary vascular function.

Pulmonary arterial pressure and electrocardiograms in broiler chickens infused intravenously with L-NAME, an inhibitor of nitric oxide synthase, or sodium nitroprusside (SNP), a nitric oxide donor

1. Broilers were divided at 42 to 44 d of age into a Control group (n=30) and a Treatment group (n=30). The mean pulmonary arterial pressure (mPAP) and electrocardiogram (ECG) leads II and aV(F) were measured 1, 2 and 4 h after an intravenous injection of 0.9% saline (Control group) or Nomega-nitro-L-arginine methyl esther (L-NAME), an inhibitor of nitric oxide synthase and thus an inhibitor of endothelial nitric oxide (NO) production (Treatment group). 2. At 1 and 2 h but not 4 h post-injection, L-NAME significantly increased the mPAP and the amplitudes of the ECG S-wave and RS-wave leads II and aVF when compared with Control values. 3. The correlation coefficients between the mPAP and the ECG S-wave and RS-wave amplitudes for lead II within the Treatment group were -0.848 and -0.553 at 1 h and -0.798 and -0.512 at 2 h, respectively. The corresponding coefficients for lead aVF were -0.735, -0.596, -0.663 and -0.724, respectively. 4. After suitable mPAP and ECG values had been recorded at each time interval, sodium nitroprusside (SNP), which acts as a short-lived NO donor molecule, was injected intravenously via a right-cardiac catheter. Within 5 min after the SNP injection, the mPAP and the ECG lead II S-wave and RS-wave amplitudes were transiently reduced to levels that, at 1 and 2 h after L-NAME injection, did not differ from Control values. Within 10 min after the SNP injection, all values returned to the levels previously induced by L-NAME. 5. These results demonstrate that L-NAME increased the myocardial contractility and PAP, whereas SNP transiently reversed the effects of L-NAME on myocardial contractility and PAP. It appears likely from these results that the pulmonary vascular endothelium releases NO that in turn reduces the pulmonary vascular resistance or attenuates myocardial contractility in broiler chickens.

Faster rise of exhaled breath temperature in asthma: a novel marker of airway inflammation?

In asthma there is increased vascularity of the airway mucosa, altering heat loss in the airways. We hypothesized that as a result of these inflammatory changes, asthmatic patients would have elevated rates of the exhaled air temperature increase (Deltae degrees T). We measured Deltae degrees T in 18 asthmatic subjects (mean age +/- SEM, 38 +/- 8 yr; 9 male, FEV(1) 74 +/- 10%) and 16 normal volunteers (mean age +/- SEM, 33 +/- 3 yr) and compared it with exhaled nitric oxide (NO) as a marker of inflammation. Deltae degrees T was measured during a flow- and pressure-controlled single exhalation with a fast response (1 ms) thermometer. The end-expiratory plateau temperature was similar in asthmatic compared with normal subjects (35.75 +/- 0.6 degrees C and 34.45 +/- 0.8 degrees C, p > 0.05). However, Deltae degrees T was greater in asthmatic subjects (8.17 +/- 0.83 degrees C/s and 4.12 +/- 0.41 degrees C/s, p < 0.01) and correlated with NO (r = 0.65, p = 0.034). Deltae degrees T was increased in normal subjects (from 4.28 +/- 0.8 degrees C/s to 7.60 +/- 0.5 degrees C/s, p < 0.01) but not in asthmatic patients (from 8.28 +/- 0.41 degrees C/s to 8.80 +/- 0.41 degrees C/s, p > 0.05) after the inhalation of albuterol, indicating that Deltae degrees T may reflect bronchial blood flow. Asthmatic subjects have elevated Deltae degrees T. This may represent a novel, noninvasive means of measuring airway blood flow and inflammation in asthma.

Secondhand tobacco smoke impairs rabbit pulmonary artery endothelium-dependent relaxation

OBJECTIVES

To determine whether secondhand smoke (SHS) induces pulmonary artery endothelial dysfunction, and whether dietary L-arginine supplementation is preventive.

BACKGROUND

SHS causes coronary and peripheral arterial endothelial dysfunction.

METHODS

The effects of L-arginine supplementation (2.25% solution) and SHS (10 weeks) on pulmonary vascular reactivity were examined in 32 rabbits fed a normal diet. Endothelium-dependent relaxation of precontracted pulmonary artery segments was studied using acetylcholine and calcium ionophore. Endothelium-independent relaxation was studied using nitroglycerin. Endothelial and serum L-arginine levels were measured by chromatography. In eight SHS-exposed and in eight control rats, pulmonary artery nitric oxide synthase (NOS) activity and arginase activity were studied using the titrated arginine to citrulline conversion assay.

RESULTS

SHS reduced maximal acetylcholine-induced (p = 0.04) and calcium ionophore-induced (p = 0.02) relaxation. L-Arginine increased maximal acetylcholine-induced (p = 0.047) vasodilation. SHS and L-arginine did not influence nitroglycerin-induced relaxation. SHS reduced endothelial L-arginine (p = 0.04) but not serum L-arginine. L-Arginine supplementation increased endothelial (p = 0.007) and serum L-arginine (p < 0.0005). Endothelium-dependent relaxation induced by acetylcholine and calcium ionophore varied directly with endothelial (r = 0.67, r = 0.67) and serum L-arginine (r = 0.43, r = 0.45), respectively. SHS reduced constitutive NOS activity (p = 0.03).

CONCLUSIONS

SHS reduces pulmonary artery endothelium-dependent relaxation by decreasing NOS activity and possibly by decreasing endothelial arginine content. L-Arginine supplementation increases serum and endothelial L-arginine stores and prevents SHS-induced endothelial dysfunction. L-Arginine may offset the deleterious effect of SHS on pulmonary arteries by substrate loading of the nitric oxide pathway.

Role of airway nitric oxide on the regulation of pulmonary circulation by carbon dioxide

The effects of hypercapnia (CO(2)) confined to either the alveolar space or the intravascular perfusate on exhaled nitric oxide (NO), perfusate NO metabolites (NOx), and pulmonary arterial pressure (Ppa) were examined during normoxia and progressive 20-min hypoxia in isolated blood- and buffer-perfused rabbit lungs. In blood-perfused lungs, when alveolar CO(2) concentration was increased from 0 to 12%, exhaled NO decreased, whereas Ppa increased. Increments of intravascular CO(2) levels increased Ppa without changes in exhaled NO. In buffer-perfused lungs, alveolar CO(2) increased Ppa with reductions in both exhaled NO from 93.8 to 61.7 (SE) nl/min (P < 0.01) and perfusate NOx from 4.8 to 1.8 nmol/min (P < 0.01). In contrast, intravascular CO(2) did not affect either exhaled NO or Ppa despite a tendency for perfusate NOx to decline. Progressive hypoxia elevated Ppa by 28% from baseline with a reduction in exhaled NO during normocapnia. Alveolar hypercapnia enhanced hypoxic Ppa response up to 50% with a further decline in exhaled NO. Hypercapnia did not alter the apparent K(m) for O(2), whereas it significantly decreased the V(max) from 66.7 to 55.6 nl/min. These results suggest that alveolar CO(2) inhibits epithelial NO synthase activity noncompetitively and that the suppressed NO production by hypercapnia augments hypoxic pulmonary vasoconstriction, resulting in improved ventilation-perfusion matching.

Reduced expression of endothelial nitric oxide synthase in pulmonary arteries of smokers

Cigarette smoking has been associated with alterations in the structure and endothelial function of pulmonary arteries. Nitric oxide (NO) and endothelin-1 are endothelium-derived mediators with opposite effects on vascular tone and cell growth. To investigate whether cigarette smoking could induce changes in the synthesis of these mediators in pulmonary arteries, we compared the expression of both endothelial NO synthase (eNOS) and endothelin-1 in the lungs of smokers with that in nonsmokers. Lung tissue samples of 23 smokers and nine nonsmokers were studied. Expression of eNOS and endothelin-1 in pulmonary artery endothelium was evaluated by immunohistochemistry. In protein extracts of lung tissue, the content of eNOS protein was assessed by Western blot analysis and that of endothelin-1 by radioimmunoassay. The immunohistochemical expression of eNOS in arterial endothelium and the eNOS protein content in lung tissue were lower in the smokers than in the nonsmokers. No differences were shown in cell expression and protein content of endothelin-1 between both groups. We conclude that cigarette smoking is associated with reduced expression of eNOS in pulmonary arteries. The diminished synthesis of nitric oxide may contribute to the alterations in the structure and endothelial function of pulmonary vessels in cigarette-smoke-induced respiratory disease.

Inhaled nitric oxide in combination with volume resuscitation refines a porcine model of endotoxic shock

BACKGROUND

Existing porcine models of endotoxic shock poorly represent the human situation.

AIMS

To assess whether the cardiovascular profile of a porcine model could be improved by refining the protocol.

METHODS

In 30 pigs, right and left heart pressures and cardiac output were measured. Lipopolysaccharide (LPS) was administered as a bolus (n=12), as a 30 minute infusion (n=6) or as a 30 minute infusion along with inhaled NO and volume resuscitation (n=6) and six sham-treated pigs received normal saline. Haemodynamic values were measured over three hours.

RESULTS

LPS increased pulmonary vascular resistance (PVR) (13.3 +/- 1.4 to 37.0 +/- 3.9kPa/l per sec, p<0.05) and reduced cardiac output (6.0 +/- 0.6 to 4.8 +/- 0.41/min). Mortality was 50% within 30 minutes. Inhaled NO and volume resuscitation controlled pulmonary vascular resistance (PVR) and preserved CO. Systemic vascular resistance (SVR) declined in the first hour (118.4 +/- 11.8 to 65.8 +/- 8.2kPa/l per sec, p<0.05) and remained low.

CONCLUSIONS

Porcine models of endotoxaemia based on LPS administration are a poor model of human septic shock, but can be improved by regulating PVR and supporting CO which may contribute to future studies of septic shock

Exhaled nitric oxide in patients with PiZZ phenotype-related alpha1-anti-trypsin deficiency

There is no report of exhaled NO (eNO) in subjects with different phenotypes of alpha1-anti-trypsin (AAT) deficiency. Exhaled nitric oxide was evaluated by means of single-breath chemiluminescence analysis (fractional exhaled concentration at the plateau level [plFE(NO)]) in 40 patients with AAT deficiency. Patients were divided according to the protease inhibitor (Pi) phenotype: PiMZ/MS, n = 25; PiSZ n = 6; PiZZ, n = 9. Nineteen healthy subjects served as controls. Levels of eNO in PiZZ patients were also compared with those of subjects, without AAT deficiency (PiMM), matched for diagnosis, sex, age, smoking habit and forced expiratory volume in 1 sec (FEV1). In AAT deficiency subjects airway hyper-responsiveness to methacholine (PD20 FEV1) was also assessed. plFE(NO) was significantly lower in the PiZZ group (4.5+/-1.4 ppb) than in matched PiMM subjects (8.2+/-3.8 ppb), in healthy controls (9.3+/-2.8 ppb) and in patients of other phenotypes. Dynamic lung volumes and DL(CO) were significantly lower in PiZZ than in other AAT-deficient patients. Bronchial hyper-responsiveness was not different among AAT phenotypes. These results suggest that eNO may be significantly reduced in PiZZ as compared to healthy control subjects and to AAT subjects with other phenotypes, independent of the level of airway obstruction. Whether, at least potentially, eNO may be considered as an early marker of lung involvement in AAT deficiency must be confirmed with studies on larger number of subjects.

Increased nitric oxide in exhaled air in patients with rheumatic heart disease

BACKGROUND

Endogenous production of nitric oxide and its presence in exhaled air was observed in humans. Prior studies have yielded contrasting information about the production of nitric oxide in patients with heart failure.

AIMS

The aim of this study was to measure nitric oxide in the exhaled air of patients with chronic rheumatic heart disease with and without pulmonary hypertension.

METHODS

Seventy-four patients (6 patients had isolated mitral stenosis; 13 patients had combined mitral stenosis and mitral regurgitation; 1 patient had isolated mitral regurgitation; 54 patients had combined mitral and aortic valve disease) and 27 healthy subjects were entered in the study. The nitric oxide concentration in exhaled air was determined with a chemiluminescence analyser. Echocardiography was performed in all patients to assess the severity of the valve disease and for the measurement of pulmonary artery pressure.

RESULTS

The level of exhaled nitric oxide was significantly greater in patients with rheumatic heart disease than in controls. The value of nitric oxide concentration in exhaled air was significantly increased in patients with pulmonary hypertension, as compared with patients who had normal pulmonary artery systolic pressure.

CONCLUSION

We found increased nitric oxide in the exhaled air in patients with rheumatic heart disease, especially in those with pulmonary hypertension, compared with healthy patients.

Role of nitric oxide in the pathogenesis of chronic pulmonary hypertension

Chronic pulmonary hypertension is a serious complication of a number of chronic lung and heart diseases. In addition to vasoconstriction, its pathogenesis includes injury to the peripheral pulmonary arteries leading to their structural remodeling. Increased pulmonary vascular synthesis of an endogenous vasodilator, nitric oxide (NO), opposes excessive increases of intravascular pressure during acute pulmonary vasoconstriction and chronic pulmonary hypertension, although evidence for reduced NO activity in pulmonary hypertension has also been presented. NO can modulate the degree of vascular injury and subsequent fibroproduction, which both underlie the development of chronic pulmonary hypertension. On one hand, NO can interrupt vascular wall injury by oxygen radicals produced in increased amounts in pulmonary hypertension. NO can also inhibit pulmonary vascular smooth muscle and fibroblast proliferative response to the injury. On the other hand, NO may combine with oxygen radicals to yield peroxynitrite and other related, highly reactive compounds. The oxidants formed in this manner may exert cytotoxic and collagenolytic effects and, therefore, promote the process of reparative vascular remodeling. The balance between the protective and adverse effects of NO is determined by the relative amounts of NO and reactive oxygen species. We speculate that this balance may be shifted toward more severe injury especially during exacerbations of chronic diseases associated with pulmonary hypertension. Targeting these adverse effects of NO-derived radicals on vascular structure represents a potential novel therapeutic approach to pulmonary hypertension in chronic lung diseases.

Inhibition of nitric oxide synthesis augments pulmonary oedema in isolated perfused rabbit lung

The role of nitric oxide (NO) in precipitating pulmonary oedema in acute lung injury remains unclear. We have investigated the mechanism of involvement of NO in the maintenance of liquid balance in the isolated rabbit lung. Thirty pairs of lungs were perfused with colloid for up to 6 h, during which pulmonary vascular resistance (PVR) and capillary pressure (PCP) were measured frequently, and time to gain 5 g in weight (t5) was recorded. Four protocols with different perfusate additives were studied: (i) none (control, n = 11); (ii) 10 mmol NG-nitro-L-arginine methyl ester (L-NAME) (n = 6); (iii) 10 mmol L-NAME with 100 mumol lodoxamide, an inhibitor of mast cell degranulation (n = 7); (iv) 10 mmol L-NAME with 10 mumol 8-bromo-3',5'-cyclic guanosine monophosphate (8Br-cGMP), an analogue of cGMP that may reduce vascular permeability by relaxing contractile elements in endothelial cells (n = 6). Neither PVR nor PCP differed between protocols. L-NAME markedly reduced t5 from 248 (27) min (mean (SEM)) in protocol (i) to 144 (5) min in protocol (ii) (P < 0.05). Both lodoxamide (t5 = 178 (7) min) and 8Br-cGMP (t5 = 204 (10) min) substantially corrected the effect of L-NAME (P < 0.005). Results suggest that maintenance of a low permeability by NO may involve mast cell stabilization and endothelial cell relaxation.

Production of endogenous nitric oxide in chronic obstructive pulmonary disease and patients with cor pulmonale. Correlates with echo-Doppler assessment

Exhaled nitric oxide (NO) production in stable chronic obstructive pulmonary disease (COPD) has been loosely related to the severity of illness, being significantly reduced in the most severe cases. Pulmonary hypertension is associated with lower NO output from the lung. In this study expired NO was measured in patients with severe stable COPD with or without cor pulmonale (CP). Echocardiographic estimates of right heart function, lung function, diffusion capacity, respiratory muscle strength, and arterial blood gases were obtained in 34 consecutive patients with stable COPD (mean age, 68 +/- 7 yr). Expired NO was measured by chemiluminiscence to obtain fractional exhaled concentrations at peak (FENOp) and at plateau (FENOpl) points of the single-breath curve and resting NO output (V NO). All measurements of expired NO output, FENOp, FENOpl and V NO showed a negative correlation with both systolic pulmonary artery pressure (Pspa) (r = -0.51, -0.63, and -0.63, respectively, p < 0.01 for all) and right ventricle wall dimension (r = -0.41, -0.59, and -0.43, respectively, p < 0.05 for all), but not with any measurement of lung function. When the patients were divided according to the Pspa using a cutoff limit of 35 mm Hg, those subjects with CP showed lower FENOp (13.2 +/- 4.0 versus 36.7 +/- 30.8 ppb, p < 0.05), FENOpl (5.7 +/- 1.9 versus 8.9 +/- 4.7 ppb, p < 0.05), and V NO (69. 2 +/- 5.6 versus 107.6 +/- 14.6 nl/ min, p = 0.02) than did those with a normal resting Pspa. NO production from the airways was significantly lower and inversely related to development of CP in patients with severe COPD. Impaired endothelial release may account for the reduced levels of expired NO.

Combined therapy with zaprinast and inhaled nitric oxide abolishes hypoxic pulmonary hypertension

OBJECTIVE

To determine whether the combination of the phosphodiesterase 5 inhibitor zaprinast and inhaled nitric oxide (NO) decreases hypoxic pulmonary hypertension in the rat.

DESIGN

Prospective, experimental study.

SETTING

Animal laboratory of a university medical center.

SUBJECTS

Male Sprague-Dawley rats.

INTERVENTIONS

Anesthetized rats were mechanically ventilated and instrumented for measurement of mean systemic arterial pressure, pulmonary arterial pressure, and cardiac output. In group 1, four acute hypoxic challenges (FIO2 = 0.17 for 5 mins) were performed: initial, during 40 ppm inhaled NO, immediately after discontinuation of 5 mins of inhaled NO, and final. In group 2 rats, an initial hypoxic challenge was performed and rats then received zaprinast (3 mg/kg bolus followed by 0.3 mg/kg/min infusion). Four hypoxic challenges analogous to group 1 were then performed during zaprinast administration.

MEASUREMENTS AND MAIN RESULTS

Initial hypoxic challenge produced similar increases in pulmonary arterial pressure in both groups. In group 1, inhaled NO either only before or only during hypoxia decreased the pulmonary hypertensive response to hypoxia. In group 2, zaprinast administration did not alter hemodynamics. Zaprinast alone decreased the pulmonary hypertensive response to hypoxia. The combination of zaprinast and inhaled NO (either before or during hypoxia) abolished the pulmonary hypertensive response to hypoxia.

CONCLUSIONS

Treatment with inhaled NO for 5 mins before but not during hypoxia is as effective as inhaled NO during hypoxia. Inhaled NO and zaprinast both decrease the pulmonary hypertensive response to hypoxia, and the combination abolishes the response. The combination of a phosphodiesterase 5 inhibitor and inhaled NO may have clinical applicability in the treatment of pulmonary hypertension.

Hypoxic pulmonary blood flow redistribution and arterial oxygenation in endotoxin-challenged NOS2-deficient mice

Sepsis and endotoxemia impair hypoxic pulmonary vasoconstriction (HPV), thereby reducing arterial oxygenation and enhancing hypoxemia. Endotoxin induces nitric oxide (NO) production by NO synthase 2 (NOS2). To assess the role of NO and NOS2 in the impairment of HPV during endotoxemia, we measured in vivo the distribution of total pulmonary blood flow (QPA) between the right (QRPA) and left (QLPA) pulmonary arteries before and after left mainstem bronchus occlusion (LMBO) in mice with and without a congenital deficiency of NOS2. LMBO reduced QLPA/QPA equally in saline-treated wild-type and NOS2-deficient mice. However, prior challenge with Escherichia coli endotoxin markedly impaired the ability of LMBO to reduce QLPA/QPA in wild-type, but not in NOS2-deficient, mice. After endotoxin challenge and LMBO, systemic oxygenation was impaired to a greater extent in wild-type than in NOS2-deficient mice. When administered shortly after endotoxin treatment, the selective NOS2 inhibitor L-NIL preserved HPV in wild-type mice. High concentrations of inhaled NO attenuated HPV in NOS2-deficient mice challenged with endotoxin. These findings demonstrate that increased pulmonary NO levels (produced by NOS2 or inhaled at high levels from exogenous sources) are necessary during the septic process to impair HPV, ventilation/perfusion matching and arterial oxygenation in a murine sepsis model.

The acute effects of dexfenfluramine on human and porcine pulmonary vascular tone and resistance

STUDY OBJECTIVES

Treatment with anorectics has become an important aspect of care for the severely obese. One such anorectic, the phenylethylamine dexfenfluramine (dFen), has been associated with the development of pulmonary hypertension. It works by reducing the neuronal uptake of 5-hydroxytryptamine (5-HT; serotonin) through inhibition of the 5-HT transporter. In this study we investigated whether dFen has a direct vasoconstrictor action on human and porcine pulmonary vasculature.

DESIGN

For the human study, tissue was obtained from patients who had undergone lung and heart-lung transplantation. The effect of dFen was studied in seven isolated colloid perfused human lungs and in rings of human pulmonary artery (PA) dissected from the lungs of a further 19 patients. For the porcine study, regional pulmonary vascular resistances (PVRs) were measured in isolated perfused porcine lungs. Vasoconstriction was assessed following dFen alone and in combination with hypoxia, cyclo-oxygenase blockade (indomethacin, 10(-5) mol/L), or nitric oxide synthase (NOS) blockade (N(G)-nitro-L-arginine, 10(-5) mol/L).

RESULTS

In the human study, 5-HT and dFen caused only limited increases in tension of isolated rings of PA. The concentration of dFen, 10(-4) mol/L, that was needed to increase tension was higher than that found normally in treated patients where peak levels are 3. 3 x 10(-7) mol/L. Other vasoconstrictors such as prostaglandin F(2)alpha, 10(-5) mol/L, and the thromboxane analog U46619, 10(-6) mol/L, produced far greater increases in tension. Ketanserin, 10(-4) mol/L, attenuated the constrictor response to 5-HT but had no effect on the constrictor response to dFen. Removal of the endothelium did not influence the response to dFen. In the isolated ventilated and perfused lungs, dFen caused an increase in PVR again only at a comparatively high concentration, 10(-4) mol/L. In the porcine study, dFen, 10(-4) mol/L, did not increase any PVR during normoxia or following NOS blockade. Small insignificant increases in PVR occurred during hypoxia and after cyclo-oxygenase blockade.

CONCLUSION

These results do not support the view that dFen would act as a direct vasoconstrictor when given in the usual doses. However, delayed elimination of dFen could raise tissue concentrations to high levels and give rise to vasoconstriction and pulmonary hypertension.

Enhanced expression of inducible nitric oxide synthase without vasodilator effect in chronically infected lungs

We hypothesized that abnormal ventilation-perfusion matching in chronically infected lungs was in part due to excess nitric oxide (NO) production after upregulation of inducible NO synthase (iNOS) expression. Rats were anesthetized and inoculated intratracheally with Pseudomonas aeruginosa incorporated into agar beads (chronically infected) or with sterile agar beads (placebo inoculated) and killed 10-15 days later. Immunohistochemistry demonstrated increased expression of iNOS and reduced expression of endothelial NOS (eNOS) in chronically infected compared with placebo-inoculated or noninoculated lungs. In isolated lungs from chronically infected rats, NOS inhibition with N(omega)-nitro-L-arginine methyl ester increased the mean perfusion pressure (14.4 +/- 2.7 mmHg) significantly more than in the placebo-inoculated (4.8 +/- 1.0 mmHg) or noninoculated (5.3 +/- 0.8 mmHg) lungs (P < 0.01). Although the chronically infected lungs were more sensitive to NOS inhibition, further evidence suggested that the increased iNOS expression was not associated with enhanced iNOS activity. Selective inhibitors of iNOS did not produce an increase in vascular resistance similar to that produced by nonselective inhibitors. Accumulation of nitrate/nitrite in the perfusate of isolated lungs was unchanged by chronic infection. Thus although iNOS expression was increased in chronic pulmonary infection, iNOS activity in the intact lung was not. Nonetheless, endogenous NO production was essential to maintain normal vascular resistance in these lungs.

Relative contributions of endothelial, inducible, and neuronal NOS to tone in the murine pulmonary circulation

Nitric oxide plays an important role in modulating pulmonary vascular tone. All three isoforms of nitric oxide synthase (NOS), neuronal (nNOS, NOS I), inducible (iNOS, NOS II), and endothelial (eNOS, NOS III), are expressed in the lung. Recent reports have suggested an important role for eNOS in the modulation of pulmonary vascular tone chronically; however, the relative contribution of the three isoforms to acute modulation of pulmonary vascular tone is uncertain. We therefore tested the effect of targeted disruption of each isoform on pulmonary vascular reactivity in transgenic mice. Isolated perfused mouse lungs were used to evaluate the effect of selective loss of pulmonary nNOS, iNOS, and eNOS with respect to hypoxic pulmonary vasoconstriction (HPV) and endothelium-dependent and -independent vasodilation. eNOS null mice had augmented HPV (225 +/- 65% control, P < 0.02, mean +/- SE) and absent endothelium-dependent vasodilation, whereas endothelium-independent vasodilation was preserved. HPV was minimally elevated in iNOS null mice and normal in nNOS null mice. Both nNOS and iNOS null mice had normal endothelium-dependent vasodilation. In wild-type lungs, nonselective NOS inhibition doubled HPV, whereas selective iNOS inhibition had no detectable effect. In intact, lightly sedated mice, right ventricular systolic pressure was elevated in eNOS-deficient (42.3 +/- 1.2 mmHg, P < 0.001) and, to a lesser extent, in iNOS-deficient (37.2 +/- 0.8 mmHg, P < 0.001) mice, whereas it was normal in nNOS-deficient mice (30.9 +/- 0.7 mmHg, P = not significant) compared with wild-type controls (31.3 +/- 0.7 mmHg). We conclude that in the normal murine pulmonary circulation 1) nNOS does not modulate tone, 2) eNOS-derived nitric oxide is the principle mediator of endothelium-dependent vasodilation in the pulmonary circulation, and 3) both eNOS and iNOS play a role in modulating basal tone chronically.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.