Endogenous nitric oxide in expired air: effects of acute exercise in humans

Health effects of exposure to chlorination by-products in swimming pools

Concerns have been raised regarding the potential negative effects on human health of water disinfectants used in swimming pools. Among the disinfection options, the approaches using chlorine-based products have been typically preferred. Chlorine readily reacts with natural organic matter that are introduced in the water mainly through the bathers, leading to the formation of potentially harmful chlorination by-products (CBPs). The formation of CBPs is of particular concern since some have been epidemiologically associated with the development of various clinical manifestations. The higher the concentration of volatile CBPs in the water, the higher their concentration in the air above the pool, and different routes of exposure to chemicals in swimming pools (water ingestion, skin absorption, and inhalation) contribute to the individual exposome. Some CBPs may affect the respiratory and skin health of those who stay indoor for long periods, such as swimming instructors, pool staff, and competitive swimmers. Whether those who use chlorinated pools as customers, particularly children, may also be affected has been a matter of debate. In this article, we discuss the current evidence regarding the health effects of both acute and chronic exposures in different populations (work-related exposures, intensive sports, and recreational attendance) and identify the main recommendations and unmet needs for research in this area.

Pulmonary Effects Due to Physical Exercise in Polluted Air: Evidence from Studies Conducted on Healthy Humans

Physical inactivity has caused serious effects on the health of the population, having an impact on the quality of life and the cost of healthcare for many countries. This has motivated government and private institutions to promote regular physical activity, which, paradoxically, can involve health risks when it is carried out in areas with poor air quality. This review collects information from studies conducted on healthy humans related to the pulmonary effects caused by the practice of physical activity when there is poor air quality. In addition, several challenges related to the technological and educational areas, as well as to applied and basic research, have been identified to facilitate the rational practice of exercise in poor air quality conditions.

Exercise and NO production: relevance and implications in the cardiopulmonary system

This article reviews the existing knowledge about the effects of physical exercise on nitric oxide (NO) production in the cardiopulmonary system. The authors review the sources of NO in the cardiopulmonary system; involvement of three forms of NO synthases (eNOS, nNOS, and iNOS) in exercise physiology; exercise-induced modulation of NO and/or NOS in physiological and pathophysiological conditions in human subjects and animal models in the absence and presence of pharmacological modulators; and significance of exercise-induced NO production in health and disease. The authors suggest that physical activity significantly improves functioning of the cardiovascular system through an increase in NO bioavailability, potentiation of antioxidant defense, and decrease in the expression of reactive oxygen species-forming enzymes. Regular physical exercises are considered a useful approach to treat cardiovascular diseases. Future studies should focus on detailed identification of (i) the exercise-mediated mechanisms of NO exchange; (ii) optimal exercise approaches to improve cardiovascular function in health and disease; and (iii) physical effort thresholds.

Exhaled nitric oxide concentration in the period of 60 min after submaximal exercise in the cold

BACKGROUND

Fractional expired nitric oxide (FENO ) is decreased after exercise. The effect of exercise in the cold upon FENO is unknown.

PURPOSE

To examine changes in FENO after a short, high intensive exercise test in a cold and in a temperate environment.

METHODS

Twenty healthy well-trained subjects (eight females) aged 18-28 years performed an 8-min exercise test at 18°C (SD = 1.0) and -10°C (SD = 1.2) ambient temperature. The tests were performed in a climate chamber in random order. The workload corresponded to 90-95% of peak heart rate (HRpeak ) during the last 4 min. FENO was measured offline. Exhaled gas was sampled in Mylar(®) bags using a collector kit with a flow restrictor and analysed within 2 h. FENO was measured before exercise and repeatedly during the first hour after. ANOVA for repeated measures was used to compare differences in FENO after exercise between environments.

RESULTS

There was no difference in baseline FENO . A significant difference in FENO between environments was found after warm-up and from 20 to 30 min after exercise, with FENO being lower after exercise in the cold (P<0.05). The maximal reduction in FENO was seen 5 min after exercise and was not different between environments.

CONCLUSION

Recovery of FENO was slower after exercising in -10°C compared with 18°C.

Nitric oxide concentrations in gas emanating from the tails of obese rats

This study was undertaken to investigate the effects of oral L-arginine administration and exercising training on the NO concentration emanating from rat tail and NOx in plasma. Obese (fa/fa) Zucker rats (n = 22) were divided into four groups: (1) oral L-arginine administration (A) (n = 6), (2) exercise training (E), (3) exercise training + L-arginine administration (E + A) (n = 5), and (4) non-exercise training + non-L-arginine administration (N) (n = 6). The control (+/+) Zucker rats (n = 22) were also divided into the same four groups. The body weight of the E + A and the A groups was significantly lower than that of the N group. The NO concentration emitted from the tail was higher in the L-arginine (E + A and A) groups than in the non-L-arginine (E and N) groups in both obese and control rats. Exercise training did not affect the skin gas NO concentration in either obese or control rats. Plasma NOx concentrations in four obese rats were significantly higher than those observed in control rats. Exercise training did not influence the level of plasma NOx in obese or control rats. In conclusion, this study confirmed that L-arginine administration increases the skin gas NO concentration and obesity increases the plasma NOx level. The plasma NOx concentrations were not affected by L-arginine administration or exercise training in obese or control rats.

Exercise-induced bronchoconstriction alters airway nitric oxide exchange in a pattern distinct from spirometry

Exhaled nitric oxide (NO) is altered in asthmatic subjects with exercise-induced bronchoconstriction (EIB). However, the physiological interpretation of exhaled NO is limited because of its dependence on exhalation flow and the inability to distinguish completely proximal (large airway) from peripheral (small airway and alveolar) contributions. We estimated flow-independent NO exchange parameters that partition exhaled NO into proximal and peripheral contributions at baseline, postexercise challenge, and postbronchodilator administration in steroid-naive mild-intermittent asthmatic subjects with EIB (24-43 yr old, n = 9) and healthy controls (20-31 yr old, n = 9). The mean +/- SD maximum airway wall flux and airway diffusing capacity were elevated and forced expiratory flow, midexpiratory phase (FEF(25-75)), forced expiratory volume in 1 s (FEV(1)), and FEV(1)/forced vital capacity (FVC) were reduced at baseline in subjects with EIB compared with healthy controls, whereas the steady-state alveolar concentration of NO and FVC were not different. Compared with the response of healthy controls, exercise challenge significantly reduced FEV(1) (-23 +/- 15%), FEF(25-75) (-37 +/- 18%), FVC (-12 +/- 12%), FEV(1)/FVC (-13 +/- 8%), and maximum airway wall flux (-35 +/- 11%) relative to baseline in subjects with EIB, whereas bronchodilator administration only increased FEV(1) (+20 +/- 21%), FEF(25-75) (+56 +/- 41%), and FEV(1)/FVC (+13 +/- 9%). We conclude that mild-intermittent steroid-naive asthmatic subjects with EIB have altered airway NO exchange dynamics at baseline and after exercise challenge but that these changes occur by distinct mechanisms and are not correlated with alterations in spirometry.

The effects of hyperpnea on exhaled nitric oxide synthesis in normal subjects

STUDY OBJECTIVES

To determine if the concentration of nitric oxide (NO) in the lungs increases with hyperpnea by contrasting calculated production (ie, the product of the fractional expired NO concentration [FeNO] and minute ventilation [Ve]) [Vno] with the amount of NO in equilibrium with the conducting airways (eNOair) and the amount of NO diffusing from the alveoli (eNOalv).

DESIGN

Observational study.

SETTING

University teaching hospital.

PARTICIPANTS

Normal subjects.

INTERVENTIONS

Measurements were made in 16 healthy people during and after 4 min of tidal breathing (10 L/min) and isocapnic hyperventilation of 60 L/min.

MEASUREMENTS AND RESULTS

FeNO was measured by collecting the exhaled air during the last minute of each trial and passing it through a chemiluminescence analyzer. The expired NO levels in the plateau phases of slow (30 mL/s) and fast (200 mL/s) single-breath exhalations were also obtained before and after hyperventilation. The Vno (mean +/- SEM) increased from 89.8 +/- 12.3 to 329.1 +/- 36.2 nL/min as Ve rose (p < 0.001). However, neither the quantities of eNOair nor eNOalv changed with hyperventilation (eNOair range before to after, 34.9 +/- 7.7 to 30.9 +/- 6.4 parts per billion [ppb], p = 0.96; eNOalv range before to after, 7.3 +/- 1.5 to 6.5 +/- 1.1 ppb, p = 0.97).

CONCLUSIONS

These data demonstrate that the amount of NO in equilibrium with the airway walls and alveoli are not altered by hyperpnea. Rather, the apparent augmentation in Vno in such circumstances appears to be an arithmetic artifact.

The effect of spirometry and exercise on exhaled nitric oxide in asthmatic children

American Thoracic Society (ATS) guidelines recommend to refrain from spirometry or exercise before measuring fractional exhaled nitric oxide (FENO) because forced breathing maneuvers might influence FENO values. However the few studies already reported in children have given conflicting results. The aim of the study was to observe to what extent spirometry or exercise could affect FENO in asthmatic children. Twenty-four asthmatic children (mean age 12.8 yr) were enrolled. Measurements of FENO were performed before and 5, 15, 30, 45 and 60 min after spirometry or a 6-min walk test, on two separate days in random order. Geometric mean FENO at baseline was 25.6 parts per billion (ppb) before spirometry and 23.5 ppb before exercise. A small drop of FENO to 24.2 and 23.7 ppb was found 5 and 15 min after spirometry (both p = 0.04). After exercise, FENO values showed a larger drop to 18.5 ppb after 5 min and 20.7 ppb after 15 min (p < 0.001; p = 0.004 respectively). Changes in FENO occurred after exercise irrespective of baseline FENO and values returned to baseline within 30 min. We conclude that both spirometry and exercise affect FENO in asthmatic children. As the changes after exercise may lead to erroneous interpretations, children should refrain from physical exercise during at least 30 min before FENO measurements.

Vascular endothelial dysfunction and mortality risk in patients with chronic heart failure

BACKGROUND

Endothelial function is known to be impaired in subjects with chronic heart failure (CHF), but the association between endothelial function and subsequent mortality risk in CHF has not been previously reported.

METHODS AND RESULTS

Biomarkers of endothelial function in the systemic arterial circulation (flow-mediated dilation [FMD] in the brachial artery) and the pulmonary circulation (exhaled nitric oxide [NO] production during submaximal exercise) were prospectively assessed in 259 subjects with New York Heart Association class II-III CHF. In subjects with FMD measurements (n=149), there were 12 deaths and 5 urgent transplantations over a median follow-up period of 841 days. In subjects with exhaled NO production measurements (n=110), there were 18 deaths and 1 urgent transplantation over a median follow-up period of 396 days. Both decreased FMD and decreased exhaled NO production were associated with increased risk of death or urgent transplantation after adjustment for other known CHF prognostic factors (age, etiology of CHF, functional class, left ventricular ejection fraction) in Cox multivariate proportional-hazards models (adjusted hazard ratio [HR] estimate for a 1% decrease in FMD=1.20; 95% confidence interval [CI], 1.03 to 1.45; P=0.027; adjusted HR estimate for a 1-ppb/min decrease in exhaled NO production=1.31, 95% CI, 1.01 to 1.69, P=0.04).

CONCLUSIONS

Endothelial dysfunction in CHF, as assessed by FMD in the brachial artery and exhaled NO production during submaximal exercise, is associated with an increased mortality risk in subjects with both ischemic and nonischemic CHF.

Nitric oxide exhalation correlates with ventilatory response to exercise in patients with heart disease

AIMS

It is controversial whether or not pulmonary nitric oxide (NO) production, reflected in the end-tidal alveolar NO concentration, is diminished in patients with heart failure. Since pulmonary perfusion is regulated by NO production, decreased NO production in the pulmonary vasculature is assumed to result in diminished lung perfusion and further increases in ventilation-perfusion mismatch. The aim of this study is to investigate whether exhaled NO correlates with both exercise-induced hyperpnea and exercise tolerance in patients with heart disease.

METHODS AND RESULTS

Forty-two patients with heart disease were enrolled (history of prior myocardial infarction (n=19), dilated cardiomyopathy (n=2), hypertensive heart disease (n=5) and prior open-heart surgery (n=16)). During cardiopulmonary exercise testing, exhaled air was collected and end-tidal NO (ETNO) was measured using a chemiluminescent method. Peak ETNO was found to correlate positively with both ventilatory anaerobic threshold (r=0.468) and peak VO(2) (r=0.562). The VE-CO(2) slope, which reflects the ventilatory response to exercise, correlated negatively with peak ETNO (r=-0.588).

CONCLUSION

These data indicate that NO exhalation correlates, inversely, with the ventilatory response to exercise and directly with exercise intolerance, although the weakness of the correlation coefficient suggests there may be other possible mechanisms.

Impact of high-intensity exercise on nitric oxide exchange in healthy adults

PURPOSE

After exercise, exhaled NO concentration has been reported to decrease, remain unchanged, or increase. A more mechanistic understanding of NO exchange dynamics after exercise is needed to understand the relationship between exercise and NO exchange.

METHODS

We measured several flow-independent NO exchange parameters characteristic of airway and alveolar regions using a single breath maneuver and a two-compartment model (maximum flux of NO from the airways, J'(awNO), pL x s-1; diffusing capacity of NO in the airways, D(awNO), pL x s-1 x ppb-1; steady state alveolar concentration, C(alv,ss), ppb; mean airway tissue NO concentration, C(awNO), ppb), as well as serum IL-6 at baseline, 3, 30, and 120 min after a high-intensity exercise challenge in 10 healthy adults (21-37 yr old).

RESULTS

D(awNO) (mean +/- SD) increased (37.1 +/- 44.4%), whereas J'(awNO) and C(awNO) decreased (-7.27 +/- 11.1%, -26.1 +/- 24.6%, respectively) 3 min postexercise. IL-6 increased steadily after exercise to 481% +/- 562% above baseline 120 min postexercise.

CONCLUSION

High-intensity exercise acutely enhances the ability of NO to diffuse between the airway tissue and the gas phase, and exhaled NO might be used to probe both the metabolic and physical properties of the airways.

Exhaled nitric oxide and exercise tolerance in severe COPD patients

To answer the question as to whether pulmonary rehabilitation programs (PRP) induced increase in exercise tolerance (ET) is associated with increased levels of exhaled nitric oxide (eNO) in COPD patients of different degrees of severity, we designed a prospective and controlled study. Forty-seven stable COPD patients underwent an 8-week outpatient multidisciplinary PRP including supervised incremental exercise. Fractional eNO concentration (FE(NO)) and peak work-rate (W(peak) were assessed baseline (T-1), atthe end of 1-month run-in period (T0), and after (T1) the PRP. Lung function, walking test, health-related quality of life (HRQL) were also recorded. Patients were divided into three groups according to disease severity: 17 severe [FEV1 35 (5)% pred] COPD patients, seven of them with cor pulmonale; 15 mild [FEV1 78 (6)% pred], and 15 moderate [FEV1 56 (6)% pred] COPD patients. FE(NO) did not differ at T-1 and T0 (mean absolute change (SD): 0.03 (0.09) 95% CI-0.01, 0.16, 0.06 (1.03) 95% CI 0.03, 0.75 and 0.05 (0.06) 95% CI 0.02, 0.11 ppb in mild, moderate and severe patients, respectively). As compared to T0, both W(peak) (by 17,15 and 10%, respectively) and FE(NO) (by 29, 24 and 16%, respectively) significantly increased in all groups, but not in patients with cor pulmonale. A significant correlation between pre- and post-PRP changes in Wpeak and FE(NO) was found both in mild to moderate (r = 0.79, P < 0.00001) and severe (r = 0.76, P < 0.001) COPD patients. After a PRP, improvement in ET is associated with an increase in eNO also in most severe COPD patients, but not in those with cor pulmonale.

Effect of pulmonary rehabilitation on exhaled nitric oxide in patients with chronic obstructive pulmonary disease

BACKGROUND

In patients with mild to moderate chronic obstructive pulmonary disease (COPD) the exercise induced increase in exhaled nitric oxide (eNO) parallels that observed in normal untrained subjects. There is no information on the effects of the level of exercise tolerance on eNO in these patients. The aim of this study was to evaluate the effect of a pulmonary rehabilitation programme including exercise training on eNO in patients with COPD.

METHODS

In 14 consecutive male patients with stable COPD of mean (SD) age 64 (9) years and forced expiratory volume in one second (FEV1) 55 (14)% predicted, fractional eNO concentration (FeNO), peak work rate (Wpeak) and oxygen uptake (VO2peak) were assessed at baseline (T-1), at the end of a 1 month run in period (T0), and after an 8 week outpatient multidisciplinary pulmonary rehabilitation programme (T1) including cycloergometer training.

RESULTS

FeNO did not significantly differ at T-1 and T0 (mean (SE) 4.3 (0.6) and 4.4 (0.6) ppb, respectively), whereas it rose significantly at T1 to 6.4 (0.7) ppb (p<0.02). Compared with T0, both Wpeak and VO2 were significantly (p<0.05) increased at T1 (mean (SE) Wpeak from 89 (5.6) W to 109 (6.9) W); VO2peak from 1.27 (0.1) l/min to 1.48 (0.1) l/min). A significant correlation was found between baseline FEV1 and the change in FeNO following the rehabilitation programme (r=-0.71; p<0.05) and between changes in FeNO and Wpeak from T0 to T1(r=0.60; p<0.05).

CONCLUSIONS

Pulmonary rehabilitation in patients with mild to moderate COPD is associated with an increase in exhaled nitric oxide.

Effect of pulmonary rehabilitation on exhaled nitric oxide in patients with chronic obstructive pulmonary disease

BACKGROUND

In patients with mild to moderate chronic obstructive pulmonary disease (COPD) the exercise induced increase in exhaled nitric oxide (eNO) parallels that observed in normal untrained subjects. There is no information on the effects of the level of exercise tolerance on eNO in these patients. The aim of this study was to evaluate the effect of a pulmonary rehabilitation programme including exercise training on eNO in patients with COPD.

METHODS

In 14 consecutive male patients with stable COPD of mean (SD) age 64 (9) years and forced expiratory volume in one second (FEV1) 55 (14)% predicted, fractional eNO concentration (Feno), peak work rate (Wpeak) and oxygen uptake (V˙o2peak) were assessed at baseline (T–1), at the end of a 1 month run in period (T0), and after an 8 week outpatient multidisciplinary pulmonary rehabilitation programme (T1) including cycloergometer training.

RESULTS

Fenodid not significantly differ at T–1 and T0 (mean (SE) 4.3 (0.6) and 4.4 (0.6) ppb, respectively), whereas it rose significantly at T1 to 6.4 (0.7) ppb (p<0.02). Compared with T0, both Wpeak andV˙o2 were significantly (p<0.05) increased at T1 (mean (SE) Wpeak from 89 (5.6) W to 109 (6.9) W);V˙o2peak from 1.27 (0.1) l/min to 1.48 (0.1) l/min). A significant correlation was found between baseline FEV1 and the change in Feno following the rehabilitation programme (r=–0.71; p<0.05) and between changes in Feno and Wpeak from T0 to T1(r=0.60; p<0.05).

CONCLUSIONS

Pulmonary rehabilitation in patients with mild to moderate COPD is associated with an increase in exhaled nitric oxide.

Role of exhaled nitric oxide in asthma

Nitric oxide (NO), an evanescent atmospheric gas, has recently been discovered to be an important biological mediator in animals and humans. Nitric oxide plays a key role within the lung in the modulation of a wide variety of functions including pulmonary vascular tone, nonadrenergic non-cholinergic (NANC) transmission and modification of the inflammatory response. Asthma is characterized by chronic airway inflammation and increased synthesis of NO and other highly reactive and toxic substances (reactive oxygen species). Pro- inflammatory cytokines such as TNFalpha and IL-1beta are secreted in asthma and result in inflammatory cell recruitment, but also induce calcium- and calmodulin-independent nitric oxide synthases (iNOS) and perpetuate the inflammatory response within the airways. Nitric oxide is released by several pulmonary cells including epithelial cells, eosinophils and macrophages, and NO has been shown to be increased in conditions associated with airway inflammation, such as asthma and viral infections. Nitric oxide can be measured in the expired air of several species, and exhaled NO can now be rapidly and easily measured by the use of chemiluminescence analysers in humans. Exhaled NO is increased in steroid-naive asthmatic subjects and during an asthma exacerbation, although it returns to baseline levels with appropriate anti-inflammatory treatment, and such measurements have been proposed as a simple non-invasive method of measuring airway inflammation in asthma. Here the chemical and biological properties of NO are briefly discussed, followed by a summary of the methodological considerations relevant to the measurement of exhaled NO and its role in lung diseases including asthma. The origin of exhaled NO is considered, and brief mention made of other potential markers of airway inflammation or oxidant stress in exhaled breath.

Role of nitric oxide in the airway response to exercise in healthy and asthmatic subjects

A role of nitric oxide (NO) has been suggested in the airway response to exercise. However, it is unclear whether NO may act as a protective or a stimulatory factor. Therefore, we examined the role of NO in the airway response to exercise by using N-monomethyl-L-arginine (L-NMMA, an NO synthase inhibitor), L-arginine (the NO synthase substrate), or placebo as pretreatment to exercise challenge in 12 healthy nonsmoking, nonatopic subjects and 12 nonsmoking, atopic asthmatic patients in a double-blind, crossover study. Fifteen minutes after inhalation of L-NMMA (10 mg), L-arginine (375 mg), or placebo, standardized bicycle ergometry was performed for 6 min using dry air, while ventilation was kept constant. The forced expiratory volume in 1-s response was expressed as area under the time-response curve (AUC) over 30 min. In healthy subjects, there was no significant change in AUC between L-NMMA and placebo treatment [28.6 +/- 17.0 and 1.3 +/- 20.4 (SE) for placebo and L-NMMA, respectively, P = 0.2]. In the asthmatic group, L-NMMA and L-arginine induced significant changes in exhaled NO (P < 0.01) but had no significant effect on AUC compared with placebo (geometric mean +/- SE: -204.3 +/- 1.5, -186.9 +/- 1.4, and -318.1 +/- 1.2%. h for placebo, L-NMMA, and L-arginine, respectively, P > 0.2). However, there was a borderline significant difference in AUC between L-NMMA and L-arginine treatment (P = 0.052). We conclude that modulation of NO synthesis has no effect on the airway response to exercise in healthy subjects but that NO synthesis inhibition slightly attenuates exercise-induced bronchoconstriction compared with NO synthase substrate supplementation in asthma. These data suggest that the net effect of endogenous NO is not inhibitory during exercise-induced bronchoconstriction in asthma.

Nitric oxide in the nasal airway: a new dimension in otorhinolaryngology

The discovery that the gas nitric oxide (NO) is an important signaling molecule in the cardiovascular system earned its Nobel prize in 1998. NO has since been found to play important roles in a variety of physiologic and pathophysiologic processes in the body including vasoregulation, hemostasis, neurotransmission, immune defense, and respiration. The surprisingly high concentrations of NO in the nasal airway and paranasal sinuses has important implications for the field of otorhinolaryngology. NO provides a first-line defense against micro-organisms through its antiviral and antimicrobial activity and by its upregulation of ciliary motility. Nasal treatments such as polypectomy, sinus surgery, removal of hypertrophic adenoids and tonsils, and treatment of allergic rhinitis may alter NO output and, therefore, the microbial colonization of the upper airways. Nasal surgery aimed at relieving nasal obstruction may do the same but would also be expected to improve pulmonary function in patients with asthma and upper airway obstruction. NO output rises in a number of conditions associated with chronic airway inflammation, but not all of them. Concentrations are increased in asthma, allergic rhinitis, and viral respiratory infections, but reduced in sinusitis, cystic fibrosis, primary ciliary dysfunction, chronic cough, and after exposure to tobacco and alcohol. Therefore, NO, similar to several other inflammatory mediators, probably subserves different functions as local conditions dictate. At present, it seems that the measurement of NO in the upper airway may prove valuable as a simple, noninvasive diagnostic marker of airway pathologies. The objective of this review is to highlight some aspects of the origin, physiology, and functions of upper airway NO, and to discuss the particular methodological problems that result from the complex anatomy.

Effect of enalapril on exhaled nitric oxide in normotensive and hypertensive subjects

We investigated whether an angiotensin-converting enzyme (ACE) inhibitor increases the production of nitric oxide (NO) in exhaled air in normotensive and hypertensive subjects. In study 1, 8 normotensive male subjects received a single oral dose of enalapril (5 mg) or nitrendipine (10 mg) in a crossover manner. Exhaled air was collected at baseline, and at 2, 4, and 8 hours after administration of the drug. In study 2, 10 normotensive subjects (6 men and 4 women) and 10 hypertensive subjects (6 men and 4 women) received a single oral dose of enalapril (5 mg). Exhaled air was collected at baseline and at 2 and 4 hours after administration of the drug. In study 1, enalapril significantly increased the NO release rate from the lung in normotensive subjects (36.9+/-5.1 pmol/s at baseline versus 58.3+/-7.3 pmol/s at 4 hours, P<0.01). Nitrendipine did not change the NO release rate. In study 2, enalapril significantly increased the release of NO from the lung in normotensive subjects (40.4+/-6.0 pmol/s at baseline versus 70. 3+/-11.4 pmol/s at 4 hours, P<0.01) but not in hypertensive subjects. ACE inhibition increased NO production from the lung in normotensive subjects but not in hypertensive patients. The reduction of angiotensin II production and/or the accumulation of bradykinin in the pulmonary tissue may be responsible for increased NO production in components of the lung, such as the pulmonary vascular endothelium, bronchial epithelial cells, macrophages, nasopharyngeal cells, and neurons. However, the effects of ACE inhibition on NO production from the lung differ between hypertensive subjects and normotensive subjects.

Relationship between decreased oxyhaemoglobin saturation and exhaled nitric oxide during exercise

Decreases in oxyhaemoglobin saturation (SaO2) are frequently observed in highly trained male endurance athletes during heavy work and has been termed exercise-induced hypoxaemia (EIH). Ventilation perfusion (VA/Q) mismatching and diffusion limitations are thought to be responsible. Nitric oxide (NO), a potent vasodilator, is present in the exhaled air of resting and exercising humans. Endogenously produced NO is thought to play a role in VA/Q matching and maintenance of low pulmonary vascular resistance. The purpose of this study was to determine the relationship between exhaled NO and EIH. It was hypothesized that athletes with EIH would have lower NO levels compared with non-EIH athletes. Eighteen highly trained male cyclists (VO2max=67.7 +/- 5.2 mL kg-1 min-1, mean +/- SD) were divided into normal (NORM, n=12, SaO2= 93.9 +/- 0.8) or low (LOW, n=6, SaO2=90.3 +/- 1.0) group, based on significantly different peak exercise SaO2 values (P < 0.05). All other descriptive and physiological characteristics were similar between the groups. Subjects performed a ramped cycle test to exhaustion breathing NO-free gas. The concentration (CNO) and production rate (VNO) of NO were determined from mixed gas samples at rest and during exercise at 100, 200, 250, 300, 350, 400 and 450 W using a chemiluminescent analyser. CNO remained unchanged from resting values in all subjects. VNO increased significantly during exercise in all subjects but was not different between LOW and NORM groups. The correlation between change in SaO2 and VNO from rest to maximal exercise was not significant (r=-0.12, P > 0.05). Collectively, these data suggest that exhaled NO is not related to decreased SaO2 during heavy exercise in highly trained male cyclists.

Exhaled nitric oxide and exercise in stable COPD patients

STUDY OBJECTIVE

To evaluate exhaled nitric oxide (eNO) during exercise in patients with stable COPD.

SETTING

Outpatient evaluation in a rehabilitation center.

PATIENTS

Eleven consecutive male patients with stable COPD (age, 65 +/- 6 years; FEV(1), 56 +/- 10% predicted). Eight healthy (six men; age, 51 +/- 16 years) nonsmoking, nonatopic volunteers served as control subjects.

METHODS

In each subject, a symptom-limited cycle ergometry test was performed by monitoring eNO with the tidal-breath method to assess eNO concentration (FENO) and output (VNO) at rest, peak exercise, and recovery time.

RESULTS

Resting FENO (9.8 +/- 5.1 and 14.1 +/- 6.3 parts per billion, respectively) and VNO (4.2 +/- 2.0 and 5.9 +/- 3.4 nmol/min, respectively) were lower, although not significantly, in COPD patients than in control subjects. In both groups, FENO significantly decreased whereas VNO significantly increased during exercise. Both variables returned to baseline during the recovery time. Peak exercise VNO, but not FENO, was significantly lower in COPD patients than in control subjects (7.9 +/- 5.4 and 12.7 +/- 6.0 nmol/min, respectively, p < 0.05). The rise in VNO was weakly correlated to oxygen consumption VO(2)) both in control subjects (r = 0.31, p = 0. 002) and in COPD patients (r = 0.22, p = 0.03). FENO showed an inverse correlation to VO(2) in both groups (r = -0.53, p = 0.000; r = -0.31, p = 0.003 in control subjects and COPD patients, respectively).

CONCLUSIONS

In patients with mild and moderate COPD, eNO during exercise parallels that observed in normal control subjects. VNO, but not FENO, is significantly reduced at peak exercise in COPD patients as compared with control subjects. The long-term effects of exercise training on eNO has to be evaluated by further studies.

Exhaled nitric oxide measurements in childhood asthma: techniques and interpretation

In this review, we outline the role of nitric oxide in airway inflammation in children with asthma. We also discuss the various methods reported for measuring exhaled nitric oxide and provide some insight as to the pros and cons and pitfalls of these techniques. Guidelines for measurements of exhaled nitric oxide based on our experience are provided, as well as suggestions for the use of this technique as a new "airway inflammation test."

Assessment of nitric oxide formation during exercise

We measured the end-tidal plateau in exhaled NO concentration (CETNO) by chemiluminescence and calculated the product of V E and CETNO (V NO) in nine healthy subjects at rest and during three intensities of cycling exercise (30%, 60%, and 90% V O2max), two levels of hyperventilation (V E = 42.8 +/- 9.1 L/min and 84.2 +/- 6. 6 L/min), and during breathing of hypoxic gas mixtures (five subjects, FIO2 = 14%) at rest and during exercise at 90% V O2max. Immediately after each trial we also measured exhaled [NO] at constant expiratory flow rates ([NO]CF) of 46 ml/s and 950 ml/s, utilizing added expiratory resistance to increase mouth pressure and close the velum (Silkoff and colleagues, Am. J. Respir. Crit. Care Med. 1997;155:260). CETNO decreased and V NO increased above resting levels with increasing exercise intensity during hyperventilation and during hypoxic exercise (p < 0.05). [NO]CF, measured at either 46 ml/s or 950 ml/s, did not increase under any of the conditions investigated (exercise, hyperventilation, or hypoxia). Venous blood from seven of the subjects was sampled for the measurement of plasma [NO3-]. Resting plasma [NO3-] averaged 42.5 +/- 14.7 micromol/L, with no change during exercise, hyperventilation, or hypoxia. On the basis of these results we conclude that reported increases in V NO do not reflect an exercise-induced augmentation of systemic and/or airway NO production. Rather, the increases in V NO during exercise or hyperventilation are a function of high airflow rates, which reduce the luminal [NO]. This decreases the concentration gradient for NO between the alveolar space and pulmonary capillary blood, which results in a decrease in the fraction of NO taken up by the blood and an increase in the volume of NO recovered in the exhaled air (V NO).

Increased exhaled nitric oxide and impaired oxygen uptake (VO2) kinetics during exercise in patients with chronic heart failure

Vascular endothelial function is abnormal in patients with congestive heart failure (CHF). Exhaled nitric oxide (NO) output is a marker of pulmonary endothelial NO release. The present study examined the relation between exhaled NO output and oxygen uptake (VO2) kinetics at the onset of exercise, which reflects blood flow response. Sixteen patients with CHF and 7 volunteers underwent constant bicycle exercise. Oxygen deficit and time constant for VO2 increment at the onset of exercise were analyzed. Exhaled NO concentration was measured by a chemiluminescence analyzer and exhaled NO output was calculated by multiplexing ventilation. Exhaled NO output was significantly greater in the CHF group than in the control group at rest (86+/-65 nl min(-1) m(-2) vs 298+/-135 nl min(-1) m(-2), p<0.001) and during exercise (152+/-98 nl min(-1) m(-2) vs 455+/-190 nl min(-1) m(-2), p<0.001). However, the %increase of NO output was significantly smaller in the CHF group than in the control group (70+/-26% vs 109+/-85%, p<0.05). Oxygen deficit was significantly greater in the CHF group than in the control group (240+/-70 ml vs 372+/-107 ml, p<0.01) and the time constant for VO2 increment was also significantly prolonged in the CHF group (35.1+/-8.0 s vs 50.1+/-16.3 s, p<0.05). Exhaled NO output during exercise significantly correlated with oxygen deficit (r=0.67, p<0.001) and the time constant for VO2 increment (r=0.74, p<0.001). Increased NO output played a counter-regulatory role in the impaired blood flow in CHF.

Postexercise increase in nitric oxide in football players with muscle cramps

Nitric oxide, a free radical inter- and intracellular messenger molecule, is important in exercise physiology. This study tested the hypothesis that serum nitric oxide concentrations change after strenuous exercise with severe generalized muscle cramps. The study group consisted of 77 professional football players in preseason training. All players' concentrations of serum nitrite and of other serum chemicals were determined during their preseason evaluations and compared with the concentrations in 40 serum samples taken from 25 of those same players who required intravenous rehydration for severe generalized muscle cramps after a training session. Player weight and percentage of body fat were significantly higher in players who received intravenous fluids than in players who did not. The serum of players requiring intravenous hydration showed evidence of skeletal muscle breakdown (increases in lactate dehydrogenase, creatinine phosphokinase, aspartate aminotransferase, and alanine aminotransferase) and of dehydration (elevations in protein, blood urea nitrogen, and cholesterol). The major finding, however, was a nearly 300% increase in serum nitrite concentrations in players requiring rehydration. There were no correlations between concentrations of nitrate and of any of the other serum chemicals. These data support the hypothesis that large amounts of nitric oxide are synthesized in professional football players after strenuous exercise with severe muscle cramps. The study design did not allow us to determine whether this increase in nitric oxide was due to exercise or muscle cramps or both, but it does provide a basis for evaluating these relationships.

Intrathoracic and extrathoracic sources of exhaled nitric oxide in porcine endotoxemic shock

OBJECTIVES

Nitric oxide (NO), a highly reactive species produced by the activity of NO synthases (NOS), is normally present in the exhaled air of humans and animals. Exhaled NO concentration increases significantly in humans with sepsis and animals, but neither the source nor NOS isoforms responsible for this rise in pulmonary NO production are known. The main objective of this study is to determine the sites and the mechanisms of enhanced NO production in the exhaled air of endotoxemic pigs.

DESIGN

Randomized, controlled, animal study.

SETTING

University-based animal research facility.

SUBJECTS

Thirteen pathogen-free adult female pigs (22 to 27 kg).

INTERVENTIONS

Anesthetized pigs were divided into two groups: control and lipopolysaccharides (LPS) (septic) groups. In both groups, extrathoracic (upper airways, nasal, and paranasal) and intrathoracic (bronchi, bronchioles, and alveoli) compartments were ventilated equally with two separate ventilators connected to two tracheal tubes. The LPS group received slow infusion (over 2 h) of Escherichia coli endotoxin (10 microg/kg/h), whereas saline solution was infused into the control group. Expired air of the two compartments was collected throughout the 2-h observation period. The animals were then killed and the lungs were quickly excised and frozen.

MEASUREMENTS

Hemodynamic variables were measured in both groups. NO concentration in the exhaled air of both compartments was measured with a chemiluminescence analyser. Pulmonary NOS activity was evaluated by measuring the conversion of L-[2,3H]-arginine to L-[2,3H]-citrulline, and pulmonary expression of NOS was evaluated by immunoblotting.

RESULTS

Baseline NO concentration in both groups was significantly higher in the extrathoracic vs intrathoracic compartment (average of 5.2 vs 3.4 parts per billion). Endotoxin infusion elicited a significant and early (after 45 min) rise in exhaled NO concentration in the extrathoracic compartment. Exhaled NO in the intrathoracic compartment also rose significantly but after 90 min of endotoxin infusion. Measurement of lung NOS activity showed a substantial rise in Ca++/calmodulin-dependent activity in the LPS group with no rise in Ca++/calmodulin-independent activity. Immunoblotting of lung tissue samples indicated the absence of the inducible isoform in both groups of animals. Moreover, LPS injection elicited no significant alterations in the pulmonary expression of the endothelial and the neuronal isoforms.

CONCLUSIONS

Both extrathoracic and intrathoracic compartments contribute to the rise in exhaled NO production in experimental septic shock. The rise in exhaled NO production is due to increased activity of constitutive NOS isoforms as a result of increased cofactor availability and/or downregulation of the endogenous inhibitors of NOS.

A two-compartment model of pulmonary nitric oxide exchange dynamics

The relatively recent detection of nitric oxide (NO) in the exhaled breath has prompted a great deal of experimentation in an effort to understand the pulmonary exchange dynamics. There has been very little progress in theoretical studies to assist in the interpretation of the experimental results. We have developed a two-compartment model of the lungs in an effort to explain several fundamental experimental observations. The model consists of a nonexpansile compartment representing the conducting airways and an expansile compartment representing the alveolar region of the lungs. Each compartment is surrounded by a layer of tissue that is capable of producing and consuming NO. Beyond the tissue barrier in each compartment is a layer of blood representing the bronchial circulation or the pulmonary circulation, which are both considered an infinite sink for NO. All parameters were estimated from data in the literature, including the production rates of NO in the tissue layers, which were estimated from experimental plots of the elimination rate of NO at end exhalation (ENO) vs. the exhalation flow rate (VE). The model is able to simulate the shape of the NO exhalation profile and to successfully simulate the following experimental features of endogenous NO exchange: 1) an inverse relationship between exhaled NO concentration and VE, 2) the dynamic relationship between the phase III slope and VE, and 3) the positive relationship between ENO and VE. The model predicts that these relationships can be explained by significant contributions of NO in the exhaled breath from the nonexpansile airways and the expansile alveoli. In addition, the model predicts that the relationship between ENO and VE can be used as an index of the relative contributions of the airways and the alveoli to exhaled NO.

Role of nitric oxide in exercise-induced vasodilation in man

Nitric oxide (NO) is a potent endothelium-derived vasodilator, which is known to play an important role in the regulation of resting vascular tone in animals and humans. However, the degree to which NO is involved in exercise-induced vasodilation in the skeletal muscle remains unclear. We studied the effect of N-monomethyl-L-arginine (L-NMMA) in a randomized, double-blind, placebo controlled cross over study in 16 young, healthy volunteers ( 8 male, 8 female) at rest and during bicycle exercise stress test. L-NMMA was given as a bolus of 3 mg/kg over 5 minutes followed by a continuous i.v. infusion of 50 microg/kg/min over 75 minutes. Subjects underwent a symptom-limited graded bicycle stress test with a 25 Watt increase in workload every 5 minutes. Skin and muscle blood flow were measured by laser Doppler flowmetry. L-NMMA slightly increased mean arterial blood pressure and decreased NO exhalation, but had no effect on pulse rate, oxygen consumption (VO2), skin or muscle blood flow at rest. Moreover, L-NMMA exerted no effect on exercise-induced changes in hemodynamics. Our results suggest that submaximal inhibition of NO-synthase with L-NMMA at doses that induce moderate hemodynamic changes does not affect exercise induced vasodilation.

Effects of nitroglycerin and sodium nitroprusside on endexpiratory concentrations of nitric oxide in healthy humans

The cellular origin of nitric oxide (NO) in exhaled air of healthy humans is unknown. It is currently not known, whether changes in NO concentrations that originate from pulmonary vessels, can be detected as changes in exhaled NO. Thus, we have studied the effects of increased intravascular NO generation on endexpiratory NO-levels. Twenty-four young healthy volunteers received nitroglycerin (GTN), sodium nitroprusside (SNP) or placebo i.v. in a randomized, double blind cross-over trial. Diastolic blood pressure decreased from 59 mmHg (95% confidence interval: 56-62) during placebo to 48 mmHg (CI: 45-51) and to 48 mmHg (CI: 45-50) after infusions of GTN and SNP, respectively. Heart rate increased from 69 (CI: 65-73) during placebo to 78 (CI: 72-84) and to 84 (CI: 77-92) after infusions of GTN and SNP, respectively (p<0.01 for all comparisons). However, no increase in exhaled NO was detected: endexpiratory NO-concentrations averaged 6.1 ppb (CI: 4.9-7.4), 5.7 ppb (CI: 4.4-7.0) and 6.4 ppb (CI: 5.3-7.6) under placebo, GTN and SNP infusions, respectively (Friedman ANOVA p=0.328). NO release from within the pulmonary vasculature does not significantly contribute to endexpiratory NO concentrations in non-intubated healthy humans suggesting that such NO measurements quantify NO production mainly from non-vascular pulmonary cells.

Air contamination with nitric oxide: effect on exhaled nitric oxide response

This study examines the response of exhaled nitric oxide (NO) concentration (ECNO) and quantity of exhaled NO over time (EVNO) in 10 healthy subjects breathing into five polyethylene bags, one in which synthetic air was free of NO and four in which NO was diluted to concentrations of 20 +/- 0.6, 49 +/- 0.8, 98 +/- 2, and 148 +/- 2 ppb, respectively. Each subject was connected to each bag for 10 min at random. Minute ventilation and ECNO were measured continuously, and EVNO was calculated continuously. ECNO and EVNO values were significantly higher for an inhaled NO concentration of 20 ppb than for NO-free air. Above 20 ppb, ECNO and EVNO increased linearly with inhaled NO concentration. It is reasonable to assume that a share of the quantity of inspired NO over time (InspVNO) because of air contamination by pollution is rejected by the ventilatory pathway. Insofar as InspVNO does not affect endogenous production or the metabolic fate of NO in the airway, this share may be estimated as being approximately one third of InspVNO, the remainder being taken by the endogenous pathway. Thus, air contamination by the NO resulting from pollution greatly increases the NO response in exhaled air.

Determination of production of nitric oxide by lower airways of humans--theory

Exercise and inflammatory lung disorders such as asthma and acute lung injury increase exhaled nitric oxide (NO). This finding is interpreted as a rise in production of NO by the lungs (VNO) but fails to take into account the diffusing capacity for NO (DNO) that carries NO into the pulmonary capillary blood. We have derived equations to measure VNO from the following rates, which determine NO tension in the lungs (PL) at any moment from 1) production (VNO); 2) diffusion, where DNO(PL) = rate of removal by lung capillary blood; and 3) ventilation, where V A(PL)/(PB - 47) = the rate of NO removal by alveolar ventilation (V A) and PB is barometric pressure. During open-circuit breathing when PL is not in equilibrium, d/dt PL[V(L)/ (PB - 47)] (where V(L) is volume of NO in the lower airways) = VNO - DNO(PL) - V A(PL)/(PB - 47). When PL reaches a steady state so that d/dt = 0 and V A is eliminated by rebreathing or breath holding, then PL = VNO/DNO. PL can be interpreted as NO production per unit of DNO. This equation predicts that diseases that diminish DNO but do not alter VNO will increase expired NO levels. These equations permit precise measurements of VNO that can be applied to determining factors controlling NO production by the lungs.

Nitric oxide response in exhaled air during an incremental exhaustive exercise

This study examines the response of the exhaled nitric oxide (NO) concentration (CNO) and the exhaled NO output (VNO) during incremental exercise and during recovery in six sedentary women, seven sedentary men, and eight trained men. The protocol consisted of increasing the exercise intensity by 30 W every 3 min until exhaustion, followed by 5 min of recovery. Minute ventilation (VE), oxygen consumption (VO2), carbon dioxide production, heart rate, CNO, and VNO were measured continuously. The CNO in exhaled air decreased significantly provided that the exercise intensity exceeded 65% of the peak VO2. It reached similar values, at exhaustion, in all three groups. The VNO increased proportionally with exercise intensity up to exhaustion and decreased rapidly during recovery. At exhaustion, the mean values were significantly higher for trained men than for sedentary men and sedentary women. During exercise, VNO correlates well with VO2, carbon dioxide production, VE, and heart rate. For the same submaximal intensity, and thus a given VO2 and probably a similar cardiac output, VNO appeared to be similar in all three groups, even if the VE was different. These results suggest that, during exercise, VNO is mainly related to the magnitude of aerobic metabolism and that this relationship is not affected by gender differences or by noticeable differences in the level of physical training.

Oxidant injury, nitric oxide and pulmonary vascular function: implications for the exercising horse

The athletic ability of the horse is facilitated by vital physiological adaptations to high-intensity exercise, including a thin (but strong) pulmonary blood-gas barrier, a large pulmonary functional reserve capacity and a consequent maximum oxygen uptake (VO2max) far higher than in other species. A high pulmonary artery pressure also serves to enhance pulmonary function, although stress failure of lung capillaries at high pulmonary transmural pressures, and the contribution of other factors which act in the exercising horse to increase pulmonary vascular tone, may lead to pathological or pathophysiological sequelae, such as exercise-induced pulmonary haemorrhage (EIPH). Reactive oxygen species (ROS) are an important component of the mammalian inflammatory response. They are released during tissue injury and form a necessary component of cellular defences against pathogens and disease processes. The effects of ROS are normally limited or neutralized by a multifactorial system of antioxidant defences, although excessive production and/or deficient antioxidant defences may expose healthy tissue to oxidant damage. In the lung, ROS can damage pulmonary structures both directly and by initiating the release of other inflammatory mediators, including proteases and eicosanoids. Vascular endothelial cells are particularly susceptible to ROS-induced oxidant injury in the lung, and both the destruction of the pulmonary blood-gas barrier and the action of vasoactive substances will increase pulmonary vascular resistance. Moreover, ROS can degrade endothelium-derived nitric oxide (NO), a major pulmonary vasodilator, thereby, with exercise, synergistically increasing the likelihood of stress failure of pulmonary capillaries, a contributing factor to EIPH. This review considers the implications for the exercising horse of oxidant injury, pulmonary vascular function and NO and the contribution of these factors to the pathogenesis of equine respiratory diseases.

Exhaled nitric oxide as a marker for serum nitric oxide concentration in acute endotoxemia

PURPOSE

The main aim of this study was to assess the correlation between exhaled nitric oxide (NO) and serum NO concentrations during the course of endotoxemia. We also assessed whether or not the inducible isoform of NO synthase is responsible for the increase in NO production in endotoxemia animals.

MATERIALS AND METHODS

Anesthetized and mechanically ventilated dogs were injected with either saline (control) or Escherichia coli endotoxin (LPS [Lipopolysaccharides]), and the animals were sacrificed 150 minutes later. We measured hemodynamics, exhaled NO, and serum arterial and mixed venous NO concentrations. Western blotting was performed on lung, pulmonary artery, aorta, and kidney tissue samples using anti-inducible NO synthase antibody.

RESULTS

Arterial pressure, cardiac output, and pulmonary arterial pressure in the control group remained unchanged, whereas a significant decline in these parameters was observed in the LPS group. Exhaled NO and serum arterial NO concentrations rose significantly within 30 minutes of endotoxin injection and remained higher than baseline values, whereas mixed venous serum NO did not change from baseline values. There was a significant linear relationship between exhaled NO and arterial serum NO concentrations. By comparison, exhaled NO, and arterial and mixed venous serum NO levels remained unchanged in the control group. Western blotting showed no expression of inducible NO synthase (iNOS) isoform in the control or LPS groups.

CONCLUSIONS

These results suggest that exhaled NO accurately reflects changes in arterial serum NO concentration and that the source of enhanced NO release in acute endotoxemia is not the iNOS isoform.

Nitric oxide and exercise in the horse

1. The effects of exercise on the production rate of nitric oxide (NO) in exhaled air (VNO) and the effects of inhaled NO (80 p.p.m.) on cardiovascular and respiratory parameters were investigated in five Throughbred horses. 2. The concentration of NO ([NO]) in exhaled air collected from within the nasal opening was lower when collected at a high flow rate of 80 l min-1 than at a low flow rate of 20 l min-1: when trotting at 3.7 m s-1 the values were 0.78 +/- 0.15 and 1.23 +/- 9.14 p.p.b., respectively, and when cantering at 9 m s-1 the values were 1.69 +/- 0.31 and 2.25 +/- 0.32 p.p.b., respectively. 3. Nebulized methoxamine (40 mg ml-1 for 60 s), an alpha 1-adrenergic agonist, further reduced [NO] during the 9 m s-1 canter to 1.05 +/- 0.14 and 1.99 +/- 0.41 p.p.b. when collected at 80 and 20 l min-1, respectively, and induced cyclical changes in the breathing pattern. 4. Exercise induced a linear increase in VNO with work intensity to a maximum (428.1 +/- 31.6 pmol min-1 kg-1) which coincided with the maximal oxygen uptake for the horses (138.3 +/- 11.7 ml min-1 kg-1), although a further increase in VNO (779.3 +/- 38.4 pmol min-1 kg-1) occurred immediately after exercise. The changes in VNO correlated well with the tidal volume (r = 0.968; P < 0.01) and the haematocrit (r = 0.855; P < 0.01). 5. In the first 2 min of high intensity exercise, inhaled NO (80 p.p.m.) significantly (P < 0.05) reduced the pulmonary artery pressure: during the first minute, pulmonary artery pressure was 83.1 +/- 7.6 mmHg compared with a control value of 94.4 +/- 6.3 mmHg, and during the second minute, 84.2 +/- 7.1 mmHg compared with a control value of 98.4 +/- 4.7 mmHg. There were no other significant changes in cardiovascular or respiratory indices, including cardiac output, measured during exercise between control and inhaled NO tests. 6. The results show that exhaled NO is released from the airways of the horse and may contribute to the regulation of pulmonary vascular tone during exercise.

Nitric oxide and lung surfactant

Inhalation of nitric oxide (NO) is an experimental treatment for severe pulmonary hypertension. Being rapidly metabolized by hemoglobin, inhaled NO causes selective vasodilation in the pulmonary vascular bed. In addition to the vascular smooth muscle, other pulmonary structures are exposed to inhaled NO, resulting in suppression of NO synthesis in a variety of pulmonary cells and in potential toxicity. NO is a free radical that interacts with a number of proteins, particularly metalloproteins. Together with superoxide radical, it rapidly forms highly toxic peroxynitrite. Peroxynitrite is involved in the killing of microbes by activated phagocytosing macrophages. In severe inflammation, peroxynitrite may be responsible for damaging proteins, lipids, and DNA. Peroxynitrite added to surfactant in vitro is capable of decreasing the surface activity, inducing lipid peroxidation, decreasing the function of surfactant proteins, SP-A and SP-B, and inducing protein-associated nitro-tyrosine. Exposure of animals for prolonged periods (48 to 72 hours) to inhaled NO (80 to 120 ppm) has been associated with a decrease in surface activity. This is caused by binding of surfactant to iron-proteins that are modified by NO (particularly methemoglobin), or by peroxynitrite induced damage of surfactant. In contrast, exposure of isolated surfactant complex to NO during surface cycling strikingly decreases the inactivation of surfactant, preventing the conversion of surfactant to small vesicles that are no longer surface-active, and preventing lipid peroxidation. This finding is consistent with the function of NO as a lipid-soluble chain-braking antioxidant. It is possible that this lipophilic gas has as yet undefined roles in regulation of surfactant metabolism and maintenance of surface activity. Deficiency in pulmonary NO may be present during the early neonatal period in respiratory distress syndrome and in persistent fetal circulation. The premature lung is likely to be sensitive to NO toxicity that may include lung damage, abnormal alveolarization, and mutagenicity. Defining of the indications, the dosage, and the toxicity of inhaled NO therapy remains the challenge for experimental and clinical research.

Sex differences in concentrations of exhaled nitric oxide and plasma nitrate

Nitric oxide (NO) is generally considered as an endogenous vasoprotective agent. Various studies indicate that the female sex hormone estradiol, that contributes to the well known gender differences in cardiovascular disease, may enhance NO-production. Thus we studied sex differences in NO-generation by measuring single breath NO-exhalation and plasma levels of nitrate (NO3), the stable endmetabolite of NO. In this observational trial 22 male and 21 female volunteers, 19 to 38 years of age, were studied on 3 days at weekly intervals. Median concentrations of NO were 20 parts per billion (95% CI: 16 to 32 ppb) in women and 34 ppb (95% CI: 31 to 58 ppb) in men. The median plasma concentrations of NO3 were 14 microM/L (95% CI: 11 to 23 microM/L) in women and 27 microM/L (95% CI: 24 to 47 microM/L) in men. Thus, men exhaled 59% more NO (p < 0.001) and had 99% higher NO3 levels than women (p < 0.0001). Even when exhaled NO concentrations were corrected for body weight, men exhaled 50% more NO than women (p = 0.024). No significant changes in measured endpoints were seen during the menstrual cycle (p > 0.05) in women. In view of the diversity of NO-actions, the finding of marked sex differences in NO-production is basic to the elucidation of gender differences in a number of (patho)-physiologic conditions.