This Month in the Journal

Patients with essential hypertension exhibit blunted endothelium-dependent vasodilator responses, which may be largely attributable to reduced bioactivity of nitric oxide (NO). Therefore, we measured the end product of NO, nitrate plus nitrite (nitrogen oxide), and examined the relationship between the degree of hypertension and plasma nitrate plus nitrite levels in patients with essential hypertension. The combined plasma concentration of nitrate plus nitrite, end products of NO metabolism, was reduced in individuals with essential hypertension relative to that in control subjects (15.7+/-1.1 versus 22.8+/-1.4 mmol x L(-1), P<.001); individuals with borderline hypertension showed values that were intermediate between those of the other two groups (18.2+/-1.2 mmol x L(-1), P<.001). The plasma nitrogen oxide concentration showed significant inverse correlations with both systolic and diastolic blood pressures. The basal concentration of nitrogen oxide in the plasma was reduced, at least in the peripheral circulation, in individuals with essential hypertension.

Cerebrospinal and blood nitric oxide in tubercular meningitis

A balance between endothelins (ET) and nitric oxide (NO) might interfere with liver haemodynamics and disease progression in various liver diseases. Increased levels of endothelin 1 (ET‐1) and nitrites and nitrates (NOx, the end products of NO metabolism) have been reported in hepatocellular carcinoma (HCC), but the balance has not been studied. The purpose of this study was to assess the ratio of NOx to ET‐1 in patients with virus‐related hepatocellular carcinoma and to investigate its correlation with the extent of the disease. Eighteen patients with virus‐related HCC (six Okuda stage I, six Okuda stage II and six Okuda stage III) were included in the study and were compared with 22 patients with viral cirrhosis (14 decompensated, eight compensated) and seven normal controls. ET‐1 was measured with an ELISA assay and NOx with a modification of the Griess reaction. Patients with virus‐related HCC had the highest levels of circulating ET‐1 and NOx (13.24 ± 0.82 pg/ml and 112.28 ± 18.56 μmol/l) compared to compensated cirrhosis (9.47 ± 0.50 pg/ml, P &lt; 0.004 and 54.47 ± 2.36 μmol/l, P &lt; 0.01), decompensated cirrhosis (9.57 ± 0.32 pg/ml, P &lt; 0.001 and 90.20 ± 11.23 μmol/l, NS) and normal controls (8.84 ± 0.61 pg/ml, P &lt; 0.001 and 51.17 ± 6.18 μmol/l, P &lt; 0.01). There was a significant increase of ET‐1 and NOx at HCC stage III compared to HCC stages I and II, cirhotics and controls. HCC stage III patients also had a NOx/ET‐1 ratio that was higher than HCC stages I and II patients, normal controls and patients with compensated cirrhosis. Virus‐related HCC patients have high levels of circulating ET‐1, compared to compensated or decompensated cirrhosis. Highest levels of ET‐1 are produced in Okuda III tumours. NOx are also increased but only in Okuda stage III tumours. The NOx/ET‐1 ratio is increased in virus‐related HCC and DC. This increase may account for the known increase in tumour blood flow.

To assess the efficacy of inhaled nitric oxide in improving pulmonary hypertension and gas exchange following oleic acid-induced acute lung injury. Prospective, pharmacologic study. Surgical research laboratory at the University of Pittsburgh, Pittsburgh, PA. Instrumented, intubated pigs weighing 16 to 27 kg. Intravenous oleic acid and inhaled nitric oxide. All pigs treated with intravenous oleic acid (0.11 mL/kg) developed a severe lung injury with pulmonary hypertension, accompanied by impaired oxygenation, intrapulmonary shunting, and increased extravascular lung water (p < .05 compared with baseline). Following nitric oxide inhalation, although pulmonary hypertension decreased in a dose-dependent fashion, no amelioration in pulmonary gas exchange was observed, as reflected by PaO2 and intrapulmonary shunt. Plasma nitrite and nitrate concentrations, the stable end products of nitric oxide metabolism, did not increase following nitric oxide exposure in this model of severe lung injury. The effect of inhaled nitric oxide, restricted to relieving pulmonary vasoconstriction in this model of lung injury, may have limited benefit in improving pulmonary gas exchange when diffusion is impaired by severe lung injury and inflammatory thickening of the alveolar-capillary barrier. Nitric oxide inhalation may have better results when used at an earlier, less severe stage of acute lung injury.

Nitric oxide (NO) is a lipid soluble, diatomic gas that affects a plethora of biological functions from immune defence and neurotransmission to blood flow regulation and skeletal muscle force production. The ubiquity of NO and its short half-life necessitates that the right concentration, at the right time, in a specific location, may mediate physiological outcomes. The article by Wylie and colleagues in this issue of The Journal of Physiology (Wylie et al. 2019) explores the potential that skeletal muscle could serve as a reservoir of nitrogen oxides (nitrate and nitrite), which, under certain physiological circumstances, could be transported between tissues and converted to NO. It combines the expertise of Piknova and Schechter (National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), USA) in NO signalling and muscle biology with that of the University of Exeter (UK) group in exercise science and inorganic nitrate supplementation. These human subject data demonstrate, under resting conditions, a concentration gradient of nitrate and nitrite from skeletal muscle tissue to the vascular compartment. Previous work using nNOS−/− rodents attributed this gradient to skeletal muscle neuronal nitric oxide synthase (nNOS) production of NO and subsequent oxidation (Piknova et al. 2015). The presence of nNOS protein expression in this human study adds credence to this conclusion. Following oral inorganic nitrate supplementation (12.8 mmol), large increases in plasma nitrate (and nitrite) were accompanied by elevated skeletal muscle nitrate (∼900–1000 nmol g−1). This complements earlier murine data which revealed liver tissue nitrate concentrations to be lower than in the plasma, suggesting a potential transport gradient between the compartments (Piknova et al. 2015). Furthermore, a 6.5 min bout of high intensity exercise significantly reduced skeletal muscle nitrate while plasma levels remained constant. Previous human exercise studies have shown both reductions and no changes in plasma nitrite and nitrate following exercise stress of various intensities and/or durations in subjects with a wide variety of health status. Given the multiple ways NO has been implicated in mediating mitochondrial function, skeletal muscle contractile efficiency and tissue perfusion/oxygenation during exercise, the idea that skeletal muscle could act as a nitrogen oxide reservoir that can be sequestered to maintain circulating levels of nitrate and nitrite for distribution is provocative. Evidence of the presence of sialin, an active nitrate transporter, in skeletal muscle provides a potential mechanism by which this skeletal muscle nitrate loading could occur and strengthens this hypothesis. This finding likely needs further confirmation given the variability in sialin expression between subjects, and a lack of relative control tissues for comparison (although the ubiquity of sialin and the required extra tissue sampling in this human study makes the latter difficult). A second possibility for storing and releasing NO when needed is intra-compartment oxidation and reduction. NO can be converted to nitrite and nitrate in an oxidative environment and in the presence of oxymyoglobin (oxy-Mb). Conversely, nitrate can be reduced to nitrite via oral bacteria and potentially xanthine oxidoreductase (XOR). Nitrite in turn is easily reduced to NO via a variety of pathways including protons, deoxymyoglobin (deoxy-Mb) and XOR, which may be facilitated in a low environment. Previously, the authors have shown an upregulation of XOR (and sialin) in Mb−/− mice suggesting it may be a compensatory mechanism to maintain skeletal muscle nitrogen oxide homeostasis (Park et al. 2019). In the current paper, they present evidence of XOR expression in human skeletal muscle tissue. During high intensity exercise, the relative reduction in both and pH would favour nitrite reduction to NO and theoretically XOR-mediated reduction of nitrate to nitrite. They previously demonstrated a decrease in rodent skeletal nitrate, accompanied by an increase in nitrite after a single bout of exercise (Piknova et al. 2016). Conversely, they also showed that despite expression of XOR in rat skeletal muscle there was no production of nitrite with increasing dosages of nitrate or 24 h of incubation (Piknova et al. 2015). It would appear that the possibility of nitrate to nitrite conversion by XOR in skeletal muscle is feasible; however, the amounts of XOR protein expression compared to tissues such as the liver is extremely low. In the current paper, there was a large between-subject variability in skeletal muscle XOR protein expression and no XOR relative-tissue controls to quantify the amounts. How much XOR in the skeletal muscle is needed to play a significant role in nitrogen oxide signalling is unknown but given 30–40% of a healthy person's body mass is muscle, even low concentrations of XOR could potentially play a significant role. In the last 10 years, there has been increased interest in the role of inorganic nitrate supplementation to enhance exercise performance. In healthy human studies the results are mixed with meta-analyses reporting overall no benefit for maximal graded exercise and time trial performance testing, but likely a benefit in time to exhaustion tests. A beneficial effect also appears more likely following chronic dosing regimens in less conditioned individuals (including those with cardiovascular impairments) employing higher intensity activities which utilize fast twitch muscle fibres (Woessner et al. 2018). In the current study a single dose of inorganic nitrate was used in 13 healthy, relatively fit subjects ( ∼50 ml kg−1 min−1) which could partially explain a lack of changes in time to task failure, despite high intensity activity being utilized. In the supplemented condition, there was a substantial decrease in skeletal muscle nitrate (∼700 nmol g−1) and plasma nitrite decreased by ∼0.2 nmol g−1. The lack of ergogenic effect, however, makes it difficult to speculate on what these changes mean. More may not always be better. Perhaps the right concentration, at the right time, in the right location is the key to physiological and physical benefits? Given the plethora of studies connecting vascular NO bioavailability with markers of vascular health such as blood pressure and endothelial function, further exploration of this topic is clearly warranted. This paper, and previous work by these investigators, presents thought-provoking data that will stimulate exploration to clarify the mechanisms underpinning intra- and inter-compartmental nitrogen oxide chemistry and resultant physiological outcomes, such as cardiovascular health and exercise in larger more heterogeneous groups of subjects. None declared. Both authors have approved the final version of the manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. None.

Nitric oxide (NO), a biologically active mediator generated in many cell types by the enzyme NO synthase, may play an important role in cardiovascular toxicity that is frequently observed in cancer patients during intravenous (i.v.) interleukin 2 (IL-2) therapy. The induction of NO synthase and the production of NO seem to be involved in the pathogenesis of the vascular leakage syndrome, as well as in the regulation of myocardial contractility. In the present study, we evaluated the pattern of plasmatic NO changes during multiple cycles of continuous i.v. infusion (CIVI) of IL-2 in ten advanced cancer patients (five males, five females, median age 59 years, range 33-67 years; eight affected by renal cell cancer and two affected by malignant melanoma). The patients received IL-2 at 18 MIU m-2 day-1 (14 cycles) or 9 MIU m-2 day-1 (seven cycles) for 96 h, repeated every 3 weeks. Interferon alpha (IFN alpha) was also administered subcutaneously (s.c) during the 3 week interval between IL-2 cycles. For each cycle, plasma samples were collected before treatment (t0), 24 h (t1), 48 h (t2), 72 h (t3) and 96 h (t4) after the start of IL-2 infusion, and 24 h after the end of the cycle. NO concentration was determined spectrophotometrically by measuring the accumulation of both nitrite and nitrate (after reduction to nitrite). The following observations may be drawn from data analysis: (1) plasma nitrate + nitrite significantly raised during treatment (P = 0.0226 for t0 vs t3), but statistical significance was retained only when cycles administered with IL-2 18 MIU m-2 day-1 are considered (P = 0.0329 for t0 vs t3; P = 0.0354 for t0 vs t2 vs t4) (dose-dependent pattern); (2) during subsequent cycles a significant trend toward a progressive increase of plasma nitrate + nitrite levels, with increasing cumulative dose of IL-2, was observed (linear regression coefficient r = 0.62, P = 0.0141 for t0; r = 0.80, P = 0.0003 for t1; r = 0.62, P = 0.013 for t2; r = 0.69, P = 0.045 for t3); (3) plasma nitrate + nitrite levels peaked earlier in subsequent cycles than in the first cycle; (4) all patients experienced hypotension. The mean of the systolic blood pressure values was significantly lower at the time of plasma nitrate + nitrite peak than at t0 (P = 0.0004); (5) the two cases of grade III hypotension occurred in patients with the higher mean and peak plasma nitrate + nitrite values. We conclude that determination of plasma nitrate + nitrite levels during CIVI IL-2 can usefully estimate, in a dose-dependent pattern, the degree of peripheral vascular relaxation and capillary leakage associated with cytokine action, clinically manifested as hypotension. However, isolated cardiac toxicity that continues to represent a relevant problem during IL-2 therapy, does not appear to correlate with plasma nitrate + nitrite levels; therefore, further studies are required to understand adequately the mechanisms underlying IL-2-induced cardiac toxicity.

It has been suggested that dietary nitrate, after concentration in the saliva and reduction to nitrite by tongue surface bacteria, is chemically reduced to nitric oxide (NO) in the acidic conditions of the stomach. This study aimed to quantify this in humans. Ten healthy fasting volunteers were studied twice, after oral administration of 2 mmol of potassium nitrate or potassium chloride. Plasma, salivary and gastric nitrate, salivary and gastric nitrite, and gastric headspace NO concentrations were measured over six hours. On the control day the parameters measured varied little from basal values. Gastric nitrate concentration was 105.3 (13) mumol/l (mean (SEM), plasma nitrate concentration was 17.9 (2.4) mumol/l, salivary nitrate concentration 92.6 (31.6) mumol/l, and nitrite concentration 53.9 (22.8) mumol/l. Gastric nitrite concentrations were minimal (< 1 mumol/l). Gastric headspace gas NO concentration was 16.4 (5.8) parts per million (ppm). After nitrate ingestion, gastric nitrate peaked at 20 minutes at 3430 (832) mumol/l, plasma nitrate at 134 (7.2) mumol/l, salivary nitrate at 1516.7 (280.5) mumol/l, and salivary nitrite at 761.5 (187.7) mumol/l after 20-40 minutes. Gastric nitrite concentrations tended to be low, variable, and any rise was non-sustained. Gastric NO concentrations rose considerably from 14.8 (3.1) ppm to 89.4 (28.6) ppm (p < 0.0001) after 60 minutes. All parameters remained increased significantly for the duration of the study. A very large and sustained increase in chemically derived gastric NO concentrations after an oral nitrate load was shown, which may be important both in host defence against swallowed pathogens and in gastric physiology.

IntroductionHeart failure (HF) often leads to secondary renal dysfunction. Morbidity and mortality in HF patients worsens steeply when concomitant renal injury is present and current treatments fail to rescue renal function in these patients. Reduced nitric oxide (NO) levels are associated with both heart and renal failure. We hypothesised that reduced NO bioavailability is central to the development of renal inflammation, fibrosis and ultimate failure of the kidney in HF. L‐arginine is the sole substrate for NO formation and increasing cellular L‐arginine transport can increase NO levels. Serelaxin can also increase NO levels in HF.MethodsAdult male transgenic mice (18–26 weeks of age) that develop cardiomyopathy as a result of cardiac specific overexpression of MST‐1 (DCM mice) were used. NO levels in DCM mice were increased via endothelial specific overexpression of the predominant L‐arginine transporter, cationic amino acid transporter‐1 (CAT1), and by administration of serelaxin.There were five treatment groups; wild type mice (WT; n=8), DCM mice (n=8), DCM mice overexpressing CAT1 (n=8), DCM mice administered serelaxin vehicle (20 mM sodium acetate, pH 5.0; n=8) and DCM mice administered serelaxin (500μg/kg/day; 8 weeks; subcutaneous minipumps; n=8). In all mice, cardiac structure and function were assessed via echocardiography, renal fibrosis was assessed via Masson's Trichrome staining, plasma nitrate and nitrite levels (an index of NO levels) were assessed via a commercially available ELISA kit and mRNA expression of inflammatory markers was assessed via PCR.ResultsEjection fraction was 33% less in 18 week old DCM mice than in 18 week old WT (P = 0.01). Plasma nitrate and nitrite levels were 78% less in 18 week old DCM mice than in 18 week old WT (P&lt;0.05). Plasma nitrate and nitrite levels were normalised in 18 week old DCM mice overexpressing CAT1. Renal tubulointerstitial and glomerular fibrosis were 89% and 76% greater respectively, in 18 week old DCM mice than in age matched WT (P≤0.05). Renal tubulointerstitial and glomerular fibrosis were less (by 77 and 54% respectively; P ≤ 0.05) in 18 week old DCM mice overexpressing CAT1 compared 18 week old DCM mice that do not overexpress CAT1. Renal expression of inflammatory markers, Il6 and Il1β were less while renal expression of anti‐inflammatory marker Il‐10 was greater in the former genotype compared to the latter (all P&lt;0.05).Renal tubulointerstitial and glomerular fibrosis were less by 46% and 45% respectively, in serelaxin treated 26 week old DCM mice compared to age matched vehicle treated DCM mice (P≤0.01). Renal mRNA expression of inflammatory marker Tnfα was 75% greater in 26 week old DCM mice compared to 26 week old WT (P&lt;0.01). Renal Tnfα mRNA expression was 57% less in serelaxin treated 26 week old DCM mice than in 26 week old DCM mice treated with vehicle (P=0.05).ConclusionThese data indicate that augmented L‐arginine transport and serelaxin can reduce renal inflammation and fibrosis in chronic HF potentially by restoring NO levels.Support or Funding InformationNHMRC Program Grant to DK, Investigator led project grant from Novartis to NR and DKThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

PurposeDietary nitrate supplementation increases nitric oxide (NO) bioavailability and reduces blood pressure (BP). Inter-individual differences in these responses are suspected but have not been investigated using robust designs, e.g., replicate crossover, and appropriate statistical models. We examined the within-individual consistency of the effects of dietary nitrate supplementation on NO biomarkers and BP, and quantified inter-individual response differences.MethodsFifteen healthy males visited the laboratory four times. On two visits, participants consumed 140 ml nitrate-rich beetroot juice (~ 14.0mmol nitrate) and, on the other two visits, they consumed 140 ml nitrate-depleted beetroot juice (~ 0.03mmol nitrate). Plasma nitrate and nitrite concentrations were measured 2.5 h post-supplementation. BP was measured pre- and 2.5 h post-supplementation. Between-replicate correlations were quantified for the placebo-adjusted post-supplementation plasma nitrate and nitrite concentrations and pre-to-post changes in BP. Within-participant linear mixed models and a meta-analytic approach estimated participant-by-condition treatment response variability.ResultsNitrate-rich beetroot juice supplementation elevated plasma nitrate and nitrite concentrations and reduced systolic (mean:-7mmHg, 95%CI: -3 to -11mmHg) and diastolic (mean:-6mmHg, 95%CI: -2 to -9mmHg) BP versus placebo. The participant-by-condition interaction response variability from the mixed model was ± 7mmHg (95%CI: 3 to 9mmHg) for systolic BP and consistent with the treatment effect heterogeneity t = ± 7mmHg (95%CI: 5 to 12mmHg) derived from the meta-analytic approach. The between-replicate correlations were moderate-to-large for plasma nitrate, nitrite and systolic BP (r = 0.55 to 0.91).ConclusionsThe effects of dietary nitrate supplementation on NO biomarkers and systolic BP varied significantly from participant to participant. The causes of this inter-individual variation deserve further investigation. Trial registration: https://clinicaltrials.gov/study/NCT05514821.

To examine the role of nitric oxide in the cardiovascular system in spontaneous hypertension. In particular, we wanted to know whether the production of nitric oxide in the cardiovascular system of the spontaneously hypertensive rat is different from that of the normotensive Wistar-Kyoto rat and whether nitric oxide is biologically effective in this system. We studied various aspects of the L-arginine-nitric oxide pathway in the cardiovascular system of spontaneously hypertensive rats and Wistar-Kyoto rats. To address the first objective we analysed the expression of endothelial nitric oxide synthase in the heart by Western blotting and the activity of constitutive nitric oxide synthase in resistance microvessels obtained from the mesenterium, both from spontaneously hypertensive rats and Wistar-Kyoto rats aged 14-18 weeks. We also analysed the concentration of the oxidative product of nitric oxide, nitrate, in plasma from these rats. To address the second objective, that is, to assess the bioactivity of nitric oxide, we studied the accumulation in tissue of cyclic guanosine 3',5'-monophosphate (GMP), as well as the acute and chronic effects of withdrawing the nitric oxide vasodilatory tone with the inhibitor of nitric oxide synthesis NG-nitro-L-arginine methyl ester on Wistar-Kyoto rats and spontaneously hypertensive rats. We found that the expression of endothelial nitric oxide synthase in the heart, the activity of constitutive nitric oxide synthase in resistance microvessels and the concentration of nitrate in plasma were all significantly higher in the spontaneously hypertensive rats. In contrast, neither cyclic GMP levels nor the effects of NG-nitro-L-arginine methyl ester were greater in the spontaneously hypertensive rat than they were in the Wistar-Kyoto rat. The nitric oxide pathway is upregulated in the resistance circulation and the heart of the spontaneously hypertensive rat by a mechanism involving induction of the constitutive nitric oxide synthase and overproduction of nitric oxide. However, nitric oxide is not sufficiently bioactive to stimulate the formation of cyclic GMP and to maintain an adequate nitric oxide-dependent vasodilatory tone.

To determine a mechanism by which nitric oxide alters induction of stress-induced endothelial cell apoptosis in vitro. Apoptosis is a form of cellular suicide that has been implicated in the pathogenesis of multiple organ dysfunction syndrome. Prospective, controlled trial. Research laboratory of a large, academic medical center. Cultured primary porcine aortic endothelial cells. Cells were treated with a range of doses of agents that either spontaneously generate nitric oxide (S-nitroso-N-acetyl-D,L-penicillamine [SNAP] or (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1- ium-1,2-diolate [DETA-NO]) or block nitric oxide production (Nomega-methyl-L-arginine [L-NMA]). The ability of these agents to alter the rate of cell death by apoptosis (induced by the sequence stimuli lipopolysaccharide [LPS] followed by sodium arsenite) was measured. Mechanistic studies included examining the ability of: a) nitric oxide "donors" to alter nuclear factor kappa B (NF-kappaB) DNA binding activity and the level of IkappaBalpha accumulation; and b) a stable cyclic guanosine monophosphate (cGMP) analog (8-bromo-cGMP) to mimic the effect of nitric oxide donors. The sequence LPS/sodium arsenite increased the rate of endothelial cell apoptosis (47.4%, p< .05 vs. control), as measured by fluorescent-activated cell scanning using annexin V/propidium iodide staining. DETA-NO generated nitric oxide (as indicated by an increase in the concentration of the stable end-products of nitric oxide metabolism) and decreased the rate of endothelial cell apoptosis (20.6% at a dose of 2 mM, p=.0001 vs. control). DETA-NO also decreased NF-kappaB DNA binding activity and the apparent accumulation of its endogenous inhibitor, IkappaBalpha. The 8-bromo-cGMP did not mimic the effects of nitric oxide donors (DETA-NO) on apoptosis. These data suggest that exogenous nitric oxide can block stress-induced endothelial cell apoptosis in vitro. The mechanistic studies are consistent with our hypothesis that inhibitors of NF-kappaB DNA binding activity are associated with protection against apoptosis-inducing stimuli. The results do not support a role for cGMP in mediating the protective effect of DETA-NO in our model.

Nitric oxide (NO) is produced in mammals by the enzyme NO synthase (NOS) in response to a number of agents, including the experimental antitumour agent flavone acetic acid (FAA) and the cytokine tumour necrosis factor-alpha (TNF). NO is converted rapidly in the presence of oxygen, water and haemoglobin to oxidation products, largely nitrate. To quantitate the production of nitric oxide it is necessary to know the clearance of nitrate. The concentration of nitrite and nitrate ion in the plasma of C3H and BDF1 (C57BL6 x DBA2) mice was assessed before and after injection of sodium nitrate and sodium nitrite. Nitrite was covered rapidly to nitrate and the kinetics of elimination of nitrate were determined. There was no significant difference between results obtained with different mouse strains, between levels of nitrite and nitrate, or between i.p. and i.v. administration, and the observations were therefore combined. The volume of distribution of nitrate was 0.71 +/- 0.04 l/kg and the clearance was 0.32 +/- 0.02 l/h-1/kg-1 (plasma half-life, 1.54 h). Using previously published data, we developed a pharmacokinetic-pharmacodynamic model that relates the production of TNF in response to administration of FAA, the enhancement of NOS activity in response to TNF, and the elevation of plasma nitrate in response to NO production. This information permits the prediction from observed plasma nitrate values of the amount of NOS induced in vivo.

Effects of nitric oxide gas on cat carotid body chemosensory response to hypoxia

Nitric oxide (NO) produced within the carotid body (CB) is an inhibitory modulator of hypoxic chemoreception (Chugh et al., 1994; Wang et al., 1994, 1995; Iturriaga et al, 1998). Administration of NO donors and NO gas to the cat CB reduces the chemosensory response to hypoxia (Chugh et al., 1994; Iturriaga et al., 1998; Iturriaga et al, 2000b). Conversely, the inhibition of nitric oxide synthase (NOS) increases the frequency of carotid chemosensory discharges (f x) in the cat CB in situ and in vitro (Wang et al., 1994; Iturriaga et al., 1998). It has been proposed that NO produce vasodilatation in the CB (Chugh et al., 1994; Wang et al., 1994; Lahiri and Buerk, 1998), retrograde inhibition of glomus cell’s excitability (Wang et al., 1994), inhibition of glomus cell’s Ca+2 channels activity (Summers et al., 1999), modulation of petrosal ganglion neurons excitability (Alcayaga et al., 1997), and inhibition of mitochondrial metabolism (Iturriaga et al., 2000b). In the CB, the endothelial NOS (eNOS) is located in the endothelial cells and the neuronal (nNOS) in the sensory terminals of C fibers and parasympathetic neurons (Chugh et al., 1994; Wang et al, 1994, 1995).

Evidence by gas chromatography–mass spectrometry of ex vivo nitrite and nitrate formation from air nitrogen oxides in human plasma, serum, and urine samples