Dietary nitrate attenuates high-fat diet-induced obesity via mechanisms involving higher adipocyte respiration and alterations in inflammatory status.

Emerging evidence indicates that dietary nitrate can reverse several features of the metabolic syndrome, but the underlying molecular mechanisms still remain elusive. The aim of the present study was to explore mechanisms involved in the effects of dietary nitrate on the metabolic dysfunctions induced by high-fat diet (HFD) in mice. Four weeks old C57BL/6 male mice, exposed to HFD for ten weeks, were characterised by increased body weight, fat content, increased fasting glucose and impaired glucose clearance. All these metabolic abnormalities were significantly attenuated by dietary nitrate. Mechanistically, subcutaneous primary mouse adipocytes exposed to palmitate (PA) and treated with nitrite exhibited higher mitochondrial respiration, increased protein expression of total mitochondrial complexes and elevated gene expression of the thermogenesis gene UCP-1, as well as of the creatine transporter SLC6A8. Finally, dietary nitrate increased the expression of anti-inflammatory markers in visceral fat, plasma and bone marrow-derived macrophages (Arginase-1, Egr-2, IL-10), which was associated with reduction of NADPH oxidase-derived superoxide production in macrophages. In conclusion, dietary nitrate may have therapeutic utility against obesity and associated metabolic complications possibly by increasing adipocyte mitochondrial respiration and by dampening inflammation and oxidative stress.

Mechanisms underlying blood pressure reduction by dietary inorganic nitrate.

Nitric oxide (NO) importantly contributes to cardiovascular homeostasis by regulating blood flow and maintaining endothelial integrity. Conversely, reduced NO bioavailability is a central feature during natural ageing and in many cardiovascular disorders, including hypertension. The inorganic anions nitrate and nitrite are endogenously formed after oxidation of NO synthase (NOS)-derived NO and are also present in our daily diet. Knowledge accumulated over the past two decades has demonstrated that these anions can be recycled back to NO and other bioactive nitrogen oxides via serial reductions that involve oral commensal bacteria and various enzymatic systems. Intake of inorganic nitrate, which is predominantly found in green leafy vegetables and beets, has a variety of favourable cardiovascular effects. As hypertension is a major risk factor of morbidity and mortality worldwide, much attention has been paid to the blood pressure reducing effect of inorganic nitrate. Here, we describe how dietary nitrate, via stimulation of the nitrate-nitrite-NO pathway, affects various organ systems and discuss underlying mechanisms that may contribute to the observed blood pressure-lowering effect.

Therapeutic effects of inorganic nitrate and nitrite in cardiovascular and metabolic diseases.

Nitric oxide (NO) is generated endogenously by NO synthases to regulate a number of physiological processes including cardiovascular and metabolic functions. A decrease in the production and bioavailability of NO is a hallmark of many major chronic diseases including hypertension, ischaemia-reperfusion injury, atherosclerosis and diabetes. This NO deficiency is mainly caused by dysfunctional NO synthases and increased scavenging of NO by the formation of reactive oxygen species. Inorganic nitrate and nitrite are emerging as substrates for in vivo NO synthase-independent formation of NO bioactivity. These anions are oxidation products of endogenous NO generation and are also present in the diet, with green leafy vegetables having a high nitrate content. The effects of nitrate and nitrite are diverse and include vasodilatation, improved endothelial function, enhanced mitochondrial efficiency and reduced generation of reactive oxygen species. Administration of nitrate or nitrite in animal models of cardiovascular disease shows promising results, and clinical trials are currently ongoing to investigate the therapeutic potential of nitrate and nitrite in hypertension, pulmonary hypertension, peripheral artery disease and myocardial infarction. In addition, the nutritional aspects of the nitrate-nitrite-NO pathway are interesting as diets suggested to protect against cardiovascular disease, such as the Mediterranean diet, are especially high in nitrate. Here, we discuss the potential therapeutic opportunities for nitrate and nitrite in prevention and treatment of cardiovascular and metabolic diseases.

Clinical evidence demonstrating the utility of inorganic nitrate in cardiovascular health.

The discovery of nitric oxide and its role in almost every facet of human biology opened a new avenue for treatment through manipulation of its canonical signaling and by attempts to augment endogenous nitric oxide generation through provision of substrate and co-factors to the endothelial nitric oxide synthase complex. This has been particularly so in the cardiovascular system and it is well recognized that there is reduced bioavailable nitric oxide in patients with both cardiovascular risk factors and manifest vascular disease. However, these attempts have failed to deliver the expected benefits of such an approach. Recently, an alternative pathway for nitric oxide synthesis has been elucidated that can produce authentic nitric oxide from the 1 electron reduction of inorganic nitrite. Furthermore, it has long been known that symbiotic, facultative, oral microflora can facilitate the reduction of inorganic nitrate, that is ingested in the average diet in millimolar amounts, to inorganic nitrite itself. Thus, there exists an alternative reductive pathway from nitrate, via nitrite as an intermediate, to nitric oxide that provides a novel pathway that may be amenable to therapeutic manipulation. As such, various research groups have explored the utility of manipulation of this nitrate-nitrite-nitric oxide pathway in situations in which nitric oxide is known to have a prominent role. Animal and early-phase human studies of both inorganic nitrite and nitrate supplementation have shown beneficial effects in blood pressure control, platelet function, vascular health and exercise capacity. This review considers in detail the pathways of inorganic nitrate bioactivation and the evidence of clinical utility to date on the cardiovascular system.

L-arginine or tempol supplementation improves renal and cardiovascular function in rats with reduced renal mass and chronic high salt intake.

AIM: Early life reduction in nephron number and chronic high salt intake cause development of renal and cardiovascular disease, which has been associated with oxidative stress and nitric oxide (NO) deficiency. We investigated the hypothesis that interventions stimulating NO signalling or reducing oxidative stress may restore renal autoregulation, attenuate hypertension and reduce renal and cardiovascular injuries following reduction in renal mass and chronic high salt intake. METHODS: Male Sprague-Dawley rats were uninephrectomized (UNX) or sham-operated at 3 weeks of age and given either a normal-salt (NS) or high-salt (HS) diet. Effects on renal and cardiovascular functions were assessed in rats supplemented with substrate for NO synthase (L-Arg) or a superoxide dismutase mimetic (Tempol). RESULTS: Rats with UNX + HS developed hypertension and displayed increased renal NADPH oxidase activity, elevated levels of oxidative stress markers in plasma and urine, and reduced cGMP in plasma. Histological analysis showed signs of cardiac and renal inflammation and fibrosis. These changes were linked with abnormal renal autoregulation, measured as a stronger tubuloglomerular feedback (TGF) response. Simultaneous treatment with L-Arg or Tempol restored cGMP levels in plasma and increased markers of NO signalling in the kidney. This was associated with normalized TGF responses, attenuated hypertension and reduced signs of histopathological changes in the kidney and in the heart. CONCLUSION: Reduction in nephron number during early life followed by chronic HS intake is associated with oxidative stress, impaired renal autoregulation and development of hypertension. Treatment strategies that increase NO bioavailability, or reduce levels of reactive oxygen species, were proven beneficial in this model of renal and cardiovascular disease.

Nitric oxide and endothelin-1 release after one-lung ventilation during thoracoabdominal esophagectomy.

One-lung ventilation (OLV) is applied during esophagectomy to improve exposure during the thoracic part of the operation. Collapse of lung tissue, shunting of pulmonary blood flow, and changes in alveolar oxygenation during and after OLV may possibly induce an ischemia-reperfusion response in the lung, which may affect the pulmonary endothelium. Such a reaction might thereby contribute to the frequently occurring respiratory complications among these patients. In this small trial, 30 patients were randomized to either OLV (n= 16) or two-lung ventilation (TLV, n= 14) during esophagectomy. Central venous and arterial plasma samples were taken before and after OLV/TLV for analysis of nitrite and a metabolite of nitric oxide (NO), and also during the 1st, 2nd, 3rd, and 10th postoperative day for analysis of endothelin, another endothelium-derived vasoactive mediator. Lung biopsies were taken before and after OLV or TLV, and analyzed regarding immunofluorescence for isoform of NO synthase, a protein upregulated during inflammatory response and also vascular congestion. No changes in lung isoform of NO synthase immunofluorescence or vascular congestion were registered after neither OLV nor TLV. Plasma nitrite and endothelin levels were similar in the two study groups. We conclude that OLV does not seem to have any influence on key regulators of pulmonary vascular tone and inflammation, i.e. NO and endothelin. From this perspective, OLV seems to be a safe method, which defends its clinical position to facilitate surgical exposure during thoracoabdominal esophagectomy.

Importance and regulation of the colonic mucus barrier in a mouse model of colitis.

The colonic mucus layer serves as an important barrier and prevents colonic bacteria from invading the mucosa and cause inflammation. The regulation of colonic mucus secretion is poorly understood. The aim of this study was to investigate the role of the mucus barrier in induction of colitis. Furthermore, regulation of mucus secretion by luminal bacterial products was studied. The colon of anesthetized Muc2(-/-), Muc1(-/-), wild-type (wt), and germ-free mice was exteriorized, the mucosal surface was visualized, and mucus thickness was measured with micropipettes. Colitis was induced by DSS (dextran sodium sulfate, 3%, in drinking water), and disease activity index (DAI) was assessed daily. The colonic mucosa of germ-free and conventionally housed mice was exposed to the bacterial products LPS (lipopolysaccharide) and PGN (peptidoglycan). After DSS induction of colitis, the thickness of the firmly adherent mucus layer was significantly thinner after 5 days and onward, which paralleled the increment of DAI. Muc2(-/-) mice, which lacked firmly adherent mucus, were predisposed to colitis, whereas Muc1(-/-) mice were protected with significantly lower DAI by DSS compared with wt mice. The mucus barrier increased in Muc1(-/-) mice in response to DSS, whereas significantly fewer T cells were recruited to the inflamed colon. Mice housed under germ-free conditions had an extremely thin adherent colonic mucus layer, but when exposed to bacterial products (PGN or LPS) the thickness of the adherent mucus layer was quickly restored to levels observed in conventionally housed mice. This study demonstrates a correlation between decreasing mucus barrier and increasing clinical symptoms during onset of colitis. Mice lacking colonic mucus (Muc2(-/-)) were hypersensitive to DSS-induced colitis, whereas Muc1(-/-) were protected, probably through the ability to increase the mucus barrier but also by decreased T cell recruitment to the afflicted site. Furthermore, the ability of bacteria to regulate the thickness of the colonic mucus was demonstrated.

Validation study of nasal nitric oxide measurements using a hand-held electrochemical analyser.

BACKGROUND: Exhaled nitric oxide (NO) measurement is a simple and non-invasive method for monitoring airway inflammation. Similarly, nasal NO has been proposed as a surrogate marker in inflammatory diseases of the upper airways, e.g. allergic rhinitis. A new portable analyser using an electrochemical sensor has been developed for measurements of exhaled NO, and its reproducibility and comparison with other analysers has been tested recently in healthy subjects and in patients with lower airways disease. The application of this hand-held analyser in nasal NO analysis was tested and compared to the gold standard represented by a chemiluminescence analyser. MATERIALS AND METHODS: Thirty subjects including 15 patients with allergic rhinitis (AR) and 15 healthy subjects (HS) were studied. The intraindividual variability, calculated as the difference in nasal NO levels between two measurements from a single nasally exhaled breath manoeuvre, and the comparison between the electrochemical analyser (NIOX MINO, Aerocrine) and a chemiluminescence analyser (NOA, Sievers) were performed. RESULTS: In AR patients mean nasal NO was 59.0 +/- 16.3 p.p.b. with the MINO and 58.3 +/- 15.6 p.p.b. with the NOA. In HS nasal NO was 49.1 +/- 10.8 p.p.b. with the MINO and 49.8 +/- 8.2 p.p.b. with the NOA. The Bland-Altman analysis showed bias values of 0.005 +/- 3.6 with the 95% limits of agreement from -6.97 to 6.98 p.p.b. CONCLUSION: Measurements of nasal NO levels with a hand-held electrochemical analyser are reproducible and the results are comparable to a stationary chemiluminescence analyser.

Effects of dietary nitrate on oxygen cost during exercise.

AIM: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO(3) (-)) and nitrite (NO(2) (-)). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise. METHOD: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg(-1) day-1) or an equal amount of sodium chloride (placebo). RESULTS: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo(2) decreased from 2.98 +/- 0.57 during CON to 2.82 +/- 0.58 L min(-1) during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 +/- 1.6 during CON to 21.1 +/- 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo(2) or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates. CONCLUSION: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.

Early changes in rectal nitric oxide and mucosal inflammatory mediators in Crohn's colitis in response to infliximab treatment.

BACKGROUND: Treatment with tumor necrosis factor-alpha monoclonal antibody (infliximab) reduces clinical activity and intestinal inflammation in Crohn's disease. AIM: To study the time-course of the effects of infliximab with reference to mucosal cytokine and inducible nitric oxide synthase expression. METHODS: Thirty-two patients with Crohn's disease were treated with single dose infliximab (5 mg/kg). Disease activity was assessed days 1, 3, 7 and 28 using Harvey-Bradshaw index. Rectal nitric oxide levels were determined and rectal biopsies collected before treatment, 1 h after infusion and on days 3, 7 and 28. Immunohistochemical staining against inducible nitric oxide synthase, tumor necrosis factor-alpha, interleukin-1beta and interferon-gamma were performed. RESULTS: Clinical response was seen in 14 patients with down-regulation of global immunohistochemistry expression, reaching nadir day 3. Rectal nitric oxide was increased at baseline (3578 +/- 1199 parts per billion, ppb) compared with controls (89 +/- 13 ppb) (P < 0.001). In patients with clinical response, rectal nitric oxide decreased from 3926 +/- 1687 ppb to 1050 +/- 428 ppb day 28 (P < 0.05). CONCLUSIONS: Down-regulation of mucosal inflammatory mediators occurs after infliximab. Rectal nitric oxide levels parallel down-regulation of inducible nitric oxide synthase, tumor necrosis factor-alpha, interleukin-1beta and interferon-gamma and may serve as a quantitative biomarker of intestinal inflammation.

Sounding airflow enhances aerosol delivery into the paranasal sinuses.

BACKGROUND: The use of aerosol therapy is commonly suggested in the treatment of paranasal disorders but it is difficult to achieve an effective penetration of drugs into the sinuses. The authors have recently shown that an oscillating airflow produced by phonation (nasal humming) causes a large increase in the gas exchange between the nose and the paranasal sinuses. This is reflected by a high peak in nasally exhaled nitric oxide (NO) levels because NO accumulated in the sinuses is rapidly washed-out via the sinus ostia. OBJECTIVE: This study was designed to test whether the increase in sinus gas exchange caused by an oscillating airflow could be used to enhance penetration of a drug into the sinuses. MATERIALS AND METHODS: In six healthy subjects a nitric oxide-synthase inhibitor L-NAME was administrated into the nostrils by a jet nebulizer connected to a duck call, which could be modified to generate either a sounding airflow or a non-sounding airflow. The degree of L-NAME penetration into the sinuses was judged from the reduction in nasal NO during humming exhalations. Sinus drug deposition was also studied in a model of the nose and sinus. RESULTS: In humans the delivery of L-NAME with the non-sounding airflow had no effect on the NO levels achieved during humming, whereas L-NAME administration with sound caused a significant 22-35% reduction in nasal NO. In the model the aerosol delivery with the sounding airflow caused a fourfold increase in sinus drug deposition as compared with an aerosol without sound. CONCLUSION: A sounding airflow increases the delivery of an aerosolized drug into the paranasal sinuses.

Gastrointestinal bacteria generate nitric oxide from nitrate and nitrite.

Denitrifying bacteria in soil generate nitric oxide (NO) from nitrite as a part of the nitrogen cycle, but little is known about NO production by commensal bacteria. We used a chemiluminescence assay to explore if human faeces and different representative gut bacteria are able to generate NO. Bacteria were incubated anaerobically in gas-tight bags, with or without nitrate or nitrite in the growth medium. In addition, luminal NO levels were measured in vivo in the intestines in germ-free and conventional rats, and in rats mono-associated with lactobacilli. We show that human faeces can generate NO after nitrate or nitrite supplementation. Lactobacilli and bifidobacteria generated much NO from nitrite, but only a few of the tested strains produced NO from nitrate and at much lower levels. In contrast, Escherichia coli, Bacteroides thetaiotaomicron, and Clostridium difficile did not produce significant amounts of NO either with nitrate or nitrite. NO generation in the gut lumen was also observed in vivo in conventional rats but not in germ-free rats or in rats mono-associated with lactobacilli. We conclude that NO can be generated by the anaerobic gut flora in the presence of nitrate or nitrite. Future studies will reveal its biological significance in regulation of gastrointestinal integrity.

Birth-related increase in intracolonic hydrogen gas and nitric oxide as indicator of host-microbial interactions.

BACKGROUND: Bacterial colonization of the intestine early in life might have implications for allergy development. We studied early host-bacterial interactions in the gut by simultaneous measurements of hydrogen gas (H(2)) and faecal short chain fatty acid pattern (SCFAs), i.e. bacterial products, as well as of nitric oxide (NO), a marker of mucosal immune activation. METHODS: A novel minimally invasive technique was used for repeated measurements of luminal colonic H(2) and NO in 32 healthy newborn infants delivered vaginally or by Caesarean section. Luminal gas was sampled and analysed at five occasions: immediately after birth, day 1, days 3-5, 1 and 5-6 months after birth. RESULTS: Colonic H(2), NO and faecal SCFAs were undetectable at birth. The H(2) and SCFAs appeared within 24 h and continued to increase during the 6 months follow-up. Nitric oxide remained very low until 3-5 days after birth at which time it markedly increased. In some apparently healthy infants NO transiently reached levels similar to those seen in adults with inflammatory bowel disease. CONCLUSION: Intracolonic measurements of H(2) and NO may be useful to monitor the developmental colonization process as well as mucosal responses.

Exhaled nitric oxide before and after cardiac surgery with cardiopulmonary bypass--response to acetylcholine and nitroglycerin.

BACKGROUND: Pulmonary endothelial dysfunction may occur after ischaemia-reperfusion injury and can be revealed as a reduced vasodilatory response upon administration of acetylcholine (ACh). ACh also releases the endothelium-derived vasodilator nitric oxide but direct measurements of this gas are difficult to perform in vivo. We wanted to study the effects of i.v. administration of ACh and the endothelium-independent vasodilator nitroglycerin on exhaled nitric oxide in relation to pulmonary endothelial dysfunction after open-heart surgery and cardiopulmonary bypass (CPB). METHODS: Basal exhaled nitric oxide and the response in exhaled nitric oxide to i.v. injections of ACh and nitroglycerin were measured with chemiluminescence in 10 patients before and after open-heart surgery. RESULTS: Exhaled nitric oxide decreased significantly after CPB. I.V. bolus injections of ACh induced a reproducible and dose-dependent increase in exhaled nitric oxide that was unaltered after CPB. In contrast, the increase in exhaled nitric oxide evoked by nitroglycerin was attenuated after CPB. The response in pulmonary vascular resistance index (PVRI) to an infusion of ACh decreased after CPB, indicating endothelial dysfunction. The decrease in PVRI response to ACh correlated to the duration of CPB. CONCLUSIONS: Interestingly, pulmonary vascular dysfunction after CPB was accompanied by a reduction in the exhaled nitric oxide response to nitroglycerin and lower levels of basal exhaled nitric oxide. The ACh-induced responses in exhaled nitric oxide were unchanged, which could indicate nitric oxide-independent mechanisms behind the endothelial dysfunction in this study. The possibility of using exhaled nitric oxide dynamics to investigate pulmonary endothelial dysfunction merits further studies.

Humming-induced release of nasal nitric oxide for assessment of sinus obstruction in allergic rhinitis: pilot study.

BACKGROUND: Humming greatly increases nasal nitric oxide (NO) in healthy people by causing a rapid washout of NO from the sinuses. This increase is abolished in patients with complete sinus ostial obstruction. OBJECTIVE: Allergic rhinitis is a risk factor for development of sinusitis and we wanted to study whether nasal NO measurement during humming could be used to detect sinus abnormalities in this disorder. METHODS: Fifty-nine consecutive subjects with mild to moderate allergic rhinitis were studied. Their present nasal symptoms were recorded. Then NO levels were measured by chemiluminescence during quiet single-breath nasal exhalations and humming exhalations at a fixed exhalation flow of 0.2 L s(-1). Based on the NO results the patients were divided into two groups: those with a great increase in nasal NO during humming (humming responders, n = 46) and those without a significant increase (humming nonresponders, n = 13). In 11 of the nonresponders and in 22 of the responders the passage to the osteomeatal complex area was assessed and scored by nasal endoscopy. This was carried out by an oto-rhino-laryngologist unaware of the NO results. RESULTS: Among the nonresponders nine of 11 patients (80%) had endoscopic signs of bilateral sinus obstruction, compared with one of the 22 (< 5%) humming responders. Baseline nasal symptom score and NO levels during quiet exhalation were not significantly different between the groups CONCLUSION: Absence of a nasal NO peak during humming is associated with endoscopic findings suggestive of sinus ostial obstruction in subjects with allergic rhinitis. Measurement of nasal NO during humming may be a simple method to detect sinus abnormalities in these patients.

Effect of intravenous L-NMMA on nitric oxide production in collagenous colitis.

BACKGROUND: Nitric oxide (NO) is greatly increased in the colon of patients with inflammatory bowel disease of different aetiology, including collagenous colitis. In man, NO can be generated from NO synthases as well as from non-enzymatic sources. The source of the NO found in luminal intestinal gas has not been exactly pinpointed. We investigated the effect of the NO synthase inhibitor L-NMMA on intestinal concentrations of NO in patients with clinically active collagenous colitis. In addition, we measured NO levels from the respiratory tract. METHODS: Ten patients with active collagenous colitis were studied. NO levels were measured from the respiratory tract and in the rectum before and after i.v. administration of L-NMMA (7.5 mg/kg) using a chemiluminescence method. RESULTS: Airway NO release decreased markedly, and mean arterial blood pressure increased in all patients following L-NMMA treatment. Basal rectal NO levels were high (median > 10000 ppb) and decreased markedly in 5 patients after L-NMMA. In contrast, NO levels remained completely unchanged or even increased in the other 5 patients. CONCLUSION: Rectal levels of NO are greatly increased in patients with symptomatic collagenous colitis. Intravenous administration of an NO synthase inhibitor reduced rectal NO only in half of the patients despite clear evidence of effective systemic NO synthase inhibition. This could indicate alternative NOS-independent sources of intestinal NO in this disease.

Complement activation, endothelin-1 and neuropeptide Y in relation to the cardiovascular response to endotoxin-induced systemic inflammation in healthy volunteers.

BACKGROUND: Endotoxin is a major stimulus for triggering the host response in septicaemia. The pathophysiology of sepsis involves activation of the vascular endothelium and leukocytes, resulting in the release of various mediators, e.g. cytokines, nitric oxide (NO), endothelin (ET-1) and complement factors. We evaluated the blood levels of complement activation, ET-1 and neuropeptide Y (NPY) in parallel with the haemodynamic and oxygen transport response during human experimental endotoxemia. METHODS: Eleven healthy men had venous, arterial and pulmonary arterial catheters placed for continuous haemodynamic measuring. After 30 min rest endotoxin (E. Coli 4 ng kg(-1), Lot G1) was intravenously administered. Blood samples from pulmonary and arterial catheters were collected hourly over 4 h. RESULTS: Body temperature augmented significantly from baseline values (36.7 +/- 0.7 degrees C, mean +/- SEM) with a maximum after 3.5 h (39.1 +/- 0.3 degrees C, P < 0.001). Cardiac output increased by 100%, systemic vascular resistance decreased by 50%, the oxygen consumption and the tissue oxygen transport increased. Activation of the complement system was indicated by an increase in SC5b-9. Endothelin-1-like immunoreactivity (ET-1-LI) increased over time in arterial blood. NPY-like immunoreactivity (NPY-LI) did not change over time. CONCLUSION: A dose of endotoxin associated with reproducible systemic vasodilation and fever in healthy subjects causes complement activation and increased systemic levels of ET-1-LI, illustrating that the model is a useful tool for inducing moderate systemic inflammation where several mediator systems are activated.

Nasal nitric oxide measurements before and after repeated humming maneuvers.

BACKGROUND: It has been recently shown that humming greatly increases nasal nitric oxide (NO). This is most likely owing to a rapid washout of sinus NO caused by the oscillating sound waves. During repeated humming manoeuvres nasal NO gradually decreases, likely because NO accumulated in the sinuses is washed out. AIM: We studied whether humming before measurements would affect nasally exhaled NO. MATERIALS AND METHODS: NO output was measured by the chemiluminescence technique in orally and nasally exhaled air in 38 subjects: 18 healthy subjects (HS), 15 subjects with allergic rhinitis (AR) and five subjects with allergic nasal polyposis (AP). Each subject performed a NO measurement during quiet nasal exhalation either preceded by a period of silence/free speaking or immediately after five consecutive humming manoeuvres (posthumming). RESULTS: Mean nasal NO output (95% CI) after a period of silence/free speaking was 231 nL min-1 (178-284) in HS, 434 nL min-1 (347-522) in AR (P < 0.001) and 262 nL min-1 (163-361) in AP. Post-humming nasal NO output was 16% (5 to 50%) lower in HS and 14% (1 to 49%) lower in AR, while it remained unchanged in AP subjects. Intra-subject coefficient of variation of quiet nasal exhalation was 12% in HS, 13% in AR and 5% in AP. Post humming intraindividual coefficient of variation significantly decreased in both HS and AR, but it did not change in AP. CONCLUSIONS: Nasal NO levels measured immediately after repeated humming manoeuvres are consistently lower and more reproducible than nasal NO levels measured after a period of silence or free speaking. Repeated humming effectively empties the sinuses, thereby probably minimizing the normal contribution from the sinuses to nasal NO. This may be useful to better estimate NO output from the nasal cavity mucosa in health and disease.

In vitro evaluation of a new treatment for urinary tract infections caused by nitrate-reducing bacteria.

Dietary and endogenous nitrates are excreted in urine, and during infection with nitrate-reducing bacteria they are reduced to nitrite. At a low pH nitrite is converted to a variety of nitrogen oxides that are toxic to bacteria. We hypothesized that acidification of nitrite-rich infected urine would result in the killing of the nitrate-reducing bacteria. An Escherichia coli control strain and a mutant lacking nitrate reductase activity were preincubated in urine supplemented with sodium nitrate (0 to 10 mM) at pH 7.0. Then, the nitrite-containing bacterial culture was transferred (and diluted 1/10) to slightly acidic urine (pH 5 and 5.5) containing ascorbic acid (10 mM) and growth was monitored. The control strain produced nitrite in amounts related to the amount of nitrate added. This strain was killed when the culture was transferred to acidic urine. In contrast, the mutant that did not produce nitrite retained full viability. When control bacteria were grown in acidic urine with nitrate and ascorbic acid present from the start of the experiment, no inhibition of growth was noted. The MICs and minimal bactericidal concentrations of sodium nitrite-ascorbic acid in acidic urine were comparable to those of conventional antibiotics. Preincubation of nitrate-reducing E. coli in nitrate-rich urine leads to the accumulation of nitrite. Subsequent acidification of the urine results in generation of nitrogen oxides that are bactericidal. Killing, however, requires a sequential procedure in which the bacteria are first allowed to grow in a nitrate-rich neutral environment, later followed by acidification. We speculate that ingestion of nitrate followed some hours later by acidification of urine could be a new therapeutic strategy for the treatment of urinary tract infections.

Assessment of nasal and sinus nitric oxide output using single-breath humming exhalations.

Nasal nitric oxide (NO) levels increase greatly during humming compared to silent exhalation. In this study, the physiological and anatomical factors that regulate NO release during humming have been characterised in 10 healthy subjects and in a model of the sinus and the nose. Single-breath humming caused a large initial peak in nasal NO output, followed by a progressive decline. The NO peak decreased in a step-wise manner during repeated consecutive humming manoeuvres but recovered completely after a silent period of 3 min. Topical nasal application of an NO synthase inhibitor reduced nasal NO by >50% but had no effect on the increase evoked by humming. Silently exhaled nasal NO measured immediately after repeated humming manoeuvres was between 5-50% lower than basal silent NO exhalation, suggesting variable continuous contribution from the sinuses to nasal NO. Among the factors known to influence normal sinus ventilation, ostium size was the most critical during humming, but humming frequency was also of importance. In conclusion, humming results in a large increase in nasal nitric oxide, which is caused by a rapid gas exchange in the paranasal sinuses. Combined nasal nitric oxide measurement with and without humming could be of use to estimate sinus ventilation and to better separate nasal mucosal nitric oxide output from sinus nitric oxide in health and disease.