Pulmonary nitric oxide in astronauts before and during long-term spaceflight.

Introduction: During exploratory space flights astronauts risk exposure to toxic planetary dust. Exhaled nitric oxide partial pressure (PENO) is a simple method to monitor lung health by detecting airway inflammation after dust inhalation. The turnover of NO in the lungs is dependent on several factors which will be altered during planetary exploration such as gravity (G) and gas density. To investigate the impacts of these factors on normal PENO, we took measurements before and during a stay at the International Space Station, at both normal and reduced atmospheric pressures. We expected stable PENO levels during the preflight and inflight periods, with lower values inflight. With reduced pressure we expected no net changes of PENO. Material and methods: Ten astronauts were studied during the pre-flight (1 G) and inflight (µG) periods at normal pressure [1.0 ata (atmospheres absolute)], with six of them also monitored at reduced (0.7 ata) pressure and gas density. The average observation period was from 191 days before launch until 105 days after launch. PENO was measured together with estimates of alveolar NO and the airway contribution to the exhaled NO flux. Results: The levels of PENO at 50 mL/s (PENO50) were not stable during the preflight and inflight periods respectively but decreased with time (p = 0.0284) at a rate of 0.55 (0.24) [mean (SD)] mPa per 180 days throughout the observation period, so that there was a significant difference (p < 0.01, N = 10) between gravity conditions. Thus, PENO50 averaged 2.28 (0.70) mPa at 1 G and 1.65 (0.51) mPa during µG (-27%). Reduced atmospheric pressure had no net impact on PENO50 but increased the airway contribution to exhaled NO. Discussion: The time courses of PENO50 suggest an initial airway inflammation, which gradually subsided. Our previous hypothesis of an increased uptake of NO to the blood by means of an expanded gas-blood interface in µG leading to decreased PENO50 is neither supported nor contradicted by the present findings. Baseline PENO50 values for lung health monitoring in astronauts should be obtained not only on ground but also during the relevant gravity conditions and before the possibility of inhaling toxic planetary dust.

Treatment with new organic nitrites in pulmonary hypertension of acute experimental pulmonary embolism.

Acute pulmonary embolism may cause right heart failure due to increased pulmonary vascular resistance and arterial hypoxemia. Effective vasodilator therapy of the pulmonary hypertension is highly needed. Therefore, we investigated the effects of a newly developed effective pulmonary vasodilator, the organic mononitrites of 1,2-propanediol (PDNO), in a rabbit model of acute pulmonary embolism. In anesthetized and ventilated rabbits, systemic and pulmonary hemodynamics, exhaled nitric oxide (NO), plasma nitrite concentration, and blood gases were monitored. First, dose-response experiments with intravenous and left heart ventricle infusions of PDNO and inorganic nitrite were done in naive animals and in pulmonary hypertension induced by a thromboxane A2 analogue. Second, acute pulmonary embolism was induced and either PDNO or placebo were administered intravenously within 20 minutes and evaluated within 1 hour after pulmonary embolization. PDNO intravenously, in contrast to inorganic nitrite intravenously, increased exhaled NO and counteracted pulmonary hypertension and vasodilated the systemic circulation, dose-dependently, thereby showing efficient NO donation. Pulmonary embolization induced pulmonary hypertension and gas exchange disturbances. PDNO significantly decreased and normalized pulmonary vascular resistance and the right ventricle rate-pressure product, without causing tolerance, with no significant side effects on the systemic circulation, nor on blood-gas values or on methemoglobin formation. In conclusion, PDNO is a NO donor and an efficient vasodilator in the pulmonary circulation. Treatment with this or similar organic nitrites intravenously may be a future option to avoid right heart failure in life-threatening acute pulmonary embolism.

Organic mononitrites of 1,2-propanediol act as an effective NO-releasing vasodilator in pulmonary hypertension and exhibit no cross-tolerance with nitroglycerin in anesthetized pigs.

PURPOSE: Clinically available intravenous (IV) nitric oxide (NO) donor drugs such as nitroglycerin (GTN) cause systemic hypotension and/or tolerance development. In a porcine model, novel NO donor compounds - the organic mononitrites of 1,2-propanediol (PDNO) - were compared to GTN with regard to pulmonary selectivity and tolerance development. The vasodilatory effects of inorganic nitrite were investigated. MATERIALS AND METHODS: In anesthetized piglets, central hemodynamics were monitored. At normal pulmonary vascular resistance (PVR), IV infusions of PDNO (15-60 nmol kg-1 min-1), GTN (13-132 nmol kg-1 min-1), and inorganic nitrite (dosed as PDNO) were administered. At increased PVR (by U46619 IV), IV infusions of PDNO (60-240 nmol kg-1 min-1) and GTN (75-300 nmol kg-1 min-1) before and after a 5 h infusion of GTN (45 nmol kg-1 min-1) were given. RESULTS: At normal PVR, PDNO (n=12) and GTN (n=7) caused significant dose-dependent decreases in mean systemic and pulmonary arterial pressures, whereas inorganic nitrite (n=13) had no significant effect. At increased PVR, PDNO (n=6) and GTN (n=6) significantly decreased mean systemic and pulmonary pressures and resistances, but only PDNO reduced the ratio between pulmonary and systemic vascular resistances significantly. After the 5 h GTN infusion, the hemodynamic response to GTN infusions (n=6) was significantly suppressed, whereas PDNO (n=6) produced similar hemodynamic effects to those observed before the GTN infusion. CONCLUSION: PDNO is a vasodilator with selectivity for pulmonary circulation exhibiting no cross-tolerance to GTN, but GTN causes non selective vasodilatation with substantial tolerance development in the pulmonary and systemic circulations. Inorganic nitrite has no vasodilatory properties at relevant doses.

The novel nitric oxide donor PDNO attenuates ovine ischemia-reperfusion induced renal failure.

BACKGROUND: Renal ischemia-reperfusion injury is a common cause of acute kidney injury in intensive care and surgery. Recently, novel organic mononitrites of 1,2-propanediol (PDNO) were synthesized and shown to rapidly and controllably deploy nitric oxide in the circulation when administered intravenously. We hypothesized that intravenous infusion of PDNO during renal ischemia reperfusion would improve post-ischemic renal function and microcirculation. METHODS: Sixteen sheep were anesthetized, mechanically ventilated, and surgically instrumented. The left renal artery was clamped for 90 min, and the effects of ischemia were studied for a total of 8 h. Fifteen minutes prior to the release of the clamp, intravenous infusions of PDNO (n = 8) or vehicle (1,2 propanediol + inorganic nitrite, n = 8) were initiated (180 nmol/kg/min for 30 min, thereafter 60 nmol/kg/min for the remainder of the experiment). RESULTS: Renal artery blood flow, cortical and medullary perfusion, and diuresis and creatinine clearance decreased in the left kidney post ischemia. However, in the sheep treated with PDNO, diuresis and creatinine clearance in the left kidney were significantly higher post ischemia compared to vehicle-treated animals (1.7 ± 0.5 vs 0.7 ± 0.3 ml/kg/h, p = 0.04 and 7.5 ± 2.1 vs 1.7 ± 0.6 ml/min, p = 0.02, respectively). Left renal medullary perfusion and oxygen uptake were higher in the PDNO group (73 ± 9 vs 37 ± 5% of baseline, p = 0.004 and 2.6 ± 0.4 vs 1.6 ± 0.3 ml/min, p = 0.02, respectively). PDNO significantly increased renal oxygen consumption and reduced the oxygen utilization for sodium reabsorption (p = 0.03 for both). Mean arterial blood pressure was significantly reduced by PDNO (83 ± 3 vs 94 ± 3 mmHg, p = 0.02) but was still within normal limits. Total renal blood flow was not affected, and there were no signs of increased blood methemoglobin concentrations or tachyphylaxis. CONCLUSIONS: The novel nitric oxide donor PDNO improved renal function after ischemia. PDNO also prevented the persistent reduction in medullary perfusion during reperfusion and improved renal oxygen utilization without severe side effects.

Antidiabetic and gastric emptying inhibitory effect of herbal Melia azedarach leaf extract in rodent models of diabetes type 2 mellitus.

Diabetes type 2 is associated with impaired insulin production and increased insulin resistance. Treatment with antidiabetic drugs and insulin strives for normalizing glucose homeostasis. In Ethiopian traditional medicine, plant extracts of Melia azedarach are used to control diabetes mellitus and various gastrointestinal disorders. The objective of this study was to clarify the antidiabetic effects of M. azedarach leaf extracts in diabetic type 2 experimental animals. In this study, mice were injected with Melia extract intraperitoneally. Plasma glucose was studied by using tail vein sampling in acute experiments over 4 h and chronic experiments over 21 days with concurrent insulin and body weight assessments. Glucose tolerance was studied by using intraperitoneal glucose (2 mg/g) tolerance test over 120 min. Gastric emptying of a metabolically inert meal was studied by the gastric retention of a radioactive marker over 20 min. Melia extracts displayed acute, dose-dependent antidiabetic effects in ob/ob mice similar to glibenclamide (p<0.05-0.001). Long-term administration of Melia extract reduced plasma glucose (p<0.001) and insulin (p<0.01-0.001) levels over 21 days, concurrent with body weight loss. Glucose tolerance test showed reduced basal glucose levels (p<0.05-0.01), but no difference was found in glucose disposal after long-term treatment with Melia extract. In addition, the Melia extract at 400 mg/kg slowed gastric emptying rate of normal Sprague-Dawley (p<0.001) and diabetic Goto-Kakizaki rats (p<0.001) compared with controls. It is concluded that the M. azedarach leaf extract elicits diabetic activity through a multitargeted action. Primarily an increased insulin-sensitizing effect is at hand, resulting in blood glucose reduction and improved peripheral glucose disposal, but also through reduced gastric emptying and decreased insulin demand.

Inhibitory Effects of Urothelium-related Factors.

The urothelium of the bladder has long been recognized as a protective barrier between detrusor and urine. In recent years, it has become more evident that the urothelium plays a role as an active source of mediators. The urothelium can release neurotransmitters and modulators such as acetylcholine, ATP, nitric oxide, prostaglandins and neuropeptides. They exert both excitatory and inhibitory effects in modulating urinary tract motility. In addition, several studies have reported the existence of an urothelium-derived unknown inhibitory factor in the urinary bladder. By the use of a new serial cascade superfusion bioassay on guinea pig ureter, recent studies confirm that the guinea pig bladder urothelium releases a substance with inhibitory bioactivity, which was resistant to treatment with nitric oxide synthase inhibitor and cyclooxygenase inhibitor and to adenosine A1/A2 receptor blockade. Lately, a marked and quickly inactivated novel release of PGD2 from the bladder urothelium was discovered, together with localization of prostaglandin D synthase therein. PGD2 was found to have an inhibitory influence on nerve-induced contractions in guinea pig urinary bladder and on spontaneous contractions in the out-flow region. An altered release of excitatory and inhibitory factors is likely to play an important part in bladder motility disturbances, of which the prostanoids are a notable group. Due to the fact that the bladder is relaxed 99% of the time, not only excitatory mechanisms in the bladder are necessary to study, but also inhibitory mechanisms need considerable attention, which will contribute to the discovery of new targets to treat bladder motility disorders.

Prostaglandin D2 effects and DP1 /DP2 receptor distribution in guinea pig urinary bladder out-flow region.

The proximal urethra and urinary bladder trigone play important roles in continence. We have previously shown that PGD2 is released from guinea pig bladder urothelium/suburothelium and can inhibit detrusor contractile responses. We presently wished to investigate PGD2 actions in guinea pig out-flow region and the distribution of DP1 /DP2 receptors. The effects of PGD2 on urothelium-intact trigone and proximal urethra contractility were studied in organ bath experiments. Expression of DP1 /DP2 receptor proteins was analysed by western blot. Immunohistochemistry was used to identify distribution of DP1 /DP2 receptors. PGD2 in a dose-dependent manner inhibited trigone contractions induced by electrical field stimulation (EFS) and inhibited spontaneous contractions of the proximal urethra. PGD2 was equally (trigone) or slightly less potent (urethra) compared with PGE2 . Expression of DP1 and DP2 receptors was found in male guinea pig bladder trigone, neck and proximal urethra. In the trigone and proximal urethra, DP1 receptors were found on the membrane of smooth muscle cells and weak immunoreactivty was observed in the urothelium. DP2 receptors were distributed more widespread, weakly and evenly in the urothelium and smooth muscles. Inhibitory effects by PGD2 on motor activity of guinea pig trigone and proximal urethra are consistent with finding DP1 and DP2 receptors located in the urothelium and smooth muscle cells of the trigone and proximal urethra, and PGD2 may therefore be a modulator of the bladder out-flow region, possibly having a function in regulation of micturition and a role in overactive bladder syndrome.

Receptors involved in the modulation of guinea pig urinary bladder motility by prostaglandin D2.

BACKGROUND AND PURPOSE: We have described a urothelium-dependent release of PGD2 -like activity which had inhibitory effects on the motility of guinea pig urinary bladder. Here, we have pharmacologically characterized the receptors involved and localized the sites of PGD2 formation and of its receptors. EXPERIMENTAL APPROACH: In the presence of selective DP and TP receptor antagonists alone or combined, PGD2 was applied to urothelium-denuded diclofenac-treated urinary bladder strips mounted in organ baths. Antibodies against PGD2 synthase and DP1 receptors were used with Western blots and for histochemistry. KEY RESULTS: PGD2 inhibited nerve stimulation -induced contractions in strips of guinea pig urinary bladder with estimated pIC50 of 7.55 ± 0.15 (n = 13), an effect blocked by the DP1 receptor antagonist BW-A868C. After blockade of DP1 receptors, PGD2 enhanced the contractions, an effect abolished by the TP receptor antagonist SQ-29548. Histochemistry revealed strong immunoreactivity for PGD synthase in the urothelium/suburothelium with strongest reaction in the suburothelium. Immunoreactive DP1 receptors were found in the smooth muscle of the bladder wall with a dominant localization to smooth muscle membranes. CONCLUSIONS AND IMPLICATIONS: In guinea pig urinary bladder, the main effect of PGD2 is an inhibitory action via DP1 receptors localized to the smooth muscle, but an excitatory effect via TP receptors can also be evoked. The urothelium with its suburothelium might signal to the smooth muscle which is rich in PGD2 receptors of the DP1 type. The results are important for our understanding of regulation of bladder motility.

Release and inhibitory effects of prostaglandin D2 in guinea pig urinary bladder and the role of urothelium.

BACKGROUND: While studying a urothelium-derived inhibitory factor in guinea pig urinary bladders we observed considerable release of prostanoids, including PGD2-like activity. The present study was carried out to identify the prostanoids and to study their roles in modulating guinea pig urinary bladder motility. METHODS: Release of PGE2 and PGD2 in isolated guinea pig urinary bladder preparations was analyzed by high performance liquid chromatography (HPLC) combined with bioassay on bladder strips. Isolated urothelium-intact (UI) or -denuded (UD) bladder strips were subjected to electrical field stimulation (EFS) and applications of PGE2 and PGD2. RESULTS: A resting release of 95±9 (n=5) nggtissue(-1)h(-1) PGE2-like activity and 210±34 (n=4) nggtissue(-1)h(-1) PGD2-like activity was found, where PGD2-like was subject to marked spontaneous inactivation during isolation. Prostanoids release was decreased by 70-90% by the cyclo-oxygenase inhibitor diclofenac in UI preparations. Urothelium removal decreased prostanoids release by more than 90%. PGE2 increased basal tone and spontaneous contractions, whereas PGD2 had little or no effect on these. Exogenous PGE2 enhanced and PGD2 inhibited contractile responses to EFS, exogenous acetylcholine- and ATP, whereas PGD2 caused marked dose-dependent inhibition. PGE2 and PGD2 effects were more pronounced in diclofenac-treated UD tissues. CONCLUSIONS: PGD2 and PGE2 are released from guinea pig bladder urothelium and PGD2 has inhibitory effects on bladder motility, mainly through a postjunctional action on smooth muscle responsiveness. GENERAL SIGNIFICANCE: The release and inhibitory effects merit further studies in relation to normal biological function as well as overactive bladder syndrome.

Cascade bioassay evidence for the existence of urothelium-derived inhibitory factor in Guinea pig urinary bladder.

Our aim was to investigate whether guinea pig urothelium-derived bioactivities compatible with the existence of urothelium-derived inhibitory factor could be demonstrated by in vitro serial bioassay and whether purinergic P1 receptor agonists, nitric oxide, nitrite or prostaglandins might explain observed activities. In a cascade superfusion system, urothelium-denuded guinea pig ureters were used as bioassay tissues, recording their spontaneous rhythmic contractions in presence of scopolamine. Urothelium-intact or -denuded guinea pig urinary bladders were used as donor tissues, stimulated by intermittent application of carbachol before or during the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), the adenosine/P1 nucleoside receptor antagonist 8-(p-sulfophenyl)theophylline (8-PST) or the cyclo-oxygenase inhibitor diclofenac infused to bath donor and bioassay tissues. The spontaneous contractions of bioassay ureters were unaltered by application of carbachol 1-5 µM in the presence of scopolamine 5-30 µM. When carbachol was applied over the urothelium-denuded bladder, the assay ureter contraction rate was unaltered. Introducing carbachol over the everted urothelium-intact bladder significantly inhibited the contraction frequency of the assay ureter, suggesting the transfer of an inhibitory activity from the bladder to the assay ureter. The transmissible inhibitory activity was not markedly antagonized by L-NAME, 8-PST or diclofenac, while L-NAME nearly abolished nitrite release from the urothelium-intact bladder preparations. We suggest that urothelium-derived inhibitory factor is a transmissible entity over a significant distance as demonstrated in this novel cascade superfusion assay and seems less likely to be nitric oxide, nitrite, an adenosine receptor agonist or subject to inhibition by administration of a cyclo-oxygenase inhibitor.

Lung diffusing capacity for nitric oxide at lowered and raised ambient pressures.

Lung diffusing capacity for NO (DLNO) was determined in eight subjects at ambient pressures of 505, 1015, and 4053hPa (379, 761 and 3040mmHg) as they breathed normoxic gases. Mean values were 116.9±11.1 (SEM), 113.4±11.1 and 99.3±10.1mlmin(-1)hPa(-1)at 505, 1015, and 4053hPa, with a 13% difference between the two higher pressures (P=0.017). The data were applied to a model with two serially coupled conductances; the gas phase (DgNO, variable with pressure), and the alveolo-capillary membrane (DmNO, constant). The data fitted the model well and we conclude that diffusive transport of NO in the peripheral lung is inversely related to gas density. At normal pressure DmNO was approximately 5% larger than DLNO, suggesting that the Dg factor then is not negligible. We also conclude that the density of the breathing gas is likely to impact the backdiffusion of naturally formed NO from conducting airways to the alveoli.

Effects of ambient pressure on pulmonary nitric oxide.

Airway nitric oxide (NO) has been proposed to play a role in the development of high-altitude pulmonary edema. We undertook a study of the effects of acute changes of ambient pressure on exhaled and alveolar NO in the range 0.5-4 atmospheres absolute (ATA, 379-3,040 mmHg) in eight healthy subjects breathing normoxic nitrogen-oxygen mixtures. On the basis of previous work with inhalation of low-density helium-oxygen gas, we expected facilitated backdiffusion and lowered exhaled NO at 0.5 ATA and the opposite at 4 ATA. Instead, the exhaled NO partial pressure (Pe(NO)) did not differ between pressures and averaged 1.21 ± 0.16 (SE) mPa across pressures. As a consequence, exhaled NO fractions varied inversely with pressure. Alveolar estimates of the NO partial pressure differed between pressures and averaged 88 (P = 0.04) and 176 (P = 0.009) percent of control (1 ATA) at 0.5 and 4 ATA, respectively. The airway contribution to exhaled NO was reduced to 79% of control (P = 0.009) at 4 ATA. Our finding of the same Pe(NO) at 0.5 and 1 ATA is at variance with previous findings of a reduced Pe(NO) with inhalation of low-density gas at normal pressure, and this discrepancy may be due to the much longer durations of low-density gas breathing in the present study compared with previous studies with helium-oxygen breathing. The present data are compatible with the notion of an enhanced convective backtransport of NO, compensating for attenuated backdiffusion of NO with increasing pressure. An alternative interpretation is a pressure-induced suppression of NO formation in the airways.

Formation of new bioactive organic nitrites and their identification with gas chromatography-mass spectrometry and liquid chromatography coupled to nitrite reduction.

Nitric oxide (NO) donors, notably organic nitrates and nitrites are used therapeutically but tolerance develops rapidly, making the use of e.g. nitroglycerin difficult. NO donation in the pulmonary vascular bed might be useful in critically ill patients. Organic nitrites are not associated with tachyphylaxis but may induce methaemoglobinemia and systemic hypotension which might hamper their use. We hypothesised that new lung-selective NO donors can be identified by utilizing exhaled NO as measure for pulmonary NO donation and systemic arterial pressure to monitor hypotension and tolerance development. Solutions of alcohols and carbohydrates were reacted with NO gas and administered to ventilated rabbits for evaluation of in vivo NO donation. Chemical characterization was made by liquid chromatography with on-line nitrite reduction (LC-NO) and by gas chromatography-mass spectrometry (GC-MS). In vivo experiments showed that the hydroxyl-containing compounds treated with NO gas yielded potent NO donors, via nitrosylation to organic nitrites. Analyses by LC-NO showed that the reaction products were able to release NO in vitro. In GC-MS the reaction products were determined to be the organic nitrites, where some are new chemical entities. Non-polar donors preferentially increased exhaled NO with less effect on systemic blood pressure whereas more polar molecules had larger effects on systemic blood pressure and less on exhaled NO. We conclude that new organic nitrites suitable for intravenous administration are produced by reacting NO gas and certain hydroxyl-containing compounds in aqueous solutions. Selectivity of different organic nitrites towards the pulmonary and systemic circulation, respectively, may be determined by molecular polarity.

Microgravity decreases and hypergravity increases exhaled nitric oxide.

Inhalation of toxic dust during planetary space missions may cause airway inflammation, which can be monitored with exhaled nitric oxide (NO). Gravity will differ from earth, and we hypothesized that gravity changes would influence exhaled NO by altering lung diffusing capacity and alveolar uptake of NO. Five subjects were studied during microgravity aboard the International Space Station, and 10 subjects were studied during hypergravity in a human centrifuge. Exhaled NO concentrations were measured during flows of 50 (all gravity conditions), 100, 200, and 500 ml/s (hypergravity). During microgravity, exhaled NO fell from a ground control value of 12.3 +/- 4.7 parts/billion (mean +/- SD) to 6.6 +/- 4.4 parts/billion (P = 0.016). In the centrifuge experiments and at the same flow, exhaled NO values were 16.0 +/- 4.3, 19.5 +/- 5.1, and 18.6 +/- 4.7 parts/billion at one, two, and three times normal gravity, where exhaled NO in hypergravity was significantly elevated compared with normal gravity (P

Brain-derived neurotrophic factor enhances histamine-induced airway responses and changes levels of exhaled nitric oxide in guinea pigs in vivo.

The neurotrophin brain-derived neurotrophic factor (BDNF) occurs in elevated levels during airway inflammation, including asthma and hypoxic lung injury, and has been suggested to be associated with airway hyperresponsiveness in these conditions. The aim of the present study was to examine whether airway responses to histamine challenge and levels of exhaled nitric oxide (NO) in vivo might be altered upon BDNF treatment. Pulmonary resistance, lung compliance, insufflation pressure, and levels of exhaled NO were measured in anaesthetized guinea pigs exposed to BDNF prior to challenge with histamine and with intact or inhibited endogenous NO production. BDNF pretreatment significantly enhanced histamine-evoked increase in pulmonary resistance and insufflation pressure, as well as the decrease in lung compliance. BDNF markedly accentuated the reduction in exhaled NO following histamine challenge. In animals with inhibited endogenous NO production BDNF induced a significantly earlier histamine-evoked increase in airway responses. The present data show that BDNF can induce an augmentation of histamine-evoked airway responses and reduce levels of NO in exhaled air in vivo. Endogenous NO seems to exert a braking action on BDNF-induced enhancement of airway responses and a reduced ability to release NO may be one mechanism for increased airway response during elevated BDNF levels. Taken together this indicates that BDNF may be of importance for airway hyperresponsiveness in vivo. The interaction between BDNF and airway NO formation, and its relation to airway responses, merit further investigation.

Nerve growth factor enhances neurokinin A-induced airway responses and exhaled nitric oxide via a histamine-dependent mechanism.

The neurotrophin nerve growth factor (NGF) is elevated in serum and locally in the lung in asthmatics and has been suggested to evoke airway hyperresponsiveness. The aim of this study was to explore mechanisms behind NGF-evoked changes in airway responsiveness. We studied if NGF could evoke increased airway responsiveness to tachykinins, such as neurokinin A (NKA), in a similar way as for histamine and, if so, whether an NGF-evoked increase in NKA airway responsiveness could involve a histamine receptor-dependent mechanism. Contractile responses to cumulative doses of histamine or NKA were studied in guinea-pig tracheal rings in vitro in organ baths. Furthermore, insufflation pressure (IP), pulmonary resistance, lung compliance and exhaled NO (FeNO) were measured in vivo in anaesthetised guinea-pigs challenged with histamine or NKA. NGF pre-treatment in vitro increased the contractile response evoked by histamine, but not by NKA, in tracheal rings. NGF pre-treatment in vivo increased IP, pulmonary resistance and levels of FeNO, and further decreased lung compliance, upon histamine and NKA challenge. The NGF-evoked enhancement of IP, pulmonary resistance, lung compliance as well as FeNO in response to NKA was reversed by the histamine receptor antagonist mepyramine. We suggest that NGF can induce an increase in tachykinin-evoked airway responses and NO formation via a histamine receptor-dependent pathway. This points to an important role for the mast cell in neurotrophin-evoked airway hyperresponsiveness and changes in exhaled NO.

Transdermally administered nitric oxide by application of acidified nitrite increases blood flow in rat epigastric island skin flaps.

Surgical flaps are commonly used in the reconstruction of tissue defects after tumour surgery and trauma. Flap failure continues to be a clinical problem and the underlying causes are not fully understood. In the present study a system that generates nitric oxide (NO) in a non-enzymatic fashion was created through the acidification with vitamin C of a cream containing increasing concentrations (0.125%, 0.25%, 0.5%, 1.25% and 2.5%) of nitrite (NO(2)(-)). The cream was applied for 30 min to a modified epigastric island skin flap in the rat. Blood flow in the supplying artery was measured by transit-time ultrasound flowmetry throughout the experiment and superficial skin blood flow was measured by laser Doppler perfusion imaging before and after treatment. Mean arterial blood pressure was also monitored. NO and the gas nitrogen dioxide (NO(2)), which is formed when NO reacts with atmospheric oxygen, were measured above the cream using chemiluminescence. In flaps treated with the NO generating cream, a concentration-dependent increase in blood flow in the supplying artery and flap skin of up to 130% was observed. Cream base alone or cream base acidified with vitamin C had no effect on blood flow. Also, concentration-dependent formation of both NO and NO(2) was seen. NO increases both supplying artery blood flow and superficial cutaneous blood flow in an epigastric island skin flap model in the rat indicating that NO is of importance in flap physiology and possibly also for flap survival.

Workplace NO and NO2 during combined treatment of infants with nasal CPAP and NO.

OBJECTIVE: To determine the workplace concentrations of NO and NO(2) in and around a paediatric incubator during inhaled NO (iNO) treatment and during an accidental emptying of NO cylinders into room air. DESIGN: We simulated iNO-nasal CPAP treatment in order to assess the impact on the occupational environment. Furthermore, two full NO cylinders for therapy, 1,000 ppm, 20 litres, 150 bar and 400 ppm, 10 litres, 150 bar, were emptied as rapidly as possible into an intensive care unit (ICU) room. SETTING: University hospital ICU. MEASUREMENTS AND RESULTS: To correctly gauge the contribution from iNO-CPAP we constructed a system measuring breathing zone and room ventilation inlet-outlet values during a 10-ppm iNO treatment of a simulated infant. Maximal breathing zone values were 17.9 +/- 7.0 (mean +/- 95% CI) ppb for NO and 25.2 +/- 4.8 ppb for NO(2). If room inlet values were subtracted, the contributions to breathing zone values emanating from iNO-CPAP were 14.8 +/- 4.6 ppb for NO and 14.6 +/- 4.6 ppb for NO(2). At the ventilation outlet the maximal contributions were 4.2 +/- 2.9 ppb NO and 9.6 +/- 4.3 ppb NO(2). During rapid total release of a gas cylinder in the ICU room, simulating an accident, we found transient NO levels comparable to the high therapeutic dosing range, but only low NO(2) levels. CONCLUSIONS: Neither 8-h time-weighted average (TWA) nor 15 min short-term exposure limits (STEL) were exceeded during normal operation or during a simulated accident. The contribution of nitrogen oxides from treatment to workplace air were minor compared to those from ambient air.

Comparison between effects of intravenous and nebulized histamine in guinea pigs: correlation between changes in respiratory mechanics and exhaled nitric oxide.

Nitric oxide (NO) is a marker of airway inflammation in humans, despite not having effects on basal bronchial tone. Inhibition of NO synthesis can lead to enhanced airway reactivity in humans and it is therefore of importance to understand how bronchial provocation can affect endogenous NO. Presently, we have studied the role of exhaled nitric oxide in airway reactivity by measuring changes in pulmonary mechanics in response to histamine in anaesthetized guinea pigs. Two groups were challenged i.v. and four groups were challenged by aerosol at different doses. One of the i.v. and one of the aerosol groups received an inhibitor of NO synthesis, N(omega)-nitro-L-arginine methyl ester (L-NAME), to reduce endogenous production of NO before histamine challenge. All animals with intact NO production showed a decrease in exhaled nitric oxide after challenge. There were positive correlations between the peak in exhaled nitric oxide and pulmonary resistance, and between the decrease in exhaled nitric oxide and lung compliance. L-NAME pretreatment increased the reactivity to aerosolized histamine but not to i.v. histamine. We conclude that the different ways of administration elicit different response patterns of exhaled nitric oxide, resistance, and compliance, even when compared at similar insufflation pressure changes. The effects of L-NAME suggest that, although different mechanisms might be responsible for the changes in pulmonary mechanics, inhibition of endogenous NO enhances decrements in pulmonary function when histamine is administered in an aerosol. The close relationship between changes in exhaled nitric oxide and changes in lung compliance and pulmonary resistance merits further studies on the relationship between NO and airway reactivity.

Generation of NO by probiotic bacteria in the gastrointestinal tract.

Probiotic bacteria elicit a number of beneficial effects in the gut but the mechanisms for these health promoting effects are not entirely understood. Recent in vitro data suggest that lactobacilli can utilise nitrate and nitrite to generate nitric oxide, a gas with immunomodulating and antibacterial properties. Here we further characterised intestinal NO generation by bacteria. In rats, dietary supplementation with lactobacilli and nitrate resulted in a 3-8 fold NO increase in the small intestine and caecum, but not in colon. Caecal NO levels correlated to nitrite concentration in luminal contents. In neonates, colonic NO levels correlated to the nitrite content of breast milk and faeces. Lactobacilli and bifidobacteria isolated from the stools of two neonates, generated NO from nitrite in vitro, whereas S. aureus and E. coli rapidly consumed NO. We here show that commensal bacteria can be a significant source of NO in the gut in addition to the mucosal NO production. Intestinal NO generation can be stimulated by dietary supplementation with substrate and lactobacilli. The generation of NO by some probiotic bacteria can be counteracted by rapid NO consumption by other strains. Future studies will clarify the biological role of the bacteria-derived intestinal NO in health and disease.