Estimation of endogenous adenosine activity at adenosine receptors in guinea-pig ileum using a new pharmacological method

AIM

Adenosine modulates neurotransmission and in the intestine adenosine is continuously released both from nerves and from smooth muscle. The main effect is modulation of contractile activity by inhibition of neurotransmitter release and by direct smooth muscle relaxation. Estimation of adenosine concentration at the receptors is difficult due to metabolic inactivation. We hypothesized that endogenous adenosine concentrations can be calculated by using adenosine receptor antagonist and agonist and dose ratio (DR) equations.

METHODS

Plexus-containing guinea-pig ileum longitudinal smooth muscle preparations were made to contract intermittently by electrical field stimulation in organ baths. Schild plot regressions were constructed with 2-chloroadenosine (agonist) and 8-(p-sulfophenyl)theophylline (8-PST; antagonist). In separate experiments the reversing or enhancing effect of 8-PST and the inhibiting effect of 2-chloroadenosine (CADO) were analysed in the absence or presence of an adenosine uptake inhibitor (dilazep), and nucleoside overflow was measured by HPLC.

RESULTS

Using the obtained DR, baseline adenosine concentration was calculated to 28 nm expressed as CADO activity, which increased dose dependently after addition of 10(-6) m dilazep to 150 nm (P < 0.05). HPLC measurements yielded a lower fractional increment (80%) in adenosine during dilazep, than found in the pharmacological determination (440%).

CONCLUSION

Endogenous adenosine is an important modulator of intestinal neuro-effector activity, operating in the linear part of the dose-response curve. Other adenosine-like agonists might contribute to neuromodulation and the derived formulas can be used to calculate endogenous agonist activity, which is markedly affected by nucleoside uptake inhibition. The method described should be suitable for other endogenous signalling molecules in many biological systems.

Increase in exhaled nitric oxide and protective role of the nitric oxide system in experimental pulmonary embolism

BACKGROUND AND PURPOSE

Pulmonary embolism (PE) represents a real diagnostic challenge. PE is associated with pulmonary hypertension due to pulmonary vascular obstruction and vasoconstriction. We recently reported that pulmonary gas embolism transiently increases exhaled nitric oxide (FENO), but it is not known whether solid emboli may alter FENO, and whether an intact endogenous NO synthesis has a beneficial effect in experimental solid pulmonary embolism.

EXPERIMENTAL APPROACH

We used anaesthetised and ventilated rabbits in these experiments. To mimic PE, a single intravenous infusion of homogenized autologous skeletal muscle tissue (MPE) was given to rabbits with intact NO production (MPE of 60, 15, or 7.5 mg kg(-1); group 1) and to another group (group 2) with inhibited NO synthesis (L-NAME 30 mg kg(-1); MPE of 7.5, 15 or 30 mg kg(-1)).

KEY RESULTS

In group 1, after MPE, FENO increased rapidly and dose-dependently and FENO was still significantly elevated after 60 min with the two highest emboli doses. All these animals survived more than 60 min after embolization. In group 2, MPE of 7.5, 15 and 30 mg kg(-1), in combination with NO synthesis inhibition, resulted in 67%, 50% and 25% survival at 60 min respectively, representing a statistically significant decrease in survival. Cardiovascular and blood-gas changes after MPE were intensified by pre-treatment with NO synthesis inhibitor.

CONCLUSIONS AND IMPLICATIONS

We conclude that solid PE causes a sustained, dose-dependent increase in FENO, giving FENO a diagnostic potential in PE. Furthermore, intact NO production appears critical for tolerance to acute PE.

Inhibitors of phosphodiesterase 5 (PDE 5) inhibit the nerve-induced release of nitric oxide from the rabbit corpus cavernosum

BACKGROUND AND PURPOSE

Nitrergic neurons are important for erectile responses in the corpus cavernosum and impaired signalling results in erectile dysfunction, today treated successfully by oral administration of the selective phosphodiesterase 5 (PDE 5) inhibitors sildenafil, tadalafil and vardenafil. Although the importance of nitrergic neurons in urogenital function has become evident, it has not been investigated if the PDE 5 inhibitors affect the nerve-induced release of nitric oxide (NO). In a previous study we found that the soluble guanylate cyclase (sGC)/cyclic guanosine 3',5'-monophosphate (cGMP) pathway might modulate nerve-induced release of NO in isolated cavernous tissue.

EXPERIMENTAL APPROACH

Electrical field stimulation (EFS 5 Hz, 40 V, 0.3 ms pulse duration, 25 pulses at intervals of 2 min) of rabbit isolated cavernous tissue elicited reproducible, nerve-mediated relaxations in the presence of scopolamine (10(-5) M), guanethidine (10(-5) M) and phenylephrine (3 x 10(-6) M). In superfusion experiments, nerve stimulation (20 Hz, 40 V, 1 ms) of the cavernous tissue evoked release of NO/NO2-, measured by chemiluminescence.

KEY RESULTS

Sildenafil, tadalafil and vardenafil decreased the muscular tone and prolonged the relaxations to nerve stimulation. The evoked release of NO decreased to 72+/-11%, 55+/-16% and 61+/-14% of control, respectively after addition of sildenafil, tadalafil or vardenafil (all 10(-4) M, n=6-8, p<0.05).

CONCLUSIONS AND IMPLICATIONS

Selective PDE 5 inhibitors influence the nerve-induced release of NO, probably via cGMP-mediated negative feedback. This negative feedback might explain why priapism is not seen during monotherapy with the PDE inhibitors.

Early rise in exhaled nitric oxide and mast cell activation in repeated low-dose allergen challenge

Repeated low-dose allergen inhalation challenge mimics natural allergen exposure, providing a model for early mechanisms in the triggering of asthma. The current authors performed a controlled study to evaluate the time course of changes in exhaled nitric oxide fraction (F(e,NO)) and urinary biomarkers of airway inflammation. Eight subjects with mild allergic asthma completed two 7-day repeated low-dose challenge periods, with diluent and allergen, respectively. Subjects were symptom free at inclusion and were investigated when not exposed to specific allergen. Pulmonary function and symptoms were followed, and F(e,NO) and urinary mediators were correlated to changes in airway responsiveness to histamine and adenosine. Despite no change in pulmonary function (forced expiratory volume in one second mean+/-sem fall 0.3+/-0.7 versus 0.6+/-1.0%, for diluent and allergen, respectively) and no asthma symptoms, repeated allergen exposure, in contrast to diluent, caused significant increases in histamine responsiveness (2.3 doubling doses), an early and gradual increase in F(e,NO) (up to a doubling from baseline) and a small increase in the mast cell marker 9alpha11beta-prostaglandin F(2) after adenosine challenge. In conclusion, serial measurements of exhaled nitric oxide fraction have the potential to provide a very sensitive strategy for early detection of emerging airway inflammation and subsequent changes in airway hyperresponsiveness to histamine.

Nerve-induced release of nitric oxide from the rabbit corpus cavernosum is modulated by cyclic guanosine 3',5'-monophosphate

Nitric oxide (NO) is a neurotransmitter of the autonomic nerves in the urogenital tract, in particular the release of NO in the cavernous tissue is of importance for maintaining erection. However, the regulation of NO formation in neurons of the corpus cavernosum is poorly understood. Here, we report, that upon electrical stimulation of isolated rabbit corpus cavernosum, NO/NO(2-) was formed and released in a reproducible fashion. The NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester decreased the amount of NO/NO(2-) released to 50+/-18% (P<0.05). The neurotoxin tetrodotoxin diminished the nerve-induced release of NO/NO(2-), to 35+/-10% (P<0.001). Blockage of the cholinergic and noradrenergic pathways by application of scopolamine and guanethidin (both 10(-5) M) did not alter the basal or nerve-evoked formation of NO/NO(2-). We also applied modulators of the soluble guanylate cyclase (sGC)/cyclic guanosine 3',5'-monophosphate (cGMP) pathway to study if and to what extent cGMP might affect the release of NO from the erectile tissue. In the presence of the cGMP analog 8-Br-cGMP (10(-4) M), and, the sGC stimulator 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (10(-4) M), the release of NO/NO(2-) was increased to 385+/-120% (P<0.05) and 282+/-78% (P<0.05), respectively. The effect of the phosphodiesterase inhibitor zaprinast (10(-4) M), was not significant (209+/-53%, n.s). In contrast, inhibition of sGC by 1-H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (10(-5) M) decreased the release of NO/NO(2-) to 64+/-14% (P<0.05). Our results suggest that NO/NO(2-) is released by nitrergic neurons within the rabbit corpus cavernosum and that the release is subject to modulation by the sGC/cGMP pathway, but not to modulation by acetylcholine or noradrenaline.

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.

Absence of mast cell involvement in active systemic anaphylaxis in rats

This study investigates the role of mast cells in the hypotension induced by antigen-mediated anaphylaxis, compound 48/80 and dextran in mast cell-deficient white spotting (Ws/Ws) and normal wild type (+/+) rats. Rats were sensitized with 10 microg of intraperitoneal ovalbumin in saline or saline alone (sham-sensitized). Sensitized rats, both Ws/Ws and +/+ but not sham-sensitized rats, challenged intravenously with ovalbumin exhibited hypotensive responses. There was no evidence of mast cell activation in rat mesentery 20 min after intravenous antigen challenge in sensitized +/+ rats. Hypotension induced by intravenous injection of dextran (Dextran-162, 6%, 2 ml kg(-1)) or compound 48/80 (1 mg kg(-1)) occurred in +/+ rats, but not in Ws/Ws rats, and was inhibited by pretreatment with a combination of chlorpheniramine and cimetidine. Taken together, these data indicate that the hypotensive response induced by antigen-mediated anaphylaxis is independent of mast cell activation, whereas mast cell amines play the main role in the hypotensive response induced by dextran or compound 48/80.

Nerve growth factor increases airway responses and decreases levels of exhaled nitric oxide during histamine challenge in an in vivo guinea-pig model

There is a growing body of evidence supporting the idea that nerve growth factor (NGF) may be involved in the development of asthma-associated symptoms, such as airway hyper-responsiveness. Increased levels of NGF have recently been described in serum and in the airways of asthmatics. We have examined whether exhaled nitric oxide (NO) levels might be altered during the increased airway responses upon NGF treatment in guinea-pigs in vivo. Intravenous (i.v.) administration of histamine normally elicits a rapid peak in insufflation pressure (IP) and in exhaled NO, followed by a period of decreased concentrations of exhaled NO. Anaesthetized guinea-pigs were pre-treated intravenously with either saline, 4 or 80 ng x kg(-1) NGF 30 min before i.v. challenge with 16 microg x kg(-1) histamine. At 80 ng x kg(-1) NGF significantly enhanced the airway obstruction caused by histamine, whereas the peak acute increase in exhaled NO was not enhanced. Following the increase, came a rapid drop, an effect enforced in the NGF treated animals. Subsequently, the time to return to 90% of resting exhaled NO was increased, from 12 min in saline-treated animals to 48 min in NGF-treated animals. Our data confirm that NGF can enhance airway responses to histamine. Moreover, our study shows a decrease in exhaled NO following a histamine challenge, an effect enhanced by NGF. A reduced ability to release exhaled NO may be a mechanism for increased airway responses during elevated NGF levels. The interaction between NGF and airway NO formation, and its relation to airway responses, merit further investigation.

Basic experimental studies and clinical aspects of gadolinium salts and chelates

Gadolinium is a lanthanide that has in recent years become more commonly present in our society. Organic chelates of gadolinium are increasingly used as contrast agents for the imaging of body fluids. Although adverse reactions to these agents are uncommon, it is known that gadolinium salts can bring about a wide variety of changes in physiology. Gadolinium chloride is widely used experimentally as an inhibitor of stretch-activated ion channels and physiological responses of tissues to mechanical stimulation. It is also employed as a selective inhibitor of macrophages in vivo. In this review, the known biochemical actions of gadolinium are brought together with its in vivo pharmacology and toxicology.

Modulation of neuronal nitric oxide release by soluble guanylyl cyclase in guinea pig colon

Peripheral autonomic neurones release nitric oxide (NO) upon nerve activation. However, the regulation of neuronal NO formation is poorly understood. We used the cyclic guanosine 3',5'-monophosphate (cGMP) analogue 8-Br-cGMP, the soluble guanylyl cyclase (sGC) stimulator YC-1, the phosphodiesterase inhibitor zaprinast and the sGC inhibitor ODQ to study whether the sGC/cGMP pathway is involved in regulation of neuronal NO release in nerve plexus-containing smooth muscle preparations from guinea pig colon. Electrical stimulation of the preparation evoked release of NO/NO(-)(2). In the presence of 8-Br-cGMP, YC-1 and zaprinast (all at 10(-4) M) the NO/NO(-)(2)-release increased to 152 +/- 16% (P < 0.05), 164 +/- 37% (P < 0.05) and 290 +/- 67% (P < 0.05) of controls, respectively. Conversely, ODQ (10(-5) M) decreased the evoked release of NO/NO(-)(2) to 49 +/- 7% (P < 0.05) of controls. Our data suggest that the sGC/cGMP pathway modulates NO release. Thus it is likely that NO exerts a positive feedback on its own release from peripheral autonomic neurones.

Activation of sympathoadrenomedullary system increases pulmonary nitric oxide production in the rabbit

Nitric oxide (NO) is continuously produced in the lung and can be measured in exhaled gas of different species. To investigate a possible neuro-humoral regulation of pulmonary NO production in vivo we injected veratrine, an activator of Na(+) channels known to activate the sympathoadrenal system, in anaesthetized, mechanically ventilated and laparotomized rabbits. Exhaled NO concentration increased by 38+/-3% when plasma adrenaline rose from 12.3+/-3.1 to 49.5+/-10.7 pmol ml(-1) in response to veratrine (500 microg kg(-1), i.v.). Pretreatment with atenolol, a beta(1)-adrenoceptor antagonist (1 mg kg(-1)), or bilateral ligation of adrenal blood vessels inhibited the increase in exhaled NO in response to veratrine. Atenolol also decreased basal NO, suggesting an endogenous regulation of pulmonary NO by adrenaline. Neither phentolamine (1 mg kg(-1)), atropine (1 mg kg(-1)) nor vagotomy inhibited the veratrine-induced pulmonary NO production. These results suggest a role of the sympathoadrenal system in the regulation of pulmonary NO production.

Single breath analysis of endogenous nitric oxide in the newborn

Nitric oxide (NO) is found in the exhaled gas of humans immediately after birth. However, variations of endogenous NO concentration during the breathing cycle have not been studied in newborns. We examined 24 newborns without acute respiratory compromise during spontaneous nasal breathing. Gas was sampled from the tip of a thin nasal catheter placed in the hypopharynx. Endogenous NO concentrations measured by chemiluminescence were assigned to the breathing cycle using synchronized CO2 recording. Exhaled NO could reproducibly be measured at 1.9 +/- 0.2 parts per billion (ppb, mean +/- SEM). Autoinhaled nasal NO peaks during regular breathing were 12.0 +/- 1.7 ppb and reached intermittent maxima of 52.2 +/- 5.8 ppb. During regular breathing 6 infants exhibited sudden decreases of nasal NO peaks to periods with <50% amplitude suggesting transient shortage of autoinhaled nasal NO. We conclude that tidal NO analysis can be used to assess upper and lower airway NO production noninvasively during spontaneous breathing in the newborn.

Evidence for nonvesicular nitric oxide release evoked by nerve activation

The gaseous nature of nitric oxide (NO) has led to the general assumption that its release from neurons during nerve stimulation is independent of vesicular storage. However, recent findings have shown that NO can exist intracellularly as part of more stable bioactive molecules, suggesting that the role of vesicular exocytosis for NO release cannot be excluded simply based on the chemical nature of NO itself. We have used botulinum toxin B (BTX B) to directly address the role of vesicular exocytosis for NO release. BTX B cleaves the synaptic vesicle protein synaptobrevin/VAMP, and by this inhibits Ca++-mediated exocytic release of neurotransmitters. As a target organ we used the guinea-pig enteric nervous system, which innervates the gastrointestinal tract, and in which both classical neurotransmitters as well as NO are released and influence smooth muscle activity. As expected, BTX B (0.1 microM) blocked the nerve stimulation-induced cholinergic and tachykininergic smooth muscle contractions, and markedly inhibited the nerve stimulation-evoked release of [3H]-choline. In contrast, BTX B (0.1 microM) had no effect on nerve stimulation-evoked relaxations, which were equally inhibited by an NO-synthase inhibitor as well as by a selective inhibitor of soluble guanylyl cyclase. In addition, nerve stimulation-evoked NO synthase-dependent outflow of NO/NO2- was unaffected by BTX B (0.1 microM). These findings suggest that the neuronal release of endogenous NO is independent of intact synaptobrevin/VAMP, and therefore provide further evidence that nerve-mediated release of further NO is nonvesicular.

Nitric oxide generation, tachyphylaxis and cross-tachyphylaxis from nitrovasodilators in vivo

Nitric oxide (NO) increments in exhaled air and changes in mean arterial pressure of anaesthetised rabbits were measured in order to study the NO generation from NO donors and tachyphylaxis in NO formation from nitroglycerin. Continuous infusions of isosorbide dinitrate, isosorbide-5-mononitrate and 3-morpholino-sydnonimine (SIN-1) evoked dose-dependent increases in exhaled NO, paralleled by decrements in mean arterial pressure. Repeated infusions of nitroglycerin resulted in attenuation (P<0.01) of the NO increase from a given dose. Concurrent infusions of isosorbide dinitrate, isosorbide-5-mononitrate or nitroglycerin reduced the amount of NO emanating from the bioconversion of a given dose nitroglycerin as measured in the expired air (P<0.01 for all drugs), indicating cross-tachyphylaxis. SIN-1 did not exhibit such cross-tachyphylaxis. In conclusion, measurements of exhaled NO can be a useful tool for exploration of nitrovasodilator tachyphylaxis. Cross-tachyphylaxis is only shared between some nitrovasodilators and is possibly not due to feedback from the generated NO.

Regulation of pulmonary nitric oxide by carbon dioxide is intrinsic to the lung

Nitric oxide (NO) is present in exhaled air and is a regulator of airways and pulmonary vasculature. Exhaled NO can be depressed by inhaled carbon dioxide (CO2). To further characterize this, single-breath exhaled NO of rabbits was measured in vivo as well as in buffer-perfused lungs. Effects of bilateral carotid occlusion or reduction of extracellular pH were also studied. During control conditions NO single-breath peaks in exhaled air in vivo were 25 +/- 1 parts per billion (p.p.b.) as compared with 79 +/- 13 p.p.b. in the buffer-perfused lungs. Inhaled carbon dioxide (FI co2=10%) within 10-20 s caused a depression of exhaled NO in vivo (to 21 +/- 1 p.p.b., P < 0.05) and in perfused lungs (to 64 +/- 8 p.p.b., P < 0. 05). In vivo, the CO2-induced change in exhaled NO was unaffected by bilateral vagotomy, or by additional guanethidine treatment. Bilateral carotid occlusion did not affect exhaled NO. In perfused lungs, changes in pH (6.5-7.4) did not alter exhaled NO. Endogenous pulmonary nitric oxide production is thus measurable in single breaths in a small animal and is depressed by high airway concentration of carbon dioxide both in vivo and in the perfused rabbit lung. The effect by CO2 is independent of sympathetic outflow and the central nervous system and is not caused by changes in extracellular pH. Carbon dioxide thus exerts a local regulatory effect on lung nitric oxide.

Visualization of nitric oxide formation in cell cultures and living tissue

We have visualized nitric oxide (NO) released from cell cultures and living tissue. NO was visualized by a reaction with luminol and hydrogen peroxide to yield photons which were counted using a microscope coupled to a photon counting camera. Murine macrophages were activated with interferon-gamma (IFN-gamma) and endotoxin (LPS). Cultured endothelial cells were stimulated with bradykinin, and neurones in the guinea-pig myenteric plexus and the rabbit hypogastric nerve trunk were electrically stimulated. There was a marked increase in photons emitted from the cultured cells as well as from the living tissues during stimulation. The stimulation-induced photon emission was markedly reduced by inhibition of nitric oxide synthase (NOS); removal of L-arginine from the medium also decreased photon counts. The present method allowed integration times in the order of minutes to improve signal-to-noise ratio. However, the high sensitivity of this method also makes it possible to generate an image in seconds, allowing the production of real time films. Photon emission was enhanced under conditions known to increase NO production, and diminished in the presence of NO inhibitors. Thus, this method has demonstrated specificity for the L-arginine:NO pathway from a wide range of biological sources such as cultured cells and living tissues, and has the potential for real time imaging of NO formation, with high temporal and spatial resolution.

Exhaled nitric oxide increases during high frequency oscillatory ventilation in rabbits

This study compared the effects of high frequency oscillatory ventilation (HFOV) and intermittent mandatory ventilation (IMV) on the homeostasis of nitric oxide (NO) in the lower respiratory tract of healthy rabbits. The mechanisms underlying a putative stretch response of NO formation in the airways were further elucidated. Male New Zealand White rabbits were anaesthetized, tracheotomized and ventilated with IMV or HFOV in random order. Total NO excretion increased from 9.6 +/- 0.8 nl min-1 (mean +/- S.E.M.) during IMV to 22.6 +/- 2.7 nl min-1 during HFOV (P < 0.001). This increase was not explained by changes of functional residual capacity ([Delta]FRC). A similar increase in NO excretion during HFOV was seen in isolated buffer-perfused lungs under constant circulatory conditions (P < 0. 05, n = 4). Intratracheal mean CO2 and NO concentrations, measured at 2.5, 5, 7.5 and 10 cm below tracheostomy, increased significantly with increasing distance into the lung during both IMV and HFOV (P < 0.001 for each comparison). At every intratracheal location of the sampling catheter, particularly low in the airways, both CO2 and NO concentrations were significantly higher during HFOV than during IMV (P < 0.01 for each comparison). We conclude that HFOV increases pulmonary NO production in healthy rabbits. Increased stretch activation of the respiratory system during HFOV is suggested as a possible underlying mechanism. The increase in mean airway NO concentrations may have biological effects in the respiratory tract. Whether it can account for some of the benefits of HFOV treatment needs to be considered.

Formation of nitrogen dioxide from nitric oxide and their measurement in clinically relevant circumstances

Therapy with inhaled nitric oxide in oxygen requires adequate monitoring of nitric oxide and nitrogen dioxide. The characteristics of chemiluminescence and electrochemical measurement techniques were determined by analysis of continuously flowing gas mixtures and comparisons with traceable gas standards. Gas mixtures were also diluted with mass flow controllers and in addition created in ventilator breathing systems. Factors influencing the formation of nitrogen dioxide were defined. Both techniques accurately measured nitric oxide (10-80 parts per million, ppm) and nitrogen dioxide (0.5-5 ppm) in normoxic and hyperoxic (90% oxygen) gas in the studied ranges. Nitrogen dioxide in hyperoxic gas had three origins: (1) from the premixing point of nitric oxide in nitrogen, (2) as a result of the mixing process, and (3) from post-mixing and time-dependent continuous formation of nitrogen dioxide in oxygen. We conclude that adequate monitoring is possible and that factors affecting nitrogen dioxide generation can be defined.

Beta-adrenoceptor agonist stimulation of pulmonary nitric oxide production in the rabbit

Nitric oxide (NO) is continuously produced in the lung and is present in exhaled air. We examined the effect of beta-adrenoceptor stimulation on the production of pulmonary NO in rabbits. Exhaled NO was measured by chemiluminescence in anaesthetized and mechanically ventilated rabbits and in buffer-perfused rabbit lungs. Intravenous infusions of adrenaline (0.1-10 microg kg(-1) min(-1)) elicited dose-dependent increases in exhaled NO. The increases in exhaled NO comprised an initial peak followed by a lower plateau level. The increase in exhaled NO was inhibited by propranolol (1 mg kg(-1)) but not by phentolamine (1 mg kg(-1)). Prenalterol, a beta1-adrenoceptor agonist, and terbutaline, a beta2-adrenoceptor agonist, also caused dose-dependent increases in exhaled NO. However, prenalterol was >100 times more potent than terbutaline. Infusions of forskolin (0.01-0.03 micromol kg(-1) min(-1)), an adenylate cyclase stimulator, elicited dose-dependent decreases in blood pressure and concomitant increases in heart rate but caused no alterations in exhaled NO. Nimodipine, a L-type calcium channel blocker, antagonized the increases in exhaled NO in response to prenalterol infusions. The increases in exhaled NO in response to adrenaline and prenalterol were also present in blood-free, buffer perfused lungs during constant-flow conditions. These results demonstrate that pulmonary nitric oxide production can be enhanced by beta-adrenoceptor stimulation. Furthermore, the results indicate that the beta-adrenergic stimulation of pulmonary NO production is not critically dependent on cyclic AMP formation but may require intact calcium-channels.

Gadolinium chloride inhibition of pulmonary nitric oxide production and effects on pulmonary circulation in the rabbit

Nitric oxide is an important regulator of pulmonary vascular resistance. Pulmonary nitric oxide formation is detectable in exhaled air and the synthesis is partly stretch-dependent. Gadolinium chloride (GdCl3) reduces pulmonary nitric oxide formation, possibly by interference with stretch-activated cellular calcium influx, but the effect on pulmonary circulation is not known. We therefore measured exhaled nitric oxide and pulmonary vascular resistance in anaesthetised rabbits, and compared the effects of GdCl3 with those of an nitric oxide-synthase inhibitor (L-N omega-nitro-arginine methyl ester, L-NAME). Both GdCl3 and L-NAME reduced nitric oxide in exhaled air and increased pulmonary vascular resistance. However, the increase in pulmonary vascular resistance was more pronounced with GdCl3 than with L-NAME. A 50% reduction of exhaled nitric oxide caused by either GdCl3 or L-NAME was accompanied by a 90% or 17% increase in pulmonary vascular resistance respectively. Inhaled nitric oxide (40 ppm) reduced pulmonary vascular resistance after L-NAME, but not after GdCl3 infusion. Infusion of glyceryltrinitrate reduced pulmonary vascular resistance after GdCl3 infusion. GdCl3 caused hypoxaemia, probably due to vasoconstriction since lung weight was unaltered. Thus GdCl3 can induce a marked increase in pulmonary vascular resistance, which partly may be caused by inhibition of pulmonary nitric oxide formation. Intact stretch-activated calcium channels may be important for maintenance of normal pulmonary vascular function.

Blockade of nitrergic neuroeffector transmission in guinea-pig colon by a selective inhibitor of soluble guanylyl cyclase

The role of soluble guanylyl cyclase in nitrergic inhibitory neuroeffector transmission was investigated in the longitudinal muscle from guinea-pig colon, by using an inhibitor of soluble guanylyl cyclase, 1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one (ODQ). In preparations precontracted with histamine, electrical field stimulation (EFS) or exogenous nitric oxide (NO) induced relaxations. The relaxation induced by NO-application was abolished by ODQ. Both ODQ and the NO-synthase inhibitor N omega-nitro-L-arginine (L-NOARG) partially inhibited the EFS-evoked relaxation to a similar extent. These effects were dose-dependent. The inhibition was more pronounced in the late phase of the EFS-induced relaxation. The inhibitory effect of ODQ on EFS-induced relaxation was not affected by additional application of L-NOARG. When NO-formation was blocked by L-NOARG, a subsequent addition of ODQ gave no further inhibition of the relaxation. These findings suggest that inhibitory non-adrenergic, non-cholinergic neurotransmission in guinea-pig colon is dependent on endogenous formation of NO, and that the NO-effect is exclusively mediated via the soluble guanylyl cyclase pathway. The existence of an NO-independent inhibitory transmission, which is not mediated through the cyclic GMP pathway, is also indicated. Furthermore, it is demonstrated that the NO/soluble guanylyl cyclase-independent transmission has an earlier onset as compared with the NO/soluble guanylyl cyclase-dependent pathway.

Endogenous nitric oxide in the upper airways of premature and term infants

Concentrations of endogenous nitric oxide (NO) were measured in premature (n = 18) and term infants (n = 7). Nasal gas was aspirated continuously and after timed occlusions, 15 s and 60 s, by a fast-response chemiluminescence analyser. The sampling flow rate was 20 ml min-1. Typical NO recordings consisted of plateaux and postocclusive peaks. In term infants peak NO concentrations (60 s occlusion) were 2.71 +/- 0.44 parts per million (ppm) within 10 min after birth, increasing (p < 0.05) to 3.81 +/- 0.25 ppm at 4-7 d postnatally. Peak NO values (15 s occlusion) averaged 1.22 +/- 0.16 ppm in premature infants (postconceptional age 25-37 weeks, body weight 623-2844 g) and the NO concentrations increased significantly with postconceptional age (p < 0.05). Nasal excretion rate, estimated from plateau NO concentrations and sampling flow rate, was 0.10 +/- 0.01 nmol min-1 kg-1 in both groups. We conclude that premature and term newborn infants excrete considerable amounts of NO in the upper airways, with hitherto not fully known functions.

Blockade of nitric oxide-evoked smooth muscle contractions by an inhibitor of guanylyl cyclase

Nitric oxide-induced contractile responses of smooth muscle were studied in vitro in guinea-pig small intestine. Application of nitric oxide (NO; 0.3-30 microM) evoked a small initial relaxation followed by a marked contractile response in plexus-containing longitudinal smooth muscle preparations from small intestine. The extent of the NO-evoked contractile response was dose-dependent and the response was blocked by tetrodotoxin. Atropine significantly reduced the NO-evoked contraction and the remaining part was abolished by the NK1-receptor antagonist CP 96,345. An inhibitor of soluble guanylyl cyclase, ODQ (1H-[1,2,4]oxadiazolo[4,3,-a]quinoxalin-1-one), abolished the NO-evoked contractile response. The results suggest that NO, in addition to the classical direct smooth muscle relaxing effect, causes activation of excitatory neurones, via a pathway utilizing soluble guanylyl cyclase, which leads to a smooth muscle contraction.

Endogenous nitric oxide in the airways of different animal species

BACKGROUND

High amounts of endogenous nitric oxide (NO) have been demonstrated in the human upper airway, but the role of nasal NO is still unclear. The present study aims to describe nasal NO excretion in different animal species with special living conditions or anatomy.

METHODS

Domestic animals (horse, cow, pig, sheep, dog, cat) and zoo-animals (Rhesus monkey, chimpanzee, gorilla, elephant, fur seal, alpaca, yak, dolphin, camel, capybara, bear, tiger, wolf, giraffe, alligator, Harris' hawk, kangaroo) were studied awake, resting or anaesthetised. NO concentrations were measured by chemiluminescence using different analysers and techniques, including measurements on mixed exhaled air, during continuous or intermittent gas sampling, and on single breaths.

RESULTS

Rhesus monkeys (number of individuals N = 5) and pigs (N = 2) were compared and displayed quite different excretion patterns. Allowing NO to accumulate in the nose during timed occlusions yielded peak concentrations in monkeys of 0.46 +/- 0.07 parts per million (ppm, mean +/- SEM), 0.59 +/- 0.08 ppm, 0.70 +/- 0.08 ppm and 1.02 +/- 0.05 ppm NO after 15, 30, 60 and 120 s of occlusion. In pigs, 0.012-0.021 ppm NO were recorded, independent of occlusion time. The chimpanzee was similar to the Rhesus monkey and the highest NO value, 2.9 ppm, was recorded after 4-5 min of occlusion. In single breaths from 3 elephants 0.031-0.082 ppm, from 1 gorilla 0.029 ppm, and from 1 chimpanzee 0.069 +/- 0.003 ppm NO (8 observations) were recorded.

CONCLUSIONS

We found considerable species difference in nasal NO excretion with pronounced amounts only in primates and elephants. The physiological implications of these findings remain to be defined.

Inhaled carbon dioxide inhibits lower airway nitric oxide formation in the guinea pig

The present study addressed the effect of inhaled carbon dioxide on lower airway nitric oxide formation in normoxic anaesthetized guinea pigs. Ventilation with carbon dioxide (1.5, 3, 6, 9 and 12%) induced a concentration-dependent decrease in the basal concentration of nitric oxide in exhaled tracheal air. A maximal reduction in exhaled nitric oxide of approximately 25% was induced by 12% carbon dioxide in inhaled air. Ventilation with positive end-expiratory pressure (7 cmH2O) increased the concentration of exhaled nitric oxide. Inhalation of carbon dioxide had a larger, concentration-dependent, inhibitory effect (maximally 60%) on the lower airway nitric oxide formation induced by ventilation with positive end-expiratory pressure, as compared with the effect on the basal concentration of nitric oxide. The results show that inhaled carbon dioxide suppresses lower airway nitric oxide excretion in the guinea pig. Endogenous carbon dioxide might exert effects through regulation of endogenous nitric oxide formation, for example in the regulation of airway tone or in ventilation-perfusion matching.

Nerve stimulation-induced nitric oxide release as a consequence of muscarinic M1 receptor activation

The aim of the present study was to investigate whether nerve stimulation-induced nitric oxide (NO) release in the guinea-pig colon is affected by acetylcholine and to identify the muscarinic receptor subtype involved. Nerve-smooth muscle preparations were suspended in a superfusion chamber and NO/NO2- overflow in the superfusate was detected by chemiluminescence analysis. Transmural nerve stimulation evoked a significant increase in NO/NO2- release, which was inhibited by N(omega)-nitro-L-arginine methyl ester (L-NAME) and abolished by tetrodotoxin. Exogenous acetylcholine concentration-dependently increased NO/NO2- release and atropine reduced nerve stimulation-evoked NO/NO2- release. The muscarinic M1 receptor selective antagonist telenzepine (10(-8) M) was as effective as atropine (10(-6) M) in inhibiting NO/NO2- release. The muscarinic M3 receptor antagonists 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) and para-fluoro-hexahydrosila-difenidol (p-F-HHSiD) markedly inhibited cholinergic contractions at 3 x 10(-8) M and 3 x 10(-7) M respectively, but did not affect NO/NO2- release. In conclusion, nerve-induced NO/NO2- release in the guinea-pig colon is to a substantial part due to muscarinic M1 receptor activation. Thus acetylcholine, a major contractile neurotransmitter in the gut, can release NO which could act as a negative feedback mechanism on intestinal smooth muscle or neuronal activity.

Stretch-induced stimulation of lower airway nitric oxide formation in the guinea-pig: inhibition by gadolinium chloride

The effect of stretch on lower airway nitric oxide formation was studied in normoxic tracheostomized anaesthetized guinea-pigs. Increase of level of positive end-expiratory pressure caused increased lower airway nitric oxide formation, as measured by its presence in exhaled tracheal air. The L-type calcium channel blocker, verapamil, did not decrease lower airway nitric oxide formation. Neither the local anaesthetic xylocaine nor the ganglion blocker trimetaphan affected exhaled nitric oxide, excluding local and centrally-mediated neuronal reflexes. Intravenous administration of gadolinium chloride (GdCl3, 50 mg/kg) induced a rapid and pronounced decrease (75%) in the basal level of exhaled nitric oxide. GdCl3 completely abolished lower airway nitric oxide formation induced by ventilation with positive end-expiratory pressure (7 cm H2O). GdCl3 induced hypoxaemia, but there was no indication for the development of lung oedema. The results indicate that positive end-expiratory pressure stimulates lower airway nitric oxide formation in the guinea-pig. GdCl3 inhibits lower airway nitric oxide formation in the guinea-pig in vivo, perhaps by interference with stretch-induced cellular calcium-influx.

Nerve-induced release of nitric oxide in the rabbit gastrointestinal tract as measured by in vivo microdialysis

1. Nitric oxide (NO) has been suggested as a gastrointestinal neurotransmitter, mediating the gastric receptive relaxation and the relaxation in the peristaltic reflex. The aim of the present study was to measure nerve-induced NO formation in vivo in the gastrointestinal tract. 2. Formation of the nitric oxide oxidation products nitrite and nitrate during vagal nerve stimulation were measured in the anaesthetized rabbit. Microdialysis probes were inserted into the wall of the stomach and proximal colon, and nitrite and nitrate in dialysate measured by capillary electrophoresis. 3. During bilateral vagal nerve stimulation there was an increase in nitrite and nitrate formation at the level of the stomach and in nitrite formation at the level of the colon. This increase was inhibited by intravenous administration of the NO synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME 30 mg kg-1). Furthermore, L-NAME significantly increased nerve-induced gastric and colonic contractions, as well as spontaneous colonic contractions. 4. In summary, we present a new methodological procedure for quantification of small changes in nitric oxide formation in vivo. This study provides evidence that nitric oxide is released in the stomach and colonic wall during vagal nerve activity, at concentrations able to cause inhibition of smooth muscle contractions in vivo.

Visualisation of nitric oxide released by nerve stimulation

We have visualised nitric oxide (NO) released from the electrically stimulated myenteric plexus and hypogastric nerve. NO was visualised by a reaction with luminol and hydrogen peroxide to generate photons which were counted using a microscope coupled to a photon counting camera. Electrical stimulation of the tissues induced an increase in photon counts which was frequency-dependent and prevented by inhibition of the NO synthase or by tetrodotoxin. The light emitted during nerve stimulation was not only observed at the nerve terminals but also at the axon and soma. Our results indicate that NO released from the whole nerve cell may affect target cells surrounding all parts of the nitrergic neuron. Thus, NO functions as a unique mechanism of synaptic and non-synaptic communication in the nervous system.

Lung distension and carbon dioxide affect pulmonary nitric oxide formation in the anaesthetized rabbit

Positive end-exspiratory pressure (PEEP) and nitric oxide (NO) can influence lung VA/Q-matching and pulmonary vascular resistance, and application of PEEP can increase exhaled NO in animals. To obtain a better understanding of these mechanisms, we examined how different types of ventilation or changes in CO2 affect the formation of endogenous NO. Exhaled NO in pentobarbital-anaesthetized rabbits was monitored by chemiluminescence. The animals were enclosed in a chamber and subjected to various modes of positive as well as negative pressure ventilation which was adjusted to induce similar changes in functional residual capacity (FRC) with maintained ventilatory rate and tidal volume. In addition, stepwise increase in FiCO2 (1.0-10%) was studied. Negative extrathoracic end-exspiratory pressure during negative extrathoracic pressure ventilation produced an increase in NO production similar to that of positive end-exspiratory pressure during positive pressure ventilation, the increase consisting of an initial peak followed by a plateau. The faster the FRC was increased, the higher was the initial peak in NO. The greater the increase in FRC, the higher was the plateau NO concentration. Increased FiCO2 caused a dose-dependent reduction in exhaled NO. The observations of lung distension effects on exhaled NO suggest the possibility of stretch receptors or -receptive mechanisms coupled to NO formation within the lung. In addition, NO formation in the lung is influenced by CO2 in a reciprocal fashion.

Endogenous nitric oxide in the upper airways of healthy newborn infants

The endogenous production of nitric oxide (NO) in the upper airways was studied in healthy newborn infants within the first minutes after delivery (N = 2) and at postnatal ages of 1 and 24 h (N = 13). Measurements were made in infants born vaginally or by cesarean section and at various times after the rupture of membranes. Gas was sampled from the nose and pharynx, and NO concentrations were determined by a fast response chemiluminescence analyzer. Sampling from the nose at a constant flow of 20 mL/min gave 0.27 +/- 0.01 parts per million (mean +/- SEM, ppm) of NO, independent of age and mode of delivery (vaginal delivery and cesarean section). Allowing NO to accumulate in the nose for 15-120 s yielded peak concentrations up to 4.6 ppm. A 30% increase was noted between 1 and 24 h of age. We conclude that nasal peak NO concentrations in the ppm range can be demonstrated in the healthy newborn infant within the first hour after birth. Consequently autoinhalation of endogenously produced upper airway NO may play a role in the adaptation of the respiratory system to postnatal life in the human.

The promotion of patent airways and inhibition of antigen-induced bronchial obstruction by endogenous nitric oxide

1. The aim of the present study was to investigate the role of nitric oxide (NO), histamine and leukotrienes in bronchial obstruction. For this, guinea-pigs immunised against ovalbumin were studied under anaesthesia during challenge with antigen or agonists. 2. Challenge with nebulised antigen (0.1-1 mg) elicited dose-dependent increases in insufflation pressure which were abolished by combined administration of histamine and leukotriene antagonists. 3. Challenge with nebulised antigen (0.1-1 mg) also elicited dose-dependent increases in the concentration of endogenous nitric oxide in the exhaled air. After an initial peak, exhaled NO concentrations returned to pre-challenge levels. 4. The increase in insufflation pressure and in exhaled NO caused by ovalbumin challenge was inhibited by combined administration of histamine and leukotriene antagonists. 5. In non-immunised guinea-pigs, challenge of the airways with nebulised histamine (10-1000 nmol) or leukotriene C4 (LTC4, 30-300 pmol) elicited dose-dependent increases in insufflation pressure and in concentrations of endogenous NO in exhaled air. 6. The increase in exhaled NO correlated with the increase in insufflation pressure in response to ovalbumin, histamine and LTC4. An inhibitor of endogenous NO synthesis, N omega-nitro-L-arginine methylester (L-NAME, 30 mg kg-1 i.v.) abolished NO exhalation, and markedly augmented the airway responses to ovalbumin, histamine, or LTC4. 7. The potentiation by L-NAME of the increase in insufflation pressure in response to ovalbumin or histamine was prevented by exogenous NO (20 p.p.m.) in the inhaled air. 8. The results indicate that endogenous NO has an inhibitory effect on bronchial obstruction. Increased NO release during allergen challenge is likely to be due to actions of histamine and leukotrienes.

Modulation of smooth muscle activity by nitric oxide in the human upper urinary tract

The aim of the study was to ascertain whether nitric oxide (NO) might regulate motility in the human upper urinary tract. Smooth muscle activity in the human renal pelvis and proximal ureter was studied in vitro in organ baths, and nitric oxide synthase (NOS) activity was studied by measurement of citrulline formation. NO, glyceryl trinitrate (GTN) and sodium nitroprusside (SNP) significantly reduced the frequency of spontaneous rhythmic contractions in renal pelvis and proximal ureter. Exogenously applied NO elicited relaxations in pre-contracted renal pelvis. Calcium-dependent NOS activity was significant in the renal pelvis but undetectable in the ureter. Also, NOS activity was absent in hydronephrotic renal pelvis. NO, SNP and GTN inhibited smooth muscle activity in the human upper urinary tract. NOS activity was obtained in normal renal pelvis but not in hydronephrotic renal pelvis. Regulation of urinary tract NO concentrations might offer a strategy for treatment of renal colic and disturbances in upper urinary tract motility.

Contribution from upper and lower airways to exhaled endogenous nitric oxide in humans

Endogenous nitric oxide (NO) is thought to regulate many biological functions, including pulmonary circulation and bronchomotion, and it has been found in exhaled air. Our aim was to study the excretion of NO in different parts of the respiratory system. Exhaled concentrations of NO were measured by chemiluminescence in chronic tracheostomy outpatients (group 1), in patients admitted for minor abdominal surgery (group 2), and in patients with acute respiratory failure (ARF) during mechanical ventilation (group 3). In awake volunteers (group 4), 0.57 L/min gas was aspirated through the nasal cavity into the chemiluminescence device. In group 1 (tracheostomy, n = 5) we detected 16 +/- 2 (mean +/- s.e. mean) parts per billion (ppb) NO when exhaling through the mouth, and a lower (P < 0.05) value of 4.6 +/- 0.8 ppb NO when exhaling through the tracheostomy. Before anaesthesia, group 2 (n = 11) exhibited 18 +/- 2.4 ppb NO in orally exhaled gas, increasing considerably during exhalation through the nose. Upon endotracheal intubation exhaled NO concentration dropped to 1.3 +/- 0.2 ppb (P < 0.05). In group 3 (ARF, n = 7) tracheal NO concentrations were 0.8 +/- 0.2 ppb. In group 4 (volunteers, n = 6) 394 +/- 23 ppb NO was recorded in air from the nasal cavity. In both healthy subjects and patients with respiratory failure a significant NO excretion occurs in the lower airways and lungs. The upper airways, especially the nose, contribute the largest amount of NO (> 90%) to exhaled air. The physiological implications of an upper airway source of NO remain to be defined.

Positive end-expiratory pressure ventilation elicits increases in endogenously formed nitric oxide as detected in air exhaled by rabbits

BACKGROUND

Nitric oxide (NO) formed from L-arginine is exhaled by mammals and regulates pulmonary vascular tone. Little is known about how its formation is stimulated.

METHODS

The concentration of NO in exhaled air was monitored by chemiluminescence in pentobarbital-anesthetized rabbits receiving mechanical ventilation by tracheostomy with graded positive end-expiratory pressure (PEEP).

RESULTS

Introduction of PEEP (2.5-15 cmH2O) elicited dose-dependent and reproducible increments in exhaled NO and in arterial oxygen tension (PaO2). The increase in exhaled NO exhibited a biphasic pattern, with an initial peak followed by a partial reversal during the 4-min period at each level of PEEP. Thus, at a PEEP of 10 cmH2O, exhaled NO initially increased from 19 +/- 4 to 30 +/- 5 parts per billion (ppb) (P < 0.001, n = 9) and then decreased to 27 +/- 5 ppb (P < 0.005) at the end of the 4-min observation period. Simultaneously, PaO2 increased from 75 +/- 12 mmHg in the control situation to 105 +/- 11 mmHg (P < 0.05) at a PEEP of 10 cmH2O. After bilateral vagotomy, including bilateral transection of the depressor nerves, the increase in exhaled NO in response to PEEP was significantly reduced (P < 0.01). Thus, after vagotomy, a PEEP of 10 cmH2O elicited an increase in the concentration of exhaled NO from 13 +/- 3 to 17 +/- 3 ppb (n = 7). Vagotomy did not affect the baseline concentration of NO in exhaled air. The PEEP-induced increments in PaO2 were not affected by the NO synthase inhibitor L-N omega-arginine-methylester (30 mg.kg-1 intravenously). In open-chest experiments, PEEP (10 cmH2O) induced a reduction in cardiac output from 317 +/- 36 to 235 +/- 30 ml.min-1 and an increase in exhaled NO from 23 +/- 6 to 30 +/- 7 ppb (P < 0.05, n = 5). Reduction in cardiac output from 300 +/- 67 to 223 +/- 52 ml.min-1 by partial obstruction of the pulmonary artery did not significantly increase exhaled NO (from 23 +/- 7 to 25 +/- 6, difference not significant; n = 3).

CONCLUSIONS

PEEP elicited increments in exhaled NO, perhaps by a stretch-dependent effect on the respiratory system. This finding may be attributed in part to a vagally influenced mechanism.

Rapid tolerance to formation of authentic NO from nitroglycerin in vivo

Direct evidence for in vivo NO formation from nitroglycerin (GTN) was obtained by measurements of exhaled nitric oxide in anaesthetized. Infusions of GTN (1-100 micrograms kg-1 min-1 i.v.) induced dose-dependent and biphasic increments in exhaled NO parallelled by reductions in systemic blood pressure. The NO detected during GTN infusion was unaffected by the nitric oxide synthase inhibitor L-NAME or acute i.v. administration of L-cysteine, N-acetyl-L-cysteine or glutathione. The present data demonstrate that NO is formed from GTN in vivo, and that tolerance in vivo is due to decreased formation of NO.

Smooth muscle relaxing effects of NO, nitrosothiols and a nerve-induced relaxing factor released in guinea-pig colon

1. The aim of the present study was to compare the biological activity of S-nitroso-L-cysteine (CYSNO), S-nitrosoglutathione (GSNO), S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and hydroxylamine to that of nitric oxide (NO) and a vascular relaxing factor released by nerve stimulation in the guinea-pig intestine. The biological activity was examined in a bioassay system with guinea-pig colon as donor tissue and a series of spiral strips of rabbit aorta without endothelium as detector tissues. 2. Electrical stimulation of the guinea-pig colon released a vascular relaxing factor. The half-life of the relaxing factor down the bioassay cascade was the same as exogenously applied NO. N omega-nitro-L-arginine (L-NOARG) inhibited the release of bioactivity. 3. The relaxations of the assay tissues caused by exogenous CYSNO also declined during the passage down the cascade. However, in the presence of L-cysteine (10(-5) M) the half-life of CYSNO increased and there was no significant breakdown through the cascade. In contrast, the half-life of applied NO and the vascular relaxing factor released by nerve stimulation was unaffected by the presence of L-cysteine. 4. Exogenously applied GSNO (20-50 nM), SNAP (2-4 nM) and hydroxylamine (300-600 nM) caused relaxations that did not decline during the passage down the cascade. 5. In summary, the relaxation of the bioassay tissues during nerve stimulation was indistinguishable from the relaxation induced by NO, whereas relaxations induced by CYSNO, GSNO, SNAP and hydroxylamine showed different pharmacological profiles. The released bioactivity is thus likely to be NO itself.

Tumour necrosis factor-alpha and nitric oxide, determined as nitrite, in malignant pleural effusion

Pleurodesis treatment is often used to stop chronic pleural effusion in malignant pleurisy. During the treatment a strong intrapleural inflammation is induced leading to the cessation of exudation. In this study the concentrations of tumour necrosis factor (TNF-alpha) and nitric oxide (NO), determined as its immediate metabolite nitrite, were measured in pleural fluid, in order to investigate if they were involved in pleural inflammation and pleural fluid exudation. Determinations were made in pleural fluid from patients with malignant pleural effusion, before and during therapeutic quinacrine-induced pleural inflammation. TNF-alpha concentrations were measured by ELISA-technique and NO/nitrite by chemiluminescence. TNF-alpha increased significantly after quinacrine instillation. NO/nitrite was initially present at the same concentrations as found in normal serum, and increased significantly during treatment. Concentrations of TNF-alpha correlate with the amount of pleural fluid production after quinacrine instillation, in that a higher level of TNF-alpha is associated with more pleural fluid production. No correlation was found between TNF-alpha and NO/nitrite, whereas a weak but significant correlation was found between NO/nitrite and concentrations of another cytokine, interleukin-1 beta (IL-1 beta). The results suggest that TNF-alpha might contribute to pleural fluid exudation and that TNF-alpha and NO are of importance in induced pleural inflammation. IL-1 beta might be one of several stimuli for NO formation in this setting.

Nitric oxide-like activity in guinea pig colon as determined by effector responses, bioassay and chemiluminescence analysis

The role of nerve-induced release of nitric oxide (NO) as a modulator of neuroeffector transmission was studied in the longitudinal muscle of the guinea pig colon. The biological activity of a vascular relaxing factor released by nerve stimulation was examined in a bioassay cascade system. Furthermore, biochemical measurements of nerve-induced release of the NO metabolite nitrite (NO2-) were made with a chemiluminescence technique. Transmural nerve stimulation elicited contractile responses that were partly blocked by atropine and further inhibited after additional application of the tachykinin receptor antagonist CP-96, 345. The NO-synthase inhibitor N omega-nitro-L-arginine (NOARG) enhanced the nerve-induced contractions and concomitantly increased the basal degree of contraction ('tone'). The relaxations obtained by nerve stimulation after treatment with atropine and histamine were inhibited by NOARG. Electrical stimulation of the guinea pig colon released a non-adrenergic non-cholinergic (NANC) vascular relaxing factor into the tissue superfusate. The half-life of this factor down the cascade was the same as that observed with exogenous application of NO NOARG and tetrodotoxin (TTX) inhibited the release of the relaxing factor. During transmural nerve stimulation there was a significant increase in NO/NO2- release. This increase was inhibited by TTX and N omega-nitro-L-arginine methyl ester (L-NAME). In conclusion, pharmacological analysis as well as bioassay and biochemical measurements suggest that NO is released during nerve stimulation in the guinea pig colon, where it mediates smooth muscle relaxation.

Ca(2+)-dependent and Ca(2+)-independent exhaled nitric oxide, presence in germ-free animals, and inhibition by arginine analogues

Nitric oxide (NO) was detected by chemiluminescence in exhaled air from awake humans, anaesthetized rabbits, guinea pigs, germ-free rats and conventional rats. Rabbits exhibited the highest concentrations, followed by guinea pigs, humans and rats. There was no significant difference between germ-free rats and control rats. The authenticity of NO was confirmed in cold-trap experiments. Intravenous administration of inhibitors of NO synthase (0.01-300 mg kg-1) to guinea pigs dose dependently reduced NO concentrations in exhaled air with the following potency order: L-N omega-nitro-arginine-methylester > asymmetric NG,NG-dimethyl-L-arginine-dihydrochloride = L-NG-mono-methyl -arginine = L-N5- (1-iminoethyl)-ornithine = aminoguanidine > L-canavanine. The effect of the NO synthase inhibitors was partly or fully reversed by L-arginine (1 g kg-1 i.v.), and L-arginine per se induced a significant increment of NO in exhaled air. In rats, L-N omega-nitro-arginine-methylester was considerably less potent than in guinea pigs. The concentration of NO in exhaled air increased 3-fold when changing from in situ blood auto-perfusion of rabbit lungs to in situ perfusion with saline medium. Addition of L-N omega-nitro-arginine-methylester to the saline perfusion medium evoked a reduction of NO concentrations in the air from the ventilated perfused lungs. Perfusion of lungs with Ca(2+)-free medium induced significant decrements in NO concentrations in exhaled air, an effect partly reversed upon reintroducing Ca2+ into the medium. In conclusion, NO was detected in exhaled air from humans and animals by chemiluminescence.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol causes decrements in airway excretion of endogenous nitric oxide in humans

Ethanol has previously been demonstrated to inhibit excretion of endogenous nitric oxide (NO) in exhaled air from experimental animals. The aim of the present study was to elucidate if this effect also occurs in human subjects. Healthy volunteers ingested ethanol (0.25 and 1 g kg-1, 20% in orange juice). Nitric oxide in exhaled air was determined by chemiluminescence. Single-breath analysis of exhaled air was performed and peak values of NO and end expiratory levels of NO and CO2 were determined. Ethanol induced dose-dependent decrements in exhaled nitric oxide. Thus, peak values for nitric oxide in exhaled air, in the first exhalation after breath-holding for 30 s, decreased to 56 +/- 10 and 37 +/- 12% of control 60 min after ingestion of ethanol at 0.25 and 1 g kg-1, respectively. Rinsing the oral cavity (including gargling) for 15 min with 20% ethanol in juice did not significantly influence NO in exhaled air. Heart rate blood pressure and end expiratory levels of CO2 were not significantly affected by ethanol ingestion. In conclusion, ethanol decreases levels of nitric oxide in exhaled air in humans, likely by inhibition of airway formation of nitric oxide. The results might be of importance in understanding effects of ethanol and other hydrocarbons.

Nitric oxide is present in exhaled breath in humans: direct GC-MS confirmation

The physiological role of nitric oxide (NO) is being investigated in many experimental and clinical settings. There is considerable evidence that NO is involved in the regulation of lung vascular function. In addition there are many studies reporting the beneficial effect of NO inhalation. NO formed from L-Arginine has been detected in exhaled breath using indirect mass spectrometry and chemiluminescence. Both methods provided good evidence for the presence of NO in breath samples but were not unequivocal. We therefore developed a method using gas-chromatography-mass spectrometry which allowed us to measure trace levels of NO in air and breath. Eight healthy volunteers supplied numerous breath samples for analysis. A clear peak for nitric oxide was observed in seven volunteers. The mean level was 13ppb (n = 7, range < 2 to 19ppb). This data is in good agreement with our previous data and unequivocally confirms the presence of nitric oxide in human breath.

Oxygen or low concentrations of nitric oxide reverse pulmonary vasoconstriction induced by nitric oxide synthesis inhibition in rabbits

The objective of this study was to investigate the role of nitric oxide and oxygen in the regulation of pulmonary vascular resistance, especially by means of substitution with nitric oxide after inhibition of endogenous nitric oxide formation. In artificially ventilated open-chest rabbits pulmonary vascular resistance at normoxic ventilation (FIO2 = 21%) was 56 +/- 6 cmH2O ml-1 min-1 1000-1 (mRUL). N omega-nitro-L-arginine methyl ester (L-NAME, 30 mg kg-1), an inhibitor of NO synthase, increased pulmonary vascular resistance to 122 +/- 17 mRUL at normoxic ventilation. In response to L-NAME there was also an increase in mean arterial blood pressure. Exogenous nitric oxide (0.014-9 p.p.m. in the inhaled air) dose-dependently and reversibly counteracted the effect of L-NAME on pulmonary vascular resistance at normoxic ventilation, without affecting systemic blood pressure. In addition, the L-NAME-induced vasoconstriction was critically dependent on oxygen. Thus, during hypoxic ventilation (FIO2 = 10%) the pulmonary vascular resistance was increased approximately four-fold by the presence of L-NAME (30 mg kg-1), and increments in FIO2 (21-100%) dose-dependently and reversibly counteracted the effect of L-NAME on pulmonary vascular resistance. Taken together these findings demonstrate that inhalation of low doses of NO may act as a replacement when endogenous NO synthesis is inhibited, and that pulmonary vasoconstriction induced by NO synthesis inhibition is likely to be the result of interference with oxygen-dependent regulatory mechanisms. Endogenous NO co-operates with oxygen to evoke a vasodilator component of the pulmonary hypoxic pressor response, balancing a hitherto unknown constrictor mechanism.

Neurogenic vasodilation in rabbit hindlimb mediated by tachykinins and nitric oxide

We investigated the role of nitric oxide (NO) in the mediation of nerve stimulation-induced vasodilation in skeletal muscle. Hindlimb blood flow and vascular resistance were measured in pentobarbital-anesthetized, paralyzed, and guanethidine-treated rabbits. Centrifugal electrical stimulation of the sciatic nerve bundle induced reproducible, frequency-, voltage-, and pulse duration-dependent decrements in vascular resistance. The tachykinin antagonist CP-96,345 (1 mg/kg intravenously, i.v.) attenuated the vasodilation induced by intraarterially (i.a.) administered substance P but not by adenosine. Furthermore, CP-96,345 attenuated the decrease in vascular resistance in response to nerve stimulation, from 22.9 +/- 3.2 to 4.5 +/- 4.1% of control resting resistance (p < 0.005), without affecting basal vascular resistance. An inhibitor of NO formation, N omega-nitro-L-arginine methyl ester (L-NAME, 30 mg/kg i.v.), increased vascular resistance from 6.1 +/- 0.5 to 9.1 +/- 1.2 resistance units (p < 0.05) and significantly attenuated the vascular response to i.a. administered substance P but not adenosine. Finally, nerve stimulation-induced reduction in vascular resistance was attenuated by L-NAME, from 22.6 +/- 2.7 to 7.0 +/- 1.0% of control (p < 0.001). These findings suggest that tachykinins and NO are involved in mediation of vasodilation in response to the present type of nerve stimulation. The data are consistent with the hypothesis that NO is produced subsequent to neural release of tachykinin-type transmitter(s).

Direct demonstration of NO formation in vivo from organic nitrites and nitrates, and correlation to effects on blood pressure and to in vitro effects

Previous studies, utilizing nitric oxide synthase inhibitors and nitric oxide application, indicate that nitric oxide has the capacity to modulate contractile responses in pulmonary vessels. In the present study, in vitro effects of organic nitrates/nitrites were compared with their in vivo ability to generate nitric oxide and their effects on blood pressure. Glyceryl trinitrate, ethyl nitrite, isobutyl nitrate, isobutyl nitrite, isoamyl nitrite and butyl nitrite inhibited contractions in response to nerve stimulation in guinea pig pulmonary artery and vas deferens. Glyceryl trinitrate (also known as nitroglycerin) was the most potent and isobutyl nitrate the least potent substance with this action (IC50 4.5 +/- 0.2 x 10(-10) and 1.1 +/- 0.1 x 10(-5) M, respectively). Contractile responses to noradrenaline were inhibited, whereas noradrenaline release was unaffected by organonitrates/nitrites, indicating a post-junctional inhibitory effect. When infused intravenously to anaesthetized rabbits glyceryl trinitrate, ethyl nitrite and isobutyl nitrate generated dose-dependent increments of nitric oxide in exhaled air and dose-dependent decrements in systemic blood pressure. Significant correlations were obtained between in vivo NO generation and effects on blood pressure, as well as between NO generation in vivo and the in vitro activity of the organic nitrites and organic nitrates. In conclusion, organic nitrites and organic nitrates can modulate adrenergic neuroeffector transmission in guinea pig pulmonary artery and vas deferens, and produce detectable concentrations of nitric oxide in exhaled air in vivo, in the rabbit. The observations give direct in vivo evidence that organic nitrites and nitrates generate NO, and strongly support them exerting their action via NO formation.

Detection of nitric oxide in exhaled air during administration of nitroglycerin in vivo

1. Direct evidence for nitric oxide (NO) formation from nitroglycerin (GTN) was obtained by measurements of NO concentrations in exhaled air in artificially-ventilated, pentobarbitone-anaesthetized rabbits. 2. The concentration of endogenously formed NO was 23 +/- 5 parts per billion (p.p.b.). Infusions of GTN (1-100 micrograms kg-1 min-1, i.v.) induced dose-dependent and biphasic increments in exhaled NO and concomitant reductions in systemic blood pressure. 3. Tolerance to the blood pressure reduction developed in parallel with a decrease in GTN-induced exhaled NO, a pattern which was unaffected by administration of N omega-nitro-L-arginine methyl ester (L-NAME, 30 mg kg-1), L-cysteine (200 mg kg-1), N-acetylcysteine (200 mg kg-1) or glutathione (200 mg kg-1). 4. Intravenous infusions of adenosine (0.7 mg ml-1, 250 microliters kg-1 min-1) and GTN (1 mg ml-1, 250 microliters kg-1 min-1) elicited similar decrements in pulmonary vascular resistance. GTN elicited a substantial increase in exhaled NO (50 +/- 10 p.p.b.) whereas adenosine evoked a markedly smaller increase (7 +/- 1 p.p.b.). L-NAME (30 mg kg-1, i.v.) abolished NO in exhaled air, and evoked an increase in pulmonary vascular resistance from 116 +/- 19 to 147 +/- 9 pulmonary vascular resistance units. After L-NAME the change in pulmonary vascular resistance induced by adenosine or GTN was increased to a similar degree. However, while the increase in exhaled NO induced by nitroglycerin was unaffected, the response to adenosine was abolished. 5. The present data demonstrate that NO is formed from GTN in vivo. Furthermore, thiol availability,or nitric oxide synthase activity are not limiting factors in the conversion of nitroglycerin to NO in vivo.Finally, pulmonary haemodynamic changes per se do not explain the observed increase in NO upon nitroglycerin infusion.