Lars E. Gustafsson

Endogenous nitric oxide is present in the exhaled air of rabbits, guinea pigs and humans

The presence of nitric oxide (NO) in the exhaled air of humans and of anaesthetized rabbits and guinea pigs was demonstrated by chemiluminescence, diazotization and mass spectrometry. This NO is endogenously produced in the lung by an NO synthase, since its generation in guinea pigs and rabbits was inhibited by N omega-nitro-L-arginine methyl ester and NG-monomethyl-L-arginine, inhibitors of this enzyme. The effect of the inhibitors was reversed by the precursor of NO synthesis, L-arginine. Since NO is produced by normal vascular endothelium for the physiological regulation of blood flow and pressure and also by activated macrophages to contribute to non-specific immunity, our experiments suggest that NO may play both vascular regulatory and host defence roles in pulmonary physiology and pathophysiology.

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.

Endogenous nitric oxide as a modulator of rabbit skeletal muscle microcirculation in vivo

1 Intravital microscopy of rabbit tenuissimus muscle microvasculature was used for in vivo studies of the role of endogenous nitric oxide (NO) in local vascular control. Derivatives of arginine were applied topically in order to modulate the formation of NO from l‐arginine. 2 l‐NG‐monomethylarginine (l‐NMMA) (10–100 μm), but not d‐NG‐monomethylarginine (d‐NMMA), dose‐dependently reduced microvascular diameters. The vasoconstriction induced by l‐NMMA (100 μm) was prevented by pretreatment with l‐arginine (1 mm) but not with d‐arginine (1 mm). Intravenous infusions of l‐arginine (300 mg kg−1) reversed the effect of l‐NMMA (100 μm). l‐Arginine or d‐arginine applied topically at 1 mm per se had no effect on microvascular diameters. 3 Vasodilatation by acetylcholine (0.03‐3 μm) was significantly inhibited by l‐NMMA (100 μm), whereas vasodilatation by adenosine (0.1–100 μm) or sodium nitroprusside (100 nm) was not affected. 4 The hyperaemic response after tenuissimus muscle contractions induced by motor nerve stimulation was unaffected by the presence of l‐NMMA (100 μm). 5 Aggregates of platelets and white blood cells were seen in venules during superfusion with l‐NMMA (100 μm), but not with d‐NMMA (100 μm). 6 Our results suggest that endogenous NO formed from l‐arginine is a modulator of microvascular tone and platelet and white cell‐vessel wall interaction in vivo. Nitric oxide does not, however, appear to play a role in the mediation of functional hyperaemia in this tissue.

Modulation of cholinergic and substance P‐like neurotransmission by nitric oxide in the guinea‐pig ileum

1 The role of endogenous nitric oxide (NO) as a modulator of enteric neurotransmission was investigated in longitudinal muscle myenteric plexus (LMMP) preparations of guinea‐pig isolated ileum. 2 In tissues previously incubated with [3H]‐choline, exogenous NO inhibited electrically‐evoked [3H]‐choline overflow as well as responses to exogenous agonists, indicating that NO has the potential of neuromodulation both pre‐ and postjunctionally. 3 A series of NO synthase inhibitors enhanced contractile responses to nerve stimulation indicating inhibitory neuromodulation by endogenous NO. 4 The potency order of the NO synthase inhibitors and their consistent effects after dexamethasone, on responses to nerve stimulation, indicate action on a constitutive NO synthase. 5 Responses enhanced by NO synthase inhibitors were inhibited by the substance P receptor antagonist, spantide, suggesting a neuromodulatory influence on substance P‐like neurotransmission by the endogenous NO. 6 NO synthase inhibition did not modify contractile responses to application of acetylcholine or substance P, or [3H]‐choline overflow, indicating that endogenous NO mainly has a prejunctional inhibitory action on substance P‐like neurotransmission. Nor did it modify responses to direct electrical muscle stimulation in the presence of tetrodotoxin. This suggests a prejunctional enhancing effect by NO synthesis inhibition. 7 Evidence for endogenous NO modulation of acetylcholine release was obtained when NO synthase inhibition modified atropine‐sensitive, nerve‐mediated contractile responses. However, [3H]‐choline overflow was unaltered by NO synthase inhibition. 8 NO synthase inhibition did not modify responses to inhibitory neurotransmission. 9 The findings suggest that endogenous NO inhibits substance P‐like motor neurotransmission, probably via prejunctional mechanisms. Cholinergic transmission may also be reduced by endogenous NO, acting prejunctionally.

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 cmH2 O) 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 cmH sub 2 O, exhaled NO initially increased from 19 plus/minus 4 to 30 plus/minus 5 parts per billion (ppb) (P < 0.001, n = 9) and then decreased to 27 plus/minus 5 ppb (P < 0.005) at the end of the 4-min observation period. Simultaneously, PaO2 increased from 75 plus/minus 12 mmHg in the control situation to 105 plus/minus 11 mmHg (P < 0.05) at a PEEP of 10 cmH2 O. 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 cmH2 O elicited an increase in the concentration of exhaled NO from 13 plus/minus 3 to 17 plus/minus 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-Nomega-arginine-methylester (30 mg *symbol* kg sup -1 intravenously). In open-chest experiments, PEEP (10 cmH2 O) induced a reduction in cardiac output from 317 plus/minus 36 to 235 plus/minus 30 ml *symbol* min sup -1 and an increase in exhaled NO from 23 plus/minus 6 to 30 plus/minus 7 ppb (P < 0.05, n = 5). Reduction in cardiac output from 300 plus/minus 67 to 223 plus/minus 52 ml *symbol* min sup -1 by partial obstruction of the pulmonary artery did not significantly increase exhaled NO (from 23 plus/minus 7 to 25 plus/minus 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.

Inhaled nitric oxide therapy in neonates and children: reaching a European consensus

Inhaled nitric oxide (iNO) was first used in neonatal practice in 1992 and has subsequently been used extensively in the management of neonates and children with cardiorespiratory failure. This paper assesses evidence for the use of iNO in this population as presented to a consensus meeting jointly organised by the European Society of Paediatric and Neonatal Intensive Care, the European Society of Paediatric Research and the European Society of Neonatology. Consensus Guidelines on the Use of iNO in Neonates and Children were produced following discussion of the evidence at the consensus meeting.

Inhaled nitric oxide therapy in adults: European expert recommendations.

BackgroundInhaled nitric oxide (iNO) has been used for treatment of acute respiratory failure and pulmonary hypertension since 1991 in adult patients in the perioperative setting and in critical care.MethodsThis contribution assesses evidence for the use of iNO in this population as presented to a expert group jointly organised by the European Society of Intensive Care Medicine and the European Association of Cardiothoracic Anaesthesiologists.ConclusionsExpert recommendations on the use of iNO in adults were agreed on following presentation of the evidence at the expert meeting held in June 2004.

Ethanol can inhibit nitric oxide production.

Endogenous nitric oxide (NO) in exhaled air from anaesthetized rabbits was monitored by chemiluminescence. Ethanol (3-30 mmol kg-1) infused i.v. dose dependently reduced the levels of exhaled NO, with an IC50 of 23 +/- 3 mmol kg-1. L-Arginine (1 g kg-1) did not reverse the effect of ethanol. These results demonstrate the inhibition of NO formation by ethanol in vivo.

Cholinergic neuromodulation by endothelin in guinea pig ileum

The effect of endothelin on cholinergic neuroeffector transmission in guinea pig ileum was investigated. Endothelin was shown to inhibit the nerve-induced contractions and concomitantly to increase the basal muscle tone. Furthermore, endothelin inhibited the nerve-induced release of [3H]acetylcholine whereas the contractile response to exogenous acetylcholine was enhanced. In conclusion, our findings suggest that endothelin is a modulator of cholinergic neuroeffector transmission in guinea pig ileum with possible action via both inhibitory prejunctional and stimulatory postjunctional mechanisms.

Release of nitric oxide evoked by nerve stimulation in guinea-pig intestine.

Non-adrenergic non-cholinergic nerves provide the main inhibitory autonomic supply to intestinal smooth muscle and other organ systems. Nitric oxide is likely to act as a neurotransmitter in these nerves and a nitric oxide synthase has been demonstrated in autonomic neurons. However, there are as yet no biochemical measurements of nerve-induced release of nitric oxide or its breakdown products nitrite and nitrate. We have examined the possibility that nitric oxide is released by stimulation of autonomic nerves in the guinea-pig intestine by studying the release of nitric oxide, nitrite and nitrate. The biological activity of a vascular relaxing factor released by the activation of these nerves was compared with that of nitric oxide using a bioassay system as previously described. Nitrite and nitrate release were measured by high-performance liquid chromatography using UV absorbance. The relaxation of the bioassay tissues to nerve stimulation was indistinguishable from the relaxation induced by nitric oxide. Both relaxations were equally unstable and inhibited to a similar degree by haemoglobin and enhanced by superoxide dismutase. Furthermore, the release of the relaxing factor was attenuated by treatment with the nitric oxide synthase inhibitor N omega-nitro-L-arginine. Concomitant with the release of the relaxing factor, which was frequency dependent, there was a frequency-dependent release of nitrite and nitrate in amounts sufficient to explain the vascular relaxations observed during nerve stimulation. The release of nitrite and nitrate was also inhibited by treatment with the nitric oxide synthase inhibitor.(ABSTRACT TRUNCATED AT 250 WORDS)