Claes U. Wiklund

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.

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.

Modulation of neuroeffector transmission by endogenous nitric oxide: a role for acetylcholine receptor-activated nitric oxide formation, as indicated by measurements of nitric oxide/ nitrite release

Nitric oxide (NO) synthase inhibitors enhanced nerve-mediated contractile responses in guinea pig ileum longitudinal muscle, likely via a prejunctional effect on substance P-like neuroeffector transmission. Supporting a modulatory role for NO, application of NO through administration of acid sodium nitrite evoked marked inhibitory effects on responses to transmural nerve stimulation. Substance P-like responses to nerve stimulation were abolished by substance P receptor antagonists and were enhanced by atropine, indicating a cholinergic influence on substance P-like neuroeffector transmission. Since acetylcholine can evoke release of NO from endothelium, the possible role of acetylcholine in NO release in ileum was examined. The release of NO/nitrite, determined by chemiluminescence, was inhibited by NG-monomethyl-L-arginine (L-NMMA), by calcium removal, by tetrodotoxin or by atropine, indicating a nerve-mediated control of NO production. A basis for the NO release is likely to be spontaneous neuronal activity, where release of acetylcholine, with subsequent muscarinic receptor activation, contributes to stimulation of NO formation.

Endothelin modulation of neuroeffector transmission in rat and guinea pig vas deferens

The effects of endothelin-1 (human, porcine) on contractions induced by transmural nerve stimulation, exogenous ATP or noradrenaline, and on the release of [3H]noradrenaline were studied in guinea pig and rat vas deferens. Endothelin enhanced nerve-induced contractile responses, increased basal muscle tone and increased the contractile response to exogenous ATP in both guinea pig and rat vas deferens. Endothelin did not affect the contractile responses to exogenous noradrenaline. The calcium channel blocker felodipine antagonized the stimulating effects of endothelin in the rat vas deferens, whereas blockade of lipoxygenase and cyclooxygenase pathways by a combination of BW 755C and indomethacin was without effect. In rat vas deferens preparations preincubated with [3H]noradrenaline, endothelin inhibited the 3H overflow induced by transmural stimulation, although the contractile responses were enhanced by endothelin. Pretreatment with forskolin or felodipine did not abolish the endothelin inhibition of radiotracer overflow. In conclusion, endothelin can modulate adrenergic and purinergic neuroeffector transmission in both guinea pig and rat vas deferens via inhibitory prejunctional and stimulant postjunctional mechanisms. The stimulant postjunctional effect seemed to predominate in our experiments.

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.

Endothelin modulation of neuroeffector transmission in smooth muscle.

In a series of muscle preparations, the peptides endothelin-1 (ET-1) and endothelin-3 (ET-3) were investigated for effects on basal muscle tone, responses to transmural nerve stimulation, and release of [3H]norepinephrine or [3H]acetylcholine. ET-1 and ET-3 contracted rat vas deferens and guinea pig ileum, ET-1 being the most potent. In the guinea pig taenia coli, ET-1 induced a relaxation whereas ET-3 was almost without relaxing effect. In the rat vas deferens, ET-1 and ET-3 enhanced contractile responses to nerve stimulation, whereas the nerve-induced release of [3H]norepinephrine was inhibited by ET-1 but not by ET-3. Contractions to exogenous ATP were increased by ET-1 whereas contractions to norepinephrine were not. In the guinea pig ileum, nerve-induced contractions were inhibited by ET-1 and ET-3 as was acetylcholine release, whereas contractions to exogenous acetylcholine were enhanced by ET-1. The inhibition of nerve-induced contractions by the endothelins was not affected by treatment with 8-(p-sulfophenyl)theophylline, BW755C, or indomethacin. The relaxation by ET-1 in the guinea pig taenia coli was not affected by treatment with NG-monomethyl-L-arginine, BW755C, or indomethacin. In conclusion, ET-1 exerted a stimulatory postjunctional effect and concomitantly an inhibitory prejunctional effect on adrenergic and cholinergic neurotransmission. Also, ET-3 exerted a stimulatory postjunctional effect, whereas a prejunctional inhibitory effect of ET-3 only was evident on cholinergic neurotransmission. Blockade of the production of nitric oxide or arachidonic acid metabolites or application of an adenosine antagonist did not alter the effects of ET-1 or ET-3.

Influence of Tidal Volume on Pulse Pressure Variations in Hypovolemic Ventilated Pigs with Acute Respiratory Distress-like Syndrome

Background:Sensitivity and specificity of respiratory change in pulse pressure (&Dgr;PP) to predict preload dependency has been questioned at small tidal volumes (VT) in critically ill patients suffering from acute respiratory distress syndrome (ARDS). We studied &Dgr;PP in pigs with ARDS-like syndrome during reversible hemorrhagic shock. Methods:Prospective, observational animal study in a Laboratory Investigation Unit. Sixteen deeply sedated mechanically ventilated pigs were successively ventilated with VT of 10 ml/kg at a respiratory rate of 15 breaths/min (RR15) and VT of 6 ml/kg at RR15 and RR25. ARDS-like syndrome was produced by lung lavage in eight pigs (ARDS group). Severe hemorrhagic shock was induced by removal of 40% of total blood volume followed by restoration. Results:After bleeding, in the control group ventilated with a VT of 10 ml/kg, &Dgr;PP increased from 8.5 (95% confidence interval [CI], 7.1 to 9.9%) to 18.5% (CI, 15.3 to 21.7%; P < 0.05). In the ARDS group, this index increased similarly, from 7.1% (95% CI, 5.3 to 9.0%) to 20.1% (CI, 15.3 to 24.9%; P < 0.05). In control lungs, reduction in VT from 10 to 6 ml/kg reduced the &Dgr;PP reaction by 40%, although it remained a statistically valid indicator of hypovolemia regardless of the RR value. In contrast, in the ARDS group, &Dgr;PP was an unreliable hypovolemia marker at low VT ventilation, regardless of the RR value (p = not statistically significant). Conclusions:The present study suggests that &Dgr;PP is a reliable indicator of severe hypovolemia in pigs with healthy lungs regardless of VT or RR. In contrast, in pigs with ARDS-like syndrome ventilated with small VT, &Dgr;PP is not a good indicator of severe hemorrhage. However, in this setting, indexing &Dgr;PP to respiratory changes in transpulmonary pressure allows this marker to significantly indicate the occurrence of hypovolemia.

A ten-year retrospective case series of glucocorticoid treatment of bacterial meningitis in children.

A ten-year retrospective case series of glucocorticoid treatment of bacterial meningitis in children Sofia Ygberg (sofia.ygberg@karolinska.se), Annelie Brauner, Benedict J. Chambers, Claes Wiklund, Anna Nilsson 1.Clinical Pediatrics, Dept. of Women0s and Children0s Health, Karolinska Institutet, Stockholm, Sweden 2.Clinical Microbiology, Dept. of Microbiology, Tumor and cell biology, Karolinska University Hospital and Karolinska Institutet, Stockholm, Sweden 3.Dept. of Medicine, Center for Infectious Medicine, Karolinska Institutet, Stockholm, Sweden 4.Dept. of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden 5.Childhood Cancer Unit, Dept. of Women0s and Children0s Health, Karolinska Institutet, Stockholm, Sweden