Effect of nitric oxide on circular muscle of the canine small intestine

Enteric neuroanatomy and smooth muscle activity in the western diamondback rattlesnake (Crotalus atrox)

BACKGROUND

Gastrointestinal (GI) functions are controlled by the enteric nervous system (ENS) in vertebrates, but data on snakes are scarce, as most studies were done in mammals. However, the feeding of many snakes, including Crotalus atrox, is in strong contrast with mammals, as it consumes an immense, intact prey that is forwarded, stored, and processed by the GI tract. We performed immunohistochemistry in different regions of the GI tract to assess the neuronal density and to quantify cholinergic, nitrergic, and VIPergic enteric neurons. We recorded motility patterns and determined the role of different neurotransmitters in the control of motility. Neuroimaging experiments complemented motility findings.

RESULTS

A well-developed ganglionated myenteric plexus (MP) was found in the oesophagus, stomach, and small and large intestines. In the submucous plexus (SMP) most neurons were scattered individually without forming ganglia. The lowest number of neurons was present in the SMP of the proximal colon, while the highest was in the MP of the oesophagus. The total number of neurons in the ENS was estimated to be approx. 1.5 million. In all regions of the SMP except for the oesophagus more nitric oxide synthase+ than choline-acetyltransferase (ChAT)+ neurons were counted, while in the MP ChAT+ neurons dominated. In the SMP most nerve cells were VIP+, contrary to the MP, where numerous VIP+ nerve fibers but hardly any VIP+ neuronal cell bodies were seen. Regular contractions were observed in muscle strips from the distal stomach, but not from the proximal stomach or the colon. We identified acetylcholine as the main excitatory and nitric oxide as the main inhibitory neurotransmitter. Furthermore, 5-HT and dopamine stimulated, while VIP and the ß-receptor-agonist isoproterenol inhibited motility. ATP had only a minor inhibitory effect. Nerve-evoked contractile responses were sodium-dependent, insensitive to tetrodotoxin (TTX), but sensitive to lidocaine, supported by neuroimaging experiments.

CONCLUSIONS

The structure of the ENS, and patterns of gastric and colonic contractile activity of Crotalus atrox are strikingly different from mammalian models. However, the main excitatory and inhibitory pathways appear to be conserved. Future studies have to explore how the observed differences are an adaptation to the particular feeding strategy of the snake.

Inflammation and Impaired Gut Physiology in Post-operative Ileus: Mechanisms and the Treatment Options

Post-operative ileus (POI) is the transient cessation of coordinated gastrointestinal motility after abdominal surgical intervention. It decreases quality of life, prolongs length of hospital stay, and increases socioeconomic costs. The mechanism of POI is complex and multifactorial, and has been broadly categorized into neurogenic and inflammatory phase. Neurogenic phase mediated release of corticotropin-releasing factor (CRF) plays a central role in neuroinflammation, and affects both central autonomic response as well hypothalamic-pituitary-adrenal (HPA) axis. HPA-stress axis associated cortisol release adversely affects gut microbiota and permeability. Peripheral CRF (pCRF) is a key player in stress induced gastric emptying and colonic transit. It functions as a local effector and interacts with the CRF receptors on the mast cell to release chemical mediators of inflammation. Mast cells proteases disrupt epithelial barrier via protease activated receptor-2 (PAR-2). PAR-2 facilitates cytoskeleton contraction to reorient tight junction proteins such as occludin, claudins, junctional adhesion molecule, and zonula occludens-1 to open epithelial barrier junctions. Barrier opening affects the selectivity, and hence permeation of luminal antigens and solutes in the gastrointestinal tract. Translocation of luminal antigens perturbs mucosal immune system to further exacerbate inflammation. Stress induced dysbiosis and decrease in production of short chain fatty acids add to the inflammatory response and barrier disintegration. This review discusses potential mechanisms and factors involved in the pathophysiology of POI with special reference to inflammation and interlinked events such as epithelial barrier dysfunction and dysbiosis. Based on this review, we recommend CRF, mast cells, macrophages, and microbiota could be targeted concurrently for efficient POI management.

Nitric oxide and its role as a non-adrenergic, non-cholinergic inhibitory neurotransmitter in the gastrointestinal tract

NO is a neurotransmitter released from enteric inhibitory neurons and responsible for modulating gastrointestinal (GI) motor behaviour. Enteric neurons express nNOS (NOS1) that associates with membranes of nerve varicosities. NO released from neurons binds to soluble guanylate cyclase in post-junctional cells to generate cGMP. cGMP-dependent protein kinase type 1 (PKG1) is a major mediator but perhaps not the only pathway involved in cGMP-mediated effects in GI muscles based on gene deletion studies. NOS1+ neurons form close contacts with smooth muscle cells (SMCs), interstitial cells of Cajal (ICC) and PDGFRα+ cells, and these cells are electrically coupled (SIP syncytium). Cell-specific gene deletion studies have shown that nitrergic responses are due to mechanisms in SMCs and ICC. Controversy exists about the ion channels and other post-junctional mechanisms that mediate nitrergic responses in GI muscles. Reduced nNOS expression in enteric inhibitory motor neurons and/or reduced connectivity between nNOS+ neurons and the SIP syncytium appear to be responsible for motor defects that develop in diabetes. An overproduction of NO in some inflammatory conditions also impairs normal GI motor activity. This review summarizes recent findings regarding the role of NO as an enteric inhibitory neurotransmitter. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Inhibitory Neural Regulation of the Ca 2+ Transients in Intramuscular Interstitial Cells of Cajal in the Small Intestine

Gastrointestinal motility is coordinated by enteric neurons. Both inhibitory and excitatory motor neurons innervate the syncytium consisting of smooth muscle cells (SMCs) interstitial cells of Cajal (ICC) and PDGFRα+ cells (SIP syncytium). Confocal imaging of mouse small intestines from animals expressing GCaMP3 in ICC were used to investigate inhibitory neural regulation of ICC in the deep muscular plexus (ICC-DMP). We hypothesized that Ca2+ signaling in ICC-DMP can be modulated by inhibitory enteric neural input. ICC-DMP lie in close proximity to the varicosities of motor neurons and generate ongoing Ca2+ transients that underlie activation of Ca2+-dependent Cl- channels and regulate the excitability of SMCs in the SIP syncytium. Electrical field stimulation (EFS) caused inhibition of Ca2+ for the first 2-3 s of stimulation, and then Ca2+ transients escaped from inhibition. The NO donor (DEA-NONOate) inhibited Ca2+ transients and Nω-Nitro-L-arginine (L-NNA) or a guanylate cyclase inhibitor (ODQ) blocked inhibition induced by EFS. Purinergic neurotransmission did not affect Ca2+ transients in ICC-DMP. Purinergic neurotransmission elicits hyperpolarization of the SIP syncytium by activation of K+ channels in PDGFRα+ cells. Generalized hyperpolarization of SIP cells by pinacidil (KATP agonist) or MRS2365 (P2Y1 agonist) also had no effect on Ca2+ transients in ICC-DMP. Peptidergic transmitter receptors (VIP and PACAP) are expressed in ICC and can modulate ICC-DMP Ca2+ transients. In summary Ca2+ transients in ICC-DMP are blocked by enteric inhibitory neurotransmission. ICC-DMP lack a voltage-dependent mechanism for regulating Ca2+ release, and this protects Ca2+ handling in ICC-DMP from membrane potential changes in other SIP cells.

Pathophysiological Mechanisms of Gastrointestinal Toxicity

Humans swallow a great variety and often large amounts of chemicals as nutrients, incidental food additives and contaminants, drugs, and inhaled particles and chemicals, thus exposing the gastrointestinal tract to many potentially toxic substances. It serves as a barrier in many cases to protect other components of the body from such substances and infections. Fortunately, the gastrointestinal tract is remarkably robust and generally is able to withstand multiple daily assaults by the chemicals to which it is exposed. Some chemicals, however, can affect one or more aspects of the gastrointestinal tract to produce abnormal events that reflect toxicity. It is the purpose of this chapter to evaluate the mechanisms by which toxic chemicals produce their deleterious effects and to determine the consequences of the toxicity on integrity of gastrointestinal structure and function. Probably because of the intrinsic ability of the gastrointestinal tract to resist toxic chemicals, there is a paucity of data regarding gastrointestinal toxicology. It is therefore necessary in many cases to extrapolate toxic mechanisms from infectious processes, inflammatory conditions, ischemia, and other insults in addition to more conventional chemical sources of toxicity.

Electrophysiological and Mechanical Characteristics in Human Ileal Motility: Recordings of Slow Waves Conductions and Contractions, In vitro

Little human tissue data are available for slow waves and migrating motor complexes, which are the main components of small bowel motility. We investigated the electrophysiological and mechanical characteristics of human ileal motility, in vitro. Ileum was obtained from patients undergoing bowel resection. Electrophysiological microelectrode recordings for membrane potential changes and mechanical tension recordings for contraction from smooth muscle strips and ileal segments were performed. Drugs affecting the enteric nervous system were applied to measure the changes in activity. Slow waves were detected with a frequency of 9~10/min. There were no cross-sectional differences in resting membrane potential (RMP), amplitude or frequency between outer and inner circular muscle (CM), suggesting that electrical activities could be effectively transmitted from outer to inner CM. The presence of the interstitial cell of Cajal (ICC) at the linia septa was verified by immunohistochemistry. Contractions of strips and segments occurred at a frequency of 3~4/min and 1~2/min, respectively. The frequency, amplitude and area under the curve were similar between CM and LM. In segments, contractions of CM were associated with LM, but propagation varied with antegrade and retrograde directions. Atropine, N^W-oxide-L-arginine, and sodium nitroprusside exhibited different effects on RMP and contractions. There were no cross-sectional differences with regard to the characteristics of slow waves in CM. The frequency of contractions in smooth muscle strips and ileal segments was lower than slow waves. The directions of propagation were diverse, indicating both mixing and transport functions of the ileum.

Transient receptor potential vanilloid 4 inhibits mouse colonic motility by activating NO-dependent enteric neurotransmission

Recent studies implicate TRPV4 receptors in visceral pain signaling and intestinal inflammation. Our aim was to evaluate the role of TRPV4 in the control of gastrointestinal (GI) motility and to establish the underlying mechanisms. We used immunohistochemistry and PCR to study TRPV4 expression in the GI tract. The effect of TRPV4 activation on GI motility was characterized using in vitro and in vivo motility assays. Calcium and nitric oxide (NO) imaging were performed to study the intracellular signaling pathways. Finally, TRPV4 expression was examined in the colon of healthy human subjects. We demonstrated that TRPV4 can be found on myenteric neurons of the colon and is co-localized with NO synthase (NOS-1). In vitro, the TRPV4 agonist GSK1016790A reduced colonic contractility and increased inhibitory neurotransmission. In vivo, TRPV4 activation slowed GI motility and reduced stool production in mouse models mimicking pathophysiological conditions. We also showed that TRPV4 activation inhibited GI motility by reducing NO-dependent Ca(2+) release from enteric neurons. In conclusion, TRPV4 is involved in the regulation of GI motility in health and disease.

KEY MESSAGES

• Recent studies implicate TRPV4 in pain signaling and intestinal inflammation. • Our aim was to characterize the role of TRPV4 in the control of GI motility. • We found that TRPV4 activation reduced colonic contractility. • Our studies also showed altered TRPV4 mRNA expression in IBS-C patients. • TRPV4 may be a novel pharmacological target in functional GI diseases.

Temporal sequence of activation of cells involved in purinergic neurotransmission in the colon

KEY POINTS

Platelet derived growth factor receptor α (PDGFRα(+) ) cells in colonic muscles are innervated by enteric inhibitory motor neurons. PDGFRα(+) cells generate Ca(2+) transients in response to exogenous purines and these responses were blocked by MRS-2500. Stimulation of enteric neurons, with cholinergic and nitrergic components blocked, evoked Ca(2+) transients in PDGFRα(+) and smooth muscle cells (SMCs). Responses to nerve stimulation were abolished by MRS-2500 and not observed in muscles with genetic deactivation of P2Y1 receptors. Ca(2+) transients evoked by nerve stimulation in PDGFRα(+) cells showed the same temporal characteristics as electrophysiological responses. PDGFRα(+) cells express gap junction genes, and drugs that inhibit gap junctions blocked neural responses in SMCs, but not in nerve processes or PDGFRα(+) cells. PDGFRα(+) cells are directly innervated by inhibitory motor neurons and purinergic responses are conducted to SMCs via gap junctions.

ABSTRACT

Interstitial cells, known as platelet derived growth factor receptor α (PDGFRα(+) ) cells, are closely associated with varicosities of enteric motor neurons and suggested to mediate purinergic hyperpolarization responses in smooth muscles of the gastrointestinal tract (GI), but this concept has not been demonstrated directly in intact muscles. We used confocal microscopy to monitor Ca(2+) transients in neurons and post-junctional cells of the murine colon evoked by exogenous purines or electrical field stimulation (EFS) of enteric neurons. EFS (1-20 Hz) caused Ca(2+) transients in enteric motor nerve processes and then in PDGFRα(+) cells shortly after the onset of stimulation (latency from EFS was 280 ms at 10 Hz). Responses in smooth muscle cells (SMCs) were typically a small decrease in Ca(2+) fluorescence just after the initiation of Ca(2+) transients in PDGFRα(+) cells. Upon cessation of EFS, several fast Ca(2+) transients were noted in SMCs (rebound excitation). Strong correlation was noted in the temporal characteristics of Ca(2+) transients evoked in PDGFRα(+) cells by EFS and inhibitory junction potentials (IJPs) recorded with intracellular microelectrodes. Ca(2+) transients and IJPs elicited by EFS were blocked by MRS-2500, a P2Y1 antagonist, and absent in P2ry1((-/-)) mice. PDGFRα(+) cells expressed gap junction genes, and gap junction uncouplers, 18β-glycyrrhetinic acid (18β-GA) and octanol blocked Ca(2+) transients in SMCs but not in neurons or PDGFRα(+) cells. IJPs recorded from SMCs were also blocked. These findings demonstrate direct innervation of PDGFRα(+) cells by motor neurons. PDGFRα(+) cells are primary targets for purinergic neurotransmitter(s) in enteric inhibitory neurotransmission. Hyperpolarization responses are conducted to SMCs via gap junctions.

Spontaneous transient hyperpolarizations in the rabbit small intestine

Four types of electrical activity were recorded and related to cell structure by intracellular recording and dye injection into impaled cells in muscles of rabbit small intestine. The specific cell types from which recordings were made were longitudinal smooth muscle cells (LSMCs), circular smooth muscle cells (CSMCs), interstitial cells of Cajal distributed in the myenteric region (ICC-MY) and fibroblast-like cells (FLCs). Slow waves (slow wavesSMC) were recorded from LSMCs and CSMCs. Slow waves (slow wavesICC) were of greatest amplitude (>50 mV) and highest maximum rate of rise (>10 V s(-1)) in ICC-MY. The dominant activity in FLCs was spontaneous transient hyperpolarizations (STHs), with maximum amplitudes above 30 mV. STHs were often superimposed upon small amplitude slow waves (slow wavesFLC). STHs displayed a cyclical pattern of discharge irrespective of background slow wave activity. STHs were inhibited by MRS2500 (3 μm), a P2Y1 antagonist, and abolished by apamin (0.3 μm), a blocker of small conductance Ca(2+)-activated K(+) channels. Small amplitude STHs (<15 mV) were detected in smooth muscle layers, whereas STHs were not resolved in cells identified as ICC-MY. Electrical field stimulation evoked purinergic inhibitory junction potentials (IJPs) in CSMCs. Purinergic IJPs were not recorded from ICC-MY. These results suggest that FLCs may regulate smooth muscle excitability in the rabbit small intestine via generation of rhythmic apamin-sensitive STHs. Stimulation of P2Y1 receptors modulates the amplitudes of STHs. Our results also suggest that purinergic inhibitory motor neurons regulate the motility of the rabbit small intestine by causing IJPs in FLCs that conduct to CSMCs.

Purinergic neuromuscular transmission in the gastrointestinal tract; functional basis for future clinical and pharmacological studies

Nerve-mediated relaxation is necessary for the correct accomplishment of gastrointestinal (GI) motility. In the GI tract, NO and a purine are probably released by the same inhibitory motor neuron as inhibitory co-transmitters. The P2Y1 receptor has been recently identified as the receptor responsible for purinergic smooth muscle hyperpolarization and relaxation in the human gut. This finding has been confirmed in P2Y1 -deficient mice where purinergic neurotransmission is absent and transit time impaired. However, the mechanisms responsible for nerve-mediated relaxation, including the identification of the purinergic neurotransmitter(s) itself, are still debatable. Possibly different mechanisms of nerve-mediated relaxation are present in the GI tract. Functional demonstration of purinergic neuromuscular transmission has not been correlated with structural studies. Labelling of purinergic neurons is still experimental and is not performed in routine pathology studies from human samples, even when possible neuromuscular impairment is suspected. Accordingly, the contribution of purinergic neurotransmission in neuromuscular diseases affecting GI motility is not known. In this review, we have focused on the physiological mechanisms responsible for nerve-mediated purinergic relaxation providing the functional basis for possible future clinical and pharmacological studies on GI motility targeting purine receptors.

Inflammatory responses in the muscle coat of stomach and small bowel in the postoperative ileus model of guinea pig

PURPOSE

Small intestinal function returns first after surgery, and then the function of the stomach returns to normal after postoperative ileus (POI). The aim of this study was to investigate inflammatory responses in the muscle coat of stomach and small intestine in guinea pig POI model.

MATERIALS AND METHODS

The distance of charcoal migration from pylorus to the distal intestine was measured. Hematoxylin and eosin (H&E) and immunohistochemical stain for calprotectin were done from the histologic sections of stomach, jejunum and ileum obtained at 3 and 6 hour after operation. Data were compared between sham operation and POI groups.

RESULTS

The distance of charcoal migration was significantly reduced in the 3 and 6 hour POI groups compared with sham operated groups (p<0.05). On H&E staining, the degree of inflammation was significantly higher in the stomach of 3 hour POI groups compared with jejunum and ileum of POI groups or sham operated groups (p<0.05). Calprotectin positive cells were significantly increased in the muscle coat of stomach of 3 hour POI groups compared with jejunum and ileum of POI groups or sham operated groups (p<0.05). There was strong association between the degree of inflammation and calprotectin positive cells in stomach.

CONCLUSION

Postoperative ileus induced by cecal manipulation significantly increased the degree of inflammation and calprotectin positive cells in the muscle coat of stomach as a remote organ. The relevance of degree of inflammation and the recovery time of ileus should be pursued in the future research.

Different regulatory effects of hydrogen sulfide and nitric oxide on gastric motility in mice

NO and H2S are gaseous signaling molecules that modulate smooth muscle motility. We aimed to identify expressions of enzymes that catalyze H2S and NO generation in mouse gastric smooth muscle, and determine relationships between endogenous H2S and NO in regulation of smooth muscle motility. Western blotting and immunocytochemistry methods were used to track expressions of neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS), cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) in gastric smooth muscles. Smooth muscle motility was recorded by isometric force transducers. cGMP production was measured by a specific radioimmunoassay. We found that CBS, CSE, eNOS, and nNOS were all expressed in mice gastric antral smooth muscle tissues, and in cultured gastric antral smooth muscle cells. AOAA significantly inhibited smooth muscle contractions in the gastric antrum, which was significantly recovered by NaHS, while PAG had no significant effect. l-NAME enhanced contractions. NaHS at low concentrations increased basal tension but decreased it at high concentrations. SNP significantly inhibited the contractions, which could be recovered by NaHS both in the absence and presence of CuSO4. ODQ did not block NaHS-induced excitatory effect, while IBMX partially blocked this effect. cGMP production in smooth muscle was significantly increased by SNP but was not affected by NaHS. All these results suggest that endogenous H2S and NO appear to play opposite roles in regulating gastric motility and their effects may be via separate signal transduction pathways. Intracellular H2S/NO levels may be maintained in a state of balance to warrant normal smooth muscle motility.

Hemin induction of HO-1 protects against LPS-induced septic ileus

BACKGROUND

Heme oxygenase (HO-1) protects against inflammation. In this study, we investigated the protective function of hemin-induced HO-1 against lipopolysaccharide (LPS)-induced ileus.

METHODS

Rats received LPS intraperitoneally 24 h after intraperitoneal hemin pretreatment or placebo. We also injected zinc protoporphyrin (ZnPP, 3rd group), an inhibitor of HO-1, intraperitoneally 2 h before LPS administration. To assess intestinal muscle function, we examined muscularis strip contractility in an organ bath and measured gastrointestinal transit in vivo. We investigated inflammation within the muscularis using polymerase chain reaction (interleukin [IL]-6, inducible nitric oxide synthase (iNOS), HO-1 and IL-10) 6 and 24 h after LPS.

RESULTS

Hemin significantly improved in vitro intestinal muscularis contractility (P < 0.001). In addition, hemin prevented LPS-induced dysmotility in vivo (gastrointestinal transit, geometric center: 8.39 ± 0.33 versus 5.68 ± 0.44; P < 0.001). In Zinc protoporphyrin (ZnPP)-treated animals, both parameters were significantly decreased compared with the hemin group. Messenger RNA expression demonstrated a significant reduction in IL-6 (6 h, hemin: 127.6 ± 36.7 versus LPS: 14,431 ± 5407; 24 h: 1.58 ± 0.39 versus 11.15 ± 2.59; P < 0.01) and iNOS (6 h: 2516 ± 985 versus 50,771 ± 13,321; 24 h: 55.11 ± 10.55 versus 257.1 ± 43.18; P < 0.001) in hemin-treated animals. Anti-inflammatory HO-1 messenger RNA levels (6 h, hemin: 116.3 ± 18.55 versus LPS: 26.02 ± 3.64; 24 h: 18.46 ± 2.69 versus 2.80 ± 0.32; P < 0.001) were increased. There was no significant difference in IL-10 levels at 6 and 24 h. ZnPP reversed the anti-inflammatory hemin effects.

CONCLUSIONS

Hemin induction of HO-1 diminishes LPS-induced sepsis. Heme oxygenase-1 has a central role in preventing sepsis-induced ileus. This benefit is reversed by HO-1 inhibition with ZnPP.

P2Y1 purinoreceptors are fundamental to inhibitory motor control of murine colonic excitability and transit

Activation of enteric inhibitory motor neurons causes inhibitory junctional potentials (IJPs) and muscle relaxation in mammalian gastrointestinal (GI) muscles, including humans. IJPs in many GI muscles are bi-phasic with a fast initial hyperpolarization (fIJP) due to release of a purine neurotransmitter and a slower hyperpolarization component (sIJP) due to release of nitric oxide. We sought to characterize the nature of the post-junctional receptor(s) involved in transducing purinergic neural inputs in the murine colon using mice with genetically deactivated P2ry1. Wild-type mice had characteristic biphasic IJPs and pharmacological dissection confirmed that the fIJP was purinergic and the sIJP was nitrergic. The fIJP was completely absent in P2ry1(−/−) mice and the P2Y1 receptor antagonist MRS2500 had no effect on electrical activity or responses to electrical field stimulation of intrinsic nerves in these mice. Contractile experiments confirmed that purinergic responses were abolished in P2ry1(−/−) mice. Picospritzing of neurotransmitter candidates (ATP and its primary metabolite, ADP) and β-NAD (and its primary metabolite, ADP-ribose, ADPR) caused transient hyperpolarization responses in wild-type colons, but responses to β-NAD and ADPR were completely abolished in P2ry1(−/−) mice. Hyperpolarization and relaxation responses to ATP and ADP were retained in colons of P2ry1(−/−) mice. Video imaging revealed that transit of fecal pellets was significantly delayed in colons from P2ry1(−/−) mice. These data demonstrate the importance of purinergic neurotransmission in regulating colonic motility and confirm pharmacological experiments suggesting that purinergic neurotransmission is mediated via P2Y1 receptors.

Nitric oxide in enteric nervous system mediated the inhibitory effect of vasopressin on the contraction of circular muscle strips from colon in male rats

BACKGROUND

Arginine vasopressin (AVP) is widely used in the treatment of critical diseases with hypotension, but the reports about its effect on gastrointestinal motility are controversial. The purpose of this study was to characterize the role of AVP in the regulation of colonic motility and the underlying mechanism.

METHODS

The contraction of the circular muscle strips (CM) of colon in male rats was monitored by a polygraph. The expressions of cytoplasmic inducible nitric oxide synthase (iNOS), I-κB, and the nuclear P65 in proximal colon were measured by Western blot. The V(1) receptors (V(1) Rs) and iNOS were localized by immunohistochemistry. The content of nitric oxide (NO) in the colon was measured by Griess reagent at the absorbance of 560 nm.

KEY RESULTS

Arginine vasopressin (10(-10) -10(-6) mol L(-1)) caused a concentration-dependent inhibition on CM contraction. Pretreatment with one of the following chemicals, including V-1880 (10(-7) mol L(-1)), TTX (10(-5) mol L(-1)), L-NAME (10(-4) mol L(-1)), NPLA (10(-7) mol L(-1)), SMT (10(-3) mol L(-1)), and PDTC (10(-3) mol L(-1)), attenuated the inhibitory effect of AVP on CM contraction. Arginine vasopressin increased the expression of iNOS and the content of NO in proximal colon. These effects were attenuated by pretreatment with PDTC (10(-3) mol L(-1)). Following AVP administration, the amount of cytoplasmic I-κB decreased, but that of nuclear P65 increased. Double immunofluorescence labeling revealed that V(1) Rs and iNOS were co-localized on the cells of myenteric plexus in proximal colon.

CONCLUSIONS & INFERENCES

Arginine vasopressin inhibited the contraction of CM in proximal colon. This effect was mediated by NO produced from NF-κB-iNOS pathway and neuronal NOS activation in myenteric plexus.

Nitrergic inhibition of tachykininergic neuro-muscular transmission via cyclic GMP in the hamster ileum

The present study was designed to explore the inhibitory mechanism by nitric oxide (NO) of the tachykininergic neuro-muscular transmissions in the hamster ileum. In the presence of guanethidine (1 µM), atropine (0.5 µM), nifedipine (0.1 µM) and apamin (100 nM), electrical field stimuli (EFS; 0.5 ms duration, 15 V) evoked non-adrenergic, non-cholinergic excitatory junction potentials (EJPs) in circular smooth muscle cells. The EJPs were markedly inhibited by the tachykinin NK1 receptor antagonists [D-Pro(4), D-Trp(7,9)]-SP(4-11) (3 µM). Both the NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME, 200 µM) and the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ, 10 µM), did not affect on the resting membrane potentials, but enhanced the tachykininergic EJPs. In the presence of L-NAME (200 µM), exogenously applied NO (10 µM) and the membrane permeable analogue of guanosine 3',5'-cyclic monophosphate (cGMP), 8-bromoguanosine 3',5'-cyclic monophosphate (8-Br-cGMP, 3 mM), significantly inhibited the tachykininergic EJPs. Application of EFS (0.5 msec duration, 15 V) with trains of 20 pulses at 20 Hz increased amount of released substance P (SP). The release of SP was further increased by the treatment of L-NAME or ODQ, but markedly reduced by exogenously applied NO and 8-Br-cGMP. These results suggest that the endogenous NO may inhibit the tachykininergic neuro-muscular transmissions by the decrease of SP release from the tachykininergic neurons, possibly through a guanylate cyclase-cGMP-dependent mechanism in the hamster ileum.

Norepinephrine mediates the transcriptional effects of heterotypic chronic stress on colonic motor function

Chronic stress precipitates or exacerbates the symptoms of functional bowel disorders, including motility dysfunction. The cellular mechanisms of these effects are not understood. We tested the hypothesis that heterotypic chronic stress (HeCS) elevates the release of norepinephrine from the adrenal medulla, which enhances transcription of the gene-regulating expression of Ca(v)1.2 (L-type) channels in colonic circular smooth muscle cells, resulting in enhanced colonic motor function. The experiments were performed in rats using a 9-day heterotypic chronic stress (HeCS) protocol. We found that HeCS, but not acute stress, time dependently enhances the contractile response to ACh in colonic circular smooth muscle strips and in single dissociated smooth muscle cells, the plasma levels of norepinephrine and the mRNA and protein expressions of the alpha(1C) subunit of Ca(v)1.2 channels. These effects result in faster colonic transit and increase in defecation rate. The effects of HeCS are blocked by adrenalectomy but not by depletion of norepinephrine in sympathetic neurons. The inhibition of receptors for glucocortocoids, corticotropin-releasing hormone or nicotine also does not block the effects of heterotypic chronic stress. Norepinephrine acts on alpha- and beta(3)-adrenergic receptors to induce the transcription of alpha(1C) subunit. We conclude that HeCS alters colonic motor function by elevating the plasma levels of norepinephrine. Colonic motor dysfunction is associated with enhanced gene transcription of Ca(v)1.2 channels in circular smooth muscle cells. These findings suggest the potential cellular mechanisms by which heterotypic chronic stress may exacerbate motility dysfunction in patients with irritable bowel syndrome.

Magnolol attenuates sepsis-induced gastrointestinal dysmotility in rats by modulating inflammatory mediators

AIM: To investigate the protective effects of magnolol on sepsis-induced inflammation and intestinal dysmotility.

METHODS: Sepsis was induced by a single intraperitoneal injection of lipopolysaccharide (LPS). Male Wistar rats were randomly assigned to one of three treatment groups: magnolol prior to LPS injection (LPS/Mag group); vehicle prior to LPS injection (LPS/Veh group); vehicle prior to injection of saline (Control/Veh). Intestinal transit and circular muscle mechanical activity were assessed 12 h after LPS injection. Tumor necrosis factor-α (TNF-α), interleukin-10 (IL-10), monocyte chemoattractant protein-1 (MCP-1) and inducible nitric oxide synthase (iNOS) mRNA in rat ileum were studied by RT-PCR 2 h after LPS injection. Nuclear factor-κB (NF-κB) activity in the intestine was also investigated at this time using electrophoretic mobility shift assay. In addition, antioxidant activity was determined by measuring malondialdehyde (MDA) concentration and superoxide dismutase (SOD) activity in the intestine 2 h after LPS injection.

RESULTS: Magnolol significantly increased intestinal transit and circular muscle mechanical activity in LPS-treated animals. TNF-α, MCP-1 and iNOS mRNA expression in the small intestine were significantly reduced after magnolol treatment in LPS-induced septic animals, compared with untreated septic animals. Additionally, magnolol significantly increased IL-10 mRNA expression in septic rat ileum. Magnolol also significantly suppressed NF-κB activity in septic rat intestine. In addition, magnolol significantly decreased MDA concentration and increased SOD activity in rat ileum.

CONCLUSION: Magnolol prevents sepsis-induced suppression of intestinal motility in rats. The potential mechanism of this benefit of magnolol appears to be modulation of self-amplified inflammatory events and block of oxidative stress in the intestine.

Reversal by relaxin of altered ileal spontaneous contractions in dystrophic (mdx) mice through a nitric oxide-mediated mechanism

Altered nitric oxide (NO) production/release is involved in gastrointestinal motor disorders occurring in dystrophic (mdx) mice. Since the hormone relaxin (RLX) can upregulate NO biosynthesis, its effects on spontaneous motility and NO synthase (NOS) expression in the ileum of dystrophic (mdx) mice were investigated. Mechanical responses of ileal preparations were recorded in vitro via force-displacement transducers. Evaluation of the expression of NOS isoforms was performed by immunohistochemistry and Western blot. Normal and mdx mice were distributed into three groups: untreated, RLX pretreated, and vehicle pretreated. Ileal preparations from the untreated animals showed spontaneous muscular contractions whose amplitude was significantly higher in mdx than in normal mice. Addition of RLX, alone or together with l-arginine, to the bath medium depressed the amplitude of the contractions in the mdx mice, thus reestablishing a motility pattern typical of the normal mice. The NOS inhibitor N(G)-nitro-L-arginine (L-NNA) or the guanylate cyclase inhibitor ODQ reversed the effects of RLX. In RLX-pretreated mdx mice, the amplitude of spontaneous motility was reduced, thus resembling that of the normal mice, and NOS II expression in the muscle coat was increased in respect to the vehicle-pretreated mdx animals. These results indicate that RLX can reverse the altered ileal motility of mdx mice to a normal pattern, likely by upregulating NOS II expression and NO biosynthesis in the ileal smooth muscle.

Biliverdin protects against polymicrobial sepsis by modulating inflammatory mediators

Highly inducible heme oxygenase (HO)-1 is protective against acute and chronic inflammation. HO-1 generates carbon monoxide (CO), ferrous iron, and biliverdin. The aim of this study was to investigate the protective effects of biliverdin against sepsis-induced inflammation and intestinal dysmotility. Cecal ligation and puncture (CLP) was performed on Sprague-Dawley rats under isoflurane anesthesia with and without intraperitoneal biliverdin injections, which were done before, at the time of CLP, and after CLP. In vivo gastrointestinal transit was carried out with fluorescein-labeled dextran. Jejunal circular muscle contractility was quantified in vitro using organ bath-generated bethanechol dose-response curves. Neutrophilic infiltration into the muscularis externa was quantified. The jejunal muscularis was studied for cytokine mRNA expressions [interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, inducible nitric oxide synthase, cyclooxygenase-2, biliverdin, IL-10, and HO-1] using real-time RT-PCR. Biliverdin treatment prevented the sepsis-induced suppression of gastrointestinal muscle contractility in vivo and in vitro and significantly decreased neutrophilic infiltration into the jejunal muscularis. Inflammatory mRNA expressions for small bowel IL-6 and MCP-1 were significantly reduced after biliverdin treatment in CLP-induced septic animals compared with untreated septic animals. The anti-inflammatory mediator expression of small bowel IL-10 was significantly augmented after CLP at 3 h compared with untreated septic animals. These findings demonstrate that biliverdin attenuates sepsis-induced morbidity to the intestine by selectively modulating the inflammatory cascade and its subsequent sequelae on intestinal muscularis function.

Nitric Oxide and Skeletal Muscle Reperfusion Injury: Current Controversies (Research Review)

Nitric oxide (NO) has been implicated in a large number of disease processes, including ischemia-reperfusion injury following the restoration of oxygenated blood to previously ischemic muscle, which is a recognized significant complication of vascular surgery. Altered metabolism of NO is implicated in the endothelial dysfunction that forms part of the pathophysiology of ischemia-reperfusion injury. However, NO can demonstrate either protective or cytotoxic effects during reperfusion injury. The use of transgenic mice, either NO synthase (NOS) gene knockout animals, or animals that over-express NOS isoforms, along with direct NO measurements and NO donor or inhibitor studies, have all demonstrated a role for NO in skeletal muscle reperfusion injury. There appears to be an initial stimulation of NO production in the first 20-min of ischemia, with a gradual decline through early reperfusion and a second higher peak of NO commencing in the later stages of reperfusion. The absolute levels of NO in the reperfused tissue and its regulation by the subtle interplay with superoxide and the subsequent production of the highly toxic peroxynitrite anion, are important factors in determining whether NO, in the context of ischemia-reperfusion injury, has damaging or protective effects in the body.

Inhibition of carbachol-evoked oscillatory currents by the NO donor sodium nitroprusside in guinea-pig ileal myocytes

The effect of sodium nitroprusside (SNP) on carbachol (CCh)-evoked inward cationic current (Icat) oscillations in guinea-pig ileal longitudinal myocytes was investigated using the whole-cell patch-clamp technique and permeabilized longitudinal muscle strips. SNP (10 microm) completely inhibited I(cat) oscillations evoked by 1 microm CCh. 1H-(1,2,4) Oxadiazole [4,3-a] quinoxaline-1-one (ODQ; 1 microm) almost completely prevented the inhibitory effect of SNP on Icat oscillations. 8-Bromo-guanosine 3',5'-cyclic monophosphate (8-Br-cGMP; 30 microm) in the pipette solution completely abolished Icat oscillations. However, a pipette solution containing Rp-8-Br-cGMP (30 microm) almost completely abolished the inhibitory effect of SNP on Icat oscillations. When the intracellular calcium concentration ([Ca2+]i) was held at a resting level using BAPTA (10 mm) and Ca2+ (4.6 microm) in the pipette solution, CCh (1 microm) evoked only the sustained component of Icat without any oscillations and SNP did not affect the current. A high concentration of inositol 1,4,5-trisphosphate (IP3; 30 microm) in the patch pipette solutions significantly reduced the inhibitory effect of SNP (10 microm) on Icat oscillations. SNP significantly inhibited the Ca2+ release evoked by either CCh or IP3 but not by caffeine in permeabilized preparations of longitudinal muscle strips. These results suggest that the inhibitory effects of SNP on Icat oscillations are mediated, in part, by functional modulation of the IP3 receptor, and not by the inhibition of cationic channels themselves or by muscarinic receptors in the plasma membrane. This inhibition seems to be mediated by an increased cGMP concentration in a protein kinase G-dependent manner.

Effects of Nitric Oxide Synthase Inhibitor on the Digestive System Measured by Simultaneous Monitoring of Gastric Motility, Gastric Emptying Activity and Postprandial Pancreaticobiliary Secretion in Dogs

Relationships between the NO synthase inhibitor and gastric and pancreaticobiliary functions measured simultaneously in the digestive state have been little studied. The aim of this study was to estimate the effect of NO synthase inhibitor on integrated digestive function in conscious dogs. A strain gauge force transducer was implanted on the gastric antrum of 6 mongrel dogs to measure gastric contractile activity and two duodenal cannulas were inserted into the proximal and distal sites to measure the gastric emptying rate and the pancreaticobiliary output into the duodenum using our novel method. Postprandial pancreatic and biliary secretion were presented as amylase and bile acid activity, respectively. Furthermore, a cervical cannula was placed into the superior vena cava as a route for the administration of NO synthase inhibitor, N omega-nitro-L-arginine (L-NNA), at a dose of 2.5 mg/kg-h. In a group given L-NNA, gastric contractile activity after ingestion was significantly enhanced, but the emptying rates of gastric solids and liquids were significantly suppressed in comparison with the control. The mean 0-1 h amylase integrated output was significantly (P < 0.05) decreased in comparison with the control, and the mean bile acid integration of 0-1 h output was also significantly (P < 0.01) decreased. A possible explanation for this observation is that smaller volumes of nutrient are delivered into the duodenum; however, it could also be that postprandial pancreaticobiliary secretion is inhibited by an alteration of blood flow or by a change in contractions of the sphincter of Oddi after the administration of L-NNA.

Purinergic modulation of pacemaker Ca2+ activity in interstitial cells of Cajal

Purinoceptors are widely distributed throughout the body, and are thought to have important contributions to numerous functions. In this study, we characterised the contribution of purinoceptors to the mechanisms underlying spontaneous rhythmicity of the gastro-intestinal tracts. Using cell cluster preparations (100-200 microm diameter) obtained from murine ileum, we measured spontaneous intracellular Ca2+([Ca2+]i) oscillations in the presence of nifedipine, as an index of pacemaker [Ca2+]i activity in interstitial cells of Cajal (ICCs, c-Kit-immunopositive cells), the pacemaker cells for gastrointestinal motility. This small preparation also contained smooth muscle and enteric neurones. Using various purinoceptor agonists and an antagonist, we characterised both TTX-sensitive and insensitive modulations of pacemaker [Ca2+]i activity in ICCs. Continuous application of either ATP, ATPgammaS, suramin or alpha,beta-methylene ATP (alpha,beta-meATP) suppressed pacemaker [Ca2+]i activity. The inhibitory effect of alpha,beta-meATP was completely abolished by a prior application of TTX. On the other hand, even in the presence of TTX, continuous application of 2-methylthio ATP (2-MeSATP) at concentrations greater than 30 microM caused a prompt rise followed by a slow decline of the baseline [Ca2+]i, and pacemaker [Ca2+]i oscillations were gradually suppressed during the decline. Neither UTP nor alpha,beta-meATP at high concentrations (30-100 microM) produced a similar [Ca2+]i response. These results suggest that the TTX-resistant, direct purinergic modulation of pacemaker [Ca2+]i activity in ICCs is mediated via P2X purinoceptors distinct from those involved in TTX-sensitive modulation. The slow decline may be attributed to desensitisation of these purinoceptors. The possible involvement of other purinoceptors is also discussed.

Mediators of non-adrenergic non-cholinergic inhibitory neurotransmission in porcine jejunum

The purpose of this study was to determine the non-adrenergic non-cholinergic inhibitory neurotransmitter in pig jejunum. Intracellular electrical activity was recorded from circular smooth muscle cells. Inhibitory junction potentials (IJPs) evoked by electrical field stimulation were inhibited by tetrodotoxin (1 micromol L(-1)), omega-conotoxin GVIA (0.1 micromol L(-1)) tetrodotoxin, apamin (1 micromol L(-1)), 1-[6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl]-1H-pyrrole-2,5-dione (U-73122; 10 micromol L(-1)) but not by N omega-nitro-l-arginine (l-NNA; 100 micromol L(-1)), haemoglobin (10 micromol L(-1)), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 micromol L(-1)) or 9-(tetrahydro-2-furyl)adenine (SQ-22536; 10 micromol L(-1)). S-nitroso-N-acetylpenicillamine (SNAP) hyperpolarized the membrane potential. This was inhibited by ODQ (3 micromol L(-1)) and charybdotoxin (0.1 micromol L(-1)). Adenosine-5-triphosphate (ATP; 100 micromol L(-1)) and 2-methylthio ATP (2-MeS-ATP; 100 micromol L(-1)) did not hyperpolarize the membrane potential and 6-N-N-diethyl-beta- gamma -dibromomethylene-d-adenosine-5'-triphosphate (ARL67156; 100 micromol L(-1)) did not modify IJPs. Carbon monoxide (CO; 10%) and tricarbonyl dichlororuthenium dimer ([Ru(CO3Cl2)]2; 100 micromol L(-1)) hyperpolarized the membrane potential however zinc, copper and tin protoporphyrin IX (100 micromol L(-1)) did not alter IJPs. Vasoactive intestinal peptide (VIP) hyperpolarized the membrane potential but 4-Cl-d-Phe6-Leu17-VIP (1 micromol L(-1)) did not modify IJPs. Pituitary adenylate cyclase activating peptide (PACAP)38 (0.5 micromol L(-1)) hyperpolarized the membrane potential. This was inhibited by apamin (1 micromol L(-1)) but not by tetrodotoxin (1 micromol L(-1)). Pituitary adenylate cyclase activating peptide6-38 (1 micromol L(-1)) inhibited IJPs. These data suggest that inhibitory neurotransmission in pig jejunum is mediated partly by PACAP.

Inflammatory response after abdominal surgery

Surgical manipulation of the gut elicits an inflammatory cascade within the intestinal muscularis that contributes to postoperative bowel dysmotility. A range of cytokines is sequentially released into the peritoneal fluid following abdominal surgery, their concentrations reflecting the magnitude of surgical trauma. The overproduction of inflammatory mediators might have detrimental effects on organ function and contribute to the enhanced risk of anastomotic leakage in the presence of sepsis. Specific cellular immune functions such as the microbicidal activity of peritoneal phagocytes are depressed after elective surgery, imposing a risk of infectious complications. Laparoscopic surgery decreases the local and systemic production of cytokines and acute-phase reactants, and better preserves peritoneal immunity compared with open surgery. As concluded from animal studies, the gas used for the pneumoperitoneum may possess substantial immunomodulatory activity.

Alpha2-adrenergic regulation of NO production alters postoperative intestinal smooth muscle dysfunction in rodents

Alpha2-adrenergic receptor activation plays an important role in the development of postoperative ileus. Alpha2-adrenergic receptors also regulate nitric oxide (NO) production by the mononuclear phagocyte system. We have previously shown that intestinal manipulation leads to a significant increase in NO production by infiltrating monocytes within the intestinal muscularis. The purpose of this study was to investigate whether alpha2-adrenergic blockade with yohimbine would alter postsurgical intestinal smooth muscle dysfunction and NO production by infiltrating monocytes and macrophages within the intestinal muscularis. Rats underwent small bowel intestinal manipulation with or without yohimbine. In vivo gastrointestinal transit and in vitro jejunal circular muscle contractility was measured 24 h postoperatively. RT-PCR was used to detect inducible NO synthase (iNOS) expression. NO levels in tissue culture supernatants were measured. Immunohistochemistry was used to localize alpha2-adrenergic receptor expression in the intestinal muscularis. Yohimbine significantly decreased manipulation-induced delay in gastrointestinal transit and reversed the postoperative decrease in intestinal muscle contractility. Intestinal manipulation resulted in significant iNOS mRNA induction in the intestinal muscularis, which was markedly attenuated after yohimbine treatment. Yohimbine also significantly decreased the postoperative increase in NO released into intestinal muscularis tissue culture supernatant. Immunohistochemistry identified alpha2-adrenergic receptors on monocytes recruited postoperatively into the intestinal muscularis. This study demonstrates that alpha2-adrenergic receptor stimulation of the inflamed postoperative intestinal muscularis plays a significant role in aggravating postoperative ileus through an enhanced induction of iNOS mRNA and increased release of NO from manipulated intestinal muscularis.

Nitric oxide, human diseases and the herbal products that affect the nitric oxide signalling pathway

1. Nitric oxide (NO) is formed enzymatically from l-arginine in the presence of nitric oxide synthase (NOS). Nitric oxide is generated constitutively in endothelial cells via sheer stress and blood-borne substances. Nitric oxide is also generated constitutively in neuronal cells and serves as a neurotransmitter and neuromodulator in non-adrenergic, non-cholinergic nerve endings. Furthermore, NO can also be formed via enzyme induction in many tissues in the presence of cytokines. 2. The ubiquitous presence of NO in the living body suggests that NO plays an important role in the maintenance of health. Being a free radical with vasodilatory properties, NO exerts dual effects on tissues and cells in various biological systems. At low concentrations, NO can dilate the blood vessels and improve the circulation, but at high concentrations it can cause circulatory shock and induce cell death. Thus, diseases can arise in the presence of the extreme ends of the physiological concentrations of NO. 3. The NO signalling pathway has, in recent years, become a target for new drug development. The high level of flavonoids, catechins, tannins and other polyphenolic compounds present in vegetables, fruits, soy, tea and even red wine (from grapes) is believed to contribute to their beneficial health effects. Some of these compounds induce NO formation from the endothelial cells to improve circulation and some suppress the induction of inducible NOS in inflammation and infection. 4. Many botanical medicinal herbs and drugs derived from these herbs have been shown to have effects on the NO signalling pathway. For example, the saponins from ginseng, ginsenosides, have been shown to relax blood vessels (probably contributing to the antifatigue and blood pressure-lowering effects of ginseng) and corpus cavernosum (thus, for the treatment of men suffering from erectile dysfunction; however, the legendary aphrodisiac effect of ginseng may be an overstatement). Many plant extracts or purified drugs derived from Chinese medicinal herbs with proposed actions on NO pathways are also reviewed.

Nitrergic prejunctional inhibition of purinergic neuromuscular transmission in the hamster proximal colon

Neurogenic ATP and nitric oxide (NO) may play important roles in the physiological control of gastrointestinal motility. However, the interplay between purinergic and nitrergic neurons in mediating the inhibitory neurotransmission remains uncertain. This study investigated whether neurogenic NO modulates the purinergic transmission to circular smooth muscles of the hamster proximal colon. Electrical activity was recorded from circular muscle cells of the hamster proximal colon by using the microelectrode technique. Intramural nerve stimulation with a single pulse evoked a fast purinergic inhibitory junction potential (IJP) followed by a slow nitrergic IJP. The purinergic component of the second IJP evoked by paired stimulus pulses at pulse intervals between 1 and 3 s became smaller than that of the first IJP. This purinergic IJP depression could be observed at pulse intervals <3 s, but not at longer ones, and failed to occur in the presence of NO synthase inhibitor. Exogenous NO (0.3-1 microM), at which no hyperpolarization is produced, inhibited purinergic IJPs, without altering the nitrergic IJP and exogenously applied ATP-induced hyperpolarization. In the presence of both purinoceptor antagonist and nitric oxide synthase (NOS) inhibitor, intramural nerve stimulation with 5 pulses at 20 Hz evoked vasoactive intestinal peptide (VIP)-associated IJPs, suggesting that VIP component may be masked in the IJPs of the hamster proximal colon. Our results suggest that neurogenic NO may modulate the purinergic transmission to circular smooth muscles of the hamster proximal colon via a prejunctional mechanism. In addition, VIP may be involved in the neurotransmitter in the hamster proximal colon.

Intra-abdominal activation of a local inflammatory response within the human muscularis externa during laparotomy

OBJECTIVE

To investigate the initiation of a complex inflammatory response within the human intestinal muscularis intraoperatively so as to determine the clinical applicability of the inflammatory hypothesis of postoperative ileus.

SUMMARY BACKGROUND DATA

Mild intestinal manipulation in rodents initiates the activation of transcription factors, upregulates proinflammatory cytokines, and increases the release of kinetically active mediators (nitric oxide and prostaglandins), all of which results in the recruitment of leukocytes and a suppression in motility (i.e., postoperative ileus).

METHODS

Human small bowel specimens were harvested during abdominal procedures at various times after laparotomy. Histochemical and immunohistochemical techniques were applied to intestinal muscularis whole-mounts. Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed for interleukin (IL)-6, IL-1beta, tumor necrosis factor (TNF)-alpha, inducible nitric oxide synthase (iNOS), and cyclooxygenase-2 (COX-2). Signal transducers and activators of transcription (STAT) protein phosphorylation was determined by electromobility shift assay. Organ bath experiments were performed on jejunal circular smooth muscle strips. GW274150C and DFU were used in vitro as iNOS and COX-2 inhibitors.

RESULTS

Normal human muscularis externa contained numerous macrophages that expressed increased lymphocyte function associated antigen-1 (LFA-1) immunoreactivity as a function of intraoperative time. RT-PCR demonstrated a time-dependent induction of IL-6, IL-1beta, TNF-alpha, iNOS, and COX-2 mRNAs within muscularis extracts after incision. Mediators were localized to macrophages with STAT protein activation in protein extracts demonstrating local IL-6 functional activity. DFU alone or in combination with GW274150C increased circular muscle contractility. Specimens harvested after reoperation developed leukocytic infiltrates and displayed diminished in vitro muscle contractility.

CONCLUSIONS

These human data demonstrate that surgical trauma is followed by resident muscularis macrophage activation and the upregulation, release, and functional activity of proinflammatory cytokines and kinetically active mediators.

Arginase acts as an alternative pathway of L-arginine metabolism in experimental colon anastomosis

L-Arginine is the substrate for the nitric oxide synthase (NOS) pathway that is essential for gastrointestinal wound healing. L-Arginine is also the substrate for the enzyme arginase which metabolizes L-arginine to ornithine and subsequently to proline and polyamines both known to interact in cell proliferation and collagen synthesis. Two distinct isoforms of arginase exist. The temporal expression of the L-arginine metabolism in experimental colon anastomosis was investigated. Male Lewis rats underwent laparotomy. A left-sided colotomy was performed and the colon reanastomosed using 6-0 prolene. Sham operation was performed in controls. On days 2, 5, 10, 14, and 28 after the surgery the anastomosis was excised. The tissue at the anastomosis (ANAST) as well as above and below the anastomosis (PDC) and from sham colon was harvested and analyzed for distinct arginase isoform I (AI) and arginase isoform II (AII) activity, protein and mRNA expression as well as immunohistochemistry. iNOS protein and mRNA expression were investigated in parallel. A mean of 3 to 4 separate rats were analyzed per time point. Statistical analysis was performed by student's t-test, significance was reached when P < 0.05. AI activity, protein, and mRNA expression were significantly upregulated at the anastomosis compared to sham controls and PDC colons at all time points. The maximum was achieved at days 10 to 14 after wounding, and decreased to baseline levels thereafter. Inflammatory cells stained positive for AI. AII protein was not detectable. However RT-PCR showed low baseline expression. iNOS expression was upregulated early but for a shorter time period after wounding and reverted quickly to undetectable levels. In anastomotic healing, AI upregulation suggests a prolonged metabolism of arginine via arginase to polyamines and proline to provide substrate for collagen synthesis and cell proliferation. The functional implication of this arginase pathway further needs to be elucidated.

An endothelium-derived factor modulates purinergic neurotransmission to mesenteric arterial smooth muscle of hamster

The interaction between the endothelium and purinergic perivascular nerves was investigated by measuring the changes in amplitude of excitatory junction potential (EJP) of smooth muscle cells in hamster mesenteric arteries (100-350 microm). Uridin-5'-triphosphate (UTP) (100 microM) applied to endothelium-intact preparations evoked a hyperpolarization of 17.0 +/- 0.7 mV (n=46). During this hyperpolarization, the amplitude of electrically evoked EJPs was inhibited to about 50% of that of the control. In endothelium-denuded preparations, UTP (100 microM) neither hyperpolarized the smooth muscle nor inhibited the amplitude of the EJP. Neither a nitric oxide (NO) synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) (100 microM), nor a cyclooxygenase inhibitor, indomethacin (1 microM), had an effect on the UTP-evoked hyperpolarization and inhibition of the electrically evoked EJP. The UTP-evoked membrane hyperpolarization and inhibition of the EJP amplitude was antagonized by the P2Y receptor antagonist, cibacron blue (100 microM). Endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization was inhibited by either adventitial or intimal application of apamin (0.1 micro and charybdotoxin (0.1 microM). However, the EJP inhibition was still present. In apamin- and charybdotoxin-treated preparations, focal application of adenosine 5'-triphosphate (ATP) (10 mM) evoked a depolarization of 15.5 +/- 1.3 mV (n=15). This postjunctional response was not modified by UTP (15.3 +/- 1.7 mV, n=4, P>0.05). These results suggest that exogenously applied UTP activates P2Y receptors of endothelium to release endothelium-derived factors, which in turn inhibit ATP release from purinergic nerves.

Peptidergic and nitrergic inhibitory neurotransmissions in the hamster jejunum: regulation of vasoactive intestinal peptide release by nitric oxide

Regulation of vasoactive intestinal peptide (VIP) release by nitric oxide (NO) was investigated in the hamster jejunum. Electrical field stimulation and applied NO (3-100 microM) evoked biphasic hyperpolarizations consisting of an initial transient hyperpolarizing component followed by a second more slowly developing component (late component). The NO synthase inhibitor N(G)-nitro-L-arginine methyl ester (200 microM) abolished the biphasic inhibitory junction potential evoked by electrical field stimulation. The NO scavenger oxyhemoglobin (50 microM) and the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ; 10 microM) abolished both components of the inhibitory junction potentials and the NO-induced hyperpolarizations. VIP(6-28) (1 microM), which abolished VIP (3 microM)-induced hyperpolarizations, also inhibited the late components of the inhibitory junction potentials and the NO-induced hyperpolarizations. ODQ inhibited VIP release and cAMP production by electrical field stimulation and NO application. N(6)-2,0-Dibutyryladenosine 3',5'-cyclic monophosphate (0.1-3 mM) caused a membrane hyperpolarization. These results suggest that NO may stimulate VIP release from enteric nerves in the hamster jejunum. In addition, we propose that NO and NO-stimulated VIP contribute to the early and late components of the inhibitory junction potentials, respectively, in the circular smooth muscle cells of the hamster jejunum.

Distribution of Ca2+-activated K+ channel (SK2 and SK3) immunoreactivity in intestinal smooth muscles of the guinea-pig

1. The tissue distribution of small conductance Ca(2+)-activated K(+) channels (SK2 and SK3) was examined in three preparations of the guinea-pig intestine: the taneia caeci and the circular muscle layer of the stomach and proximal colon. 2. The SK3 immunoreactive (SK3-IR) cells were bi- or multipolar in appearance with numerous short processes, which formed an interconnecting network at the myenteric and submucous borders of the stomach and proximal colon. The SK3-IR cells were also present within the circular muscle layer of these preparations and throughout the taenia caeci. 3. Although SK3-IR cells had a similar distribution as cells immunoreactive for c-Kit (c-Kit-IR), the marker for interstitial cells of Cajal (ICC), only 5-10% of c-Kit-IR ICC were also SK3-IR. 4. The SK3-IR cells were clearly ICC when examined with the electron microscope. Close associations of SK3-IR ICC (ICC-SK3) and nerves were often observed, as were gap junctions with SK3-negative ICC and smooth muscle cells. 5. Punctate SK2 and SK3 channel immunoreactivity was present on the plasmalemmal surface of all smooth muscle cells examined. 6. We conclude that ICC-SK3 are a subpopulation of ICC that are directly innervated by enteric inhibitory motor nerves.

Atypical neural messengers

Notions of what constitutes a neurotransmitter have changed markedly with the advent in the past decade of synaptic molecules, which satisfy key neurotransmitter criteria but differ radically from classical transmitters. Thus, NO and carbon monoxide are neither stored in synaptic vesicles nor released by exocytosis. These gases do not act via traditional receptors on postsynaptic membranes. In addition, zinc, stored together with glutamate in synaptic vesicles, appears to act as an 'antagonist' co-transmitter at the NMDA receptor, and although localized exclusively to glia, D-serine fulfills most neurotransmitter criteria as an endogenous ligand for the 'glycine' site of NMDA receptors.

Regulation of pacemaker currents in interstitial cells of Cajal from murine small intestine by cyclic nucleotides

1. Electrical rhythmicity (slow waves) in gastrointestinal muscles (GI) is generated by interstitial cells of Cajal (ICC). Cultured ICC from the murine small intestine were studied with the patch-clamp technique to characterize regulation of pacemaker currents by cyclic nucleotides. Cyclic nucleotide agonists were also tested on intact strips of murine small intestine. 2. Nitric oxide donors slowed the frequency of pacemaker currents in a concentration-dependent manner. These effects depended on cGMP formation and were reduced by 1H-[1,2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). The effects of nitric oxide donors were mimicked by membrane-permeable analogues of cGMP. The specific cGMP phosphodiesterase inhibitor zaprinast reduced the frequency of spontaneous pacemaker currents. 3. The cGMP-dependent effects on pacemaker currents were not affected by okadaic acid or KT-5823, an inhibitor of protein kinase G. 4. Forskolin, but not dideoxy forskolin, reduced the frequency of spontaneous pacemaker activity and activated a sustained outward current. The latter was likely to be due to ATP-dependent K+ channels because it was blocked by glibenclamide. 5. The effects of forskolin were not mimicked by membrane-permeable cAMP analogues. A membrane-permeable inhibitor of protein kinase A, myristoylated PKA inhibitor, and the adenylyl cyclase inhibitor SQ-22536, had no effect on responses to forskolin. 6. Responses of intact muscles to cGMP and cAMP agonists were similar to the responses of pacemaker cells. Changes in resting membrane potential and slow wave amplitude, however, were noted in intact jejunal muscles that were not observed in ICC. Differences in responses may have been due to the effects of cyclic nucleotide agonists on smooth muscle cells that would sum with responses of ICC in intact jejunal muscle strips. 7. A cGMP-dependent mechanism regulates slow wave frequency, but this occurs through direct action of cGMP not via protein phosphorylation. Regulation of pacemaker currents by cAMP-dependent mechanisms was not observed.

Nitrergic and cholinergic vagal pathways involved in the regulation of canine proximal gastric tone: an in vivo study

To better understand the relationship between cholinergic and nitrergic (NO) innervation in the regulation of proximal gastric (fundic) tone in vivo, the effects of nitric oxide synthase blockade on fundic tone were studied in conscious dogs using vagal cooling and an electronic barostat. Vagal cooling, atropine (0.05 mg kg-1 i. v. bolus) and hexamethonium (1 mg kg-1 i.v. bolus) all markedly decreased fundic tone as reflected by increased intragastric volume, indicating a significant contribution of vagal and enteric cholinergic pathways to the maintenance of canine fundic tone. Administration of L-NNA (10 mg kg-1 i.v. bolus) increased fundic tone and the effects of L-NNA were completely prevented by prior vagal cooling or atropine administration, but not by pretreatment with hexamethonium. The relaxation effects of neurally derived NO appear primarily related to inhibition of ongoing vagal cholinergic activity. The data are consistent with the primary site of action of nitrergic mechanisms on gastric fundic tone in conscious dogs being at a presynaptic site on vagal cholinergic efferent nerves.

Arginosuccinate synthetase, arginosuccinate lyase and NOS in canine gastrointestinal tract: immunocytochemical studies

Nitric oxide synthase (NOS) requires the substrate L-arginine for NO production to support multiple gastrointestinal functions. We asked, 'Where do enzymes to regenerate L-arginine from L-citrulline exist?'. We examined loci of immunoreactivities in the canine gastrointestinal tract for arginosuccinate synthetase and arginosuccinate lyase, enzymes that resynthesize L-arginine from L-citrulline, in relation to the distribution of nNOS immunoreactivity or NADPH-diaphorase histochemistry. Arginosuccinate synthetase and lyase were present in many neurones and nerve fibres in the myenteric plexus of the lower oesophageal sphincter (LOS), antrum, pylorus, ileum and colon; in the submucosal plexus of ileum and colon; in longitudinal muscle of ileum and colon; and in nerve bundles in circular muscle everywhere. LOS muscle was also immunoreactive for both enzymes. Circular and longitudinal muscle cells of the ileum and colon and cells resembling interstitial cells of Cajal in the deep muscular plexus of the ileum and the submuscular plexus of the colon also appeared immunoreactive. In neurones, arginosuccinate synthetase and nNOS were usually co-localized. NADPH diaphorase activity was present in LOS and likely in pylorus, but not in muscularis externa of ileum or colon. We conclude that resynthesis of L-arginine probably occurs in enteric nerves, interstitial cells of Cajal (ICC) and LOS muscle; also apparently in some cells without NOS to utilize it.

Effect of exogenous ATP on canine jejunal smooth muscle

Intracellular recordings were made from the circular smooth muscle cells of the canine jejunum to study the effect of exogenous ATP and to compare the ATP response to the nonadrenergic, noncholinergic (NANC) inhibitory junction potential (IJP) evoked by electrical field stimulation (EFS). Under NANC conditions, exogenous ATP evoked a transient hyperpolarization (6.5 +/- 0.6 mV) and EFS evoked a NANC IJP (17 +/- 0.4 mV). Omega-conotoxin GVIA (100 nM) and a low-Ca(2+), high-Mg(2+) solution abolished the NANC IJP but had no effect on the ATP-evoked hyperpolarization. The ATP-evoked hyperpolarization and the NANC IJP were abolished by apamin (1 microM) and N(G)-nitro-L-arginine (100 microM). Oxyhemoglobin (5 microM) partially (38.8 +/- 5.5%) reduced the amplitude of the NANC IJP but had no effect on the ATP-evoked hyperpolarization. Neither the NANC IJP nor the ATP-evoked hyperpolarization was affected by P2 receptor antagonists or agonists, including suramin, reactive blue 2, 1-(N, O-bis-[5-isoquinolinesulfonyl]-N-methyl-L-tyrosyl)-4-phenylpiperazine , pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid, alpha, beta-methylene ATP, 2-methylthioadenosine 5'-triphosphate tetrasodium salt, and adenosine 5'-O-2-thiodiphosphate. The data suggest that ATP evoked an apamin-sensitive hyperpolarization in circular smooth muscle cells of the canine jejunum via local production of NO in a postsynaptic target cell.

Role of inducible nitric oxide synthase in postoperative intestinal smooth muscle dysfunction in rodents

BACKGROUND & AIMS

We have shown that intestinal manipulation leads to a significant inhibition of circular muscle contraction. We hypothesized that the inflammatory mediator inducible nitric oxide (NO) plays a role in surgically induced ileus.

METHODS

Rats and inducible NO synthase (iNOS) knockout and wild-type mice underwent a simple intestinal manipulation. Reverse-transcription polymerase chain reaction and immunohistochemistry were used to detect and localize iNOS expression. Nitrite and NO production were measured in muscularis cultures. Spontaneous and bethanechol-stimulated jejunal circular muscle contractions were measured in an organ bath.

RESULTS

Intestinal manipulation resulted in significant iNOS messenger RNA induction in mucosa and muscularis. Immunohistochemistry localized iNOS in phagocytes within the muscularis. Nitrite and NO production increased 59.8-fold 24 hours after manipulation. L-n(6)-(1-iminoethyl) lysine (L-NIL) inhibited this response. In control rats, selective iNOS inhibition did not increase spontaneous muscle activity, but after manipulation L-NIL significantly improved spontaneous activity. iNOS knockout mice showed a significant 81% decrease in neutrophil infiltration into the muscularis after intestinal manipulation compared with wild-types. Contractile activity was normal in knockout mice after intestinal manipulation.

CONCLUSIONS

These results show that leukocyte-derived inducible NO inhibits gastrointestinal motility after manipulation and plays an essential role in the initiation of intestinal inflammation.

Pattern of distribution and co-localization of NOS and ATP in the myenteric plexus of human fetal stomach and intestine

The pattern of distribution and co-localization of nitric oxide synthase (NOS) and quinacrine fluorescence (indicative of vesicular adenosine 5'-triphosphate, ATP), and co-localization of NADPH-diaphorase (NADPH-d) activity and NOS-immunoreactivity in the myenteric plexus of pre-term human fetal (6-17 weeks of gestation) stomach and small intestine was examined using immunohistochemical and histochemical techniques. In all stages of gestation investigated, NOS-immunoreactive and NADPH-d-reactive myenteric neurons and nerve fibres were seen in the fetal intestine and stomach. However, in fetuses of 6-10 weeks of gestation, only 15% of the NADPH-d-positive myenteric neurons were NOS-immunoreactive, whereas a 100% co-localization was found in samples of 12-17 weeks of gestation. Quinacrine fluorescent myenteric neurons and nerve fibres were found only in the fetal intestine of 12-17 weeks of gestation, of which 25% of the NADPH-d-positive myenteric neurons in these samples were quinacrine fluorescent. These findings demonstrate the presence and co-localization of markers for nitric oxide (NO)- and ATP-utilizing myenteric neurons and nerve fibres in the early stages of gestation, suggesting possible co-transmitter and/or trophic roles of ATP and NO in the process of development and maturity of human myenteric neurons. In addition, the fact that only a small percentage of NADPH-d-reactive myenteric neurons express NOS immunoreactivity at 6-10 weeks of gestation confirms that NADPH-d-reactivity does not always represent NOS activity.

ATP released from perivascular nerves hyperpolarizes smooth muscle cells by releasing an endothelium-derived factor in hamster mesenteric arteries

1. The interaction between perivascular nerves and endothelium was investigated by measuring the changes in smooth muscle membrane potentials using intracellular microelectrode techniques in hamster mesenteric thin (100-150 microm) and thick (300-350 microm) arteries. 2. In both arteries, nerve stimulation evoked excitatory junction potentials (EJPs) which were strongly inhibited by pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) (0.5-5 microM). This result indicated that the EJPs were induced by the activation of P2X receptors. 3. Transient hyperpolarizations were evoked by trains of pulses at 20 Hz in PPADS (5 microM)-pre-treated thin arteries, but not in the thick arteries. ATP (100 microM) applied to adventitial surfaces mimicked the hyperpolarizations. Both the ATP- and nerve stimulation-induced hyperpolarizations were blocked by cibacron blue F3GA (2-100 microM) and were also abolished after endothelium removal, indicating that the neurally released ATP evoked transient hyperpolarization through the activation of P2Y receptors located on the endothelium. 4. In endothelium-intact preparations, intimal application of uridine 5'-triphosphate (UTP 100 microM), a P2Y2-like receptor agonist, but not 2-methylthio ATP (7 microM), hyperpolarized the smooth muscle. The UTP-induced hyperpolarization was significantly inhibited by cibacron blue F3GA and was abolished after endothelium removal. 5. These results suggest that ATP released from the perivascular nerves may reach the endothelium and activate P2Y2-like receptors to induce the release of an endothelium-derived hyperpolarizing factor in thin arteries.

Cyclic GMP-associated apamin-sensitive nitrergic slow inhibitory junction potential in the hamster ileum

1. The mediators of non-adrenergic, non-cholinergic (NANC) inhibitory junction potentials (i.j.ps) in the circular smooth muscle cells of the hamster ileum were studied. 2. Electrical field stimulation (EFS; 0.5 ms duration, 15 V) of the intramural nerves with a train of five pulses at 20 Hz evoked a rapidly developing hyperpolarization (fast i.j.p.) followed by a sustained hyperpolarization (slow i.j.p.). 3. NG-nitro-L-arginine methyl ester (L-NAME; 50 - 200 microM) and NG-nitro-L-arginine (L-NNA; 50 - 200 microM), NO synthase inhibitors, inhibited or abolished the EFS-induced fast and slow NANC i.j.ps. The effects of these NO synthase inhibitors were reversed by L-arginine (5 mM) but not by D-arginine (5 mM). 4. Exogenously applied nitric oxide (NO; 1 - 100 microM) induced concentration-dependent hyperpolarizations. 5. Oxyhaemoglobin (5 - 50 microM), NO scavenger, inhibited only the slow i.j.p., and the NO-induced hyperpolarization. 6. 1H-[1,2,4]oxadiazolo[4, 3-a]quinoxaline-1-one (ODQ; 10 microM) and cystamine (10 mM), guanylate cyclase inhibitors, inhibited only the slow i.j.p. Zaprinast (100 microM), a phosphodiesterase type V inhibitor, enhanced the amplitude and duration of the slow i.j.p. 7. Apamin (100 nM), a small conductance Ca2+-activated K+ channel blocker, inhibited only the slow i.j.p., and NO-induced hyperpolarization. A high concentration of 8-bromoguanosine 3':5'-cyclic monophosphate (8-bromo-cGMP; 1 mM)-induced membrane hyperpolarization which was blocked by apamin. 8. These results suggest that NO, or a related compound, may be the inhibitory transmitter underlying the apamin-sensitive NANC slow i.j.p. and cyclic GMP mediates the slow i. j.p. in the hamster ileum. It is also likely that NO, without involvement of guanylate cyclase is associated with the fast i.j.p.

LPS-induced muscularis macrophage nitric oxide suppresses rat jejunal circular muscle activity

Cellular mechanisms of sepsis-induced ileus remain an enigma. The study aim was to determine the role of nitric oxide (NO) in mediating the suppression of rat jejunal circular smooth muscle activity during endotoxemia. Isolated muscularis inducible NO synthase (iNOS) mRNA was measured by RT-PCR, immunohistochemistry was employed to localize iNOS protein, and contractile activity was measured in an organ bath. The low basal expression of muscularis iNOS mRNA expression was increased in a time-dependent fashion after lipopolysaccharide (LPS), resulting in a 20-fold increase over controls 3 h after injection. Immunohistochemistry of muscularis whole mounts and dissociated muscularis cells for iNOS revealed staining only in the muscularis macrophages 12 h after LPS. LPS caused a 68% reduction in spontaneous muscle activity 12 h after injection, which improved by 53% after the in vitro application of the selective iNOS inhibitor L-N(6)-(1-iminoethyl)lysine. Similar results were obtained in C57BL/6 mice but not in iNOS knockout mice. These data demonstrate that macrophage iNOS plays an important role in mediating LPS-induced intestinal circular muscle suppression.

ATP is a mediator of the fast inhibitory junction potential in human jejunal circular smooth muscle

The neurotransmitter(s) that generates the fast component of the inhibitory junction potential (IJP-F) in human jejunal circular smooth muscle is not known. The aim of this study was to determine the role of ATP and purinergic receptors in the generation of the IJP-F in human jejunal circular smooth muscle strips. The P2-receptor antagonist suramin (100 microM) reduced the IJP-F by 28%. Apamin (1 microM) reduced the IJP-F by 25%. Desensitization of muscle strips with the putative P2x-receptor agonist alpha, beta-methylene ATP (alpha,beta-MeATP, 100 microM) decreased the IJP-F by 44%, and desensitization with the putative P2y-receptor agonist adenosine 5'-O-2-thiodiphosphate (ADPbetaS) completely abolished the IJP-F. Desensitization with the putative P2y-receptor agonist 2-methylthioATP had no effect on the IJP-F. Exogenous ATP evoked a hyperpolarization with a time course that matched the IJP-F. The ATP-evoked hyperpolarization was reduced by apamin and suramin, reduced by desensitization with alpha,beta-MeATP (69% decrease), and abolished by desensitization with ADPbetaS. These data suggest that the IJP-F in human jejunal circular smooth muscle is mediated in part by ATP through an ADPbetaS-sensitive P2 receptor.

Effects of endotoxin on regulation of intestinal smooth muscle nitric oxide synthase and intestinal transit

BACKGROUND

The disrupted intestinal transit during endotoxemia may be mediated by nitric oxide (NO). We hypothesized that the isoforms of nitric oxide synthase (NOS) are up-regulated in intestinal smooth muscle during endotoxemia and that the scavenging of NO will normalize transit.

METHODS

Rats were given Escherichia coli lipopolysaccharide (LPS) 10 mg/kg intravenously and were killed 4 hours later. To determine the activity of NOS isoforms in the jejunum and ileum, the conversion of tritiated L-arginine to tritiated L-citrulline was measured. Western immunoblots were performed by incubating the extracted protein with specific polyclonal antibodies. To determine intestinal transit, rats were divided into 4 groups: 0.9% sodium chloride 1 mL/h intravenously for 5 hours, LPS 10 mg/kg intravenous bolus plus 1 mL/h 0.9% sodium chloride intravenously, LPS plus oxyhemoglobin 0.5 g/kg/h intravenously, and oxyhemoglobin 0.5 g/kg/h intravenously.

RESULTS

LPS increased the constitutive and inducible NOS enzyme activities in the jejunum and ileum. Western blots demonstrated that LPS up-regulates both the NOS1 and NOS2 isoforms in jejunal and ileal smooth muscle. Oxyhemoglobin alone increased intestinal transit compared with controls, whereas endotoxemia increased intestinal transit, which was ameliorated with infusions of oxyhemoglobin.

CONCLUSIONS

NO may play a major role in mediating the rapid intestinal transit induced by endotoxemia.

Nitric oxide regenerates the normal colonic peristaltic activity in mdx dystrophic mouse

We demonstrated in vitro that the colonic peristaltic activity is modified in dystrophin-deficient mdx mouse indicating a defect in the enteric nervous system (ENS). Since nitric oxide (NO) has been proposed as a putative inhibitory mediator of ENS, here we have examined the effects of both L-Arginine (L-Arg) and Nomega-nitro-L-arginine methyl ester (L-NAME) on the peristaltic activity of mdx mouse distal colon. The motor pattern of colonic segment showed irregular peristaltic waves. L-Arg (10(-7) - 10(-5) M) induced the peristaltic activity to slow down. At a concentration of 10(-5) M, L-Arg produced hypomotility, characterised by a decrease in amplitude, frequency and ejected fluid volume. Conversely, L-NAME elicited hypermotility, this effect being reversed once again by the subsequent addition of L-Arg. Interestingly the addition of 10(-5) M L-Arg to the organ bath led to the normal progression, in an oral to aboral direction, of 90% of the peristaltic waves. This last result strongly suggests that exogenous application of L-Arg restores the integrative circuits of the ENS responsible for programming and co-ordinating peristaltic activity in the distal colon of mdx mouse.