Ketamine attenuates early lipopolysaccharide-induced gastric dysfunction: role of stress-inducible phosphoproteins

BACKGROUND: Ketamine exerts anti-inflammatory actions and attenuates lipopolysaccharide (LPS)-induced gastric dysfunction by an unknown mechanism. Because stress-inducible phosphoproteins mediate many inflammatory responses, we hypothesized that ketamine would disrupt the early signaling events of LPS-induced inflammation by altering phosphorylation of stress-inducible phosphoproteins JNK, p38, and IkB. METHODS: Adult rats received saline or ketamine (70 mg/kg, intraperitoneal) 1 hour before LPS (20 mg/kg, intraperitoneal) or saline. Animals were killed at 15, 30, 45, and 60 minutes after LPS, gastric mucosa was harvested, and gastric volume and pH were recorded. Gastric mucosal phosphorylation of JNK, p38, and IkB-alpha were analyzed with a multiplexed suspension immunoassay. RESULTS: Ketamine-attenuated LPS induced increases in gastric luminal fluid and pH. Control animals receiving saline or ketamine and no LPS had gastric volumes of 0.1 mL and luminal pH of 2 at all time points. LPS upregulated phosphorylation of JNK, p38, and IkB-alpha as early as 15 minutes after LPS. Ketamine did not effect the early phosphorylation of these proteins. CONCLUSION: Endotoxin causes gastric dysfunction and upregulates stress-inducible phosphoproteins within minutes after LPS. Although ketamine attenuates gastric dysfunction, its salutary effects do not seem to be related to alterations in phosphorylation of JNK, p38, or IkB-alpha.     

Rat gastric injury after lipopolysaccharide: role of inducible nitric oxide synthase

BACKGROUND: Short-term treatment with lipopolysaccharide (LPS) causes morphologic, but not macroscopic, gastric injury and decreases gastric injury caused by a subsequent challenge with a luminal irritant. This effect is abrogated by inducible nitric oxide synthase (iNOS) inhibition. The effects of long-term treatment with LPS on gastric injury are unknown as is the role of iNOS. We hypothesized that LPS would cause macroscopic gastric injury at later time points through an iNOS-dependent pathway. METHODS: Conscious rats were given saline or LPS (1 or 20 mg/kg intraperitoneal) as a single intraperitoneal injection and killed 24 to 72 hours after injection. Macroscopic gastric injury (computerized planimetry), gastric luminal fluid volume and pH, and iNOS protein levels were assessed. RESULTS: When compared with saline, high-dose but not low-dose LPS caused macroscopic gastric injury, increased gastric luminal fluid and pH, and up-regulated iNOS at 24 and 48 hours. All assessments returned to baseline by 72 hours. Inhibition of iNOS with 1400W (1 mg/kg intraperitoneal) given 15 minutes before saline or LPS (20 mg/kg) attenuated the deleterious effects of LPS on gastric injury and pH, but not fluid accumulation. CONCLUSIONS: These data suggest that prolonged treatment with high-dose LPS causes gastric injury through an iNOS-mediated pathway.     

Ketamine attenuates liver injury attributed to endotoxemia: role of cyclooxygenase-2

BACKGROUND: Endotoxic shock can cause end-organ dysfunction and liver injury. Critically ill patients frequently require surgical intervention under general anesthesia for source control. However, the effects of anesthetics on organ function during sepsis and their influence on inflammatory mediators such as cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) remain to be fully elucidated. Because ketamine anesthesia has anti-inflammatory effects in some tissues, we hypothesized that it would attenuate lipopolysaccharide (LPS)-induced liver injury. METHODS: Adult rats were given no anesthesia (saline), continuous isoflurane inhalation, or intraperitoneal (i.p.) injection of ketamine 70 mg/kg. One hour later, the rats received saline or LPS (20 mg/kg i.p.) for 5 hours. The rats were killed, and serum hepatocellular enzymes, liver COX-2, iNOS protein (Western immunoblot), and nuclear factor kappa B (NF-kappaB)-binding activity (electrophoretic mobility shift assay) determined. In a separate study, the role of COX-2 in LPS-induced liver injury was examined by pretreating rats with the selective COX-2 inhibitor NS-398 (3 mg/kg, i.p.) and the role of iNOS examined with the use of the selective inhibitor aminoguanidine (45 mg/kg, i.p.) 1 hour before LPS. RESULTS: LPS increased serum aspartate aminotransferase and alanine aminotransferase levels, hepatic iNOS and COX-2 protein, and nuclear factor NF-kappaB. Ketamine, but not isoflurane, attenuated these effects caused by LPS. COX-2 inhibition with NS-398 as well as iNOS inhibition with aminoguanidine diminished LPS-induced changes in aspartate aminotransferase and alanine aminotransferase levels. CONCLUSIONS: These data indicate that anesthetics differ in their effects on liver injury caused by LPS. Ketamine has hepatoprotective effects, while isoflurane does not. Moreover, the protective effects of ketamine are mediated, at least in part, through a reduction in COX-2 and iNOS protein that could be regulated via changes in NF-kappaB-binding activity.     

Differential effects of anesthetics on endotoxin-induced liver injury

BACKGROUND: The liver is both a source and a target of inflammatory and anti-inflammatory mediators during sepsis. The oxidative stress proteins inducible nitric oxide synthase (iNOS) and heme oxygenase-1 (HO-1) are upregulated in the liver during sepsis but have opposite roles. Upregulation of HO-1 has hepatoprotective effects, whereas iNOS has injurious effects to the liver. Although recent studies indicate that ketamine anesthesia has anti-inflammatory effects during sepsis, the effects of other anesthetics are unknown. We hypothesized that ketamine, but not isoflurane, would attenuate lipopolysaccharide (LPS)-induced liver injury through differential modulation of iNOS and HO-1. METHODS: Adult rats were given no anesthesia (saline), continuous isoflurane inhalation, or intraperitoneal ketamine (70 mg/kg). One hour later, saline or LPS (20 mg/kg intraperitoneally) was given for 5 hours. Rats were killed, serum prepared for determination of hepatocellular enzymes, and the liver assessed for iNOS and HO-1 by Western immunoblot. RESULTS: LPS significantly increased serum aspartate aminotransferase levels, iNOS, and HO-1 immunoreactivity in the liver. Ketamine but not isoflurane attenuated LPS-induced liver injury, upregulated HO-1, and downregulated iNOS. CONCLUSION: These data indicate that anesthetics differ in their effects on the liver in a rat model of sepsis with LPS. Ketamine has hepatoprotective effects against LPS-induced liver injury that appear to be mediated, at least in part, by differential modulation of the oxidative stress proteins iNOS and HO-1. Thus, ketamine may be the anesthetic agent of choice for septic patients requiring anesthesia.     

Interactive effect of morphine and dexmedetomidine on gastric emptying and gastrointestinal transit in the rat

We studied the interactive effect of dexmedetomidine and morphine on gastric emptying and gastrointestinal transit in the rat. In one group of rats, to examine the interactive effect on gastrointestinal transit, the two drugs were injected i.p. in a fixed ratio (30: 1)--that of their ED50 values--in six doses (0.062-1.075 mg kg-1), each to a different group of 5-8 male rats for each dose. In another group, to examine the interactive effect on gastric emptying, either dexmedetomidine or saline was injected with saline or with the ED25 or ED50 of morphine (0.22 and 2.8 mg kg-1, respectively). In both groups, at 30 min, radiolabelled saline 1 ml was infused into the stomach; at 1 h, gastric emptying or gastrointestinal transit was calculated by measuring the radioactivity in the gastrointestinal tract. Morphine and dexmedetomidine produced a supra-additive inhibitory effect on gastrointestinal transit (P = 0.02). Dexmedetomidine 0.01 mg kg-1, which itself significantly inhibited gastric emptying (P < 0.01), did not significantly alter the inhibitory effect of morphine on gastric emptying. Therefore, in rats, dexmedetomidine markedly enhanced the inhibitory effect of morphine on gastrointestinal transit, but it did not significantly alter the effect on gastric emptying.      

Effects of nalbuphine, pentazocine and U50488H on gastric emptying and gastrointestinal transit in the rat

We studied the effect of mixed agonist-antagonist opioids (nalbuphine and pentazocine) and a kappa opioid agonist (U50488H) on gastric emptying and gastrointestinal transit, and their interactions with morphine in rats. In each group, nalbuphine (0.01-30 mg kg-1), pentazocine (1-30 mg kg-1), U50488H (1-100 mg kg(-1)1) or saline was injected i.p. at 0 min. Another four groups of rats received morphine 13.4 mg kg-1 (ED75) and one of the following substances: saline, nalbuphine, pentazocine or U50488H. In both groups, at 30 min, radiolabelled saline 1 ml was infused into the stomach; at 1 h, gastric emptying and gastrointestinal transit were calculated by measuring the radioactivity in the gastrointestinal tract. Slopes for dose-response curves were determined. Nalbuphine significantly, but only weakly, delayed gastric emptying (P < 0.0005) and gastrointestinal transit (P < 0.01). Pentazocine markedly inhibited both, whereas U50488H did not significantly inhibit either. The slopes of the dose-response curves for nalbuphine, but not for pentazocine, on both gastric emptying and gastrointestinal transit were significantly less steep than those for morphine. Nalbuphine significantly antagonized the inhibitory effect of morphine on gastric emptying (P = 0.005) and gastrointestinal transit (P = 0.02), whereas pentazocine and U50488H did not. Nalbuphine and pentazocine delay gastric emptying and gastrointestinal transit, possibly by different mechanisms.      

Ketamine/xylazine attenuates LPS-induced iNOS expression in various rat tissues

Ketamine and xylazine (K/X) are commonly used in combination as an anesthetic agent in experimental animal models. We previously noted that K/X attenuated lipopolysaccharide (LPS)-induced liver injury, gastric stasis, and reduced symptoms of endotoxemia. Because ketamine attenuates expression of several proinflammatory genes, we examined the effects of K/X on inducible nitric oxide synthase (iNOS), which has been implicated in endotoxin-induced tissue injury. We hypothesized that K/X would attenuate LPS-induced expression of iNOS in various organs in the rat. Rats were given either intraperitoneal saline or ketamine (70 mg/kg) and xylazine (6 mg/kg) 1 h before saline or LPS (20 mg/kg). Rats were sacrificed 5 h later and stomach, duodenum, jejunum, ileum, colon, liver, lung, kidney, and spleen were collected for determination of iNOS protein immunoreactivity by Western immunoblot. Data reported in densitometric units (DU) as mean +/- SEM (n >/= 5; ANOVA). LPS significantly increased iNOS protein immunoreactivity in all tissues examined versus saline controls (P 相似文献   

Differential effects of clonidine and dexmedetomidine on gastric emptying and gastrointestinal transit in the rat

We have studied the effect of clonidine, dexmedetomidine and morphine on gastric emptying and gastrointestinal transit in the rat. In one group, each agonist was injected i.p. in 6-12 male Wistar rats. In another group of rats, yohimbine, naloxone or saline was injected with an agonist. At 30 min, radiolabelled saline 1 ml was infused into the stomach. At 1 h, gastric emptying and gastrointestinal transit were calculated by measuring the radioactivity in the gastrointestinal tract. We found that clonidine and dexmedetomidine strongly inhibited gastrointestinal transit (ED50 0.08 and 0.04 mg kg-1, respectively). They also significantly inhibited gastric emptying (P < 0.05), but the effect was weak (95% confidence intervals for difference from saline 8.2-34.9% with clonidine 1 mg kg-1 and 3.4-15.4% with dexmedetomidine 0.03 mg kg-1). Morphine strongly inhibited both gastric emptying and gastrointestinal transit (ED50 2.8 and 1.2 mg kg-1, respectively). Yohimbine significantly antagonized the inhibitory effects of clonidine and dexmedetomidine (P < 0.05), whereas naloxone, which significantly antagonized the effect of morphine (P < 0.01), did not antagonize the effect of either of the other agonists.      

The alpha2-adrenergic receptor antagonist yohimbine improves endotoxin-induced inhibition of gastrointestinal motility in mice

Background: Sepsis inhibits gastrointestinal motility. Although the exactmechanism of this is unclear, lipopolysaccharide is known toactivate macrophages in the gastrointestinal wall, which upregulatetheir expression of inducible nitric oxide synthase (iNOS).This leads to an increased production of nitric oxide, whichrelaxes the gastrointestinal muscles. We studied endotoxaemicmice to determine whether yohimbine improved delayed gastricemptying and gastrointestinal transit. Methods: Male Balb/c mice (n = 49) were randomly allocated to two groups,and either yohimbine 25 µg or saline was injected s.c.Four hours later, mice in each group were further randomly allocatedto two groups, and either lipopolysaccharide 100 µg orsaline was injected intraperitoneally. Eight hours later, liquidcontaining fluorescent microbeads was infused into the stomach,and 30 min later, gastric emptying and gastrointestinal transitwere measured using flow cytometry. We also studied whetheryohimbine given after injection of lipopolysaccharide was effective(n = 22). In another group of mice (n = 32), iNOS in the gastrointestinaltract was measured using western blotting. Results: Lipopolysaccharide significantly inhibited gastric emptyingand gastrointestinal transit. Yohimbine, given before or afterlipopolysaccharide, significantly attenuated the inhibitoryeffects of lipopolysaccharide. Lipopolysaccharide increasedthe expression of iNOS in the small intestine and yohimbinesuppressed the effects of lipopolysaccharide. Conclusions: In endotoxaemic mice, yohimbine improved delayed gastric emptyingand gastrointestinal transit, possibly by downregulating lipopolysaccharide-inducedincreased expression of iNOS.     

Propofol and midazolam inhibit gastric emptying and gastrointestinal transit in mice

We studied the effect of propofol and midazolam on gastric emptying and gastrointestinal transit in mice. Ten minutes after intraperitoneal injection of propofol or midazolam, 0.2 mL of saline containing fluorescent microbeads was infused into the stomach. Thirty minutes later, the gastrointestinal tract was excised, and gastric emptying and gastrointestinal transit were calculated by measuring the quantity of fluorescent microbeads in the gastrointestinal tract by using a flow cytometer. At a dose that produced a light level of sedation (mice righted themselves within 2 s), both drugs significantly, but weakly, inhibited gastric emptying to a similar degree (propofol: P < 0.001 versus control value; 95% confidence interval [CI] for difference, 4.9%-20.2%; midazolam: P < 0.001 versus control value; 95% CI for difference, 7.8%-14.7%). Midazolam, but not propofol, delayed gastrointestinal transit (P < 0.001). At a larger dose that produced a deeper level of sedation (absence of righting reflex >10 s), both drugs significantly inhibited gastric emptying (propofol: P < 0.001; 95% CI for difference, 31.4%-61.2%; midazolam: P < 0.001; 95% CI for difference, 30.8%-61.1%) and gastrointestinal transit (P < 0.001 for both drugs).     

The effect of intrathecal medetomidine on small bowel transit in the rat

BACKGROUND AND OBJECTIVE: Gastrointestinal motility is influenced by abdominal trauma, laparotomy and particularly by intestinal ischaemia. The reflex inhibition of gastrointestinal motility is mediated mainly by the sympathetic nervous system. There are reports on the effects of systemically applied alpha2-adrenoceptor agonists on gastric emptying and recovery of bowel motility, but the effect of spinally applied alpha2-adrenoceptor agonists on intestinal motility has not been studied. The aim of this study was to investigate the effects of intrathecal medetomidine on gastrointestinal transit in rats after transient intestinal ischaemia. METHODS: Forty rats were randomly assigned to four groups of 10 each. Intrathecal catheter insertion and laparotomy were performed on each rat. Saline (10 microL) was injected intrathecally in Groups A and B. Medetomidine (10 microg in 10 microL) was injected intrathecally in Groups C and D. Intestinal ischaemia was induced in Groups B and D. Gastrointestinal transit was determined by measuring the length that a standardized marker meal of activated charcoal had travelled. Intrathecal medetomidine was compared to intrathecal saline in their effect on intestinal motility after 30 min period of bowel ischaemia. RESULTS: Laparotomy and intestinal ischaemia slowed gastrointestinal transit. Intrathecal medetomidine accelerated transit in both ischaemia and non-ischaemia groups. CONCLUSION: Intrathecal medetomidine markedly accelerated small intestinal transit and may also hasten the recovery from post-ischaemic paralytic ileus.     

Time-dependent aggravation or attenuation of lipopolysaccharide-induced gastric injury by nitric oxide synthase inhibition

BACKGROUND: This study was conducted to test the hypothesis that nonselective nitric oxide synthase (NOS) inhibitors have different effects on lipopolysaccharide (LPS)-induced gastric injury depending upon whether they are given concurrently with LPS or after LPS at a time point that inducible NOS is up-regulated. MATERIALS AND METHODS: Female Sprague-Dawley rats received intraperitoneal (IP) LPS (20 mg/kg) for 3 h. Western immunoblot was used to determine iNOS, eNOS, and nNOS immunoreactivity after 3 h. In an additional set of experiments, we assessed the time dependent effects of nitric oxide synthase inhibition by giving rats LPS (20 mg/kg, IP) concurrently with Nitro-l-arginine methyl ester (l-NAME; 2-5 mg/kg, SC) or l-N(G)-(1-iminoethyl) lysine (l-NIL; 10 mg/kg, IP) for 5 h or LPS and delayed administration of l-NAME or l-NIL 3 h following LPS injection in identical doses. For these NOS inhibition experiments microscopic and macroscopic injury was assessed by a blinded observer using previously published scoring systems. Injury studies were conducted by exposing the stomach to 3 ml of 5 mM acidified taurocholate for 5 minutes in an anesthetized prep. RESULTS: A 3-h treatment with LPS (20 mg/kg IP) significantly increased iNOS protein immunoreactivity (Western immunoblot) but not eNOS or nNOS. N(G)-l-NAME (2-5 mg/kg SC) dose dependently aggravated macroscopic (computerized planimetry) and morphological gastric injury caused by the intraluminal bile irritant 5 mm acidified taurocholate for 10 min when given concurrently with LPS, an effect reversed by l- but not D-arginine (300 mg/kg). In contrast, delayed administration of l-NAME (3 h after LPS) dose dependently attenuated the ability of LPS to exacerbate gastric injury from bile. Both concurrent and delayed administration of the selective iNOS inhibitor, l-NIL (10 mg/kg IP) attenuated the effects of LPS. CONCLUSIONS: These data indicate that during endotoxemia, the stomach is rendered more susceptible to damage from luminal irritants such as bile, a frequent occurrence in septic patients with a gastrointestinal ileus. In this setting, iNOS has a pathologic role while the constitutive NOS isoforms play gastroprotective roles.     

Double-blind randomized placebo-controlled trial of the effect of ketamine on postoperative morphine consumption in children following appendicectomy

BACKGROUND: Ketamine has an opioid sparing effect following surgery in adults. This study investigated whether a similar effect is seen following appendicectomy in paediatric patients. METHODS: Seventy-five ASA 1 or 2 children aged 7-16 years were recruited, and randomly allocated to one of three groups. Following a standard anaesthetic for appendicectomy, all were prescribed patient controlled analgesia (PCA) morphine with paracetamol and nonsteroidal anti-inflammatory drugs (NSAIDS) as required for postoperative analgesia. In addition the control group received a saline infusion postoperatively, the ketamine bolus group received 500 micro g.kg-1 intravenous (i.v.) ketamine preincision and a saline infusion postoperatively, and the ketamine infusion group received 500 micro g.kg-1 i.v. ketamine preincision and a ketamine infusion at 4 micro g.kg-1 min-1 postoperatively. Morphine consumption, rescue analgesia requirement and side-effects were recorded postoperatively. RESULTS: There was no difference in morphine consumption between the groups. The ketamine infusion group required more doses of rescue analgesia and reported more side-effects than the control group. Five patients, all in the ketamine infusion group, reported hallucinations. CONCLUSIONS: In this paediatric population intravenous ketamine did not have a morphine sparing effect. The increased incidence of side-effects, especially hallucinations, reported by patients given a ketamine infusion may limit the further use of postoperative ketamine in children.     

Does upregulation of inducible nitric oxide synthase (iNOS) render the stomach more susceptible to damage?

Nitric oxide from constitutive nitric oxide synthase (NOS) augments gastric mucosal blood flow and is important in mucosal defense. However, the function of the inducible isoform of NOS (iNOS) in the gastric mucosa remains to be fully elucidated. This study was done to examine the role of iNOS in gastric mucosal blood flow and gastric injury following endotoxemia. Conscious rats were given intraperitoneal saline or lipopolysaccharide (LPS, 5 or 20 mg/kg). Five hours later, rats were anesthetized, a laparotomy made, gastric fluid aspirated, and 3 ml of 20% ethanol introduced into the forestomach. Rats were sacrificed 10 min later for assessment of macroscopic injury (mm2) to the gastric mucosa. Other rats did not receive 20% ethanol, but instead, gastric mucosal blood flow was determined with laser Doppler, followed by sacrifice and removal of stomachs for determination of gastric mucosal iNOS immunoreactivity (Western immunoblot). Lipopolysaccharide dose dependently increased gastric injury, decreased gastric mucosal blood flow, and increased gastric mucosal iNOS immunoreactivity compared to rats receiving saline. In additional experiments and using a similar protocol, intraperitoneal administration of aminoguanidine (45 mg/kg), an iNOS inhibitor, reversed lipopolysaccharide-induced gastric injury and restored gastric mucosal blood flow to baseline, whereas the nonselective NOS inhibitor, NG-nitro-l-arginine methyl ester (5 mg/kg) did not. Taken together, these data suggest that upregulation of iNOS is in part responsible for the detrimental effects of LPS on the gastric mucosa, possibly from a reduction in gastric mucosal blood flow.     

Endogenous endotoxin participates in causing a panenteric inflammatory ileus after colonic surgery

OBJECTIVE: To investigate muscularis inflammation and endogenous endotoxin as causes of postoperative ileus. BACKGROUND: Postoperative inflammatory ileus of the colon is associated with a significant delay in gastrointestinal transit. We investigated whether these changes are caused by the downstream obstructive barrier of the surgically altered colon or by small intestinal muscularis inflammation itself. Furthermore, we evaluated the mechanistic role of gut derived endotoxin in the development of postoperative intestinal dysfunction. METHODS: Rats underwent surgical manipulation of the colon. Isolated gastrointestinal transit was analyzed in animals with ileostomy. The perioperative emigration of intracolonic particles was investigated by colonic luminal injection of fluorescently labeled LPS and microspheres. Mediator mRNA induction was quantified by real-time RT-PCR. Muscularis leukocytic infiltrates were characterized. In vitro circular muscle contractility was assessed in a standard organ bath. RESULTS: Ileostomy rats presented with a significant delay in small intestinal transit after colonic manipulation. This was associated with leukocyte recruitment and inflammatory mediator mRNA induction within the small intestinal muscularis. Colonic manipulation caused the transference of intracolonic LPS and microspheres into the intestinal muscularis. Postoperative in vitro small intestinal circular muscle contractility was impaired by 42% compared with controls. Gut decontamination and TLR-4 deletion significantly alleviated the small intestinal muscularis inflammation and prevented intestinal muscle dysfunction. CONCLUSIONS: Selective colonic manipulation initiates a distant inflammatory response in the small intestinal muscularis that contributes to postoperative ileus. The data provide evidence that gut-derived bacterial products are mechanistically involved in the initiation of this remote inflammatory cascade.     

Mechanisms of Direct Inhibitory Action of Ketamine on Vascular Smooth Muscle in Mesenteric Resistance Arteries

Background: Ketamine was previously suggested to relax vascular smooth muscle by reducing the intracellular Ca2+ concentration ([Ca2+]i). However, no direct evidence is available to indicate that ketamine reduces the [Ca2+]i in vascular smooth muscle of systemic resistance arteries.

Methods: Endothelium-intact or -denuded smooth muscle strips were prepared from rat small mesenteric arteries. Isometric force and [Ca2+]i were measured simultaneously in the fura-2-loaded, endothelium-denuded strips. In some experiments, only isometric force was measured in either the endothelium-intact or [beta]-escin-treated, endothelium-denuded strips.

Results: In the endothelium-intact strips, lower concentrations (<= 30 [mu]m) of ketamine slightly enhanced norepine-phrine-induced contraction, whereas higher concentrations (>= 100 [mu]m) of ketamine inhibited both norepinephrine- and KCl-induced contractions. In the fura-2-loaded strips, ketamine (>= 100 [mu]m) inhibited the increases in both [Ca2+]i and force induced by either norepinephrine or KCl. Ketamine also inhibited the norepinephrine-induced increase in [Ca2+]i after treatment with ryanodine. In the absence of extracellular Ca2+, ketamine notably inhibited the norepinephrine-induced increase in [Ca2+]i, whereas it only minimally inhibited caffeine-induced increase in [Ca2+]i. Ketamine had little influence on the [Ca2+]i-force relation during force development to stepwise increment of extracellular Ca2+ concentration during either KCl depolarization or norepinephrine stimulation. Ketamine did not affect Ca2+-activated contractions in the [beta]-escin membrane-permeabilized strips.     

Nitric Oxide Produced by Inducible Nitric Oxide Synthase Delays Gastric Emptying in Lipopolysaccharide-treated Rats

Background: Endotoxin induces nitric oxide synthase (NOS), resulting in relaxation of gastric smooth muscle. The authors examined the effect of NO produced in response to lipopolysaccharide (LPS) treatment on gastric emptying in rats, and they also examined the effects of a selective inhibitor of inducible NOS (iNOS), aminoguanidine, and a suppressor of iNOS gene expression, dexamethasone.

Methods: Male Wistar rats weighing 200-250 g were used. LPS-treated rats received LPS (0.2-10 mg/kg) diluted in physiologic saline intraperitoneally. Before and at different intervals up to 8 h after administration of LPS, measurements of gastric emptying were performed in groups of 3-5 rats, by determining the amount of phenol red remaining in the stomach 20 min after intragastric instillation. In additional group of LPS (2 mg/kg)-treated rats, the gastric fundus was isolated 6 h after administration, and the tension changes in response to L-arginine, a substrate for NOS, and electrical transmural stimulation (3 Hz, 5 s) were recorded isometrically.

Results: (1) Gastric emptying was delayed by pretreatment with LPS in a dose- and time-dependent fashion (reduction from 68 +/- 12% to 22 +/- 7% with a dose of 2 mg/kg for 6 h). Aminoguanidine (50 mg/kg) or dexamethasone (5 mg/kg) partially inhibited the delay (to 39 +/- 4% or to 40 +/- 10%, respectively). (2) L-arginine (0.1 mM) produced a relaxation (28 +/- 2% reduction in active tension) in the gastric fundus strips isolated from LPS-treated rats but not from LPS-untreated rats. The relaxation was inhibited by aminoguanidine (1 mM). In contrast, the relaxation response to the electrical stimulation was not affected by aminoguanidine (0.1-1 mM).     

Dopamine delays gastric emptying and prolongs orocaecal transit time in volunteers

Dopamine decreases gastric tone and may therefore influence gastrointestinal motility. The aim of this investigation was to study the effects of a continuous infusion of dopamine on gastric emptying and orocaecal transit time. Nine healthy male volunteers were studied on two occasions in a randomized order. All volunteers received on separate days a continuous infusion of dopamine 5 micrograms kg-1 min-1 on one occasion and normal saline on the other occasion. Gastric emptying was measured by the paracetamol absorption test and orocaecal transit time by the hydrogen breath test. During the dopamine infusion the area under the paracetamol concentration curve was significantly smaller than during control conditions (P = 0.02). Orocaecal transit time was prolonged during the dopamine infusion (P = 0.02). Dopamine delays gastric emptying and prolongs orocaecal transit time.     

Mechanisms of direct inhibitory action of ketamine on vascular smooth muscle in mesenteric resistance arteries

BACKGROUND: Ketamine was previously suggested to relax vascular smooth muscle by reducing the intracellular Ca2+ concentration ([Ca2+]i). However, no direct evidence is available to indicate that ketamine reduces the [Ca2+]i in vascular smooth muscle of systemic resistance arteries. METHODS: Endothelium-intact or -denuded smooth muscle strips were prepared from rat small mesenteric arteries. Isometric force and [Ca2+]i were measured simultaneously in the fura-2-loaded, endothelium-denuded strips. In some experiments, only isometric force was measured in either the endothelium-intact or beta-escin-treated, endothelium-denuded strips. RESULTS: In the endothelium-intact strips, lower concentrations (< or = 30 microm) of ketamine slightly enhanced norepinephrine-induced contraction, whereas higher concentrations (> or = 100 microM) of ketamine inhibited both norepinephrine- and KCl-induced contractions. In the fura-2-loaded strips, ketamine (> or = 100 microM) inhibited the increases in both [Ca2+]i and force induced by either norepinephrine or KCl. Ketamine also inhibited the norepinephrine-induced increase in [Ca2+]i after treatment with ryanodine. In the absence of extracellular Ca2+, ketamine notably inhibited the norepinephrine-induced increase in [Ca2+]i, whereas it only minimally inhibited caffeine-induced increase in [Ca2+]i. Ketamine had little influence on the [Ca2+]i-force relation during force development to stepwise increment of extracellular Ca2+ concentration during either KCl depolarization or norepinephrine stimulation. Ketamine did not affect Ca2+-activated contractions in the beta-escin membrane-permeabilized strips. CONCLUSIONS: The action of ketamine on contractile response to norepinephrine consists of endothelium-dependent vasoconstricting and endothelium-independent vasodilating components. The direct vasorelaxation is largely a result of reduction of[Ca2+]i in vascular smooth muscle cells. The [Ca2+]i-reducing effects are caused by inhibitions of both voltage-gated Ca2+ influx and norepinephrine-induced Ca2+ release from the intracellular stores.     

Carbachol stimulation of gastrointestinal transit in the postoperative lleus rat

Postoperative ileus was studied in a rat model which allowed simultaneous and quantitative measurement of gastric emptying (GE), small intestinal transit (SIT), and colonic transit (CT). Measurement of CT for the first time in an animal ileus model was made possible by the injection of solidified, ink-stained agar into the proximal colon. Methoxyflurane and Cyclopal anesthesia were found to delay GE. Abdominal skin incision, but not dorsal skin incision, decreased SIT. Laparotomy caused maximal decrease in GE, SIT, and CT, but laparotomy coupled with intestinal manipulations slowed the spontaneous recovery of the small intestine. The colon regained normal propulsion 9 hr after surgery, followed by the small intestine (12 hr), and then the stomach (18 hr). Carbachol given before or after surgery increased propulsive ability of all three organs, normalizing GE and CT, but not SIT. The rat appears to be an appropriate model for studying postoperative ileus if care is taken to measure transit in each part of the gastrointestinal tract with separate transit markers. The stomach, small intestine, and colon respond differently to various conditions and possibly have dissimilar neuronal inputs controlling propulsion.