Differential peristaltic motor effects of prostanoid (DP, EP, IP, TP) and leukotriene receptor agonists in the guinea-pig isolated small intestine

Inhibitory mechanisms of docosahexaenoic acid on carbachol-, angiotensin II-, and bradykinin-induced contractions in guinea pig gastric fundus smooth muscle

We studied the inhibitory actions of docosahexaenoic acid (DHA) on the contractions induced by carbachol (CCh), angiotensin II (Ang II), and bradykinin (BK) in guinea pig (GP) gastric fundus smooth muscle (GFSM), particularly focusing on the possible inhibition of store-operated Ca2+ channels (SOCCs). DHA significantly suppressed the contractions induced by CCh, Ang II, and BK; the inhibition of BK-induced contractions was the strongest. Although all contractions were greatly dependent on external Ca2+, more than 80% of BK-induced contractions remained even in the presence of verapamil, a voltage-dependent Ca2+ channel inhibitor. BK-induced contractions in the presence of verapamil were not suppressed by LOE-908 (a receptor-operated Ca2+ channel (ROCC) inhibitor) but were suppressed by SKF-96365 (an SOCC and ROCC inhibitor). BK-induced contractions in the presence of verapamil plus LOE-908 were strongly inhibited by DHA. Furthermore, DHA inhibited GFSM contractions induced by cyclopiazonic acid (CPA) in the presence of verapamil plus LOE-908 and inhibited the intracellular Ca2+ increase due to Ca2+ addition in CPA-treated 293T cells. These findings indicate that Ca2+ influx through SOCCs plays a crucial role in BK-induced contraction in GP GFSM and that this inhibition by DHA is a new mechanism by which this fatty acid inhibits GFSM contractions.

Prostaglandin E2 receptors and their role in gastrointestinal motility - Potential therapeutic targets

Prostaglandin E2 (PGE2) is found throughout the gastrointestinal tract in a diverse variety of functions and roles. The recent discovery of four PGE2 receptor subtypes in intestinal muscle layers as well as in the enteric plexus has led to much interest in the study of their roles in gut motility. Gut dysmotility has been implicated in functional disease processes including irritable bowel syndrome (IBS) and slow transit constipation, and lubiprostone, a PGE2 derivative, has recently been licensed to treat both conditions. The diversity of actions of PGE2 in the intestinal tract is attributed to its differing effects on its downstream receptor types, as well as their varied distribution in the gut, in both health and disease. This review aims to identify the role and distribution of PGE2 receptors in the intestinal tract, and aims to elucidate their distinct role in gut motor function, with a specific focus on functional intestinal pathologies.

Paracetamol - An old drug with new mechanisms of action

Paracetamol (acetaminophen) is the most commonly used over-the-counter (OTC) drug in the world. Despite its popularity and use for many years, the safety of its application and its mechanism of action are still unclear. Currently, it is believed that paracetamol is a multidirectional drug and at least several metabolic pathways are involved in its analgesic and antipyretic action. The mechanism of paracetamol action consists in inhibition of cyclooxygenases (COX-1, COX-2, and COX-3) and involvement in the endocannabinoid system and serotonergic pathways. Additionally, paracetamol influences transient receptor potential (TRP) channels and voltage-gated Kv7 potassium channels and inhibits T-type Cav3.2 calcium channels. It also exerts an impact on L-arginine in the nitric oxide (NO) synthesis pathway. However, not all of these effects have been clearly confirmed. Therefore, the aim of our paper was to summarize the current state of knowledge of the mechanism of paracetamol action with special attention to its safety concerns.

Antidiarrheal activity of α-terpineol in mice

Diarrhea is one of the leading causes of infant death in the world accounting for high child mortality rate. It is also present in different pathophysiologies related to several etiological agents. The aim of this study is to investigate the antidiarrheal effect of α -Terpineol (α-TPN) in different diarrhea models in rodents. The antidiarrheal effect of α-TPN in the treatment of acute diarrhea and enteropooling induced by castor oil or PGE₂ in Swiss mice pretreated orally with saline (NaCl 0.9%), Loperamide (5 mg/kg) and α-TPN (6.25, 12.5, 25 and 50 mg/kg) was analyzed. Additionally, parameters of severity, total weight of faeces and post-treatment for 4 h were evaluated. Modulation of the opioid and cholinergic pathways was performed and intestinal transit model using activated charcoal as marker was also used. The effect of α-TPN on secretory diarrhea was investigated using the model of fluid secretion in intestinal loops isolated from cholera toxin-treated mice. α-TPN showed antidiarrheal effect (*p < 0.05), reducing the total stool amount (*55%, *48%, *44%, *24%) and diarrheal (*47%, *66%; *56%, 10%) respectively for the doses tested. All doses investigated in the enteropooling test presented significant changes (*46%, *78%, *66%, *41% respectively) in relation to the control. α-TPN through the muscarinic pathway reduced the gastrointestinal transit (*31%), besides inhibiting PGE₂-induced diarrhea (*39%). α-TPN also reduced fluid formation and loss of Cl^- ions, by interacting directly with GM1 receptors and cholera toxin, thus increasing the uptake of intestinal fluids. The results suggest an anti-diarrheal activity of α-TPN due to its anticholinergic action, ability to block PGE₂ and GM1 receptors and interaction with cholera toxin in secretory diarrhea, making it a promising candidate drug for the treatment of diarrheal diseases.

Anti-inflammatory Effects of Enhanced Recovery Programs on Early-Stage Colorectal Cancer Surgery

BACKGROUND

Postoperative ileus (POI) is observed in 20-30% of patients undergoing colorectal cancer surgery, despite enhanced recovery programs (ERPs). Cyclooxygenase (COX)-2 is identified as a key enzyme in POI, but other arachidonic acid pathway enzymes have received little attention despite their potential as selective targets to prevent POI. The objectives were to compare the expression of arachidonic acid metabolism (AAM) enzymes (1) between patients who underwent colorectal cancer surgery and followed an ERP or not (NERP), (2) and between ERP patients who experimented POI or not and (3) to determine the ability of antagonists of these pathways to modulate contractile activity of colonic muscle.

METHODS

This was a translational study. Main outcome measures were gastrointestinal motility recovery data, mRNA expressions of key enzymes involved in AAM (RT-qPCR) and ex vivo motility values of the circular colon muscle. Twenty-eight prospectively included ERP patients were compared to eleven retrospectively included NERP patients that underwent colorectal cancer surgery.

RESULTS

ERP reduced colonic mucosal COX-2, microsomal prostaglandin E synthase (mPGES1) and hematopoietic prostaglandin D synthase (HPGDS) mRNA expression. mPGES1 and HPGDS mRNA expression were significantly associated with ERP compliance (respectively, r2 = 0.25, p = 0.002 and r2 = 0.6, p < 0.001). In muscularis propria, HPGDS mRNA expression was correlated with GI motility recovery (p = 0.002). The pharmacological inhibition of mPGES1 increased spontaneous ex vivo contractile activity in circular muscle (p = 0.03).

CONCLUSION

The effects of ERP on GI recovery are correlated with the compliance of ERP and could be mediated at least in part by mPGES1, HPGDS and COX-2. Furthermore, mPGES1 shows promise as a therapeutic target to further reduce POI duration among ERP patients.

Prostanoid EP3 receptor agonist sulprostone enhances pacemaker activity of colonic interstitial cells of Cajal

EP receptor activation by PGE2 regulates gastrointestinal motility by modulating smooth muscle contractility. Interstitial cells of Cajal (ICCs) are pacemaker cells that regulate smooth muscle activity. We aimed to determine effects of the EP3 receptor agonist sulprostone on pacemaker potentials in colonic ICCs. We performed a whole cell patch clamp, RT-PCR, and Ca²⁺ imaging in cultured ICCs from mouse colon. Sulprostone depolarized the membrane and increased pacemaker frequency. EP3 receptor antagonist blocked these sulprostone-induced effects. EP3 receptors were expressed in ANO1-positive ICCs. Phospholipase C inhibitor or Ca²⁺-ATPase inhibitor from the endoplasmic reticulum blocked the sulprostone-induced effects and sulprostone increased intracellular Ca²⁺ ([Ca²⁺]_i) oscillations. Hyperpolarization-activated cyclic nucleotide-gated (HCN) channel blockers also suppressed the sulprostone-induced effects. Sulprostone enhanced pacemaker activity through EP3 receptors by activating HCN channels via the [Ca²⁺]_i release pathway. Therefore, EP3 receptor activation in ICCs may modulate colonic motility and could be a therapeutic target for enhancing colonic GI motility.

Therapeutic implications of the prostaglandin pathway in Alzheimer's disease

An important pathologic hallmark of Alzheimer's disease (AD) is neuroinflammation, a process characterized in AD by disproportionate activation of cells (microglia and astrocytes, primarily) of the non-specific innate immune system within the CNS. While inflammation itself is not intrinsically detrimental, a delicate balance of pro- and anti-inflammatory signals must be maintained to ensure that long-term exaggerated responses do not damage the brain over time. Non-steroidal anti-inflammatory drugs (NSAIDs) represent a broad class of powerful therapeutics that temper inflammation by inhibiting cyclooxygenase-mediated signaling pathways including prostaglandins, which are the principal mediators of CNS neuroinflammation. While historically used to treat discrete or systemic inflammatory conditions, epidemiologic evidence suggests that protracted NSAID use may delay AD onset, as well as decrease disease severity and rate of progression. Unfortunately, clinical trials with NSAIDs have thus far yielded disappointing results, including premature discontinuation of a large-scale prevention trial due to unexpected cardiovascular side effects. Here we review the literature and make the argument that more targeted exploitation of downstream prostaglandin signaling pathways may offer significant therapeutic benefits for AD while minimizing adverse side effects. Directed strategies such as these may ultimately help to delay the deleterious consequences of brain aging and might someday lead to new therapies for AD and other chronic neurodegenerative diseases.

Eicosanoid modulation by the short-chain fatty acid n-butyrate in human monocytes

n-Butyrate deriving from bacterial fermentation in the mammalian intestine is a key determinant in gastrointestinal homeostasis. We examined the effects of this short-chain fatty acid and Toll-like receptor 2 (TLR) and TLR4 engagement on inflammatory/immunity-associated genes, cyclo-oxygenases (COXs), prostaglandins (PGs) and leukotrienes (LTs) in human monocytes. Before RNA isolation, freshly isolated human monocytes were co-incubated for different time-points with 1 mm n-butyrate alone or in combination with bacterial stimuli. Based on a knowledge-driven approach, a signature of 180 immunity/inflammation-associated genes was picked and real-time PCR analysis was performed. Pathway analysis was carried out using a web-based database analysing program. Based on these gene expression studies the findings were evaluated at the protein/mediator level by Western blot analysis, FACS and ELISA. Following co-incubation with n-butyrate and lipopolysaccharide, key enzymes of the eicosanoid pathway, like PTGS2 (COX-2), TXS, ALOX5, LTA4H and LTC4S, were significantly up-regulated compared with stimulation with lipopolysaccharide alone. Furthermore, release of the lipid mediators PGE(2), 15d-PGJ(2), LTB(4) and thromboxane B(2) was increased by n-butyrate. Regarding signalling, n-butyrate had no additional effect on mitogen-activated protein kinase and interfered differently with early and late phases of nuclear factor-κB signalling. Our results suggest that among many other mediators of eicosanoid signalling n-butyrate massively induces PGE(2) production by increasing the expression of PTGS2 (COX-2) in monocytes following TLR4 and TLR2 activation and induces secretion of LTB(4) and thromboxane B(2). This underscores the role of n-butyrate as a crucial mediator of gut-specific immunity.

Role of prostaglandin D2 in mast cell activation-induced sensitization of esophageal vagal afferents

Sensitization of esophageal afferents plays an important role in esophageal nociception, but the mechanism is less clear. Our previous studies demonstrated that mast cell (MC) activation releases the preformed mediators histamine and tryptase, which play important roles in sensitization of esophageal vagal nociceptive C fibers. PGD2 is a lipid mediator released by activated MCs. Whether PGD2 plays a role in this sensitization process has yet to be determined. Expression of the PGD2 DP1 and DP2 receptors in nodose ganglion neurons was determined by immunofluorescence staining, Western blotting, and RT-PCR. Extracellular recordings were performed in ex vivo esophageal-vagal preparations. Action potentials evoked by esophageal distension were compared before and after perfusion of PGD2, DP1 and DP2 receptor agonists, and MC activation, with or without pretreatment with antagonists. The effect of PGD2 on 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI)-labeled esophageal nodose neurons was determined by patch-clamp recording. Our results demonstrate that DP1 and DP2 receptor mRNA and protein were expressed mainly in small- and medium-diameter neurons in nodose ganglia. PGD2 significantly increased esophageal distension-evoked action potential discharges in esophageal nodose C fibers. The DP1 receptor agonist BW 245C mimicked this effect. PGD2 directly sensitized DiI-labeled esophageal nodose neurons by decreasing the action potential threshold. Pretreatment with the DP1 receptor antagonist BW A868C significantly inhibited PGD2 perfusion- or MC activation-induced increases in esophageal distension-evoked action potential discharges in esophageal nodose C fibers. In conclusion, PGD2 plays an important role in MC activation-induced sensitization of esophageal nodose C fibers. This adds a novel mechanism of visceral afferent sensitization.

Castor oil induces laxation and uterus contraction via ricinoleic acid activating prostaglandin EP3 receptors

Castor oil is one of the oldest drugs. When given orally, it has a laxative effect and induces labor in pregnant females. The effects of castor oil are mediated by ricinoleic acid, a hydroxylated fatty acid released from castor oil by intestinal lipases. Despite the wide-spread use of castor oil in conventional and folk medicine, the molecular mechanism by which ricinoleic acid acts remains unknown. Here we show that the EP(3) prostanoid receptor is specifically activated by ricinoleic acid and that it mediates the pharmacological effects of castor oil. In mice lacking EP(3) receptors, the laxative effect and the uterus contraction induced via ricinoleic acid are absent. Although a conditional deletion of the EP(3) receptor gene in intestinal epithelial cells did not affect castor oil-induced diarrhea, mice lacking EP(3) receptors only in smooth-muscle cells were unresponsive to this drug. Thus, the castor oil metabolite ricinoleic acid activates intestinal and uterine smooth-muscle cells via EP(3) prostanoid receptors. These findings identify the cellular and molecular mechanism underlying the pharmacological effects of castor oil and indicate a role of the EP(3) receptor as a target to induce laxative effects.

A prostaglandin D2 receptor antagonist modifies experimental asthma in sheep

BACKGROUND

Prostaglandin (PG) D(2) is the major cylooxygenase metabolite released by mast cells upon allergen stimulation, and elicits responses through either the prostanoid DP1 receptor and/or the chemoattractant receptor homologous molecule expressed on T-helper type 2 (Th2) cells (CRTH2/DP2). Experimental evidence suggests that stimulation of one or both these receptors contributes to asthma pathophysiology.

OBJECTIVE

The aim of this study was to test the hypothesis that the prostanoid DP1 receptor contributes to asthma pathophysiology by determining the efficacy of an orally active antagonist for this receptor, S-5751, on allergen-induced bronchoconstriction, airway hyperresponsiveness (AHR) and cellular inflammation in the sheep model of asthma.

METHODS

PGD(2)-induced cyclic adenosine monophosphate (cAMP) production in platelet-rich plasma was used to establish the in vitro efficacy of S-5751. In vivo, sheep naturally allergic to Ascaris suum were challenged with an aerosolized antigen with and without S-5751 treatment (given 4 days before and for 6 days after the challenge).

RESULTS

S-5751 inhibited PGD(2)-induced cAMP production in platelet-rich plasma with an IC(50) value of 0.12 microm. S-5751 at 30 mg/kg, but not at 3 mg/kg, reduced the early bronchoconstriction and inhibited the late bronchoconstriction. AHR and inflammatory cell infiltration in bronchoalveolar lavage fluid at days 1 and 7 were also inhibited with the 30 mg/kg dose. The responses observed with S-5751 at 30 mg/kg were comparable with those with montelukast treatment (0.15 mg/kg, twice a day, intravenous); however, S-5751 did not block inhaled leukotrieneD(4)-induced broncoconstriction.

CONCLUSION

Prostanoid DP1 receptor inhibition may represent an alternative target for asthma therapy.

Mechanism of the prostanoid TP receptor agonist U46619 for inducing emesis in the ferret

U46619 is a potent thromboxane A(2) mimetic with emesis-inducing actions that are mediated via prostanoid TP receptors. We investigated its emetic mechanism of action in more detail using the ferret as model animal. The emesis induced by U46619 (30 microg/kg, intraperitoneal) was antagonized significantly by (+)-(2S,3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine hydrochloride (CP-99,994; 1 and 10 mg/kg; P < 0.05) and metoclopramide (0.3 and 3 mg/kg), but not by domperidone (3 mg/kg), sulpiride (0.1 mg/kg), ondansetron (0.1 and 1 mg/kg) alone or combined with droperidol (3 mg/kg), GR125487 (1 mg/kg), promethazine (3 mg/kg), or scopolamine (3 mg/kg); GR 125487 (1 mg/kg) prevented the anti-emetic action of metoclopramide (3 mg/kg). U46619 0.3 microg administered into the fourth ventricle rapidly induced emesis. However, bilateral abdominal vagotomy was ineffective in reducing the emetic response (P > 0.05). Our data suggests that U46619 induces emesis via an extra-abdominal mechanism, probably within the brain. Metoclopramide probably has a mechanism of action to prevent U46619-induced emesis via 5-HT(4) receptor activation and NK(1) tachykinin receptor antagonists could be useful to prevent emesis induced by TP receptor activation in man.

PGE2 inhibits apical K channels in the CCD through activation of the MAPK pathway

We used the patch-clamp technique and Western blot analysis to explore the effect of PGE(2) on ROMK-like small-conductance K (SK) channels and Ca(2+)-activated big-conductance K channels (BK) in the cortical collecting duct (CCD). Application of 10 microM PGE(2) inhibited SK and BK channels in the CCD. Moreover, either inhibition of PKC or blocking mitogen-activated protein kinase (MAPK), P38 and ERK, abolished the effect of PGE(2) on SK channels in the CCD. The effect of PGE(2) on SK channels was completely blocked in the presence of SC-51089, a specific EP1 receptor antagonist, and mimicked by application of sulprostone, an agonist for EP1 and EP3 receptors. To determine whether PGE(2) stimulates the phosphorylation of P38 and ERK, we treated mouse CCD cells (M-1) with PGE(2). Application of PGE(2) significantly stimulated the phosphorylation of P38 and ERK within 5 min. The dose-response curve of PGE(2) effect shows that 1, 5, and 10 microM PGE(2) increased the phosphorylation of P38 and ERK by 20-21, 50-80, and 80-100%, respectively. The stimulatory effect of PGE(2) on MAPK phosphorylation was not affected by indomethacin but abolished by inhibition of PKC. This suggests that the effect of PGE(2) on MAPK phosphorylation is PKC dependent. Also, the expression of cyclooxygenase II and PGE(2) concentration in renal cortex and outer medulla was significantly higher in rats fed a K-deficient diet than those on a normal-K diet. We conclude that PGE(2) inhibits SK and BK channels and that there is an effect of PGE(2) on SK channels in the CCD through activation of EP1 receptor and MAPK pathways. Also, high concentrations of PGE(2) induced by K restriction may be partially responsible for increasing MAPK activity during K restriction.

Iloprost-induced desensitization of the prostacyclin receptor in isolated rabbit lungs

Background

The rapid desensitization of the human prostacyclin (IP) in response to agonist binding has been shown in cell culture. Phosphorylation of the IP receptor by protein kinase C (PKC) has been suggested to be involved in this process.

Methods and results

In this study we investigated the vasodilatory effects of iloprost, a stable prostacyclin analogue, in perfused rabbit lungs. Continuous infusion of the thromboxane mimetic U46619 was employed to establish stable pulmonary hypertension. A complete loss of the vasodilatory response to iloprost was observed in experiments with continuous iloprost perfusion, maintaining the intravascular concentration of this prostanoid over a 180 min period. When lungs under chronic iloprost infusion were acutely challenged with inhaled iloprost, a corresponding complete loss of vasoreactivity was observed. This desensitization was not dependent on upregulation of cAMP-specific phosphodiesterases or changes in adenylate cyclase activity, as suggested by unaltered dose-response curves to agents directly affecting these enzymes. Application of a prostaglandin E1 receptor antagonist 6-isopropoxy-9-oxoxanthene-2-carboxylic acid (AH 6809) or the PKC inhibitor bisindolylmaleimide I (BIM) enhanced the vasodilatory response to infused iloprost and partially prevented tachyphylaxis.

Conclusion

A three-hour infusion of iloprost in pulmonary hypertensive rabbit lungs results in complete loss of the lung vasodilatory response to this prostanoid. This rapid desensitization is apparently not linked to changes in adenylate cyclase and phosphodiesterase activation, but may involve PKC function and co-stimulation of the EP1 receptor in addition to the IP receptor by this prostacyclin analogue.

Prostaglandin E2 receptor distribution and function in the gastrointestinal tract

Prostaglandin E2 (PGE2) is one of the most important biologically active prostanoids found throughout the gastrointestinal tract. Despite the fact that PGE2 regulates many physiological functions of the gut including mucosal protection, gastrointestinal secretion and motility, it is implicated in the pathophysiology of inflammatory bowel diseases (IBD) and colorectal neoplasia. The varied biological functions exerted by PGE2 are through the pharmacologically distinct, G-protein coupled plasma membrane receptors termed EP receptors. Disruptions of various prostanoid receptor genes have helped in unravelling the physiological functions of these receptors. To date, all four subtypes of EP receptors have been individually knocked out in mice and various phenotypes have been reported for each subtype. Similarly, in vitro and in vivo studies using EP receptor agonists and antagonists have helped in uncoupling the diverse functions of PGE2 signalling involving distinct EP receptors in the gut. In this review, we will summarize and conceptualize the salient features of EP receptor subtypes, their regional functions in the gut and how expressions of EP receptors are altered during disease states.

Effect of Boswellia serrata on intestinal motility in rodents: inhibition of diarrhoea without constipation

Clinical studies suggest that the Ayurvedic plant Boswellia serrata may be effective in reducing diarrhoea in patients with inflammatory bowel disease. In the present study, we evaluated the effect of a Boswellia serrata gum resin extract (BSE) on intestinal motility and diarrhoea in rodents. BSE depressed electrically-, acetylcholine-, and barium chloride-induced contractions in the isolated guinea-pig ileum, being more potent in inhibiting the contractions induced by acetylcholine and barium chloride. The inhibitory effect of BSE on acetylcholine-induced contractions was reduced by the L-type Ca(2+) channel blockers verapamil and nifedipine, but not by the sarcoplasmic reticulum Ca(2+)-ATPase inhibitor cyclopiazonic acid, by the phosphodiesterase type IV inhibitor rolipram or by the lipoxygenase inhibitor zileuton. 3-acetyl-11-keto-beta-boswellic acid, one of the main active ingredients of B. serrata, inhibited acetylcholine-induced contractions. BSE inhibited upper gastrointestinal transit in croton oil-treated mice as well as castor oil-induced diarrhoea. However, BSE did not affect intestinal motility in control mice, both in the small and in the large intestine. It is concluded that BSE directly inhibits intestinal motility with a mechanism involving L-type Ca(2+) channels. BSE prevents diarrhoea and normalizes intestinal motility in pathophysiological states without slowing the rate of transit in control animals. These results could explain, at least in part, the clinical efficacy of this Ayurvedic remedy in reducing diarrhoea in patients with inflammatory bowel disease.

Cysteinyl leukotrienes are secretagogues in atrophic coeliac and in normal duodenal mucosa of children

OBJECTIVE

The pathophysiology of intestinal inflammation and diarrhoea is complex and involves the arachidonic acid cascade. Prostaglandins induce chloride secretion in healthy subjects and in patients with coeliac disease. Leukotrienes (LTs) are also known inflammatory mediators which have been shown to stimulate ion secretion in ileum and colon of rats and rabbits. The aim of this study was to determine the effects of leukotrienes C(4) (LTC(4)) and D(4) (LTD(4)) in normal and atrophic intestinal mucosa in children.

MATERIAL AND METHODS

Routine paediatric intestinal biopsies were obtained from 109 children. Sixty-seven control biopsies and 42 biopsies from children with different stages of coeliac disease were mounted in a modified Ussing chamber. Potential difference (Pd) was measured continuously and tissue resistance (R(t)) and the generated current (I(m)) were calculated.

RESULTS

In morphologically normal mucosa of duodenum, LTC(4) and LTD(4) increased Pd and I(m) in a dose-dependent manner. The increase was more pronounced in the distal than in the proximal part, similar to the response to prostaglandin E(2). The induced current was chloride-mediated, since replacement of Cl(-) with SO(4)(2-) in the bathing solution eliminated the response to the LTs. The LTC(4)-induced secretion was significantly decreased in atrophic mucosa, but the response was partially restored after preincubation with the cyclooxygenase inhibitor indomethacin.

CONCLUSIONS

The results showed that LTC(4) and LTD(4) are secretagogues in the duodenal mucosa from healthy children by inducing a net chloride secretion. Restoration of the response in coeliac disease by cyclooxygenase inhibition suggests interactions between the different pathways of the arachidonic cascade in the intestinal mucosa.

Endotoxin pretreatment modifies peristalsis and attenuates the antipropulsive action of adrenoceptor agonists in the guinea-pig small intestine

The action of endotoxin to alter gastrointestinal motility in vivo may reflect a direct effect on the gut or result from vascular and other systemic manifestations of this sepsis model. Here we examined whether in vivo pretreatment of guinea-pigs with endotoxin modifies peristalsis in the isolated gut and influences the antipropulsive action of adrenoceptor agonists. Distension-induced peristalsis was recorded in fluid-perfused segments of the small intestine taken from animals pretreated intraperitoneally with endotoxin (1 mg kg(-1)Escherichia coli lipopolysaccharide) or vehicle 4 or 20 h before. Clonidine, adrenaline, noradrenaline, dopamine and dobutamine inhibited peristalsis with differential potency. Endotoxin pretreatment lowered the peristaltic pressure threshold and altered other parameters of baseline peristalsis in a time-related manner. The potency and efficacy of clonidine to inhibit peristalsis were markedly decreased after endotoxin administration, while the potency of the other test drugs was less attenuated. The antipropulsive action of clonidine in control segments was reduced by yohimbine and prazosin, whereas in segments from endotoxin-pretreated animals it was antagonized by yohimbine but not prazosin. We conclude that systemic endotoxin pretreatment of guinea-pigs modifies baseline peristalsis by an action on the gut and inhibits the antipropulsive action of adrenoceptor agonists through changes in adrenoceptor activity.

Inhibition of Guinea Pig Intestinal Peristalsis by the Flavonoids Quercetin, Naringenin, Apigenin and Genistein

Flavonoids are known to relax precontracted intestinal smooth muscle and to delay intestinal transit. We therefore investigated the effects of quercetin, naringenin, apigenin and genistein on intestinal peristalsis in vitro. Peristalsis in fluid-perfused segments of the guinea pig small intestine was recorded through the intraluminal pressure changes associated with the peristaltic waves. Alterations of distension sensitivity were reflected by changes in the peristaltic pressure threshold and alterations of peristaltic performance by changes in the maximal acceleration, amplitude and residual baseline pressure of the peristaltic waves. Quercetin, naringenin, apigenin and genistein (10-300 micromol/l) depressed intestinal peristalsis in a structure- and concentration-dependent manner. The flavonoid-evoked changes in peristalsis parameters made it possible to distinguish between two patterns of peristaltic motor inhibition: a decrease in distension sensitivity and peristaltic performance (apigenin and genistein) and a decrease in distension sensitivity without a major change in peristaltic performance (quercetin and naringenin). The antiperistaltic effect of quercetin was partially prevented by apamin (0.5 micromol/l), N-nitro-L-arginine methylester (100 micromol/l) and naloxone (0.5 micromol/l), whereas the effect of genistein was hardly affected by these drugs. Peristaltic motor activity suppressed by quercetin (300 micromol/l), but not genistein (100 micromol/l), was partially restored by apamin. In contrast, neostigmine (0.3 micromol/l) caused a significant recovery of peristalsis from blockade by genistein but failed to reverse peristaltic motor blockade due to quercetin. These observations suggest that naringenin and quercetin inhibit peristalsis by facilitating inhibitory enteric pathways, whereas apigenin and genistein interfere with muscle excitation or excitation-contraction coupling.