Colonic Contractions Research Articles

Molecular and functional diversity of GABA-A receptors in the enteric nervous system of the mouse colon.

The enteric nervous system (ENS) provides the intrinsic neural control of the gastrointestinal tract (GIT) and regulates virtually all GI functions. Altered neuronal activity within the ENS underlies various GI disorders with stress being a key contributing factor. Thus, elucidating the expression and function of the neurotransmitter systems, which determine neuronal excitability within the ENS, such as the GABA-GABAA receptor (GABAAR) system, could reveal novel therapeutic targets for such GI disorders. Molecular and functionally diverse GABAARs modulate rapid GABAergic-mediated regulation of neuronal excitability throughout the nervous system. However, the cellular and subcellular GABAAR subunit expression patterns within neurochemically defined cellular circuits of the mouse ENS, together with the functional contribution of GABAAR subtypes to GI contractility remains to be determined. Immunohistochemical analyses revealed that immunoreactivity for the GABAAR gamma (γ) 2 and alphas (α) 1, 2, 3 subunits was located on somatodendritic surfaces of neurochemically distinct myenteric plexus neurons, while being on axonal compartments of submucosal plexus neurons. In contrast, immunoreactivity for the α4-5 subunits was only detected in myenteric plexus neurons. Furthermore, α-γ2 subunit immunoreactivity was located on non-neuronal interstitial cells of Cajal. In organ bath studies, GABAAR subtype-specific ligands had contrasting effects on the force and frequency of spontaneous colonic longitudinal smooth muscle contractions. Finally, enhancement of γ2-GABAAR function with alprazolam reversed the stress-induced increase in the force of spontaneous colonic contractions. The study demonstrates the molecular and functional diversity of the GABAAR system within the mouse colon providing a framework for developing GABAAR-based therapeutics in GI disorders.

Relaxant effect of flavonoid naringenin on contractile activity of rat colonic smooth muscle

Ethnopharmacological relevanceDisturbed gastrointestinal (GI) motility can be associated with smooth muscle abnormalities and dysfunction. Exploring innovative approaches that can modulate the disturbed colonic motility are of great importance for clinical therapeutics. Naringenin, a flavonoid presented in many traditional Chinese herbal medicines, has been shown to have a relaxant effect on different smooth muscles. The aim of the present study was to investigate the effect of naringenin on regulation of GI motility. Material and methodsMechanical recording was used to investigate the effect of naringenin on isolated rat colonic smooth muscle spontaneous contractions. Whole cell patch clamp, intracellular [Ca2+] concentration ([Ca2+]i) and membrane potential measurements were examined on primary cultures of colonic smooth muscle cells (SMCs). A neostigmine-stimulated rat model was utilized to investigate the effect of naringenin in vivo. ResultsNaringenin induced a concentration-dependent inhibition (1–1000μM) on rat colonic spontaneous contraction, which was reversible after wash out. The external Ca2+ influx induced contraction and [Ca2+]i increase were inhibited by naringenin (100μM). In rat colonic SMCs, naringenin-induced membrane potential hyperpolarization was sensitive to TEA and selective large-conductance calcium-activated K+ (BKCa) channel inhibitor iberiotoxin. Under whole cell patch-clamp condition, naringenin stimulated an iberiotoxin-sensitive BKCa current, which was insensitive to changes in the [Ca2+]i concentration. Furthermore, naringenin significantly suppressed neostigmine-enhanced rat colon transit in vivo. ConclusionOur results for the first time demonstrated the relaxant effect of flavonoid naringenin on colon smooth muscle both in vitro and in vivo. The relaxant effect of naringenin was attributed to direct activation of BKCa channels, which subsequently hyperpolarized the colonic SMCs and decreased Ca2+ influx through VDCC. Naringenin might be of therapeutic value in the treatment of GI motility disorders.

Identification of neurotensin and LANT-6 and localization of mRNA encoding their precursor in the chicken brain.

Neurotensin (NT) and neurotensin-related peptide (Lys(8), Asn(9), NT(8-13): LANT-6) have previously been purified from chicken intestine. However, the presence of these peptides and the localization of their precursor mRNA in the brain were not well understood. In the present study, through a comprehensive analysis of bioactive substances, NT and LANT-6 were identified in the chicken brain using tandem mass spectrometry combined with a bioassay of the colon contraction. The effect of NT and LANT-6 on the colon contraction was assessed, and NT was found to be 10 times more potent than LANT-6. Furthermore, the sites of NT/LANT-6 precursor mRNA expression in the brain were investigated using quantitative RT-PCR. The result showed that the mRNA was expressed most in the telencephalon, followed by the diencephalon. In situ hybridization analysis revealed that cells containing NT/LANT-6 precursor mRNA were widely distributed throughout the brain except for the cerebellum. Additionally, these were highly concentrated in the frontal telencephalon, including the nidopallium, hyperpallium, and hippocampus. Collectively, these results indicate that NT and LANT-6 are produced in the chicken brain, and they may participate in multiple functions.

Novel mixed NOP/MOP agonist BU08070 alleviates pain and inhibits gastrointestinal motility in mouse models mimicking diarrhea-predominant irritable bowel syndrome symptoms

The opioid and nociceptin systems play a crucial role in the maintenance of homeostasis in the gastrointestinal (GI) tract. The aim of this study was to characterize the effect of BU08070, a novel mixed MOP/NOP agonist, on mouse intestinal contractility in vitro and GI motility in vivo in physiological conditions and in animal models mimicking symptoms of irritable bowel syndrome (IBS), including diarrhea and abdominal pain. The effect of BU08070 on muscle contractility in vitro was characterized in the ileum and colon. To assess the effect of BU08070 in vivo, the following parameters were assessed: whole GI transit, gastric emptying, geometric center, colonic bead expulsion, fecal pellet output and time to castor oil-induced diarrhea. The antinociceptive activity of BU08070 was characterized in the mustard oil (MO)-induced abdominal pain model and the writhing test, alone and in the presence of MOP and NOP antagonists. in vitro, BU08070 (10−10–10−6M) inhibited colonic and ileal smooth muscle contractions in a concentration-dependent manner. in vivo, BU08070 prolonged the whole GI transit and inhibited colonic bead expulsion. The antitransit and antidiarrheal effects of BU08070 were observed already at the dose of 0.1mg/kg (i.p.). BU08070 reversed hypermotility and reduced pain in mouse models mimicking IBS-D symptoms. Our results suggest that BU08070 has a potential of becoming an efficient drug in IBS-D therapy. Here we also validate mixed NOP/MOP receptor targeting as possible future treatment of functional GI diseases.

Laparoscopically implanted system for stimulation of the hypogastric plexus induces colonic motility, defecation, and micturition: experimental study.

Modulation of the enteric nervous system seems to be promising in several functional colorectal disorders for which targeted, causal treatment methods do not exist. However, sacral nerve stimulation can induce undesirable muscle contraction or paresthesia. Therefore, we have developed a laparoscopic technique for implanting a neural electrode, placed directly over the pelvic autonomic nerve plexus. The aim of this experimental study was to evaluate the effect of stimulating the hypogastric plexus and pelvic nerves on inducing distal colon contraction, defecation, and micturition. A total of 10 white, male healthy pigs (25-30 kg) were subjected to the laparoscopic implantation of the electrode and the stimulator. In the third and fourth weeks postimplantation, the efficacy of the acute and chronic stimulation to induce defecation was evaluated. The average operative time was 105 minutes (85-150 minutes). In all pigs, acute stimulation activated induced defecation, every second day, every time on demand, with an average delay of 139.7 s. Micturition was induced incidentally. Acute or chronic stimulation did not cause any harm, pain, or suffering to the animals. No adverse effects of the stimulation were observed, and no septic complications or macroscopic fibrosis around the electrodes were found on autopsy. Hypogastric plexus stimulation can be a useful and safe option of distal colon contraction, defecation, and micturition. However, the efficacy of the stimulation was observed for a relatively short period of time, and it is not known if it will be sustained for a longer duration.

Butyrate increases and propionate decreases the frequency of propulsive contractions in guinea pig proximal colon (1110.7)

INTRODUCTION: Colonic bacteria produce short‐chain fatty acids (SCFAs) by fermentation of dietary carbohydrates and fiber. The production of SCFAs is greatest in proximal colon where propulsion is likely to be highly dependent on chemical/nutrient stimuli. AIM: To determine the effect of individual SCFAs on propulsive contractions in guinea pig proximal colon. METHODS: Proximal colon was excised, cannulated and placed in Kreb’s buffer in an organ bath. After equilibration, the colon was distended with 1 ml of Krebs’s buffer alone or containing sodium salts of acetate, butyrate, or propionate at 10‐100 mM. Motility was videorecorded, spatiotemporal maps generated, and the number of full‐length propulsive contractions during a 5 min period determined. RESULTS: The basal rate of propulsive contractions in Kreb’s buffer was 2.9±0.7 per 5 min. Butyrate and propionate had concentration‐dependent and opposing effects on propulsive contractions; acetate had no effect. Butyrate significantly increased propulsive contractions (maximal increase of 207% (p<0.05) at 30 mM) whereas propionate abolished propulsive contractions (91‐100% inhibition at 10‐30 mM). Control Kreb’s buffer containing 10‐100 mM NaCl had no effect. CONCLUSION: SCFAs have differential effects on propulsive contractions in guinea pig proximal colon with butyrate being excitatory and propionate being inhibitory.Grant Funding Source: Supported by DK34153

Acute Uterine Irritation Provokes Colonic Motility via Transient Receptor Potential A1-dependent Spinal NR2B Phosphorylation in Rats

Patients with inflammatory gynecological/obstetrical problems often complain of irritable bowel syndrome. The authors examined whether acute uterus irritation reflexively provokes colonic motility in rat preparations. A modified colon manometry and striated abdominal muscle electromyogram activity in response to mustard oil (MO) instillation into the uterine horn were continuously recorded in anesthetized rats. The lumbosacral (L6-S1) dorsal horn was dissected to assess the level and the cellular location of phosphorylated NR2B subunit using Western blotting and immunofluorescence analysis, respectively. Finally, the uterine transient receptor potential A1 or spinal NR2B subunit was pharmacologically blocked to elucidate its roles. MO (0.1%, 0.2 ml) injected into the lower uterine horn dramatically provoked colonic hypermotility characterized by rhythmic colonic contractions (about 3-4 contractions per 10 min, n = 7) accompanied by synchronized electromyogram firing in the abdominal muscle (about 4-5 folds of control, n = 7). In addition to provoking colonic hypermotility, MO administration also up-regulated phosphorylated (about 2-3 folds of control, n = 7), but not total, NR2B expression in the dorsal horn neurons. Both intrathecal Ro 25-6981 (a selective NR2B subunit antagonist; 10 μM, 10 μl) and intrauterine HC-030031 (a selective transient receptor potential A1 receptor antagonist; 30 mg/kg, 0.2 ml) injected before the MO instillation attenuated the MO-induced colonic hypermotility and spinal NR2B phosphorylation. The comorbidity of gynecological/obstetrical and gastrointestinal problems is not coincidental but rather causal in nature, and clinicians should investigate for gynecological/urological diseases in the setting of bowel problems with no known pathological etiology.

Novel Pharmacological Therapies for Management of Chronic Constipation

Chronic constipation is a common health problem that significantly affects the quality of life of patients and impacts in terms of costs; current treatments based on fiber and laxatives cause dissatisfaction to doctors and patients in more than half of the cases. New drugs are now available or in very advanced stages of research, with different and innovative mechanisms of action as prucalopride, lubiprostone, and linaclotide. Prucalopride an enterokinetic, is a selective high-affinity 5-hydroxytryptamine (5-HT)4 receptor agonist of serotonin that increases the peristaltic reflex and the colonic contractions; lubiprostone, a type 2 chlorine channel activator, or linaclotide, a guanylate cyclase-C agonist of enterocytes, both prosecretory agents, stimulate the secretion of fluid within the intestinal lumen. In general, these promising drugs have proven efficacy and safety as a specific therapeutic option in patients with chronic constipation. Yet the solution might not be sufficient for everybody and still without the ideal drug that might be useful in all cases, the pharmacological revolution for colonic motility disorders has arrived.

Magnolol inhibits colonic motility through down-regulation of voltage-sensitive L-type Ca2+ channels of colonic smooth muscle cells in rats

This study aimed to investigate the effect of magnolol (5,5′-diallyl-2,2′-biphenyldiol) on contraction in distal colonic segments of rats and the underlying mechanisms. Colonic segments were mounted in organ baths for isometric force measurement. Whole-cell voltage-sensitive L-type Ca2+ currents were recorded on isolated single colonic smooth muscle cells using patch-clamp technique. The spontaneous contractions and acetylcholine (ACh)- and Bay K 8644-induced contractions were inhibited by magnolol (3–100μM). In the presence of Bay K8644 (100nM), magnolol (10–100μM) inhibited the contraction induced by 10μM ACh. By contrast, tetrodotoxin (100nM) and Nώ-nitro-l-arginine methyl ester (l-NAME 100μM) did not change the inhibitory effect of magnolol (10μM). In addition, magnolol (3–100μM) inhibited the L-type Ca2+ currents. The present results suggest that magnolol inhibits colonic smooth muscle contraction through downregulating L-type Ca2+ channel activity.

The inhibitory effects of antimuscarinic autoantibodies in the sera of primary Sjogren syndrome patients on the gastrointestinal motility

Impairment of gastrointestinal tract (GI) function, including delayed gastric emptying and colonic dysmotility, are common features of primary Sjögren's syndrome (SS). However, the pathogenesis remains largely unknown. The aim of the current study was to investigate the role of functional autoantibodies to the muscarinic receptor in mediating GI dysfunction associated with primary SS. The effect of SS or normal immunoglobulin G (IgG) on smooth muscle (SM) motility was assessed by comparing the amplitude of carbachol (CCh) or electrical field stimulation (EFS) – induced muscle contraction before and after IgG application. Muscarinic receptor type 3 (M3R) played a dominant role in both colon and gastric SM contraction, while M2R was partly involved in gastric smooth muscle contraction. Preincubation for 1h of the colon and gastric SM strips with 1mg/ml purified IgG from the sera of four primary SS patients (SS IgG) significantly inhibited carbachol-induced smooth muscle contraction (CISC) over a range of CCh concentrations, whereas IgG from healthy controls had little effect. Incubation of the colon SM strips with SS IgG also inhibited EFS-induced colon muscle contraction, which was mimicked by the M3R-selective blocker, 4-DAMP. SR1403330, an NK1 antagonist, had little effect on EFS-mediated colonic SM contraction. The results suggest that autoantibodies isolated from primary SS patients’ sera inhibit muscarinic receptor-mediated cholinergic neurotransmission in mouse colon and stomach, which may provide clues for explaining the GI dysfunction seen in patients with primary SS.

Acute and chronic effects of desvenlafaxine on gastrointestinal transit and motility in dogs

Antidepressants are commonly used for treating functional gastrointestinal (GI) diseases. However, little is known whether antidepressants improve or impair GI motility. This study aimed at exploring possible effects of a serotonin-norepinephrine reuptake inhibitor, desvenlafaxine succinate (DVS), on GI motility in dogs. Eight dogs chronically implanted with a duodenal cannula and a colon cannula were used in the study. Experiments were performed to assess the effects of a single dose of DVS (50 or 100mg) and DVS given 50mg once a day for 2weeks on gastric emptying of solid, small intestinal transit, and colon transit and contractions. (1) DVS significantly delayed gastric emptying of solid at a single dose of 50 or 100mg. The inhibitory effect on gastric emptying was completely blocked by guanethidine (an adrenergic blocking agent). (2) DVS at a single dose of 50 or 100mg accelerated colon transit, but showed no effects on small bowel transit. (3) DVS at a single dose of 50mg enhanced colon contractions and guanethidine blocked the effect. (4) Surprisingly, DVS given at 50mg once daily for 2weeks did not alter gastric emptying, small bowel transit or colon transit. Acute DVS delays gastric emptying of solid and enhances the contractions of the colon, which may be mediated via the sympathetic mechanism. Acute DVS promotes the transit of the colon but not the small intestine. However, chronic administration of DVS does not seem to alter GI motility.

Beta-arrestin2 is involved in the increase of distal colonic contraction in diabetic rats

Colonic dysmotility occurs in diabetes and the patients exhibit diarrhea or constipation. The pathogenetic mechanisms underlying colonic dysmotility in diabetic patients remain poorly understood. The effects of β-arrestin2 on colonic contraction in diabetic rats were investigated for the first time. Male SD rats were treated with a single intraperitoneally injected dose of streptozotocin, and those displaying sustained high blood glucose were selected as diabetes mellitus models. Longitudinal muscle strips of the distal colon were prepared to monitor contraction of the colon in vitro. Expression of β-arrestin2 was investigated by Western blot analysis. Anti-β-arrestin2 antibody had no direct effect on the contraction of distal colonic strips in both normal and diabetic rats. Carbachol-induced contractions of distal colonic strips were higher in diabetic rats than in normal rats. Anti-β-arrestin2 antibody partly blocked carbachol-induced increases of distal colonic strips in diabetic rats. The expression level of β-arrestin2 protein in the colon was higher in diabetic rats than in normal rats. These results suggest that β-arrestin2 is involved in the increase of distal colonic contraction in diabetic rats.

High Resolution Colonic Manometry – What Have We Learnt?- a Review of the Literature 2012

Despite its size and physiological importance, the human colon is one of the least understood organs of the body. Many disorders arise from suspected abnormalities in colonic contractions, yet, due largely to technical constraints, investigation of human colonic motor function still remains relatively primitive. Most measures of colonic motility focus upon the transit speed (radiology, scintigraphy and, more recently, "smart pills"); however, only colonic manometry can measure pressure/force from multiple regions within the colon in real time (Dinning and Scott (Curr Opin Pharmacol 11:624-629, 2011)). Based upon data from colonic manometry studies, a number of different colonic motor patterns have been distinguished: (1) antegrade high amplitude propagating sequences (contractions), (2) low amplitude propagating sequences, (3) non-propagating contractions, and (4) and rarely episodes of retrograde (oral) propagating pressure waves (Dining and Di Lorenzo (Best Pract Res Clin Gastrolenterol 25(1): 89-101, 2011)). Abnormalities in the characteristics of these motor patterns should help to characterize dysmotility in a patient populations, and in both adults and children colonic motor abnormalities have been identified with manometry studies (Rao et al. Am J Gastroenterol 99(12):2405-2416, (2004), Di Lorenzo et al. Gut. 34(1): 803-807, (1993)). Yet, despite more than two decades of such studies, the clinical utility of colonic manometry remains marginal with no specific manometric biomarkers of colonic dysfunction being established ([Camilleri et al. Neurogastroenterol Motil. 20(12): 1269-1282, 2008). This has been highlighted recently in a colonic manometry study by Singh et al. (2013), in which 41 % of 80 patients, with confirmed slow transit constipation, were reported to have normal motility. While this may suggest that no motor abnormalities exist in a proportion of such patients, the finding may also reflect technical constraints in our ability to detail colonic motility patterns.

Mo1988 Inhibition of Corticotropin Releasing Factor (CRF) Receptor Type 2 Signaling Enhances Peripheral CRF-Induced Stimulation of Colonic Contractions in Conscious Rats

G A A b st ra ct s showed the presence of all AMPK subunits in Caco-2/15 cells, with a marked difference in their abundance, along with a predominance of AMPK α1 and the prevalence of α1/β2/ γ1 heterotrimer. AMPK was activated by AICAR and metformin, resulting in increased phosphorylation of the downstream target acetyl CoA carboxylases (ACC). Reciprocally, compound C down-regulated of AMPK phosphorylation and high glucose lowered ACC phosphorylation without affecting HMG-CoA reductase. Administration of metformin to P. obesus with insulin resistance and type 2 diabetes led to (a) an upregulation of intestinal AMPK signaling pathway typified by ascending AMPK α-Thr172 phosphorylation; (b) a reduction in ACC activity; (c) an elevation of carnitine palmitoyltransferase-1, supporting a stimulation of β-oxidation; (d) a trend of increase in insulin sensitivity portrayed by augmentation of Akt and glycogen synthase kinase 3 β phosphorylation; (e) an inactivation of the stress-responsive p38-MAPK and ERK1/2 exemplified by their phosphorylation lessening; and (f) a decrease in diabetic dyslipidemia following lowering of intracellular events that govern lipoprotein assembly. Conclusions/Interpretation: These data suggest that AMPK fulfills key functions in metabolic processes in the small intestine.

Colonic electrical stimulation: potential use for treatment of delayed colonic transit

Recently there has been an increased interest in using electrical stimulation to regulate gut motility generally and particularly for the treatment of slow-transit constipation. In this preliminary canine study, we aimed to study the effects of colonic electrical stimulation (CES) on colonic motility and transit. Nine dogs, each equipped with a pair of serosal colon electrodes and a proximal colon cannula were randomized to receive: (i) sham-CES, (ii) long pulse CES (20 cpm, 300 ms, 6 mA) or (iii) pulse train CES (40 Hz, 6 ms, 6 mA). Animals underwent assessment of colonic contractions via manometry, and of colonic transit by inserting 24 radiopaque markers via the colonic cannula and radiographically monitoring the markers at 2, 4 and 6 h following their insertion. The colonic transit was assessed by the geometric centre. We found that, compared with sham-CES, pulse train CES, but not long pulse CES, significantly increased the overall colonic motility index twofold and accelerated the colonic transit by 104% at 2 h, by 60% at 4 h and by 31% at 6 h (P = 0.01, P = 0.02 and P = 0.03 vs sham-CES at 2, 4 and 6 h, respectively). The accelerating effect of pulse train CES was found to be mediated via both cholinergic and nitrergic pathways. CES with pulse trains has prokinetic effects on colonic contractions and transit in healthy dogs, mediated via the cholinergic and nitrergic pathways. Further clinical studies are warranted to explore the therapeutic potential of CES for slow colonic transit constipation.

Comparison of glycopyrrolate and atropine in ameliorating the adverse effects of imidocarb dipropionate in horses

Imidocarb, an effective treatment for piroplasmosis, may cause colic and diarrhoea in horses. Atropine and glycopyrrolate are anticholinergics that could reduce the adverse effects of imidocarb. However, atropine and glycopyrrolate inhibit gastrointestinal motility, potentially causing ileus and colic. To compare glycopyrrolate and atropine in ameliorating the adverse effects of imidocarb dipropionate in horses and to determine the effect of combinations of these drugs on the gastrointestinal tract. A blinded, randomised, crossover study was performed in 8 healthy horses. Each horse received 0.9% saline i.m and i.v. (CON), and imidocarb 2.4 mg/kg bwt i.m. with one of 3 treatments i.v.: 0.9% saline (IMI), atropine 0.02 mg/kg bwt (IMATROP) and glycopyrrolate 0.0025 mg/kg bwt (IMGLYCO). Clinical data, gastrointestinal motility via borborygmi and frequency of contractions in the duodenum, caecum and right dorsal colon assessed with transabdominal ultrasound, and faecal data were measured. After imidocarb/saline treatment colic and diarrhoea were noted in 3 and 4 horses, respectively, faecal production and defaecation were increased for 3 h and faecal water percentage for 6 h. Colic was noted after atropine treatment in 4 horses, borborygmi and frequency of right dorsal colon contractions were significantly decreased for 2 h 15 min, and faecal production was not significantly different from CON. After glycopyrrolate treatment, colic was seen in one horse, frequency of intestinal contractions and faecal data were not significantly different from CON, and borborygmi was significantly decreased from CON at 1 h 15 min. Results of this study suggest that glycopyrrolate is superior to atropine in ameliorating the adverse effects of imidocarb. Glycopyrrolate could be administered with imidocarb in horses with piroplasmosis to reduce the adverse effects of imidocarb.

Role of the intraluminal contents and the continuity of intrinsic neurons in intracolonic capsaicin-induced contraction and defecation in dogs

We, herein, examined the role of the intraluminal contents and continuity of colonic intrinsic neurons in intracolonic capsaicin-induced enhancement of colonic motility and defecation. Five beagle dogs were equipped with three strain gauge force transducers throughout the colon. The colonic contractile activity in response to intracolonic capsaicin was studied in intact dogs, dogs after colonic cleansing and dogs with transection/re-anastomosis (T/R) between the proximal and middle colon. The effects of intravenous yohimbine, a α2 adrenergic antagonist, on the colonic motility and defecation were also studied in the same models. In intact dogs, capsaicin (10mg) and yohimbine (2mg/kg) immediately induced contractions throughout the colon, with defecation occurring in all experiments. In dogs after colonic cleansing and T/R, the capsaicin (10mg)-induced enhancement of colonic motility was decreased in the middle and distal colon, and capsaicin-induced defecation was observed in 0-20% of experiments (p<0.05 compared to intact dogs). The effect of yohimbine (2mg/kg) in inducing colonic contractions was unaltered after colonic cleansing and T/R; in contrast, yohimbine-induced defecation was not observed after colonic cleansing, but was unchanged after T/R. The continuity of the colonic intrinsic nerves as well as the intraluminal contents appear to play an important role in the colonic motor response to intracolonic capsaicin.

Role of glucagon-like peptide-1 in the pathogenesis of experimental irritable bowel syndrome rat models

Alterations in gut motility and visceral hypersensitivity are two major features of irritable bowel syndrome (IBS). The aim of this study was to investigate the roles of glucagon-like peptide-1 (GLP-1) in the pathogenesis of experimental IBS. Rat models of constipation-predominant IBS (IBS-C) and diarrhea-predominant IBS (IBS-D) were established. Fecal water content and behavioral responses to colorectal distention (CRD), using electromyography (EMG), were measured. The expression of glucagon-like peptide-1 receptor (GLP-1R) in the colon was detected by immunohistochemistry, and the serum concentration of GLP-1 was measured by ELISA assay. The movement of circular and longitudinal colonic muscle was detected using an organ bath recording technique. Compared to controls, the fecal water contents were lower in the IBS-C group, while they were higher in the IBS-D group (P<0.05). EMG response to CRD in the experimental IBS groups was increased compared with their respective controls (P<0.05). GLP-1R was localized in the mucosa layer, circular muscle and myenteric nerve plexus of the colon. Notably, the expression of GLP-1R in the IBS-C group was higher, but in the IBS-D group, it was lower compared with controls. The serum levels of GLP-1 in the IBS-C group were higher compared to those in the IBS-D group (P<0.05). In addition, administration of exogenous GLP-1 and exendin-4 inhibited colonic circular muscle contraction, particularly in the IBS-C group, while there was no significant effect on longitudinal muscle contraction. In conclusion, these results indicated that GLP-1 and GLP-1R are implicated in the pathogenesis of IBS-C and IBS-D.

5-HT3 and 5-HT4 antagonists inhibit peristaltic contractions in guinea-pig distal colon by mechanisms independent of endogenous 5-HT

Recent studies have shown that endogenous serotonin is not required for colonic peristalsis in vitro, nor gastrointestinal (GI) transit in vivo. However, antagonists of 5-Hydroxytryptamine (5-HT) receptors can inhibit peristalsis and GI-transit in mammals, including humans. This raises the question of how these antagonists inhibit GI-motility and transit, if depletion of endogenous 5-HT does not cause any significant inhibitory changes to either GI-motility or transit? We investigated the mechanism by which 5-HT3 and 5-HT4 antagonists inhibit distension-evoked peristaltic contractions in guinea-pig distal colon. In control animals, repetitive peristaltic contractions of the circular muscle were evoked in response to fixed fecal pellet distension. Distension-evoked peristaltic contractions were unaffected in animals with mucosa and submucosal plexus removed, that were also treated with reserpine (to deplete neuronal 5-HT). In control animals, peristaltic contractions were blocked temporarily by ondansetron (1–10 μM) and SDZ-205–557 (1–10 μM) in many animals. Interestingly, after this temporary blockade, and whilst in the continued presence of these antagonists, peristaltic contractions recovered, with characteristics no different from controls. Surprisingly, similar effects were seen in mucosa-free preparations, which had no detectable 5-HT, as detected by mass spectrometry. In summary, distension-evoked peristaltic reflex contractions of the circular muscle layer of the guinea-pig colon can be inhibited temporarily, or permanently, in the same preparation by selective 5-HT3 and 5-HT4 antagonists, depending on the concentration of the antagonists applied. These effects also occur in preparations that lack any detectable 5-HT. We suggest caution should be exercised when interpreting the effects of 5-HT3 and 5-HT4 antagonists; and the role of endogenous 5-HT, in the generation of distension-evoked colonic peristalsis.

Intragastric Dai-Kenchu-To, a Japanese Herbal Medicine, Stimulates Colonic Motility via Transient Receptor Potential Cation Channel Subfamily V Member 1 in Dogs

Japanese herbal medicine, also known as Kampo, is used for various diseases in Japan. One of those medicines, Dai-Kenchu-To (DKT), is considered clinically effective for adhesive bowel obstruction and chronic constipation. Although scientific evidence of DKT to improve adhesive bowel obstruction was shown in several previous reports, mechanism of DKT to improve constipation remains unknown. Our aim was to study the effect of intragastric DKT on colonic motility and defecation, and the involvement of various receptors in DKT-induced colonic contractions. Five beagle dogs were instructed with serosal strain-gauge force transducers to measure circular muscle activity at the proximal, middle, and distal colon. Dogs are suitable for a present study to administer the drugs repeatedly to the same individual and look at its effect on colonic motility. We studied the effects of DKT (2.5 or 5 g) administered into the stomach on colonic motility. Muscarinic receptor antagonist atropine, nicotinic receptor antagonist hexamthonium, or 5-hydroxytryptamine-3 receptor antagonist ondansetron was injected intravenously 10 min before DKT administration. Capsazepine, an antagonist to transient receptor potential cation channel subfamily V member 1 (TRPV1), was administered into the stomach 5 min before DKT administration. Intragastric DKT (2.5 or 5 g) induced colonic contractions within 10 min after administration but did not induce defecation. Pretreatment with atropine, hexamthonium, ondansetron, or capsazepine inhibited DKT-induced colonic contractions. These results indicate that orally administered DKT stimulates colonic motility via TRPV1, muscarinic, nicotinic, and 5-hydroxytryptamine-3 receptors, thereby providing scientific support for the efficacy of oral DKT in chronic constipation.