Effect of nitrergic system on colonic motility in a rat model of irritable bowel syndrome

The Effect of Increasing Bath Temperature on the Contractile Responses of the Large Gut in Adult and Neonate Rats

Introduction Earlier reports on the effect of temperature on gut motility concentrated on experiments conducted on the small intestines of adult animals. The effect of temperature on the large intestine, particularly in neonates, warrants further investigation. The current study investigated the effect of a temperature increase and its mechanism in the colon and rectum of neonate and adult rats. Methods and materials In an organ bath preparation, segments from the colon and rectum were subjected to increasing bath temperatures (37°C-40°C). In other groups, pretreatment with capsazepine (1 µM) and Nω-nitro-l-arginine methyl ester (L-NAME) (100 µM) was done, in different groups, to assess their impact on temperature-induced contractile response. Results Increasing the bath temperature significantly reduced the contractile tension in the colon and rectum. When L-NAME (100 µM)-pretreated segments of the colon and rectum were subjected to different bath temperatures, the contractile tension increased compared to the contractile tension at different bath temperatures without any drug. Capsazepine (1 µM) pretreatment, on the other hand, enhanced the decrease in the contractile tension in the colon and rectum of adult rats compared to the contractile tension produced at different bath temperatures without any drug, while in neonates, capsazepine (1 µM) pretreatment caused a rise in the contractile tension in the rectum with no effect in the colon. Increased bath temperature from 37°C to 40°C increased the contractile frequency in the colon and rectum in both adult and neonate rats. Pretreatment with L-NAME (100 µM) and capsazepine (1 µM) in adults and L-NAME (100 µM) in neonates caused an increase in the contractile frequency in both the colon and rectum; on the other hand, capsazepine pretreatment did not affect the contractile frequency in the colon and rectum of neonate rats compared to the contractile frequency produced at different bath temperatures without any drug. Conclusion The contractile response of rats' large intestines, colon, and rectum to increasing temperatures may involve nitric oxide (NO)-mediated and transient receptor potential vanilloid-1 (TRPV1)-mediated mechanisms. The effects of capsazepine on the colon and rectum of adults and neonates differ, possibly due to the TRPV1-mediated mechanism not developing properly in the neonate and developing later in adulthood.

Effect of phosphodiesterase-4 inhibitor rolipram on colonic hypermotility in water avoidance stress rat model

BACKGROUND

Phosphodiesterase (PDE) inhibition has been reported to play a role in regulating gut motility, but the evidence is insufficient, and the mechanism remains unknown. The aim of this study was to investigate the possible role of phosphodiesterase-4 (PDE4) inhibitor rolipram in water avoidance stress-induced colonic hypermotility.

METHODS

A rat model of irritable bowel syndrome (IBS) with diarrhea (IBS-D) was established by water avoidance stress (WAS). Intestinal motility was assessed by fecal pellets expulsion per hour. The cyclic adenosine monophosphate (cAMP) and nitric oxide (NO) level in colon tissue were detected using ELISA assay and the Griess test, respectively. Western blotting was performed to assess the protein level of PDE, PKA/p-CREB, and neuronal nitric oxide synthase (nNOS) in the colon. To determine the role of rolipram in gut motility, the rats of the WAS + Rolipram and Rolipram group were injected with rolipram intraperitoneally. The colonic contractile activity was recorded with a RM6240 multichannel physiological signal system.

KEY RESULTS

WAS-induced gastrointestinal hypermotility and increased defecation in rats. After repeated stress, protein levels of PDE4 in the colon were promoted while PKA/p-CREB and nNOS were highly decreased. cAMP content in colon tissue did not change significantly. However, NO content decreased after WAS, and rolipram partly enhanced NO in WAS-exposed rats. In addition, intraperitoneal injection of rolipram partly inhibited the colonic motility in vivo. Meanwhile, we observed rolipram inhibited the contraction of colonic smooth muscle strips, and this inhibitory effect was abolished by Nω-Nitro-L-arginine (L-NNA), a nitric oxide synthase (NOS) inhibitor, tetrodotoxin (TTX), a blocker of neuronal voltage-dependent Na⁺ channels, Rp-Adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Rp-cAMPS), an antagonist of cAMP.

CONCLUSIONS AND INFERENCES

Rolipram could relieve stress-induced gastrointestinal hypermotility. This effect may be partly through the cAMP-PKA-p-CREB pathway and NO pathway.

Otilonium Bromide treatment prevents nitrergic functional and morphological changes caused by chronic stress in the distal colon of a rat IBS model

Irritable bowel syndrome (IBS) is a highly prevalent gastrointestinal disorder characterized by periods of remission and exacerbation. Among the risk factors to develop IBS, psychosocial stress is widely acknowledged. The water avoidance stress repeatedly applied (rWAS) is considered effective to study IBS etio-pathogenesis. Otilonium bromide (OB), a drug with multiple mechanisms of action, is largely used to treat IBS patients. Orally administered, it concentrates in the large bowel and significantly ameliorates the IBS symptomatology. Presently, we tested whether rWAS rats developed neuro-muscular abnormalities in the distal colon and whether OB treatment prevented them. The investigation was focussed on the nitrergic neurotransmission by combining functional and morphological methodologies. The results confirm rWAS as reliable animal model to investigate the cellular mechanisms responsible for IBS: exposure to one-hour psychosocial stress for 10 days depressed muscle contractility and increased iNOS expression in myenteric neurons. OB treatment counteracted these effects. We hypothesize that these effects are due to the corticotropin-releasing factor (CRF) release, the main mediator of the psychosocial stress, followed by a CRF1receptor activation. OB, that was shown to prevent CRF1r activation, reasonably interrupted the cascade events that bring to the mechanical and immunohistochemical changes affecting rWAS rat colon.

Short chain fatty acids and colon motility in a mouse model of irritable bowel syndrome

Background

Irritable bowel syndrome (IBS) is defined as a multifactorial disorder associated with visceral hypersensitivity, altered gut motility and dysfunction of the brain-gut axis. Gut microbiota and its metabolites are proposed as possible etiological factors of IBS. Short chain fatty acids (SCFAs) induce both inhibitory and stimulatory action on colon motility, however, their effects on the IBS model were not investigated. The aim of our study was to investigate the level of SFCAs in feces and their effects on colon motility in a mouse model of IBS.

Methods

IBS model was induced in mice by intracolonic infusion of 1% acetic acid during the early postnatal period. Mice colon hypersensitivity was assessed by the threshold of the abdominal withdrawal reflex in response to colorectal distention. Colon contractility was studied using proximal colon specimens in isometric conditions. Transit rates were assessed by the pellet propulsion in the isolated colon. Concentrations of SCFAs in feces were measured using gas–liquid chromatography.

Results

The concentration of SCFAs in feces of IBS model mice was higher compared to the control group. Visceral sensitivity to colorectal distension and colonic transit rate were increased indicating IBS with predominant diarrhea. The frequency and amplitude of spontaneous contractions of proximal colon segments from IBS mice were higher, but carbachol induced contractions were lower compared to control. During acute application of SCFAs (sodium propionate, sodium acetate or butyric acid) dose-dependently (0.5–30 mM) decreased tonic tension, frequency and amplitude of spontaneous and carbachol-evoked contractions. In the mouse IBS group the inhibitory effects SCFAs on spontaneous and carbachol-evoked contractions were less pronounced. At the same time intraluminal administration of butyrate (5 mM) increased the transit rate in the colon of both groups, but its stimulatory effect was more pronounced in mouse IBS model group.

Conclusion

Our data indicate that the increased transit rate in the mouse IBS model group is associated with a disbalance of activating and inhibiting action of SCFAs due to chronically elevated SCFA levels, which may impact the pathogenesis of IBS with predominant diarrhea syndrome.

Possible implications of animal models for the assessment of visceral pain

Acute pain, provoked generally after the activation of peripheral nociceptors, is an adaptive sensory function that alerts the individual to avoid noxious stimuli. However, uncontrolled acute pain has a maladaptive role in sensory activity leading to development of a chronic pain state which persists even after the damage is resolved, or in some cases, in the absence of an initial local acute injury. Huge numbers of people suffer from visceral pain at least once during their life span, leading to substantial health care costs. Although studies reporting on the mechanism of visceral pain are accumulating, it is still not precisely understood. Therefore, this review aims to elucidate the mechanism of visceral pain through an evaluation of different animal models and their application to develop novel therapeutic approaches for treating visceral pain. To assess the nociceptive responses in viscera, several visceral pain models such as inflammatory, traction, stress and genetic models utilizing different methods of measurement have been devised. Among them, the inflammatory and traction models are widely used for studying the visceral pain mechanism of different disease conditions and post-operative surgery in humans and animals. A hapten, 2,4,6-trinitrobenzene sulfonic acid (TNBS), has been extensively used as an inflammatory agent to induce visceral pain. The traction model seems to cause a strong pain stimulation and autonomic reaction and could thus be the most appropriate model for studying the underlying visceral pain mechanism and for probing the therapeutic efficacies of various anesthetic and analgesics for the treatment of visceral pain and hyperalgesia.

PDTC Alleviates Depressive Symptoms and Colon Tissue Injury via Inhibiting NO Overproduction in CUMS Rats

Background

The accumulated evidence demonstrates that stress plays an important role in the pathogenesis of depression that is associated with intestinal dysfunctions. However, the mechanisms remain unresolved.

Methods

A total of 40 male Wistar rats were obtained and randomly divided into four equal-sized group: control, PDTC + chronic and unpredictable mild stress (CUMS), FLX + CUMS, and CUMS. Western blotting and qRT-PCR were used to examine the levels of nitric oxide (NO), nuclear factor kappa beta (NF-κB), inducible nitric oxide synthase (iNOS), and iNOS mRNA in spinal cord L1-2 and colon.

Key Results

Chronic and unpredictable mild stress increased the serum CORT level, decreased body weight and sucrose preference, and altered OFT performance, while increased levels of NO, iNOS mRNA, iNOS and NF-κB protein in colon and spinal cord were accompanied by histopathological changes in colon. Pretreatment with an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC), reversed these effects. Fluoxetine failed to prevent NO increase in both spinal cord and colon, while the iNOS protein level, although not statistically significantly increased compared to control, was not decreased compared to CUMS. Also, fluoxetine failed to prevent histological changes.

Conclusion

In conclusion, the NF-κB/iNOS pathway may be involved in the mechanism of CUMS-induced depressive-like behavior and colon tissue injury.

Activation of cannabinoid 2 receptor relieves colonic hypermotility in a rat model of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a common disease with intestinal dysmotility, whose mechanism remains elusive. The endocannabinoid system is emerging as an important modulator of gastrointestinal (GI) motility in multiple diseases, but its involvement in IBS is unknown. We aimed to determine whether cannabinoid 2 (CB2) receptor modulates intestinal motility associated with stress-induced IBS.

METHODS

A rat IBS model was established by chronic water avoidance stress (WAS). Colonic pathological alterations were detected histologically and intestinal motility was assessed by intestinal transit time (ITT) and fecal water content (FWC). Visceral sensitivity was determined by visceromotor response (VMR) to colorectal distension (CRD). Real-time PCR, western blot, and immunostaining were performed to identify colonic CB2 receptor expression. Colonic muscle strip contractility was studied by isometric transducers and nitric oxide (NO) was detected by the Griess test. The effects of AM1241, a selective agonist of CB2 receptors, on colonic motility were examined.

KEY RESULTS

After 10 days of WAS exposure, ITT was decreased and FWC elevated while VMR magnitude in response to CRD was significantly enhanced. Colon CB2 protein and mRNA levels increased and density of CB2-positive macrophages in the mucosa and enteric neurons in the myenteric plexus was higher than in controls. Pharmacological enhancement of CB2 activity by AM1241 relieved colonic hypermotility in WAS rats in a concentration-dependent manner via inhibition of p38 phosphorylation and elevation of NO production.

CONCLUSION

CB2 receptor may exert an important inhibitory effect in stress-induced colonic hypermotility by modulating NO synthesis through p38 mitogen-activated protein kinase signaling. AM1241 could be used as a potential drug to treat disorders with colonic hypermotility.