Activation of corticotropin-releasing factor receptor 2 mediates the colonic motor coping response to acute stress in rodents

Otilonium Bromide Prevents Cholinergic Changes in the Distal Colon Induced by Chronic Water Avoidance Stress, a Rat Model of Irritable Bowel Syndrome

Irritable Bowel syndrome (IBS) is a highly widespread gastrointestinal disorder whose symptomatology mainly affect the large intestine. Among the risk factors, psychosocial stress is the most acknowledged. The repeated water avoidance stress (rWAS) is considered an animal model of psychosocial stress that is capable of mimicking IBS. Otilonium bromide (OB), which is orally administered, concentrates in the large bowel and controls most of the IBS symptoms in humans. Several reports have shown that OB has multiple mechanisms of action and cellular targets. We investigated whether the application of rWAS to rats induced morphological and functional alterations of the cholinergic neurotransmission in the distal colon and whether OB prevented them. The results demonstrated that rWAS affects cholinergic neurotransmission by causing an increase in acid mucin secretion, in the amplitude of electrically evoked contractile responses, abolished by atropine, and in the number of myenteric neurons expressing choline acetyltransferase. OB counteracted these changes and also showed an intrinsic antimuscarinic effect on the post-synaptic muscular receptors. We assume that the rWAS consequences on the cholinergic system are linked to corticotrophin-releasing factor-1 (CRF1) receptor activation by the CRF hypothalamic hormone. OB, by interfering with the CFR/CRFr activation, interrupted the cascade events responsible for the changes affecting the rWAS rat colon.

Corticotropin-releasing factor receptor agonists decrease interstitial cells of Cajal in murine colon

BACKGROUND

Peripheral corticotropin-releasing factor (CRF) has been reported to affect gastrointestinal motility through corticotropin-releasing factor receptor located in enteric nervous system (ENS), but less is known about of the relationship between peripheral CRF and interstitial cells of Cajal (ICC).

METHODS

Mice were intraperitoneally injected with CRF receptor agonists to determine their effects on colonic ICC. Chronic heterotypic stress (CHeS) was applied to mice to determine endogenous CRF-CRF receptor signaling on colonic ICC.

RESULTS

We found that stressin1, a selective CRF receptor 1 (CRF₁ ) agonist, significantly increased the expression of CRF₁ but had no effect on the expression of CRF₂ in the smooth muscles of murine colon. The protein expression of c-Kit, Anoctamin-1 (ANO1), and stem cell factor (SCF) in the colonic smooth muscles was significantly decreased in stressin1-treated mice. Accordingly, 2-(4-Chloro-2-methylphenoxy)-N'-(2-methoxybenzylidene) acetohydrazide (Ani 9), a selective ANO1 blocker, had a less significant inhibitory effect on CMMC in stressin1-treated mice compared to the saline-treated ones. Similarly, we also found that ICC and ANO1 were reduced in the colonic smooth muscles of mice by treatment with sauvagine (ip), a CRF₂ agonist. However, different with stressin1, sauvagine decreased the expression of CRF₂ besides increasing CRF₁ expression in the colonic smooth muscles. Similar results of CRF₁ and c-Kit expressions were also obtained from the colon of CHeS-treated mice.

CONCLUSION

All these results suggest that CRF may be involved in the abnormality of colonic motility through peripheral CRF₁ to decrease the number and function of ICC, which provides a potential target for treating stress-induced gastrointestinal motility disorder.

Psychological stress induces an increase in cholinergic enteric neuromuscular pathways mediated by glucocorticoid receptors

Introduction

Repeated acute stress (RASt) is known to be associated with gastrointestinal dysfunctions. However, the mechanisms underlying these effects have not yet been fully understood. While glucocorticoids are clearly identified as stress hormones, their involvement in RASt-induced gut dysfunctions remains unclear, as does the function of glucocorticoid receptors (GR). The aim of our study was to evaluate the involvement of GR on RASt-induced changes in gut motility, particularly through the enteric nervous system (ENS).

Methods

Using a murine water avoidance stress (WAS) model, we characterized the impact of RASt upon the ENS phenotype and colonic motility. We then evaluated the expression of glucocorticoid receptors in the ENS and their functional impact upon RASt-induced changes in ENS phenotype and motor response.

Results

We showed that GR were expressed in myenteric neurons in the distal colon under basal conditions, and that RASt enhanced their nuclear translocation. RASt increased the proportion of ChAT-immunoreactive neurons, the tissue concentration of acetylcholine and enhanced cholinergic neuromuscular transmission as compared to controls. Finally, we showed that a GR-specific antagonist (CORT108297) prevented the increase of acetylcholine colonic tissue level and in vivo colonic motility.

Discussion

Our study suggests that RASt-induced functional changes in motility are, at least partly, due to a GR-dependent enhanced cholinergic component in the ENS.

Peripheral CRF-R1/CRF-R2 antagonist, astressin C, induces a long-lasting blockade of acute stress-related visceral pain in male and female rats

Peptide CRF antagonists injected peripherally alleviate stress-induced visceral hypersensitivity (SIVH) to colorectal distension (CRD) in rodents. Here we further evaluated the dose and time-dependent inhibitory activity of several long-acting peptide CRF receptor antagonists related to astressin on SIVH, focusing on astressin C (AstC), which previously showed high efficacy on stress-related alterations of HPA axis and gut secretomotor functions. Male and female Sprague-Dawley rats pretreated subcutaneously (SC) with AstC were injected intraperitoneally (IP) with CRF 15 min later. The visceromotor responses (VMR) to graded phasic CRD (10, 20, 40 and 60 mmHg) were monitored at basal, 15 min and up to 1-8 days after pretreatment. Two other astressin analogs, hexanoyl-astressin D (Hex-AstD) and [CαMeVal^19,32]-AstC, were also tested. The response to IP CRF was sex-dependent with female rats requiring a higher dose to exhibit visceral hyperalgesia. Pretreatment with AstC (30-1000 µg/kg) resulted in a dose-related inhibition of IP CRF-induced SIVH and diarrhea in both sexes. The highest dose prevented SIVH and diarrhea up to 5-7 days after a single SC injection and was lost on day 7 (females) and day 8 (males) but reinstated after a second injection of AstC on day 8 or 9 respectively. [CαMeVal^19,32]-AstC and Hex-AstD (1000 µg/kg in males) also prevented SIVH. These data show the potent long-lasting anti-hyperalgesic effect of AstC in an acute model of SIVH in both male and female rats. This highlights the potential of long-acting peripheral CRF antagonists to treat stress-sensitive irritable bowel syndrome.

Beyond depression and anxiety; a systematic review about the role of corticotropin-releasing hormone antagonists in diseases of the pelvic and abdominal organs

Evidence for beneficial effects of corticotropin releasing hormone (CRH) antagonists in abdominal and pelvic organs is emerging in preclinical studies. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement a compilation of preclinical studies using CRH receptor antagonists as a treatment for abdominal and pelvic disease was carried out. The Animal Research: Reporting of In Vivo Experiments (ARRIVE) essential 10 guidelines were used to determine quality of the included studies. A total of 40 studies from the last 15 years studying irritable bowel syndrome, inflammatory bowel disease, endometriosis, enteritis, stress impact on gastrointestinal processes and exogenous CRH administration effects were included. Blockage of the CRH receptor 1 was mainly associated with beneficial effects while that of CRH receptor 2 worsened studied effects. However, time of administration, route of administration and the animal model used, all had an impact on the beneficial outcomes. Frequency of drugs administered indicated that astressin-2B, astressin and antalarmin were among the most utilized antagonists. Of concern, studies included were predominantly carried out in male models only, representing a gender discrepancy in preclinical studies compared to the clinical scenario. The ARRIVE score average was 13 with ~60% of the studies failing to randomize or blind the experimental units. Despite the failure to date of the CRH antagonists in moving across the clinical trials pipeline, there is evidence for their beneficial effects beyond mood disorders. Future pre-clinical studies should be tailored towards effectively predicting the clinical scenario, including reduction of bias and randomization.

Corticotropin-releasing factor receptor 1 (CRF-R1) antagonists: Promising agents to prevent visceral hypersensitivity in irritable bowel syndrome

Corticotropin-releasing factor (CRF) is a 41-amino acid polypeptide that coordinates the endocrine system, autonomic nervous system, immune system, and physiological behavior. CRF is a signaling regulator in the neuro-endocrine-immune (NEI) network that mediates visceral hypersensitivity. Rodent models to simulate changes in intestinal motility similar to those reported in the irritable bowel syndrome (IBS), demonstrate that the CRF receptor 1 (CRF-R1) mediates intestinal hypersensitivity under many conditions. However, the translation of preclinical studies into clinical trials has not been successful possibly due to the lack of sufficient understanding of the multiple variants of CRF-R1 and CRF-R1 antagonists. Investigating the sites of action of central and peripheral CRF is critical for accelerating the translation from preclinical to clinical studies.

Activation of CRF1 receptors expressed in brainstem autonomic nuclei stimulates colonic enteric neurons and secreto-motor function in male rats

BACKGROUND

Hypothalamic corticotropin-releasing factor (CRF) receptor 1 (CRF1 ) plays a role in acute stress-related stimulation of colonic motor function. Less is known on CRF1 signaling in the brainstem.

METHODS

We investigate CRF1 expression in the brainstem and the colonic response to 4th ventricle (4V) injection of CRF and urocortin (Ucn) 2 (3 µg/rat) in chronically cannulated male rats.

KEY RESULTS

Transcripts of CRF1 wild-type 1a and splice variants 1c, 1e, 1f, 1o along with three novel variants 1a-2 (desK-110 in exon 5), 1p (-exon 7), and 1q (exon 5 extension) were identified in the pons and medulla. The area postrema, nucleus tractus solitarius, dorsal motor nucleus of the vagus, locus coeruleus, and Barrington's nucleus isolated by laser capture microdissection expressed 1a, 1a-2, and 1p but not 1q. Compared to 4V vehicle, 4V CRF induced fecal pellet output (FPO) and diarrhea that were blocked by the CRF antagonist, astressin-B. CRF2 agonist, Ucn2 had no effect on basal or CRF-induced FPO. CRF actions were correlated with the induction of c-Fos immunoreactivity in myenteric neurons of the proximal and distal colon (pC, dC) and submucosal neurons of dC. c-Fos immunoreactivity occurred in 39% and 37% of myenteric cholinergic and 7% and 58% of nitrergic neurons in the pC and dC, respectively.

CONCLUSIONS & INFERENCES

CRF1a and its splice variants are expressed in brainstem nuclei, and activation of CRF1 signaling at the level of the brainstem stimulates colonic secretory-motor function through activation of colonic enteric neurons.

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.

The suppression effects of feeding and mechanisms in CRF system of animals

CRF system is comprised of 4 homologous lineages, 2 main receptors (CRF-R1 and CRF-R2), and a binding protein CRF-BP. The homologous lineages are corticotropin-releasing factor (CRF), urotensin I (UI)/sauvagine (SVG)/urocortin 1 (UCN1), urocortin 2 (UCN2), and urocortin 3 (UCN3), and UI, SVG, UCN1 are orthologous genes. CRF system genes are widely distributed in the brain and gastrointestinal tract, which may relate to feeding regulation. According the research progress about CRF system on mammals and non-mammals, this paper summarized the discovery, structure, tissue distribution, appetite regulation and mechanism of CRF system in animals, which can provide the reference for further research and production of feeding regulation and growth in mammals and fish species.

Intranasal Administration of Oxytocin Attenuates Stress Responses Following Chronic Complicated Stress in Rats

Background/Aims

Gastrointestinal (GI) symptoms may develop when we fail to adapt to various stressors of our daily life. Central oxytocin (OXT) can counteract the biological actions of corticotropin-releasing factor (CRF), and in turn attenuates stress responses. Administration (intracerebroventricular) of OXT significantly antagonized the inhibitory effects of chronic complicated stress (CCS) on GI dysmotility in rats. However, intracerebroventricular administration is an invasive pathway. Intranasal administration can rapidly deliver peptides to the brain avoiding stress response. The effects of intranasal OXT on hypothalamus-pituitary-adrenal axis and GI motility in CCS conditions have not been investigated.

Methods

A CCS rat model was set up, OXT 5, 10, or 20 μg were intranasal administered, 30 minutes prior to stress loading. Central CRF and OXT expression levels were analyzed, serum corticosterone and OXT concentrations were measured, and gastric and colonic motor functions were evaluated by gastric emptying, fecal pellet output, and motility recording system.

Results

Rats in CCS condition showed significantly increased CRF expression and corticosterone concentration, which resulted in delayed gastric emptying and increased fecal pellet output, attenuated gastric motility and enhanced colonic motility were also recorded. OXT 10 μg or 20 μg significantly reduced CRF mRNA expression and the corticosterone concentration, OXT 20 μg also helped to restore GI motor dysfunction induced by CCS.

Conclusion

Intranasal administration of OXT has an anxiolytic effect and attenuates the hypothalamus-pituitary-adrenal axis in response to CCS, and gave effects which helped to restore GI dysmotility, and might be a new approach for the treatment of stress-induced GI motility disorders.

EphrinB2/ephB2-mediated myenteric synaptic plasticity: mechanisms underlying the persistent muscle hypercontractility and pain in postinfectious IBS

Patients with irritable bowel syndrome (IBS) show pain hypersensitivity and smooth muscle hypercontractility in response to colorectal distension (CRD). Synaptic plasticity, a key process of memory formation, in the enteric nervous system may be a novel explanation. This study aimed to explore the regulatory role of ephrinB2/ephB2 in enteric synaptic plasticity and colonic hyperreactive motility in IBS. Postinfectious (PI)-IBS was induced by Trichinella spiralis infection in rats. Isometric contractions of colonic circular muscle strips, particularly neural-mediated contractions, were recorded ex vivo. Meanwhile, ephrinB2/ephB2-mediated enteric structural and functional synaptic plasticity were assessed in the colonic muscularis, indicating that ephrinB2 and ephB2 were located on enteric nerves and up-regulated in the colonic muscularis of PI-IBS rats. Colonic hypersensitivity to CRD and neural-mediated colonic hypercontractility were present in PI-IBS rats, which were correlated with increased levels of cellular homologous fos protein (c-fos) and activity-regulated cystoskeleton-associated protein (arc), the synaptic plasticity-related immediate early genes, and were ameliorated by ephB2Fc (an ephB2 receptor blocker) or MK801 (an NMDA receptor inhibitor) exposure. EphrinB2/ephB2 facilitated synaptic sprouting and NMDA receptor-mediated synaptic potentiation in the colonic muscularis of PI-IBS rats and in the longitudinal muscle-myenteric plexus cultures, involving the Erk-MAPK and PI3K-protein kinase B pathways. In conclusion, ephrinB2/ephB2 promoted the synaptic sprouting and potentiation of myenteric nerves involved in persistent muscle hypercontractility and pain in PI-IBS. Hence, ephrinB2/ephB2 may be an emerging target for the treatment of IBS.-Zhang, L., Wang, R., Bai, T., Xiang, X., Qian, W., Song, J., Hou, X. EphrinB2/ephB2-mediated myenteric synaptic plasticity: mechanisms underlying the persistent muscle hypercontractility and pain in postinfectious IBS.

Brain and Gut CRF Signaling: Biological Actions and Role in the Gastrointestinal Tract

BACKGROUND

Corticotropin-releasing factor (CRF) pathways coordinate behavioral, endocrine, autonomic and visceral responses to stress. Convergent anatomical, molecular, pharmacological and functional experimental evidence supports a key role of brain CRF receptor (CRF-R) signaling in stress-related alterations of gastrointestinal functions. These include the inhibition of gastric acid secretion and gastric-small intestinal transit, stimulation of colonic enteric nervous system and secretorymotor function, increase intestinal permeability, and visceral hypersensitivity. Brain sites of CRF actions to alter gut motility encompass the paraventricular nucleus of the hypothalamus, locus coeruleus complex and the dorsal motor nucleus while those modulating visceral pain are localized in the hippocampus and central amygdala. Brain CRF actions are mediated through the autonomic nervous system (decreased gastric vagal and increased sacral parasympathetic and sympathetic activities). The activation of brain CRF-R2 subtype inhibits gastric motor function while CRF-R1 stimulates colonic secretomotor function and induces visceral hypersensitivity. CRF signaling is also located within the gut where CRF-R1 activates colonic myenteric neurons, mucosal cells secreting serotonin, mucus, prostaglandin E2, induces mast cell degranulation, enhances mucosal permeability and propulsive motor functions and induces visceral hyperalgesia in animals and humans. CRF-R1 antagonists prevent CRF- and stressrelated gut alterations in rodents while not influencing basal state.

DISCUSSION

These preclinical studies contrast with the limited clinical positive outcome of CRF-R1 antagonists to alleviate stress-sensitive functional bowel diseases such as irritable bowel syndrome.

CONCLUSION

The translational potential of CRF-R1 antagonists in gut diseases will require additional studies directed to novel anti-CRF therapies and the neurobiology of brain-gut interactions under chronic stress.

Gastric corticotropin-releasing factor influences mast cell infiltration in a rat model of functional dyspepsia

Functional gastrointestinal disorders (FGIDs) are characterized by dysregulated gut-brain interactions. Emerging evidence shows that low-grade mucosal inflammation and immune activation contribute to FGIDs, including functional dyspepsia (FD). Stress plays an important role in the onset of FD symptoms. In human subjects with FD, presence of gastric mast cells has been reported, but factors that influence mast cell infiltration remain uncharacterized. Corticotropin-releasing factor (CRF) initiates the body's stress response and is known to degranulate mast cells. In this study, we delineated the role of the CRF system in the pathogenesis of FD in a rat model. Gastric irritation in neonate rat pups with iodoacetamide (IA) was used to induce FD-like symptoms. RNA interference (RNAi) was used to silence gastric CRF expression. Mast cell infiltrate in the stomach increased by 54% in IA-treated rats compared to controls and CRF-RNAi tended to decrease gastric mast cell infiltrate. Sucrose intake decreased in IA-treated rats and mast cell numbers showed a negative association with sucrose intake. IA treatment and transient silencing of gastric CRF increased hypothalamic CRF levels. In IA-treated rats, gastric levels of CRF receptor 2 (CRF2) decreased by ~76%, whereas hypothalamic CRF receptor 1 (CRF1) levels increased. Plasma levels of TNF-α showed a positive correlation with plasma CRF levels. Levels of phosphorylated p38 and ERK1/2 in the stomach showed a positive correlation with gastric CRF levels. Thus, CRF may contribute to low grade inflammation via modulating mast cell infiltration, cytokine levels, MAPK signaling, and the gut-brain axis.

The potential role of thyrotropin-releasing hormone in colonic dysmotility induced by water avoidance stress in rats

OBJECTIVE

This study sought to investigate the effect and underlying mechanism of thyrotrophin releasing hormone (TRH) on colonic contractile disorders induced by chronic water avoidance stress (WAS).

METHODS

Male SD rats were exposed to daily 1-h WAS or sham WAS for 10 consecutive days. The presence of TRH in the serum and colonic mucosa were determined using enzyme immunoassay kits. Immunohistochemistry and western blotting were performed to detect the expression of TRH receptor 1 (TRH-R1). The contractions of proximal colonic smooth muscle were studied in an organ bath system. The whole-cell patch-clamp technique was used to record the currents of both L-type calcium currents (I_Ca,L) and large conductance Ca²⁺-activated K⁺ (BK_Ca) channels in colonic smooth muscle cells (SMCs) isolated from adult rats.

RESULTS

Enzyme immunoassay revealed that TRH was present in both serum and colonic mucosa and that this expression increased in the WAS group. Immunohistochemistry revealed that the TRH-R1 level increased in colons devoid of mucosa and submucosa from the stressed rats as compared with the control group. TRH increased the spontaneous contractions of the longitudinal muscle and circular muscle strips in a dose-dependent manner in vitro. The effect was also confirmed in an vivo experiment, where an intraperitoneal injection of TRH in rats significantly increased fecal pellet output during a 24-h period as compared with the control group. Furthermore, intraperitoneal injection of a non-specific TRH receptor antagonist, chlordiazepoxide and a TRH-R1 antibody, partially decreased the fecal pellets of WAS rats during the 10-day stress period. Furthermore, TRH increased the peak current of L-type channels in colonic smooth muscle cells (SMCs) at a membrane potential of 0 mV, while the current of large conductance Ca²⁺-activated K⁺ (BK_Ca) channels was not changed following the addition of TRH.

CONCLUSION

TRH may be involved in the dysmotility induced by chronic stress and may have some potential clinical therapeutic use in regulating gut motility.

VIP is involved in peripheral CRF-induced stimulation of propulsive colonic motor function and diarrhea in male rats

We investigated whether vasoactive intestinal peptide (VIP) and/or prostaglandins contribute to peripheral corticotropin-releasing factor (CRF)-induced CRF1 receptor-mediated stimulation of colonic motor function and diarrhea in rats. The VIP antagonist, [4Cl-D-Phe6, Leu17]VIP injected intraperitoneally completely prevented CRF (10 µg/kg ip)-induced fecal output and diarrhea occurring within the first hour after injection, whereas pretreatment with the prostaglandins synthesis inhibitor, indomethacin, had no effect. In submucosal plexus neurons, CRF induced significant c-Fos expression most prominently in the terminal ileum compared with duodenum and jejunum, whereas no c-Fos was observed in the proximal colon. c-Fos expression in ileal submucosa was colocalized in 93.4% of VIP-positive neurons and 31.1% of non-VIP-labeled neurons. CRF1 receptor immunoreactivity was found on the VIP neurons. In myenteric neurons, CRF induced only a few c-Fos-positive neurons in the ileum and a robust expression in the proximal colon (17.5 ± 2.4 vs. 0.4 ± 0.3 cells/ganglion in vehicle). The VIP antagonist prevented intraperitoneal CRF-induced c-Fos induction in the ileal submucosal plexus and proximal colon myenteric plexus. At 60 min after injection, CRF decreased VIP levels in the terminal ileum compared with saline (0.8 ± 0.3 vs. 2.5 ± 0.7 ng/g), whereas VIP mRNA level detected by qPCR was not changed. These data indicate that intraperitoneal CRF activates intestinal submucosal VIP neurons most prominently in the ileum and myenteric neurons in the colon. It also implicates VIP signaling as part of underlying mechanisms driving the acute colonic secretomotor response to a peripheral injection of CRF, whereas prostaglandins do not play a role. NEW & NOTEWORTHY Corticotropin-releasing factor (CRF) in the gut plays a physiological role in the stimulation of lower gut secretomotor function induced by stress. We showed that vasoactive intestinal peptide (VIP)-immunoreactive neurons in the ileal submucosal plexus expressed CRF1 receptor and were prominently activated by CRF, unlike colonic submucosal neurons. VIP antagonist abrogated CRF-induced ileal submucosal and colonic myenteric activation along with functional responses (defecation and diarrhea). These data point to VIP signaling in ileum and colon as downstream effectors of CRF.

Central Neuropeptide Y Plays an Important Role in Mediating the Adaptation Mechanism Against Chronic Stress in Male Rats

Exposure to continuous life stress often causes gastrointestinal (GI) symptoms. Studies have shown that neuropeptide Y (NPY) counteracts the biological actions of corticotrophin-releasing factor (CRF) and is involved in the termination of the stress response. However, in chronic repeated restraint stress (CRS) conditions, the actions of NPY on GI motility remain controversial. To evaluate the role of NPY in mediation of the adaptation mechanism and GI motility in CRS conditions, a CRS rat model was set up. Central CRF and NPY expression levels were analyzed, serum corticosterone and NPY concentrations were measured, and GI motor function was evaluated. The NPY Y1 receptor antagonist BIBP-3226 was centrally administered before stress loading, and on days 1 through 5 of repeated stress, the central CRF and the serum corticosterone concentrations were measured. In addition, gastric and colonic motor functions were evaluated. The elevated central CRF expression and corticosterone concentration caused by acute stress began to fall after 3 days of stress loading, whereas central NPY expression and serum NPY began to increase. GI dysmotility also returned to a normal level. Pretreatment with BIBP-3226 abolished the adaptation mechanism and significantly increased CRF expression and the corticosterone concentration, which resulted in delayed gastric emptying and accelerated fecal pellet output. Inhibited gastric motility and enhanced distal colonic motility were also recorded. CRS-produced adaptation, overexpressed central CRF, and GI dysmotility observed in acute restraint stress were restored to normal levels. Central NPY via the Y1 receptor plays an important role in mediating the adaptation mechanism against chronic stress.

Endocrinology and the brain: corticotropin-releasing hormone signaling

Corticotropin-releasing hormone (CRH) is a key player of basal and stress-activated responses in the hypothalamic-pituitary-adrenal axis (HPA) and in extrahypothalamic circuits, where it functions as a neuromodulator to orchestrate humoral and behavioral adaptive responses to stress. This review describes molecular components and cellular mechanisms involved in CRH signaling downstream of its G protein-coupled receptors (GPCRs) CRHR1 and CRHR2 and summarizes recent findings that challenge the classical view of GPCR signaling and impact on our understanding of CRHRs function. Special emphasis is placed on recent studies of CRH signaling that revealed new mechanistic aspects of cAMP generation and ERK1/2 activation in physiologically relevant contexts of the neurohormone action. In addition, we present an overview of the pathophysiological role of the CRH system, which highlights the need for a precise definition of CRHRs signaling at molecular level to identify novel targets for pharmacological intervention in neuroendocrine tissues and specific brain areas involved in CRH-related disorders.

Frontline Science: Corticotropin-releasing factor receptor subtype 1 is a critical modulator of mast cell degranulation and stress-induced pathophysiology

Life stress is a major risk factor in the onset and exacerbation of mast cell-associated diseases, including allergy/anaphylaxis, asthma, and irritable bowel syndrome. Although it is known that mast cells are highly activated upon stressful events, the mechanisms by which stress modulates mast cell function and disease pathophysiology remains poorly understood. Here, we investigated the role of corticotropin-releasing factor receptor subtype 1 (CRF₁) in mast cell degranulation and associated disease pathophysiology. In a mast cell-dependent model of IgE-mediated passive systemic anaphylaxis (PSA), prophylactic administration of the CRF₁-antagonist antalarmin attenuated mast cell degranulation and hypothermia. Mast cell-deficient Kit^W-sh/W-sh mice engrafted with CRF₁^-/- bone marrow-derived mast cells (BMMCs) exhibited attenuated PSA-induced serum histamine, hypothermia, and clinical scores compared with wild-type BMMC-engrafted Kit^W-sh/W-sh mice. Kit^W-sh/W-sh mice engrafted with CRF₁^-/- BMMCs also exhibited suppressed in vivo mast cell degranulation and intestinal permeability in response to acute restraint stress. Genetic and pharmacologic experiments with murine BMMCs, rat RBL-2H3, and human LAD2 mast cells demonstrated that although CRF₁ activation did not directly induce MC degranulation, CRF₁ signaling potentiated the degranulation responses triggered by diverse mast cell stimuli and was associated with enhanced release of Ca²⁺ from intracellular stores. Taken together, our results revealed a prominent role for CRF₁ signaling in mast cells as a positive modulator of stimuli-induced degranulation and in vivo pathophysiologic responses to immunologic and psychologic stress.

The Effect of Peripheral CRF Peptide and Water Avoidance Stress on Colonic and Gastric Transit in Guinea Pigs

Functional dyspepsia (FD) and irritable bowel syndrome (IBS) are common gastrointestinal (GI) diseases; however, there is frequent overlap between FD and IBS patients. Emerging evidence links the activation of corticotropin releasing factor (CRF) receptors with stress-related alterations of gastric and colonic motor function. Therefore, we investigated the effect of peripheral CRF peptide and water avoidance stress (WAS) on upper and lower GI transit in guinea pigs. Dosages 1, 3, and 10 μg/kg of CRF were injected intraperitoneally (IP) in fasted guinea pigs 30 minutes prior to the intragastric administration of charcoal mix to measure upper GI transit. Colonic transits in non-fasted guinea pigs were assessed by fecal pellet output assay after above IP CRF doses. Blockade of CRF receptors by Astressin, and its effect on GI transit was also analyzed. Guinea pigs were subjected to WAS to measure gastrocolonic transit in different sets of experiments. Dose 10 μg/kg of CRF significantly inhibited upper GI transit. In contrast, there was dose dependent acceleration of the colonic transit. Remarkably, pretreatment of astressin significantly reverses the effect of CRF peptide on GI transit. WAS significantly increase colonic transit, but failed to accelerate upper GI transit. Peripheral CRF peptide significantly suppressed upper GI transit and accelerated colon transit, while central CRF involved WAS stimulated only colonic transit. Therefore, peripheral CRF could be utilized to establish the animal model of overlap syndrome.

Corticotropin-releasing factor stimulates colonic motility via muscarinic receptors in the rat

AIM

To measure exogenous corticotropin-releasing factor (CRF)-induced motility of the isolated rat colon and to demonstrate the effect of pharmacologic inhibition on CRF-induced motility.

METHODS

The isolated vascularly-perfused rat colon was used. Luminal pressure was monitored via microtip catheter pressure transducers in the proximal and distal colon. At first, exogenous CRF was administered in a stepwise manner and the concentration of CRF yielding maximal colonic motility was selected. After recording basal colonic motility, hexamethonium, phentolamine, propranolol, atropine and tetrodotoxin were infused into the isolated colon. Initially, only the test drug was infused; then, CRF was added. The motility index was expressed as percentage change over basal level.

RESULTS

Administration of 1.4, 14.4, 144 and 288 pmol/L CRF progressively increased colonic motility in the proximal and distal colon. Infusion of atropine or tetrodotoxin reduced CRF-induced motility of both the proximal and distal colon, whereas hexamethonium, phentolamine and propranolol had no effect.

CONCLUSION

CRF-induced colonic motility appears to be mediated by local cholinergic signaling via muscarinic receptors. Muscarinic receptors are potential targets for counteracting CRF-induced colonic hypermotility.

Chronic social stress in pigs impairs intestinal barrier and nutrient transporter function, and alters neuro-immune mediator and receptor expression

Psychosocial stress is a major factor driving gastrointestinal (GI) pathophysiology and disease susceptibility in humans and animals. The mechanisms governing susceptibility to stress-induced GI disease remain poorly understood. In the present study, we investigated the influence of chronic social stress (CSS) in pigs, induced by 7 d of chronic mixing/crowding stress, on intestinal barrier and nutrient transport function, corticotropin releasing factor (CRF) signaling and immunological responses. Results from this study showed that CSS resulted in a significant impairment of ileal and colonic barrier function indicated by reduced transepithelial electrical resistance (TER) in the ileum and increased FD4 flux in the ileum (by 0.8 fold) and colon (by 0.7 fold). Ileal sodium glucose linked transporter 1 (SGLT-1) function, measured as glucose-induced changes in short-circuit current (Isc), was diminished (by 52%) in CSS pigs, associated with reduced body weight gain and feed efficiency. Although reductions in SGLT-1 function were observed in CSS pigs, mRNA expression for SGLT-1, villus heights were increased in CSS pigs. Corticotropin releasing factor (CRF) mRNA was upregulated (by 0.9 fold) in the ileum of CSS pigs but not in the colon. Urocortin 2 (Ucn2) mRNA was upregulated (by 1.5 fold) in the colon of CSS pigs, but not in the ileum. In CSS pigs, a downregulation of pro-inflammatory cytokines mRNA (IL1B, TNFA, IL8, and IL6) was observed in both ileum and colon, compared with controls. In contrast CSS induced a marked upregulation of mRNA for IL10 and mast cell chymase gene (CMA1) in the ileum and colon. Together, these data demonstrate that chronic stress in pigs results in significant alterations in intestinal barrier and nutrient transport function and neuro-immune mediator and receptor expression.

Lactobacillus rhamnosus strain JB-1 reverses restraint stress-induced gut dysmotility

BACKGROUND

Environmental stress affects the gut with dysmotility being a common consequence. Although a variety of microbes or molecules may prevent the dysmotility, none reverse the dysmotility.

METHODS

We have used a 1 hour restraint stress mouse model to test for treatment effects of the neuroactive microbe, L. rhamnosus JB-1^™ . Motility of fluid-filled ex vivo gut segments in a perfusion organ bath was recorded by video and migrating motor complexes measured using spatiotemporal maps of diameter changes.

KEY RESULTS

Stress reduced jejunal and increased colonic propagating contractile cluster velocities and frequencies, while increasing contraction amplitudes for both. Luminal application of 10E8 cfu/mL JB-1 restored motor complex variables to unstressed levels within minutes of application. L. salivarius or Na.acetate had no treatment effects, while Na.butyrate partially reversed stress effects on colonic frequency and amplitude. Na.propionate reversed the stress effects for jejunum and colon except on jejunal amplitude.

CONCLUSIONS & INFERENCES

Our findings demonstrate, for the first time, a potential for certain beneficial microbes as treatment of stress-induced intestinal dysmotility and that the mechanism for restoration of function occurs within the intestine via a rapid drug-like action on the enteric nervous system.

Repeated otilonium bromide administration prevents neurotransmitter changes in colon of rats underwent to wrap restraint stress

Otilonium bromide (OB) is a spasmolytic drug successfully used for the treatment of irritable bowel syndrome (IBS). Its efficacy has been attributed to the block of L- and T-type Ca²⁺ channels and muscarinic and tachykinin receptors in the smooth muscle. Furthermore, in healthy rats, repeated OB administration modified neurotransmitter expression and function suggesting other mechanisms of action. On this basis, we investigated whether repeated OB treatment prevented the functional and neurochemical changes observed in the colon of rats underwent to wrap restrain stress (WRS) a psychosocial stressor considered suitable to reproduce the main IBS signs and symptoms. In control, WRS and OB/WRS rats functional parameters were measured in vivo and morphological investigations were done ex vivo in the colon. The results showed that OB counteracts most of the neurotransmitters changes caused by WRS. In particular, the drug prevents the decrease in SP-, NK1r-, nNOS-, VIP-, and S100β-immunoreactivity (IR) and the increase in CGRP-, and CRF1r-IR. On the contrary, OB does not affect the increase in CRF2r-IR neurons observed in WRS rats and does not interfere with the mild mucosal inflammation due to WRS. Finally, OB per se increases the Mr2 expression in the muscle wall and decreases the number of the myenteric ChAT-IR neurons. Functional findings show a significantly reduction in the number of spontaneous abdominal contraction in OB treated rats. The ability of OB to block L-type Ca²⁺ channels, also expressed by enteric neurons, might represent a possible mechanism through which OB exerts its actions.

Changes of excitatory and inhibitory neurotransmitters in the colon of rats underwent to the wrap partial restraint stress

BACKGROUND

Animal models proposed to reproduce some of the human irritable bowel syndrome (IBS) symptoms are based on the hypothesis that psychosocial stressors play a pivotal role in the IBS etio-pathology. We investigated the wrap restraint stress (WRS) model with the aim to analyze the morphological changes of the entire colonic wall of these animals that showed some of the human IBS symptoms such as visceral hypersensitivity.

METHODS

Male Wistar rats were used and WRS was maintained for 2 h. Abdominal contractions (AC) were recorded in the colon-rectum by balloon distension. Fecal pellets were quantitated. Colonic specimens were examined by routine histology, immunohistochemistry and western blot.

KEY RESULTS

WRS animals were characterized by: (i) increase in AC number and fecal pellets mean weight; (ii) clusters of mononucleated cells, increase in eosinophilic granulocytes and mast cells in the mucosa; (iii) increase in CGRP-immunoreactive (IR) nerve fibers in the lamina propria; (iv) decrease in myenteric NK1r-IR and nNOS-IR neurons and in submucous nNOS-IR neurons; (v) decrease in SP-IR nerve fibers in the muscle wall; (vi) reduction in S100β-IR glia in the entire colonic wall; (vii) increase in CRF1r-IR myenteric neurons; (viii) no change in ChAT-IR neurons, smooth muscle cells and interstitial cells of Cajal.

CONCLUSIONS AND INFERENCES

The present results support the consistency of the WRS as a potential model where part of the human IBS signs and symptoms are reproduced. The changes in glial cells and in excitatory and inhibitory neurotransmitters might represent the substrate for the dysmotility and hypersensitivity.

Neonatal maternal separation increases susceptibility to experimental colitis and acute stress exposure in male mice

Experiencing early life stress can result in maladjusted stress response via dysregulation of the hypothalamic-pituitary-adrenal axis and serves as a risk factor for developing chronic pelvic pain disorders. We investigated whether neonatal maternal separation (NMS) would increase susceptibility to experimental colitis or exposure to acute or chronic stress. Male mice underwent NMS from postnatal day 1-21 and as adults were assessed for open field behavior, hindpaw sensitivity, and visceromotor response (VMR) to colorectal distension (CRD). VMR was also measured before and after treatment with intracolonic trinitrobenzene sulfonic acid (TNBS) or exposure to acute or chronic water avoidance stress (WAS). Myeloperoxidase (MPO) activity, proinflammatory gene and corticotropin-releasing factor (CRF) receptor expression were measured in distal colon. Baseline VMR was not affected by NMS, but undergoing CRD increased anxiety-like behaviors and mechanical hindpaw sensitivity of NMS mice. Treatment with TNBS dose-dependently decreased body weight and survival only in NMS mice. Following TNBS treatment, IL-6 and artemin mRNA levels were decreased in the distal colon of NMS mice, despite increased MPO activity. A single WAS exposure increased VMR during CRD in NMS mice and increased IL-6 mRNA and CRF₂ protein levels in the distal colon of naïve mice, whereas CRF₂ protein levels were heightened in NMS colon both at baseline and post-WAS exposure. Taken together, these results suggest that NMS in mice disrupts inflammatory- and stress-induced gene expression in the colon, potentially contributing towards an exaggerated response to specific stressors later in life.

Sex- and corticotropin-releasing factor receptor 2- dependent actions of urocortin 1 during inflammation

We investigated whether corticotropin-releasing factor receptor 2 (CRF2) and its high-affinity agonist urocortin 1 (Ucn1) mediate sex-specific signaling and immune responses. Intrarectal trinitrobenzene sulfonic acid was used to induce experimental colitis in wild-type, CRF2 knockout (CRF2KO), and heterozygous (CRF2Ht) mice of both sexes. Changes in plasma extravasation, organ weight, survival, immune cell numbers, inflammatory cytokines, and the MAPK signaling pathway were assessed. Stored intestinal biopsies from patients with Crohn's disease (CD) and age- and sex-matched individuals without inflammatory bowel disease (IBD) were examined by immunofluorescence and confocal microscopy to characterize Ucn1 and CRF receptor expression. CRF2Ht mice of both sexes showed decreased survival during colitis compared with other genotypes. Ucn1 improved survival in male mice alone. Ucn1 restored colon length and spleen and adrenal weight and decreased colonic TNF-α, IL-6, and IL-1β levels in male CRF2Ht mice alone. CRF2Ht mice of both sexes showed decreased phosphorylation of MAPK p38 and heat shock protein 27 (Hsp27) levels. Ucn1 restored p-Hsp27 levels in male CRF2Ht mice alone. Expression of the chaperone protein Hsp90 decreased during colitis, except in male CRF2Ht mice. Taken together, our data indicate that sex shows significant interaction with genotype and Ucn1 during colitis. Human duodenal and colonic biopsies revealed that sex-specific differences exist in levels of CRF receptors and Ucn1 expression in patients with CD compared with the matched non-IBD subjects. To conclude, Ucn1 mediates sex-specific immune and cellular signaling responses via CRF2, emphasizing the need for inclusion of females in preclinical studies.

Stress increases descending inhibition in mouse and human colon

BACKGROUND

A relationship between stress and the symptoms of irritable bowel syndrome (IBS) has been well established but the cellular mechanisms are poorly understood. Therefore, we investigated effects of stress and stress hormones on colonic descending inhibition and transit in mouse models and human tissues.

METHODS

Stress was applied using water avoidance stress (WAS) in the animal model or mimicked using stress hormones, adrenaline (5 nM), and corticosterone (1 μM). Intracellular recordings were obtained from colonic circular smooth muscle cells in isolated smooth muscle/myenteric plexus preparations and the inhibitory junction potential (IJP) was elicited by nerve stimulation or balloon distension oral to the site of recording.

KEY RESULTS

Water avoidance stress increased the number of fecal pellets compared to control (p < 0.05). WAS also caused a significant increase in IJP amplitude following balloon distension. Stress hormones also increased the IJP amplitude following nerve stimulation and balloon distension (p < 0.05) in control mice but had no effect in colons from stressed mice. No differences were observed with application of ATP between stress and control tissues, suggesting the actions of stress hormones were presynaptic. Stress hormones had a large effect in the nerve stimulated IJP in human colon (increased >50%). Immunohistochemical studies identified alpha and beta adrenergic receptor immunoreactivity on myenteric neurons in human colon.

CONCLUSIONS & INFERENCES

These studies suggest that WAS and stress hormones can signal via myenteric neurons to increase inhibitory neuromuscular transmission. This could lead to greater descending relaxation, decreased transit time, and subsequent diarrhea.

Water avoidance stress induces visceral hyposensitivity through peripheral corticotropin releasing factor receptor type 2 and central dopamine D2 receptor in rats

BACKGROUND

Water avoidance stress (WAS) is reported to induce functional changes in visceral sensory function in rodents, but the results which have been demonstrated so far are not consistent, i.e., hypersensitivity or hyposensitivity. We determined the effect of WAS on visceral sensation and evaluated the mechanisms of the action.

METHODS

Visceral sensation was assessed by abdominal muscle contractions induced by colonic balloon distention, i.e., visceromotor response (VMR), measured electrophysiologically in conscious rats. The electromyogram electrodes were acutely implanted under anesthesia on the day of the experiment. The threshold of VMR was measured before and after WAS for 1 h. To explore the mechanisms of WAS-induced response, drugs were administered 10 min prior to the initiation of WAS.

KEY RESULTS

WAS significantly increased the threshold of VMR, and this effect was no longer detected at 24 h after. Intraperitoneal injection of astressin2 -B (200 μg/kg), a corticotropin releasing factor (CRF) receptor type 2 antagonist abolished the response by WAS. Subcutaneous (sc) injection of sulpiride (200 mg/kg), a dopamine D2 receptor antagonist blocked the response, while sc domperidone (10 mg/kg), a peripheral dopamine D2 receptor antagonist did not alter it. Naloxone (1 mg/kg, sc), an opioid antagonist did not modify it either.

CONCLUSIONS & INFERENCES

WAS induced visceral hyposensitivity through peripheral CRF receptor type 2 and central dopamine D2 receptor, but not through opioid pathways. As altered pain inhibitory system was reported to be observed in the patients with irritable bowel syndrome, CRF and dopamine signaling might contribute to the pathophysiology.

Urocortins and CRF receptor type 2 variants in the male rat colon: gene expression and regulation by endotoxin and anti-inflammatory effect

Urocortins (Ucns) 1, 2, and 3 and corticotropin-releasing factor receptor 2 (CRF2) mRNA are prominently expressed in various layers of the upper gut. We tested whether Ucns and CRF2 variants are also expressed in the different layers of the rat colon, regulated by LPS (100 μg/kg ip) and play a modulatory role in the colonic immune response to LPS. Transcripts of Ucns and CRF2b, the most common isoform in the periphery, were detected in all laser microdissected layers, including myenteric neurons. LPS increased the mRNA level of Ucn 1, Ucn 2, and Ucn 3 and decreased that of CRF2b in both the colonic mucosa and submucosa + muscle (S+M) layers at 2, 6, and 9 h after injection with a return to basal at 24 h. In addition, CRF2a, another variant more prominent in the brain, and a novel truncated splice variant CRF2a-3 mRNA were detected in all segments of the large intestine. LPS reciprocally regulated the colonic expression of these CRF2 variants by decreasing both CRF2a and CRF2b, while increasing CRF2a-3 in the mucosa and S+M. The CRF2 antagonist astressin2-B further enhanced LPS-induced increase of mRNA level of interleukin (IL)-1β, TNF-α, and inducible nitric oxide synthase in S+M layers and IL-1β in the mucosa and evoked TNF-α expression in the mucosa. These data indicate that Ucns/CRF2 variants are widely expressed in all colonic layers and reciprocally regulated by LPS. CRF2 signaling dampens the CD14/TLR4-mediated acute inflammatory response to Gram-negative bacteria in the colon.

Endogenous CRF in rat large intestine mediates motor and secretory responses to stress

BACKGROUND

Corticotropin-releasing factor (CRF) mediates our body's overall responses to stress. The role of central CRF in stress-stimulated colonic motility is well characterized. We hypothesized that transient perturbation in expression of enteric CRF is sufficient to change stress-induced colonic motor and secretory responses.

METHODS

Sprague-Dawley rats (adult, male) were subjected to 1-h partial restraint stress (PRS) and euthanized at 0, 4, 8, and 24 h. CRF mRNA and peptide levels in the colon were quantified by real-time RT-PCR, enzyme immuno-assay and immunohistochemistry. Double-stranded RNA (dsRNA) designed to target CRF (dsCRF) was injected into the colonic wall to attain RNA interference-mediated inhibition of CRF mRNA expression. DsRNA for β-globin was used as a control (dsControl). Four days after dsRNA injection, rats were subjected to 1-h PRS. Fecal output was measured. Ussing chamber techniques were used to assess colonic mucosal ion secretion and transepithelial tissue conductance.

KEY RESULTS

Exposure to PRS elevated CRF expression and increased CRF release in the rat colon. Injection of dsCRF inhibited basal CRF expression and prevented the PRS-induced increase in CRF expression, whereas CRF expression in dsControl-injected colons remained high after PRS. In rats treated with dsControl, PRS caused a significant increase in fecal pellet output, colonic baseline ion secretion, and transepithelial tissue conductance. Inhibition of CRF expression in the colon prevented PRS-induced increase in fecal output, baseline ion secretion, and transepithelial tissue conductance.

CONCLUSIONS & INFERENCES

These results provide direct evidence that transient perturbation in peripherally expressed CRF prevents colonic responses to stress.

Corticotropin-releasing Factor Changes the Phenotype and Function of Dendritic Cells in Mouse Mesenteric Lymph Nodes

Background/Aims

Dendritic cells (DCs) are a significant contributor to the pathology of numerous chronic inflammatory autoimmune disorders; however, the effects of Corticotropin-releasing factor (CRF) on intestinal DCs are poorly understood. In this study, we investigated the role of CRF in alterations of intestinal dendritic cell phenotype and function.

Methods

Mouse mesenteric lymph node dendritic cells (MLNDCs) were obtained using magnetic bead sorting. Surface expression of CRF receptor type 1 (CRF-R1) and CRF-R2 was determined by double-labeling immunofluorescence and quantitative polymerase chain reaction (qPCR) and MLNDCs were subsequently exposed to CRF in the presence or absence of CRF-R1 and CRF-R2 antagonists. Expression of surface molecules (MHC-I and MHC-II) and co-stimulatory molecules (CD80 and CD86) was determined by flow cytometric and western blot analyses, and the T cell stimulatory capacity of MLNDCs was evaluated by mixed lymphocyte reaction.

Results

Immunofluorescent staining and quatitative polymerase chain reaction indicated that both the CRF receptors (CRF-R1 and CRF-2) are expressed on the surface of MLNDCs. Exposure to CRF increased the expression of MHC-II on MLNDCs as well as their capacity to stimulate T cell proliferation. MLNDCs treated with CRF-R1 antagonist exhibited a phenotype characterized by a less activated state and reduced surface expression of MHC-II, and consequently showed reduced capacity to stimulate T cells. In contrast, treatment of MLNDCs with CRF-R2 antagonist yielded an opposite result.

Conclusions

CRF can alter the phenotype and function of intestinal DCs through direct action on CRF-R1 and CRF-R2, and activation of the CRF-R1 and CRF-R2 pathways yields opposing outcomes.

Corticotropin-releasing factor receptor type 1 and type 2 interaction in irritable bowel syndrome

Irritable bowel syndrome (IBS) displays chronic abdominal pain or discomfort with altered defecation, and stress-induced altered gut motility and visceral sensation play an important role in the pathophysiology. Corticotropin-releasing factor (CRF) is a main mediator of stress responses and mediates these gastrointestinal functional changes. CRF in brain and periphery acts through two subtype receptors such as CRF receptor type 1 (CRF1) and type 2 (CRF2), and activating CRF1 exclusively stimulates colonic motor function and induces visceral hypersensitivity. Meanwhile, several recent studies have demonstrated that CRF2 has a counter regulatory action against CRF1, which may imply that CRF2 inhibits stress response induced by CRF1 in order to prevent it from going into an overdrive state. Colonic contractility and sensation may be explained by the state of the intensity of CRF1 signaling. CRF2 signaling may play a role in CRF1-triggered enhanced colonic functions through modulation of CRF1 activity. Blocking CRF2 further enhances CRF-induced stimulation of colonic contractility and activating CRF2 inhibits stress-induced visceral sensitization. Therefore, we proposed the hypothesis, i.e., balance theory of CRF1 and CRF2 signaling as follows. Both CRF receptors may be activated simultaneously and the signaling balance of CRF1 and CRF2 may determine the functional changes of gastrointestinal tract induced by stress. CRF signaling balance might be abnormally shifted toward CRF1, leading to enhanced colonic motility and visceral sensitization in IBS. This theory may lead to understanding the pathophysiology and provide the novel therapeutic options targeting altered signaling balance of CRF1 and CRF2 in IBS.

Porcine models of digestive disease: the future of large animal translational research

There is increasing interest in nonrodent translational models for the study of human disease. The pig, in particular, serves as a useful animal model for the study of pathophysiological conditions relevant to the human intestine. This review assesses currently used porcine models of gastrointestinal physiology and disease and provides a rationale for the use of these models for future translational studies. The pig has proven its utility for the study of fundamental disease conditions such as ischemia-reperfusion injury, stress-induced intestinal dysfunction, and short bowel syndrome. Pigs have also shown great promise for the study of intestinal barrier function, surgical tissue manipulation and intervention, as well as biomaterial implantation and tissue transplantation. Advantages of pig models highlighted by these studies include the physiological similarity to human intestine and mechanisms of human disease. Emerging future directions for porcine models of human disease include the fields of transgenics and stem cell biology, with exciting implications for regenerative medicine.

The effect of urocortin 1 on motility in isolated, vascularly perfused rat colon

BACKGROUND/AIMS

Urocortin 1, a corticotropin-releasing factor related peptide, increases colonic motility under stressful conditions. We investigated the effect of urocortin 1 on colonic motility using an experimental model with isolated rat colon in which the blood flow and intestinal nerves were preserved. Furthermore, we assessed whether this effect was mediated by adrenergic or cholinergic nerves.

METHODS

Colonic motility was measured in the proximal and distal parts of resected rat colon. The colon resected from the peritoneum was stabilized, and then urocortin 1 (13.8, 138, 277, and 1,388 pM) was administered via a blood vessel. Motility index was measured in the last 5 min of the 15 min administration of urocortin 1 and expressed as percentage change from baseline. Subsequently, the change in motility was measured by perfusing urocortin 1 in colons pretreated with phentolamine, propranolol, hexamethonium, atropine, or tetrodotoxin.

RESULTS

At concentrations of 13.8, 138, 277, and 1,388 pM, urocortin 1 increased the motility of proximal colon (20.4 ± 7.2%,48.4 ± 20.9%, 67.0 ± 25.8%, and 64.2 ± 20.9%, respectively) and the motility of distal colon (3.3 ± 3.3%, 7.8 ± 7.8%, 71.1 ± 28.6%,and 87.4 ± 32.5%, respectively). The motility induced by urocortin 1 was significantly decreased by atropine to 2.4 ± 2.4% in proximal colon and 3.4 ± 3.4% in distal colon (p <œ 0.05). However, tetrodotoxin, propranolol, phentolamine, and hexamethonium did not inhibit motility.

CONCLUSIONS

Urocortin 1 increased colonic motility and it is considered that this effect was directly mediated by local muscarinic cholinergic receptors.

Peripheral corticotropin-releasing factor receptor type 2 activation increases colonic blood flow through nitric oxide pathway in rats

BACKGROUND

Corticotropin-releasing factor (CRF) peptides exert profound effects on the secretomotor function of the gastrointestinal tract. Nevertheless, despite the presence of CRF peptides and receptors in colonic tissue, their influence on colonic blood flow (CBF) is unknown.

AIM

To determine the effect and mechanism of members of the CRF peptide family on CBF in isoflurane-anesthetized rats.

METHODS

Proximal CBF was measured with laser-Doppler flowmetry simultaneously with mean arterial blood pressure (MABP) measurement. Rats were injected with intravenous human/rat CRF (CRF1 > CRF2 affinity), mouse urocortin 2 (mUcn2, selective CRF2 agonist), or sauvagine (SVG, CRF2 > CRF1 affinity) at 1-30 µg/kg. The nitric oxide (NO) synthase inhibitor, L-NAME (3 mg/kg, iv), the cyclooxygenase inhibitor, indomethacin (Indo, 5 mg/kg, ip), or selective CRF2 antagonist, astressin2-B (Ast2B, 50 µg/kg, iv) was given before SVG injection (10 µg/kg, iv).

RESULTS

SVG and mUcn2 dose-dependently increased CBF while decreasing MABP and colonic vascular resistance (CVR). CRF had no effect on CBF, but increased CVR. The hyperemic effect of SVG was inhibited by L-NAME but not by Indo, whereas hypotension was partially reduced by L-NAME. Sensory denervation had no effect on SVG-induced changes. Ast2B inhibited SVG-induced hyperemia and decreased CVR, and partially reduced the hypotension.

CONCLUSIONS

Peripheral CRF2 activation induces colonic hyperemia through NO synthesis, without involving prostaglandin synthesis or sensory nerve activation, suggesting a direct action on the endothelium and myenteric neurons. Members of the CRF peptide family may protect the colonic mucosa via the activation of the CRF2 receptor.

Early-life dietary spray-dried plasma influences immunological and intestinal injury responses to later-life Salmonella typhimurium challenge

Increasing evidence supports the concept that early-life environmental influences, including nutrition and stress, have an impact on long-term health outcomes and disease susceptibility. The objective of the present study was to determine whether dietary spray-dried plasma (SDP), fed during the first 2 weeks post-weaning (PW), influences subsequent immunological and intestinal injury responses to Salmonella typhimurium challenge. A total of thirty-two piglets (age 16-17 d) were weaned onto nursery diets containing 0, 2·5 % SDP (fed for 7 d PW) or 5 % SDP (fed for 14 d PW), and were then fed control diets (without SDP), for the remainder of the experiment. At 34 d PW (age 50 d), pigs were challenged with 3 × 10⁹ colony-forming units of S. typhimurium. A control group (non-challenged) that was fed 0 % SDP in the nursery was included. At 2 d post-challenge, the distal ileum was harvested for the measurement of inflammatory, histological and intestinal physiological parameters. S. typhimurium challenge induced elevated ileal histological scores, myeloperoxidase (MPO), IL-8 and TNF, and increased intestinal permeability (indicated by reduced transepithelial voltage (potential difference) and elevated 4 kDa fluorescein isothiocyanate dextran (FD4) flux rates). Compared with S. typhimurium-challenged controls (0 % SDP), pigs fed the 5 % SDP-14 d diet exhibited reduced ileal histological scores, MPO levels, IL-8 levels and FD4 flux rates. Pigs fed the 5 % SDP-14 d nursery diet exhibited increased levels of plasma and ileal TNF-α in response to the challenge, compared with the other treatments. These results indicate that inclusion of SDP in PW diets can have an influence on subsequent immunological and intestinal injury responses induced by later-life S. typhimurium challenge.

Role of Corticotropin-releasing Factor Signaling in Stress-related Alterations of Colonic Motility and Hyperalgesia

The corticotropin-releasing factor (CRF) signaling systems encompass CRF and the structurally related peptide urocortin (Ucn) 1, 2, and 3 along with 2 G-protein coupled receptors, CRF₁ and CRF₂. CRF binds with high and moderate affinity to CRF₁ and CRF₂ receptors, respectively while Ucn1 is a high-affinity agonist at both receptors, and Ucn2 and Ucn3 are selective CRF₂ agonists. The CRF systems are expressed in both the brain and the colon at the gene and protein levels. Experimental studies established that the activation of CRF₁ pathway in the brain or the colon recaptures cardinal features of diarrhea predominant irritable bowel syndrome (IBS) (stimulation of colonic motility, activation of mast cells and serotonin, defecation/watery diarrhea, and visceral hyperalgesia). Conversely, selective CRF₁ antagonists or CRF₁/CRF₂ antagonists, abolished or reduced exogenous CRF and stress-induced stimulation of colonic motility, defecation, diarrhea and colonic mast cell activation and visceral hyperalgesia to colorectal distention. By contrast, the CRF₂ signaling in the colon dampened the CRF₁ mediated stimulation of colonic motor function and visceral hyperalgesia. These data provide a conceptual framework that sustained activation of the CRF₁ system at central and/or peripheral sites may be one of the underlying basis of IBS-diarrhea symptoms. While targeting these mechanisms by CRF₁ antagonists provided a relevant novel therapeutic venue, so far these promising preclinical data have not translated into therapeutic use of CRF₁ antagonists. Whether the existing or newly developed CRF₁ antagonists will progress to therapeutic benefits for stress-sensitive diseases including IBS for a subset of patients is still a work in progress.

A balance theory of peripheral corticotropin-releasing factor receptor type 1 and type 2 signaling to induce colonic contractions and visceral hyperalgesia in rats

Several recent studies suggest that peripheral corticotropin-releasing factor (CRF) receptor type 1 (CRF1) and CRF2 have a counter regulatory action on gastrointestinal functions. We hypothesized that the activity balance of each CRF subtype signaling may determine the changes in colonic motility and visceral sensation. Colonic contractions were assessed by the perfused manometry, and contractions of colonic muscle strips were measured in vitro in rats. Visceromotor response was determined by measuring contractions of abdominal muscle in response to colorectal distensions (CRDs) (60 mm Hg for 10 min twice with a 30-min rest). All drugs were administered through ip route in in vivo studies. CRF increased colonic contractions. Pretreatment with astressin, a nonselective CRF antagonist, blocked the CRF-induced response, but astressin2-B, a selective CRF2 antagonist, enhanced the response by CRF. Cortagine, a selective CRF1 agonist, increased colonic contractions. In in vitro study, CRF increased contractions of muscle strips. Urocortin 2, a selective CRF2 agonist, itself did not alter the contractions but blocked this increased response by CRF. Visceromotor response to the second CRD was significantly higher than that of the first. Astressin blocked this CRD-induced sensitization, but astressin2-B or CRF did not affect it. Meanwhile, astressin2-B together with CRF significantly enhanced the sensitization. Urocortin 2 blocked, but cortagine significantly enhanced, the sensitization. These results indicated that peripheral CRF1 signaling enhanced colonic contractility and induced visceral sensitization, and these responses were modulated by peripheral CRF2 signaling. The activity balance of each subtype signaling may determine the colonic functions in response to stress.

Urocortin 2 blocks the suppression of gastric antral contractions induced by lipopolysaccharide in freely moving conscious rats

Lipopolysaccharide (LPS) inhibits gastric antral contractions in conscious rats. Since LPS regulates corticotropin-releasing factor type 2 receptor (CRF2) expression in the rat stomach, and activation of peripheral CRF2 alters gastric motility, we tried to determine the role of peripheral CRF2 in the LPS-induced suppression of gastric antral contractions. Intraluminal gastric pressure waves were measured in freely moving conscious non-fasted rats using the perfused manometric method. We assessed the area under the manometric trace as the motor index (MI), and compared this result with those obtained 1h before and after intraperitoneal injection of drugs. LPS (0.2 mg/kg) significantly decreased MI. Indomethacin (10 mg/kg) itself did not alter MI but blocked this inhibitory action by LPS. Astressin 2-B (200 μg/kg), a selective CRF2 antagonist, modified neither the basal MI nor the action by LPS. Meanwhile, urocortin 2 (30 μg/kg), a selective CRF2 agonist, reversed the suppression by LPS without affecting the basal MI. This action by urocortin 2 was blocked by pretreatment with astressin 2-B. In conclusion, LPS inhibited gastric antral contractions possibly through a prostaglandin-dependent pathway. Peripheral CRF2 stimulation reversed this response by LPS.

Water-avoidance stress enhances gastric contractions in freely moving conscious rats: role of peripheral CRF receptors

BACKGROUND

Stress alters gastrointestinal motility through central and peripheral corticotropin-releasing factor (CRF) pathways. Accumulating evidence has demonstrated that peripheral CRF is deeply involved in the regulation of gastric motility, and enhances gastric contractions through CRF receptor type 1 (CRF1) and delays gastric emptying (GE) through CRF receptor type 2 (CRF2). Since little is known whether water-avoidance stress (WAS) alters gastric motility, the present study tried to clarify this question and the involvement of peripheral CRF receptor subtypes in the mechanisms.

METHODS

We recorded intraluminal gastric pressure waves using a perfused manometric method. The rats were anesthetized and the manometric catheter was inserted into the stomach 4-6 days before the experiments. We assessed the area under the manometric trace as the motor index (MI), and compared this result with those obtained 1 h before and after initiation of WAS in nonfasted conscious rats. Solid GE for 1 h was also measured.

RESULTS

WAS significantly increased gastric contractions. Intraperitoneal (ip) administration of astressin (100 μg/kg, 5 min prior to stress), a nonselective CRF antagonist, blocked the response to WAS. On the other hand, pretreatment (5 min prior to stress) with neither astressin2-B (200 μg/kg, ip), a selective CRF2 antagonist, nor urocortin 2 (30 μg/kg, ip), a selective CRF2 agonist, modified the response to WAS. These drugs did not alter the basal MI. WAS did not change GE.

CONCLUSIONS

WAS may activate peripheral CRF1 but not CRF2 signaling and stimulates gastric contractions without altering GE.

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

Background:

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.

Methods:

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.

Results:

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.

Conclusion:

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.

Complex interactions among diet, gastrointestinal transit, and gut microbiota in humanized mice

BACKGROUND & AIMS

Diet has major effects on the intestinal microbiota, but the exact mechanisms that alter complex microbial communities have been difficult to elucidate. In addition to the direct influence that diet exerts on microbes, changes in microbiota composition and function can alter host functions such as gastrointestinal (GI) transit time, which in turn can further affect the microbiota.

METHODS

We investigated the relationships among diet, GI motility, and the intestinal microbiota using mice that are germ-free (GF) or humanized (ex-GF mice colonized with human fecal microbiota).

RESULTS

Analysis of gut motility revealed that humanized mice fed a standard polysaccharide-rich diet had faster GI transit and increased colonic contractility compared with GF mice. Humanized mice with faster transit due to administration of polyethylene glycol or a nonfermentable cellulose-based diet had similar changes in gut microbiota composition, indicating that diet can modify GI transit, which then affects the composition of the microbial community. However, altered transit in mice fed a diet of fermentable fructooligosaccharide indicates that diet can change gut microbial function, which can affect GI transit.

CONCLUSIONS

Based on studies in humanized mice, diet can affect GI transit through microbiota-dependent or microbiota-independent pathways, depending on the type of dietary change. The effect of the microbiota on transit largely depends on the amount and type (fermentable vs nonfermentable) of polysaccharides present in the diet. These results have implications for disorders that affect GI transit and gut microbial communities, including irritable bowel syndrome and inflammatory bowel disease.

Peripheral corticotropin-releasing factor (CRF) induces stimulation of gastric contractions in freely moving conscious rats: role of CRF receptor types 1 and 2

BACKGROUND

Peripheral corticotrophin-releasing factor (CRF) plays an important role in stress-induced alterations of gastrointestinal motility. CRF injected peripherally inhibits gastric emptying, but its effect on gastric contractions has not been clarified in freely moving conscious rats.

METHODS

Intraluminal gastric pressure waves were measured in freely moving conscious non-fasted rats using the perfused manometric method. We assessed the area under the manometric trace as the motor index (MI), and compared this result with those obtained 1 h before and after drug administration.

KEY RESULTS

Subcutaneous injection (sc) of CRF (15 μg kg(-1)) increased the MI significantly. Pretreatment with intravenous astressin (100 μg kg(-1)), a non-selective CRF antagonist, blocked the sc CRF (15 μg kg(-1))-induced response, but astressin(2)-B (200 μg kg(-1), sc), a selective CRF receptor type 2 (CRF(2)) antagonist, enhanced the CRF-induced increase in MI significantly. Meanwhile urocortin 2 (15 μg kg(-1), sc), a selective CRF(2) agonist, did not alter the basal MI, but it inhibited the sc CRF (15 μg kg(-1))-induced stimulation of gastric contractions. The intraperitoneal injection of cortagine (30 μg kg(-1)), a selective CRF receptor type 1 (CRF(1)) agonist, mimicked the response induced by sc CRF.

CONCLUSIONS & INFERENCES

Peripheral CRF stimulates gastric contractions through CRF(1). CRF(2) activation inhibits the response induced by CRF, suggesting that CRF(2) may have a modulatory action to CRF(1) signaling in gastric motor activity.

Expression of corticotropin releasing factor receptor type 1 (CRF1) in the human gastrointestinal tract and upregulation in the colonic mucosa in patients with ulcerative colitis

Brain corticotropin-releasing factor (CRF) acting on CRF receptor type 1 (CRF(1)) is a main signaling pathway in the stress response. CRF is also produced in a variety of peripheral sites and acts locally as a proinflammatory mediator. We investigated CRF(1) mRNA expression in the human gastrointestinal tract, and localized CRF(1) immunoreactive cells in the colonic mucosa of healthy subjects and patients with ulcerative colitis (UC). In 4 male healthy subjects (24-29 years), CRF(1) transcript was detected by RT-PCR throughout the gastrointestinal tract with the highest levels in the ileum and rectum and the lowest level in the colon. Immunohistochemistry on whole thickness sigmoid colon sections showed that CRF(1) was localized in the lamina propria and epithelial cells and enteric neurons. In sigmoid colonic biopsies, immunohistochemically double-labeled cells with CRF(1) and CD163, a marker for macrophages, represent 79% of total CRF(1) immunoreactive (IR) cells in healthy subjects. In 10 UC patients, the total number of CRF(1) IR cells and CRF(1)/CD163 double-labeled macrophages was increased by 4.2 and 4.0 folds respectively compared to healthy subjects. These findings indicate that CRF(1) is distributed throughout the GI tract of healthy human subjects. The increase of CRF(1) IR cells prominently in macrophages of the sigmoid colonic mucosa of UC patients provides anatomical support for a role of CRF(1) signaling in modulating the immune-inflammatory process of UC.

Alteration of antral and proximal colonic motility induced by chronic psychological stress involves central urocortin 3 and vasopressin in rats

Because of the difficulties in developing suitable animal models, the pathogenesis of stress-induced functional gastrointestinal disorders is not well known. Here we applied the communication box technique to induce psychological stress in rats and then examined their gastrointestinal motility. We measured upper and lower gastrointestinal motility induced by acute and chronic psychological stress and examined the mRNA expression of various neuropeptides in the hypothalamus. Chronic psychological stress disrupted the fasted motility in the antrum and accelerated motility in the proximal colon. mRNA expression of AVP, oxytocin, and urocortin 3 was increased by chronic psychological stress. Intracerebroventricular (ICV) injection of urocortin 3 disrupted the fasted motility in the antrum, while ICV injection of Ucn3 antiserum prevented alteration in antral motility induced by chronic psychological stress. ICV injection of AVP accelerated colonic motility, while ICV injection of SSR 149415, a selective AVP V1b receptor antagonist, prevented alteration in proximal colonic motility induced by chronic psychological stress. Oxytocin and its receptor antagonist L 371257 had no effect on colonic motility in either the normal or chronic psychological stress model. These results suggest that chronic psychological stress induced by the communication box technique might disrupt fasted motility in the antrum via urocortin 3 pathways and accelerates proximal colonic motility via the AVP V1b receptor in the brain.

CRF induces intestinal epithelial barrier injury via the release of mast cell proteases and TNF-α

BACKGROUND AND AIMS

Psychological stress is a predisposing factor in the onset and exacerbation of important gastrointestinal diseases including irritable bowel syndrome (IBS) and the inflammatory bowel diseases (IBD). The pathophysiology of stress-induced intestinal disturbances is known to be mediated by corticotropin releasing factor (CRF) but the precise signaling pathways remain poorly understood. Utilizing a porcine ex vivo intestinal model, the aim of this study was to investigate the mechanisms by which CRF mediates intestinal epithelial barrier disturbances.

METHODOLOGY

Ileum was harvested from 6-8 week-old pigs, mounted on Ussing Chambers, and exposed to CRF in the presence or absence of various pharmacologic inhibitors of CRF-mediated signaling pathways. Mucosal-to-serosal flux of 4 kDa-FITC dextran (FD4) and transepithelial electrical resistance (TER) were recorded as indices of intestinal epithelial barrier function.

RESULTS

Exposure of porcine ileum to 0.05-0.5 µM CRF increased (p<0.05) paracellular flux compared with vehicle controls. CRF treatment had no deleterious effects on ileal TER. The effects of CRF on FD4 flux were inhibited with pre-treatment of tissue with the non-selective CRF(1/2) receptor antagonist Astressin B and the mast cell stabilizer sodium cromolyn (10(-4) M). Furthermore, anti-TNF-α neutralizing antibody (p<0.01), protease inhibitors (p<0.01) and the neural blocker tetrodotoxin (TTX) inhibited CRF-mediated intestinal barrier dysfunction.

CONCLUSION

These data demonstrate that CRF triggers increases in intestinal paracellular permeability via mast cell dependent release of TNF-α and proteases. Furthermore, CRF-mast cell signaling pathways and increases in intestinal permeability require critical input from the enteric nervous system. Therefore, blocking the deleterious effects of CRF may address the enteric signaling of mast cell degranulation, TNFα release, and protease secretion, hallmarks of IBS and IBD.

Plasma hormones facilitated the hypermotility of the colon in a chronic stress rat model

Objective

To study the relationship between brain-gut peptides, gastrointestinal hormones and altered motility in a rat model of repetitive water avoidance stress (WAS), which mimics the irritable bowel syndrome (IBS).

Methods

Male Wistar rats were submitted daily to 1-h of water avoidance stress (WAS) or sham WAS (SWAS) for 10 consecutive days. Plasma hormones were determined using Enzyme Immunoassay Kits. Proximal colonic smooth muscle (PCSM) contractions were studied in an organ bath system. PCSM cells were isolated by enzymatic digestion and IKv and IBKca were recorded by the patch-clamp technique.

Results

The number of fecal pellets during 1 h of acute restraint stress and the plasma hormones levels of substance P (SP), thyrotropin-releasing hormone (TRH), motilin (MTL), and cholecystokinin (CCK) in WAS rats were significantly increased compared with SWAS rats, whereas vasoactive intestinal peptide (VIP), calcitonin gene-related peptide (CGRP) and corticotropin releasing hormone (CRH) in WAS rats were not significantly changed and peptide YY (PYY) in WAS rats was significantly decreased. Likewise, the amplitudes of spontaneous contractions of PCSM in WAS rats were significantly increased comparing with SWAS rats. The plasma of WAS rats (100 µl) decreased the amplitude of spontaneous contractions of controls. The IKv and IBKCa of PCSMs were significantly decreased in WAS rats compared with SWAS rats and the plasma of WAS rats (100 µl) increased the amplitude of IKv and IBKCa in normal rats.

Conclusion

These results suggest that WAS leads to changes of plasma hormones levels and to disordered myogenic colonic motility in the short term, but that the colon rapidly establishes a new equilibrium to maintain the normal baseline functioning.

Endothelin-converting enzyme-1 actions determine differential trafficking and signaling of corticotropin-releasing factor receptor 1 at high agonist concentrations

CRF receptor 1 (CRF(1)), a key neuroendocrine mediator of the stress response, has two known agonists corticotropin-releasing factor (CRF) and urocortin 1 (Ucn1). Here we report that endothelin-converting enzyme-1 (ECE-1) differentially degrades CRF and Ucn1; ECE-1 cleaves Ucn1, but not CRF, at critical residue Arginine-34/35', which is essential for ligand-receptor binding. At near K(D) agonist concentration (30 nm), both Ucn1- and CRF-mediated Ca(2+) mobilization are ECE-1 dependent. Interestingly, at high agonist concentration (100 nm), Ucn1-mediated Ca(2+) mobilization remains ECE-1 dependent, whereas CRF-mediated mobilization becomes independent of ECE-1 activity. At high agonist concentration, ECE-1 inhibition disrupted Ucn1-, but not CRF-induced CRF(1) recycling and resensitization, but did not prolong the association of CRF(1) with β-arrestins. RNA interference-mediated knockdown of Rab suggests that both Ucn1- and CRF-induced CRF(1) resensitization is dependent on activity of Rab11, but not of Rab4. CRF(1) behaves like a class A G protein-coupled receptor with respect to transient β-arrestins interaction. We propose that differential degradation by ECE-1 is a novel mechanism by which CRF(1) receptor is protected from overactivation by physiologically relevant high concentrations of higher affinity ligand to mediate distinct resensitization and downstream signaling.