Nitric oxide in enteric nervous system mediated the inhibitory effect of vasopressin on the contraction of circular muscle strips from colon in male rats

Effect of Evodiamine on Rat Colonic Hypermotility Induced by Water Avoidance Stress and the Underlying Mechanism

Background and Aim

EVO is a natural alkaloid that reportedly has potential value in regulating gastrointestinal motility, but this conclusion remains controversial, and the molecular mechanism is unclear. In this study, we aimed to explore the effect of short-chain fatty acids on rat colonic hypermotility induced by water avoidance stress and the underlying mechanism.

Methods

We constructed a hypermotile rat model by chronic water avoidance stress, and Western blot was used to detect the protein level of nNOS in colon tissue. The organ bath and multichannel physiological signal acquisition systems were used to examine the spontaneous contractions of smooth muscle strips. The whole-cell patch-clamp technique was used to investigate L-type voltage-dependent calcium and BK_Ca channel currents in colonic smooth muscle cells.

Results

EVO inhibited the spontaneous contractions of colonic smooth muscle strips in a dose-dependent manner. Moreover, EVO decreased the fecal output induced by chronic water avoidance stress. TTX did not block the inhibitory effect of EVO on spontaneous colon contractions, while L-NNA, a selective nNOS synthase inhibitor, did partially abolish this inhibitory effect. The protein expression of nNOS in the colon tissues of rats administered EVO was significantly increased compared to that in control rats. EVO reversibly inhibited the L-type calcium channel current without changing the steady-state activation or inactivation in colonic smooth muscle cells. EVO significantly inhibited the BK_Ca current but did not change the shape of the I-V curves.

Conclusion

EVO inhibits gastrointestinal motility by inhibiting L-type calcium and BK_Ca channels in colonic smooth muscle cells and indirectly interacting with nNOS.

Potential role of fecal microbiota in patients with constipation

BACKGROUND

We evaluated the safety and efficacy of fecal microbiota transplantation (FMT) for chronic functional constipation (CFC) ineffectively treated by conventional constipation medication.

METHODS

Thirty-four patients with CFC underwent FMT treatment (three rounds, via gastroscopy). Clinical scales, including the Wexner constipation score as the main index of efficiency, were completed at baseline; after each treatment, and at 2 and 3 months of follow up. Secondary evaluation indices included the self-assessment of constipation symptoms, patient assessment constipation quality-of-life questionnaire, Bristol stool form scale, and Zung's self-rating depression and anxiety scales. Gastrointestinal motility, motilin, gastrin, nitric oxide (NO), and 5-hydroxytryptamine (5-HT) were assessed before and after treatment. Intestinal flora changes were assessed by 16S ribosomal ribonucleic acid (rRNA) sequencing.

RESULTS

There were no serious adverse reactions. The clinical cure rate was 73.5% (25/34), clinical remission rate was 14.7% (5/34), and the inefficiency rate was 11.8% (4/34). Clinical scale data indicated that the FMT treatment was effective. Furthermore, FMT treatment promoted intestinal peristalsis, increased gastrointestinal motility, and increased serum NO and 5-HT levels. The 16S rRNA sequencing data indicated that high abundances of Bacteroides, Klebsiella, Megamonas, Erysipelotrichaceae and Epulopiscium may be the cause of constipation, and high abundances of Prevotella, Acidaminococcus and Butyricimonas may be the main factors in curing constipation.

CONCLUSION

Treatment with FMT regulates the intestinal microflora and changes the abundance of CFC-associated bacterial flora to improve constipation.

Vasopressin augments TNBS-induced colitis through enteric neuronal V1a receptor-mediated COX-2-dependent prostaglandin release from mast cells in mice

BACKGROUND

Inflammatory bowel disease (IBD) is a functional disorder with chronic and relapsing clinical features. Vasopressin (VP) is a hormone responsible for water and stress homeostasis and also regulates gastrointestinal inflammation and motility. We explored whether VP was related to IBD pathogenesis and its possible pathway.

METHODS

Colitis was induced by 2,4,6-trinitrobenzenesulfonic acid (TNBS) in mice. The disease activity and colonic damage were evaluated through a scoring system. Locations of the V_1a receptor were revealed by immunochemistry method in colon. Ussing chamber technique was performed for the electrophysiological characterization by using rat ileum. The (Arg⁸ )-Vasopressin (AVP)-evoked short-circuit current (Isc) was recorded in the presence of conivaptan (V_1a and V₂ receptor antagonist), tolvaptan (V_1b receptor antagonist), tetrodotoxin (TTX), atropine, cyclooxygenase (COX) inhibitors (indomethacin, nonspecific COX antagonist; SC560, COX-1 antagonist; NS560, COX-2 antagonist), and a stabilizer of mast cell (cromolyn sodium), respectively.

KEY RESULTS

TNBS resulted in the obvious loss of body weight and tissue damages in mice. AVP significantly aggravated the TNBS-induced colitis, which was attenuated by conivaptan but not tolvaptan. V_1a receptors were found immunopositive in neurons among the enteric nervous system. AVP evoked a pulsatile response in Isc. Its amplitude, frequency, and cycle duration were around 8-15 µA/cm² , 10-11 mHz, and 1.5 minutes, respectively. Notably, the AVP-evoked change in Isc was abolished by TTX, atropine, conivaptan, indomethacin, NS560, and cromolyn sodium, respectively.

CONCLUSIONS AND INFERENCES

VP-V_1a receptor played the proinflammatory role in TNBS-induced colitis by promoting COX-2-dependent prostaglandin release from mucosal mast cells, which was mediated by the cholinergic pathway.

Increase of n-NOS and i-NOS in Rat Colon After Sacral Neuromodulation

OBJECTIVE

Sacral neuromodulation (SNM) is proposed to treat different anorectal dysfunctions but its mechanism of action is not yet known. Our previous study demonstrated how SNM can significantly increase neuronal nitric oxide synthase NOS (n-NOS) and inducible NOS (i-NOS) expression in the anus and rectum of rats. There are no reports regarding the relation between SNM and NOS in colonic cells: our aim was to assess NOS expression in colonic rat model after SNM.

MATERIALS AND METHODS

Twenty-six female Sprangue-Dawley rats were considered: group I, normal control rats; group II, sham treatment rats, in whom electrodes for electrical stimulation were placed in S1 foramen bilaterally and left in place, without performing neuromodulation; group III, rats in whom SNM was performed. After 14 days, the rats were sacrificed and we evaluated n-NOS and i-NOS in colonic specimens by immunohistochemistry and Western Blot analysis.

RESULTS

Western Blot analysis showed that levels of n-NOS and i-NOS were higher in colon of the III group rats respect to the others; in particular, immunohistochemistry revealed that, after neuromodulation, n-NOS expression in the muscle cells and i-NOS expression in glandular epithelium and nervous cells were highly represented (p < 0.05).

CONCLUSION

Our study showed that in colon, SNM is able to influence NO synthesis, activating n-NOS expression in muscle cells and i-NOS expression in glandular epithelium and nervous cells. Our study showed a complex colonic response to SNM. This experimental model could be applied to better understand the mechanism of action of SNM in bowel dysfunction.

Brain-derived neurotrophic factor accelerates gut motility in slow-transit constipation

BACKGROUND & AIMS

Brain-derived neurotrophic factor (BDNF) may play a critical role in gut motility. We aimed to investigate BDNF's physiologic effects on gut motility in slow-transit constipation (STC) and to explore the underlying molecular mechanisms.

METHODS

BDNF expression and alterations of colonic nerve fibre density in STC patients were first investigated. BDNF's effects on gastrointestinal motility of both BDNF(+/-) mice and loperamide-induced constipation mice were then examined in vivo and in vitro. Smooth muscle α-actin (α-SMA) expression, and nerve fibre, neuromuscular junction (NMJ) and smooth muscle cell (SMC) alterations were investigated. Finally, the effects of BDNF-induced TrkB-phospholipase C/inositol trisphosphate (TrkB-PLC/IP3) pathway activation on gut motility were investigated.

RESULTS

In STC patients, BDNF expression and nerve fibre density were decreased, and mucosal nerve fibre ultrastructural degenerations were demonstrated. Gut motility was decreased in vivo and in vitro in BDNF(+/-) and constipation mice, with BDNF dose-dependently increasing gut motility. In BDNF(+/-) mice, α-SMA expression and nerve fibre density were decreased, and nerve fibre, NMJ and SMC ultrastructural degenerations were observed. Finally, TrkB-PLC/IP3 pathway antagonists dramatically attenuated BDNF's excitatory effect on gut motility, and exogenous BDNF induced an obvious increase in IP3 expression.

CONCLUSIONS

BDNF plays an important regulatory role in gut motility in STC. It was mediated by altering the intestinal innervation structure, as well as smooth muscle secondary degeneration through a mechanism involving TrkB-PLC/IP3 pathway activation.

Decrease of guanylyl cyclase β1 subunit and nitric oxide (NO)-induced relaxation in mouse rectum with colitis and its reproduction on long-term NO treatment

Nitric oxide (NO) influences motility in the colon in patients with ulcerative colitis, but the exact mechanism involved remains unknown. Colitis was induced in mice by the oral administration of 2.5% dextran sodium sulfate (DSS), and the motility in longitudinal preparations from rectum and distal colon and expression of β1 subunit of soluble guanylyl cyclase (sGCβ1) were analyzed. Electrical stimulation (ES) caused a transient relaxation via the NO pathway in both rectum and colon from control mice. Stimulation with sodium nitroprusside (SNP) caused relaxation in the two regions, and the half-time (T (1/2)) of the maximal relaxation induced by 100 μM SNP was 8.1 ± 1.0 s in rectum. DSS treatment (1) abolished the ES-induced relaxation, but not dibutyryl cyclic GMP-induced response, in both regions, (2) decreased the maximal response to SNP accompanied by a loss of immunoreactive sGCβ1 protein in rectum, but did not affect the amplitude of the relaxant response or the protein in distal colon, and (3) caused an increase in the T (1/2) value in response to SNP in both regions. Pretreatment of both preparations from control mice with 600 μM SNP for 30 min decreased both ES- and SNP-induced relaxation, SNP-induced cyclic GMP formation, and immunoreactive sGCβ1 levels. NO-mediated relaxation was impaired by a dysfunctional sGC with and without a loss of immunoreactivity to sGCβ1 in rectum and colon from DSS-treated mice, respectively. Long-term exposure of the tissues with an excess amount of NO changes the sGC-mediated relaxation.