Reduced Responses of Submucous Neurons from Irritable Bowel Syndrome Patients to a Cocktail Containing Histamine, Serotonin, TNFα, and Tryptase (IBS-Cocktail).

BACKGROUND AND AIMS: Malfunctions of enteric neurons are believed to play an important role in the pathophysiology of irritable bowel syndrome (IBS). Our aim was to investigate whether neuronal activity in biopsies from IBS patients is altered in comparison to healthy controls (HC). METHODS: Activity of human submucous neurons in response to electrical nerve stimulation and local application of nicotine or a mixture of histamine, serotonin, tryptase, and TNF-α (IBS-cocktail) was recorded in biopsies from 17 HC and 35 IBS patients with the calcium-sensitive-dye Fluo-4 AM. The concentrations of the mediators resembeled those found in biopsy supernatants or blood. Neuronal activity in guinea-pig submucous neurons was studied with the voltage-sensitive-dye di-8-ANEPPS. RESULTS: Activity in submucous ganglia in response to nicotine or electrical nerve stimulation was not different between HC and IBS patients (P = 0.097 or P = 0.448). However, the neuronal response after application of the IBS-cocktail was significantly decreased (P = 0.039) independent of whether diarrhea (n = 12), constipation (n = 5) or bloating (n = 5) was the predominant symptom. In agreement with this we found that responses of submucous ganglia conditioned by overnight incubation with IBS mucosal biopsy supernatant to spritz application of this supernatant was significantly reduced (P = 0.019) when compared to incubation with HC supernatant. CONCLUSION: We demonstrated for the first time reduced neuronal responses in mucosal IBS biopsies to an IBS mediator cocktail. While excitability to classical stimuli of enteric neurons was comparable to HC, the activation by the IBS-cocktail was decreased. This was very likely due to desensitization to mediators constantly released by mucosal and immune cells in the gut wall of IBS patients.

The endocannabinoid anandamide regulates the peristaltic reflex by reducing neuro-neuronal and neuro-muscular neurotransmission in ascending myenteric reflex pathways in rats.

BACKGROUND: Endocannabinoids (EC) and the cannabinoid-1 (CB1) receptor are involved in the regulation of motility in the gastrointestinal (GI) tract. However, the underlying physiological mechanisms are not completely resolved. The purpose of this work was to study the physiological influence of the endocannabinoid anandamide, the putative endogenous CB1 active cannabinoid, and of the CB1 receptor on ascending peristaltic activity and to identify the involved neuro-neuronal, neuro-muscular and electrophysiological mechanisms. METHODS: The effects of anandamide and the CB1 receptor antagonist SR141716A were investigated on contractions of the circular smooth muscle of rat ileum and in longitudinal rat ileum segments where the ascending myenteric part of the peristaltic reflex was studied in a newly designed organ bath. Additionally intracellular recordings were performed in ileum and colon. RESULTS: Anandamide significantly reduced cholinergic twitch contractions of ileum smooth muscle whereas SR141716A caused an increase. Anandamide reduced the ascending peristaltic contraction by affecting neuro-neuronal and neuro-muscular neurotransmission. SR141716A showed opposite effects and all anandamide effects were antagonized by SR141716A (1 µM). Anandamide reduced excitatory junction potentials (EJP) and inhibitory junction potentials (IJP), whereas intestinal slow waves were not affected. CONCLUSIONS: CB1 receptors regulate force and timing of the intestinal peristaltic reflex and these actions involve interneurons and motor-neurons. The endogenous cannabinoid anandamide mediates these effects by activation of CB1 receptors. The endogenous cannabinoid system is permanently active, suggesting the CB1 receptor being a possible target for the treatment of motility related disorders.

InsP3R-associated cGMP kinase substrate (IRAG) is essential for nitric oxide-induced inhibition of calcium signaling in human colonic smooth muscle.

Nitric oxide (NO)-mediated relaxation of colonic smooth muscle is crucial for the maintenance of human gut function. The molecular mechanisms of NO-dependent smooth muscle relaxation involve cyclic GMP-mediated inhibition of store-dependent calcium signaling. Recently, IRAG (inositol 1,4,5-trisphophate receptor-associated cGMP kinase substrate) has been characterized as a novel target molecule of cGMP-dependent protein kinase (cGKI) mediating NO-/cGMP-dependent inhibition of inositol 1,4,5-trisphosphate (InsP(3))-dependent calcium release in transfected COS cells. The aim of the present study was to characterize IRAG expression and its functional role in NO-dependent signaling in human colonic smooth muscle. Reverse transcriptase-PCR revealed IRAG mRNA expression in human colon, rectum, and cultured colonic smooth muscle cells. In cultured human colonic smooth muscle cells, bradykinin (BK) elicited InsP(3)-dependent calcium transients that were repeatable and independent of extracellular calcium. The NO donor sodium nitroprusside and the specific cGK activator 8-(4-chlorophenylthio)guanosine-3',5'-cyclic-monophosphate (8-pCPT-cGMP) significantly inhibited BK-induced increase in intracellular calcium. Cells transfected with antisense oligonucleotides raised against IRAG (IRAG-AS) showed strongly decreased IRAG protein expression. In these cells, sodium nitroprusside and 8-pCPT-cGMP both failed to modulate BK-induced calcium transients. Thus, endogenous IRAG appears to be essentially involved in the NO/cGK-dependent inhibition of InsP(3)-dependent Ca(2+)-signaling in colonic smooth muscle.

Superior mesenteric artery syndrome: diagnosis and treatment from the gastroenterologist's view.

BACKGROUND: Superior mesenteric artery syndrome (SMAS) is caused by compression of the third part of the duodenum between the superior mesenteric artery and the aorta. It occurs most frequently in patients with rapid weight loss. METHODS: We report two young patients, who each presented with a longstanding history of postprandial abdominal pain, nausea, and voluminous vomiting. The diagnosis of SMAS was established by digital fluoroscopy and contrast-enhanced spiral computed tomography (CT) scan. The findings obtained by endoscopic ultrasound (EUS) at the site of duodenal compression, using a miniprobe, were of substantial diagnostic value and in good agreement with the radiological observations. RESULTS: Both patients, once diagnosed, were treated conservatively by providing enteral or parenteral high caloric nutrition. Weight gain was accompanied by the complete relief of symptoms. CONCLUSIONS: Pathogenesis, diagnostic procedures, and therapy are reviewed in order to draw attention to this rare entity.