Michel Delvaux

Mediators and Pharmacology of Visceral Sensitivity: From Basic to Clinical Investigations

Over the last decade, the role of visceral sensitivity has been largely recognized in the pathophysiology of functional digestive disorders, particularly in the irritable bowel syndrome. These studies have highlighted the role of afferent pathways arising from the gut as a possible target for new treatments intended to relieve pain or modify altered reflexes present in such patients. These pharmacological targets have been identified mainly by studies on animal models of visceral hyperalgesia of various origins including local inflammation. Locally, several mediators are of paramount importance for sensitization of nerve endings: 5-hydroxytryptamine, bradykinin, tachykinins, calcitonin gene-related peptide, and neurotrophins. Selective antagonists to various subtypes of their receptors are currently available and have been shown to be active in these animal models. Other substances, such as somatostatin, opiold peptides, cholecystokinin, oxytocin, and adenosine, modulate the transmission of nociceptive inputs from the gut to the brain and are of clinical interest. This article reviews the current understanding of these mediators. Although these agents seem to be promising tools for the treatment of visceral hyperalgesia and its consequences (abdominal pain and disturbed reflexes), their clinical efficacy remains to be shown. A better understanding of the nature and the location of the defect in the sensory pathways may permit the selection of subgroups of patients for treatment according to the pharmacological properties of these new therapeutic agents.

Evaluation of colonic sensory thresholds in IBS patients using a barostat. Definition of optimal conditions and comparison with healthy subjects.

To study the role of abnormal visceral perception in the pathophysiology of the irritable bowel syndrome (IBS), we evaluated colonic tone and visceral perception during intracolonic distension using a flaccid balloon connected to a computerized barostat and placed in the descending colon of IBS patients and healthy controls. In the first part of the study, basal colonic tone and response to pharmacological (neostigmine and glucagon) and physiological (1000-kcal meal) stimuli were recorded in nine IBS patients. Colonic tone increased by 72±27% after injection of neostigmine and decreased by 88±62% after glucagon. After the meal, the maximal increase in colonic tone was 76±31% with the total response to the meal lasting 109.7±32.0 min. In the second part of the study, symptomatic responses (discomfort and pain thresholds) and pressure variations were evaluated during two different methods of distension (stepwise and intermittent) in a randomized order in the nine IBS patients and six healthy controls. Each distension method was repeated twice in IBS patients to study reproducibility. In IBS patients, the mean discomfort threshold volume was 172±76 ml when using stepwise and 167±43 ml when using intermittent distension. The mean pain threshold volume was 250±25 ml when using stepwise and 211±22 ml when using intermittent distension, this difference being statistically significant (P<0.02). Discomfort and pain threshold volumes recorded during the first session of the same distension method were not different from those recorded during the second one. When comparing IBS patients to controls, the pain threshold was reached at a volume ≤300 ml in all IBS patients versus only one control when using stepwise distensions (P<0.001) and in all IBS patients versus no control when using intermittent distensions (P<0.001). Intracolonic pressure-volume curves were similar in patients and controls. In conclusion, isovolumic distension of the colon is a reproducible method of evaluating viscerosensitivity, which is significantly increased in IBS patients. This increased viscerosensitivity is not related to abnormal colonic compliance and may, alone or in combination with other colonic abnormalities, explain the symptoms of irritable bowel syndrome.

Endoscopic ultrasonography in chronic pancreatitis: a comparative prospective study with conventional ultrasonography, computed tomography, and ERCP.

The usefulness and accuracy rate of endoscopic ultrasonography (EUS) in the diagnosis of chronic pancreatitis (CP) were prospectively evaluated in 81 patients with suspected pancreatic disease. All underwent EUS, abdominal ultrasonography (AUS), and computed tomography (CT), and endoscopic retrograde cholangiopancreatography (ERCP) was performed in 55 of the cases. The diagnosis of CP was established in 44 patients (CP group) including 24 with a calcified form. No pancreatic disease was observed in 18 patients (control group), and 19 patients had a pancreatic tumor. In the CP group AUS was less accurate than EUS in visualizing the pancreas, performances of CT scan being identical to EUS in this respect. A good correlation was observed between EUS and ERCP for visualization and measurement of the Wirsung duct. The most significant changes observed by EUS in the CP group were dilatation of the main pancreatic duct, heterogeneous echogenicity of the pancreatic parenchyma, and cysts <20 mm in size even in noncalcified CP or with normal pancreatograms. Sensitivity of EUS for diagnosis of CP was 88% (AUS, 58%; ERCP, 74%; CT scan, 75%), the specificity being 100% for ERCP and EUS, 95% for CT scan, and 75% for AUS. The good performances of EUS allow early diagnosis of CP in symptomatic patients since heterogeneous echogenicity of the pancreatic parenchyma seems to be almost specifically associated with the disease.

Octreotide increases thresholds of colonic visceral perception in IBS patients without modifying muscle tone.

Effects of octreotide (1.25 µg/kg subcutaneously) on colonic tone and visceral perception were evaluated in 10 IBS patients, using a barostat and compared to placebo in a double-blind crossover study. Colonic sensory thresholds were also studied in healthy controls for comparison with IBS patients. Colonic tone was reflected by variations in volume of the barostat balloon. Baseline volume was 117±38 ml and was not modified by placebo (122±40 ml) or octreotide (106±42 ml). After the meal, maximal decrease in balloon volume was 75±4% following placebo (P<0.001) beginning after 9±3 min and lasting 136±17 min. Following octreotide, the maximal decrease was 69±16% (NS vs placebo), after 10±3 min and lasting 140±22 min. In the second part, discomfort and pain thresholds were evaluated during isobaric distensions (4 mm Hg increments, 5-min duration, 5-min interval with return to pressure 0 between each). The pressure inducing discomfort was 21.2±5.9 mm Hg following placebo vs 29.6±6.6 mm Hg following octreotide (P<0.01). The pressure inducing pain was 24.8±7.3 mm Hg following placebo vs 33.2±7.3 mm Hg following octreotide (P<0.01). In healthy subjects, discomfort and pain were induced by colonic distensions at a mean intraballoon pressure of 32.7±5.8 mm Hg and 36.7±3.9 mm Hg, respectively. Compliance curves were not different following placebo and octreotide. Octreotide significantly increases thresholds for visceral perception in IBS patients without modifying compliance during distension nor colonic tone.

Does the “Suspected Blood Indicator” improve the detection of bleeding lesions by capsule endoscopy?

BACKGROUNDnThe Suspected Blood Indicator (SBI), a feature included in the software for interpretation of capsule endoscopy (CE), is designed to facilitate detection of bleeding lesions in the small bowel. This study evaluated the sensitivity and the specificity of the SBI in patients who underwent CE for obscure GI bleeding (OGIB).nnnMETHODSnCE recordings from patients with OGIB recruited in 7 centers were read by experts blinded to the red SBI tags. They classified lesions of interest as bleeding or as having a potential for bleeding that was high (P2), low (P1), or absent (P0). The SBI tags then were marked by a another investigator. Concordance was acknowledged when frames selected by the expert reader, and those tagged by the SBI had the same time code.nnnRESULTSnA total of 156 recordings were evaluated. In 83, there was either no lesion (n = 71) or a P0 lesion (n = 12); these CE recordings were regarded as normal. Among the 73 abnormal recordings, 114 P2 and 92 P1 lesions were identified. A total of 154 red tags were analyzed. Sensitivity, specificity, and positive and negative predictive values of SBI were 37%, 59%, 50%, and 46%, respectively, for detection of the presence of a P2 or P1 lesion in front of a red tag.nnnCONCLUSIONSnSBI-based detection of intestinal lesions with the potential for bleeding is of limited clinical value in practice and does not reduce the time required for interpretation of CE.

Microscopic examination of bile directly collected during endoscopic cannulation of the papilla. Utility in patients with suspected microlithiasis.

The usefulness of microscopic examination of pure bile directly collected from the biliary tract during endoscopic retrograde cholangiography and without hormonal simulation was prospectively evaluated in 72 patients. According to clinical, biochemical, ultrasonographic, and radiographic data, the patients were separated into two groups: group 1, patients with proven stones (N=50), and group 2, patients with suspected microlithiasis presenting symptoms suggestive of cholelithiasis but without evidence of macroscopic stones at echography or cholangiography (N=22). Cholesterol crystals and/or bilirubinate granules were observed (eg, positive examination) in the bile of 41 of the 50 patients of group 1 (82%). Among patients of group 2, seven (32%) had a positive bile examination: cholecystectomy (N=2) or endoscopic sphincterotomy (N=5) disclosed minute stones in all cases. In the 15 patients of group 2 with a negative bile examination, cholecystectomy (N=3), sphincterotomy (N=2), and clinical (and/or echographic) 20-month follow-up (N=9) revealed biliary lithiasis in only one patient, in whom recurrent cholangitis led to disclosure of one bile duct stone. According to these results microscopic examination of bile samples collected during endoscopic retrograde cholangiography exhibited a sensitivity and a specificity for cholelithiasis recognition of 82.7% and 100%, respectively, with a positive predictive value of 88%. We conclude that the accuracy of this method makes it useful to investigate and manage patients with suspected microlithiasis.

Comparative effects of galanin on isolated smooth muscle cells from ileum in five mammalian species

Effect of galanin and CCK8 were studied on isolated smooth muscle cells obtained from pig, guinea-pig, rat, rabbit and dog ileum circular muscle layer. Galanin as well as CCK8 induced a concentration-dependent contraction of pig, rat, rabbit and guinea-pig ileum smooth muscle cells. Maximal contraction ranged between 23.7 +/- 1.9% and 26.1 +/- 3.1% decrease in cell length from control in the presence of both peptides. This maximal contraction was obtained at 1 nM galanin in pig, rat, rabbit, 1 nM CCK8 in rat, rabbit, guinea-pig, at 10 nM galanin in guinea-pig and 10 nM CCK8 in pig. Concentrations of galanin inducing a half maximal contraction (EC50) ranged between 8 pM and 80 pM in these species. In dog, CCK8 induced a concentration-dependent contraction of ileum smooth muscle cells, with a maximal contraction (24.5 +/- 2.3%) at 1nM and an EC50 of 50 pM while galanin inhibited cell contraction induced by CCK8. The CCK-induced contraction was abolished at 10 nM galanin and 10 nM VIP. Concentrations of galanin and VIP inducing a half-maximal relaxation of contracted cells were 2 pM and 3 pM respectively. It is concluded that galanin may induce cell contraction of pig, guinea-pig, rat and rabbit ileum circular muscle layer and cell relaxation of dog ileum by a direct myogenic effect.

Stimulatory (EP1 and EP3) and inhibitory (EP2) prostaglandin E2 receptors in isolated ileal smooth muscle cells

Isolated smooth muscle cells from the circular layer of pig and guinea-pig ileum were used to study the effect of prostaglandin E2 (PGE2) and three PGE2 receptor (EP) agonists; iloprost (EP1), butaprost (EP2) and enprostil (EP3). In pig cells, PGE2 and enprostil induced cell contraction (22.1 and 21.5% shortening of cell length, obtained at 10 nM for PGE2 and 1 nM for enprostil, respectively). Iloprost and butaprost had no contractile effect. However, the cholecystokinin octapeptide (CCK-8; 10 nM)-induced contraction was inhibited when cells were preincubated with iloprost or butaprost. In guinea-pig cells, PGE2, butaprost and iloprost induced cell contraction, whereas enprostil had no effect (23.1% for 10 nM PGE2, 22.8% for 1 nM butaprost and 22.6% for 10 nM iloprost). Preincubation with SC19220 (EP1 antagonist) inhibited the PGE2-, butaprost- and iloprost-induced contractions. When the contractile effect of PGE2, butaprost and iloprost was inhibited by addition of SC19220, these agents inhibited the cell contraction induced by CCK-8 (1 nM). Smooth muscle cells from guinea-pig and pig ileum express two PGE2 receptor subtypes that induce opposite effect. EP1 and EP3 receptors mediate cell contraction in guinea-pig and pig, respectively, whereas EP2 receptors mediate cell relaxation in both species.

Follow-up of patients with hyperplastic polyps of the large bowel

BACKGROUNDnAdenomatous colonic polyps are accepted as premalignant lesions. There is controversy regarding the significance of the hyperplastic polyp. The aim of this study was to determine the incidence of further polyps in patients with only hyperplastic polyps on a first colonoscopy in comparison with patients without polyps and with adenomatous polyps.nnnMETHODSnNinety patients had only hyperplastic polyps (group I). These patients were paired according to age and sex with subjects having no polyps (group II) and with patients having adenomas (group III).nnnRESULTSnFifty-six patients in group I had at least one follow-up examination. New polyps were found in 46.4% in group I versus 15.5% in group II (p < 0.001) and 50% in group III (NS). In group I, 30.7% of new polyps were hyperplastic and 69.3% were adenomas. In fact, 32.2% of group I patients developed further adenomas (mean 1.5 +/- 0.8 adenomas). These adenomas occurred 1 to 4 years after the first polypectomy (mean 2.4 +/- 0.8 years). Most of these adenomas were small and tubular, but 16.6% were villous or had severe dysplasia.nnnCONCLUSIONnPatients with hyperplastic polyps were 2.4 times more likely to have further adenomas than were those without polyps.

VIP-induced relaxation of guinea-pig intestinal smooth muscle cells: sequential involvement of cyclic AMP and nitric oxide.

1 A possible interaction between cyclic AMP and nitric oxide (NO) in mediating the relaxant effect of vasoactive intestinal polypeptide (VIP) on intestinal smooth muscle cells has been investigated. The effects of the inhibitor of NO synthesis, NG‐nitro‐L‐arginine methyl ester (L‐NAME), have been studied on VIP‐, forskolin‐, and 8 bromo‐cyclic AMP‐ induced relaxation of cells, dispersed by enzymatic digestion of muscle strips from the circular layer of guinea‐pig ileum. 2 VIP alone did not modify the length of isolated muscle cells. By contrast, when the cells were contracted by cholecystokinin octapeptide, CCK8 (10 nM), VIP inhibited this contraction, inducing a concentration‐dependent relaxation of the cells. Maximal relaxation was induced by 1 μm VIP (EC50 = 408.2 ± 16.7 pM). 3 N‐ethylmaleimide, inhibitors of adenylate cyclase or somatostatin, abolished the relaxing effect of VIP. (R)‐p‐cAMPs, an antagonist of cyclic AMP on protein kinase A also inhibited the VIP‐induced relaxation by 92.1 ± 6.3%. Inhibitors of nitric oxide synthase (NOS), L‐NAME and L‐NMMA, partially inhibited VIP‐induced relaxation. The effect of L‐NAME was reversed by L‐arginine but not by D‐arginine. 4 (R)‐p‐cAMPS and L‐NAME also inhibited the cell relaxation induced either by forskolin which directly stimulates adenylate cyclase activity or 8‐bromo‐cyclic AMP, an analogue of cyclic AMP. 5 When cells were incubated for 30 min with dexamethasone 10 μm, a glucocorticoid known to decrease the synthesis of iNOS, the relaxing effect of a maximal concentration of VIP was decreased by 52 ± 4% and L‐NMMA had no further effect on this residual VIP‐induced relaxation. Milrinone, a phosphodiesterase type III inhibitor, potentiated the relaxant effect of VIP. 6 These data demonstrate that the intracellular pathway mediating the relaxant effect of VIP in intestinal smooth muscle cells includes the sequential activation of adenylate cyclase, protein kinase A, activation of NOS and finally production of NO and cyclic GMP. NO could in turn regulate the cyclic AMP‐dependent pathway of cell relaxation.