N-Butyrate rectal transport in cirrhotic patients.

Data about colonic mucosa transport of short-chain fatty acids in cirrhotic patients are still lacking. The aim of the present study was to compare the rectal mucosa transport of n-butyrate and its effect on transport of other electrolytes and endoluminal pH in normal subjects and in cirrhotic patients by using a rectal dialysis technique. Thirteen subjects with normal hepatic function tests and 17 cirrhotic patients were enrolled. Dialysis bags containing 80 mmol/liter of butyrate in a neutral pH (6.8) electrolyte solution were placed in the rectum of enrolled subjects for 60 min. Net transport rate was calculated for butyrate, sodium, chloride, potassium, and bicarbonate. The differences in pH between initial and final dialysis solutions was also evaluated in the two groups in the study. Net butyrate absorption was significantly lower in cirrhotic patients than in controls (65.2 +/- 38.6 vs 101.2 +/- 45.3 nmol/min/cm2, respectively; P = 0.02). Furthermore, cirrhotic patients showed a lower HCO3 secretion than controls (-26.9 +/- 19.9 vs -45.1 +/- 20.0, respectively; P = 0.01). No differences were found in transport of the other electrolytes. The pH in the final dialysis solution in cirrhotic patients was not significantly lower than in the controls (7.15 vs 7.35; P = 0.1). In conclusion, the impairment of butyrate absorption and the concurrent reduction of bicarbonate secretion observed in cirrhotic patients may suggest a selective hypoactivity of apical HCO3-/SCFA- antiport located at the colonocyte apical membrane.

Contribution of NK3 tachykinin receptors to propulsion in the rabbit isolated distal colon.

The role of NK3 receptors in rabbit colonic propulsion has been investigated in vitro with the selective agonist, senktide, and two selective antagonists, SR142801 and SB222200. Peristalsis was elicited by distending a rubber balloon with 0.3 and 1.0 mL of water leading to a velocity of 2.2 and 2.8 mm s-1, respectively. At concentrations of 1 nM, senktide inhibited propulsion evoked by both distensions (range 25-40%), whereas at 6 and 60 nmol L-1 facilitated 'submaximal' propulsion by 30%. In the presence of Nomega-nitro-L-arginine (L-NNA, 200 micromol L-1), which per se caused a slight prokinetic effect, 1 nmol L-1 senktide markedly accelerated propulsion (range 35-50%). Hexamethonium (200 micromol L-1) had minor effects on propulsion. In its presence, 60 nmol L-1 senktide significantly inhibited propulsion induced by both stimuli (range 20-50%). SR142801 (0.3, 3 nmol L-1) and SB222200 (30, 300 nmol L-1) facilitated 'submaximal' propulsion (range 20-40%). Conversely, higher antagonist concentrations (SR142801: 30, 300 nM; SB222200: 1, 10 micromol L-1) inhibited propulsion to both distensions by 20%. A combination of SR142801 (300 nmol L-1) plus hexamethonium (200 micromol L-1) induced an approximately four-fold greater inhibition of propulsion than that induced by SR142801 alone. In conclusion, in the rabbit-isolated distal colon, a subset of NK3 receptors located on descending pathways mediates an inhibitory effect on propulsion by activating a NO-dependent mechanism. Another subset of NK3 receptors, located on ascending pathways mediates a facilitative effect involving a synergistic interaction with cholinergic nicotinic receptors.

Contribution of NK(2) tachykinin receptors to propulsion in the rabbit distal colon.

The role of the tachykinin neurokinin (NK)(2) receptors on rabbit distal colon propulsion was investigated by using two selective NK(2)-receptor antagonists, MEN-10627 and SR-48968. Experiments on colonic circular muscle strips showed that contractile responses to [beta-Ala(8)]NKA-(4-10) (1 nM-1 microM), a selective NK(2)-receptor agonist, were competitively antagonized by MEN-10627 (1-100 nM), whereas SR-48968 (0.1-10 nM) caused an insurmountable antagonism, thus confirming the difference in the mode of action of the two compounds. Colonic propulsion was elicited by distending a mobile rubber balloon with 0.3 ml (submaximal stimulus) or 1.0 ml (maximal stimulus) of water. The velocity of anal displacement of the balloon (mm/s) was considered the main propulsion parameter. At low concentrations (1.0-100 nM and 0.1-10 nM, respectively), MEN-10627 and SR-48968 facilitated the velocity of propulsion, whereas at high concentrations (100 nM and 1 microM, respectively) they decelerated propulsion. The excitatory and inhibitory effects of both antagonists were observed only with submaximal stimulus. We focused on the hypothesis that the facilitatory effect on propulsion may result from blockade of neuronal NK(2) receptors and the inhibitory effect from suppression of the excitatory transmission mediated by NK(2) receptors on smooth muscle cells. In the presence of N(G)-nitro-L-arginine (300 microM), a nitric oxide synthase inhibitor, MEN-10627, at a concentration (10 nM) that was found to accelerate propulsion in control experiments inhibited the velocity of propulsion. In the presence of threshold (1-10 nM) or full (1 microM) concentration of atropine, which inhibited to a great extent the velocity of propulsion, the inhibitory effect of MEN-10627 (1 microM) was markedly increased. In conclusion, in the rabbit distal colon NK(2) receptors may decelerate propulsion by activating a nitric oxide-dependent neuronal mechanism and may accelerate it by a postjunctional synergistic interaction with cholinergic muscarinic receptors.

Regulatory role of tachykinins on intestinal propulsive activity.

The role of NK1, NK2, NK3 tachykinin receptors in subserving intestinal peristalsis has been reviewed referring mainly to the latest advances in this field. The most interesting and intriguing notion emerging from recent and ongoing studies is that tachykinins present in enteric neurons may modulate propulsive activity in an opposite manner, by enhancing or inhibiting peristalsis via each of the three distinct tachykinin receptors. These studies unveiled the complexity of tachykinergic control of the intestinal motility which is due to interaction of endogenous tachykinins with receptors located on ascending excitatory and descending inhibitory pathways and on smooth muscle cells. In fact, the type of tachykinergic modulation may depend on the amount of released peptides, on the site of the bulk of peptide release along the enteric motor pattern and, consequently, on the cellular location of the activated receptor, i.e. muscular or neuronal cells. Furthermore, in the case of activation of neuronally located tachykinin receptors, the effect of tachykinins may depend on the relatively functional predominance of excitatory or inhibitory neural circuits subserving peristalsis in different intestinal tracts. Our findings obtained in a simple isolated model represent a promising start for the understanding of the complex tachykinergic modulatory role of intestinal motility even though the function of tachykinins studied "in vivo" is certainly more complex than that studied "in vitro".

Effects of cisapride on abnormally prolonged endogastric alkalinity time and delayed gastric emptying in cirrhotic patients.

BACKGROUND/AIMS: An abnormally prolonged alkalinity time in endogastric long-term pH monitoring has been previously demonstrated in cirrhotic patients. Recently a growing body of evidence suggest the existence of severe abnormalities of gastric emptying in the same patients and more generally of gastrointestinal motility changes in many portal hypertensive animal models. Assuming that there was a good correlation between endogastric alkalinity and a delayed emptying of gastric bile reflux, the aim of this study was to evaluated the effect of a gastrokinetic drug, Cisapride, both on circadian gastric pH and on gastric emptying in cirrhotic patients compared with controls. MATERIALS AND METHODS: Ten in patients with chronic liver disease and portal hypertension (six males, four females, median age 49.5, range 28-59) were enrolled. The control group included twelve inpatients without cirrhosis (seven females and five males, average age 45 years, range 31-54) free from endoscopic esophagogastro-duodenal lesions. The subjects were submitted to a 24h endogastric pH monitoring and gastric emptying study before and after administration of Cisapride (10 mg tid for three days). To gastric emptying study we used an ultrasonographic method evaluating the ratio between the antropyloric region volume before and at a fixed time after a solid/liquid standard meal. RESULTS: Basal 24 h gastric pH monitoring in cirrhotic patients showed a significant prolonged time of alkalinity (pH conventionally over 4) during the entire registration and mainly in postprandial period vs controls. The same patients group showed also a delayed gastric emptying when compared to controls. Cisapride administration significantly reduced both the abnormally prolonged alkalinity time and delayed gastric emptying in cirrhotic group without affecting the same parameters in the control group. CONCLUSIONS: Cisapride significantly reduces both the delayed gastric emptying time and the abnormally prolonged alkalinity time in cirrhotic group. Taken together, the results offered an indirect evidence that abnormally prolonged alkalinity in cirrhotic patients may be due, at least in part, to changes in gastroduodenal motility leading to a reduced gastric clearance of potentially noxious duodeno-gastric alkaline reflux.

Gastric and duodenal juxtamucosal pH and Helicobacter pylori.

One of the results of gastric cytoprotection is the generation of a juxtamucosal stable pH, maintained close to neutrality by several factors among which bicarbonate secretion and mucus layer. Since Helicobacter pylori (HP) induces structural and functional changes in the gastric mucus, this study was carried out to investigate the relationship between juxtamucosal pH and HP colonization. Thirty-one dyspeptic subjects who denied a past history of gastric or duodenal ulcer and free of endoscopic lesions were studied. Juxtamucosal pH of the gastric body, antrum and duodenum and gastric luminal fluid pH were measured during upper gastrointestinal endoscopy by a flexible glass electrode passed through the biopsy channel of a gastroscope. Multiple biopsies were subsequently taken for histological investigation, HP culture and a urea quick test. Twelve subjects (39%) were infected by HP (HP+). Juxtamucosal pH (mean +/- SE) was significantly lower (p = 0.0014) in the gastric body (5.67 +/- 0.16) in HP+ than in HP-negative (HP- 6.41 +/- 0.13 subjects, but not in the antrum (6.50 +/- 0.20 in HP+ vs. 6.52 +/- 0.09 in HP-) and in the duodenum (6.80 +/- 0.14 in HP+ vs. 6.94 +/- 0.08 in HP- subjects). No difference was found in gastric luminal fluid pH (1.71 +/- 0.23 in HP+ vs. 1.80 +/- 0.22 in HP- subjects). In conclusion, this study shows that dyspeptic HP+ patients have a reduced juxtamucosal pH in the gastric body but a pH in the antrum and duodenum similar to HP-subjects.