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Review article: proteinase-activated receptors - novel signals for gastrointestinal pathophysiology.

Proteinase-activated receptors (PARs) have the common property of being activated by the proteolytic cleavage of their extracellular N-terminal domain. The new NH2-terminus acts as a 'tethered ligand' binding and activating the receptor itself. Four members of this family have been cloned, three of which are activated by thrombin (PAR-1, PAR-3 and PAR-4) while the fourth (PAR-2) is activated by trypsin or mast cell tryptase. In physiological or pathophysiological conditions, the gastrointestinal tract is exposed more than other tissues to proteinases (digestive enzymes, proteinases from pathogens or proteinases from inflammatory cells) that can activate PARs. Since PARs are highly expressed throughout the gastrointestinal tract, the study of the role of PARs in these tissues appears to be particularly important. It has already been shown that PAR-2 activation induces calcium mobilization and eicosanoid production in enterocytes as well as changes in ion transport in jejunal tissue segments. PAR-2 activation also causes calcium mobilization and stimulates amylase release from pancreatic acini. Moreover, both PAR-1 and PAR-2 activation can alter the gastrointestinal motility. In inflammatory or allergic conditions, the proteinases that constitute the major agonists for PARs (thrombin, trypsin and mast cell tryptase) are usually released. The activation of PARs by these proteinases might contribute to the gastrointestinal disorders associated with these pathologies. A complete understanding of the role of PARs in the gastrointestinal tract will require the development of selective receptor antagonists that are not yet available. Nonetheless, the use of PAR agonists has already highlighted new potential functions for proteinases in the gastrointestinal tract, thus the control of PAR activation might represent a promising therapeutic target.

Animals↗

Decreased expression of stem cell factor in esophageal and gastric mucosa after esophagogastric anastomosis for cancer: potential relevance to motility.

BACKGROUND: Esophageal replacement with gastric tube is a well-established reconstruction of the alimentary tract after esophagectomy in cancer patients. The resulting molecular events in the transposed gastric tube and residual esophagus have yet to be investigated. Stem cell factor (SCF) was recently shown to be critical for signaling in gastrointestinal motility. SCF expression is here correlated with changes in mucosal morphology, acid and biliary reflux, and motility in the residual esophagus and gastric tube. METHODS: Thirteen patients surgically resected for squamous esophageal carcinoma with gastric tube replaced by esophagogastric anastomosis underwent upper endoscopy, esophageal manometry, 24-hour pH monitoring, and bile reflux detection. Esophageal and gastric mucosa samples were examined for SCF expression by immunohistochemical and semiquantitative reverse transcriptase-polymerase chain reaction analysis and for SCF serum levels by enzyme-linked immunosorbent assay. RESULTS: All patients showed severe residual esophagus hypoperistalsis and no gastric tube motor activity. The 24-hour pH monitoring was positive in most; 24-hour bile detection was mostly negative. SCF levels in the residual esophageal and gastric tube mucosa were dramatically decreased compared with those of normal subjects. The correlation between SCF and slow-wave activity was positive. CONCLUSIONS: Hypomotility of the residual esophagus and gastric tube seems closely associated with disruption of the SCF/c-kit signaling pathway. However, the absence of notable relations between mucosal changes after chronic exposure to acid, biliary gastric content, and SCF expression indicates that this analysis cannot be considered part of endoscopic follow-up.

Adult↗

The effect of beta-adrenoreceptor agonists and antagonists on fructose absorption in man.

To explore the effect of beta-adrenoreceptor stimulation and blockade on the extraction of monosaccharide from the upper gut, we first established the malabsorption threshold in 26 normal volunteers using a series of test meals containing varying proportions of fructose and glucose. Incomplete small intestinal extraction and consequent arrival of carbohydrate into the caecum was identified by a rise in exhaled breath hydrogen concentration. The malabsorption threshold varied between individuals from 30 to 80 g fructose (median 40 g) but was reproducible within individuals, with 90% agreement of repeat studies. The malabsorption threshold for an individual was unrelated to body height (tau = 0.007, P > 0.05) or weight (tau = 0.003, P > 0.05) but correlated closely with time to onset of the breath hydrogen rise of a standard meal (tau = 0.70, P < 0.001). Administration of the beta-adrenoreceptor antagonist propranolol (160 mg) reduced the quantity of fructose required to exceed the malabsorption threshold from 45, 30-60 (median and range) to 40, 30-50 g (P = 0.03); administration of the beta-adrenoreceptor agonist isoprenaline (0.015 micrograms.kg/min) increased the quantity of fructose required to exceed the malabsorption threshold by 10 g (55 (50-90) g; P < 0.02). The effect of both drugs correlated closely with their transit effect (tau = 0.79, P < 0.01). A beta-adrenoreceptor mediated pathway thus appears to be capable of influencing the extraction of monosaccharide from the small intestine in normal subjects both under resting and stimulated conditions, probably acting via an effect on upper gastrointestinal motility.

Adrenergic beta-Agonists↗

Clinical pharmacokinetics in patients with spinal cord injuries.

Although spinal cord injury is a catastrophic affliction with numerous victims and a variety of physiological manifestations, the associated disarray in physiology has yet to be systematically or comprehensively studied as a probable cause for altered pharmacokinetics. A significant increase in the volume of distribution of drugs such as the aminoglycosides (gentamicin, amikacin, tobramycin), which are highly distributed into the extracellular fluid space and minimally biotransformed, may be anticipated in patients with chronic spinal cord injury. Changes in total body clearance have also been observed for some of these medications. The influence of the pathophysiology of spinal cord injury on gastrointestinal motility appears to be reflected in an impairment in the bioavailability of drugs [theophylline, paracetamol (acetaminophen), doxycycline] which are passively absorbed and which require an intact postprandial gastric emptying to ensure efficient absorption. For theophylline, the impairment in gastrointestinal absorption appears to be directly proportional to both the magnitude of the impairment in gastric emptying and to the neurological level of the injury. Metoclopramide, a gastrointestinal prokinetic drug, has been shown to be extremely effective in normalising the impaired postprandial gastric emptying that characterises spinal cord injury. The systemic absorption of 2 antibiotics (gentamicin and cefotiam) injected into paralysed muscle is also impaired in patients with spinal cord injury, suggesting that a decrease in therapeutic efficacy attributable to this mode of administration may be anticipated. Despite the multiplicity of drugs commonly prescribed for patients with this injury, little is known about the influence of this illness on either bioavailability or postabsorptive pharmacokinetics. For drugs which are biotransformed and which have a relatively small volume of distribution (theophylline, lorazepam, ranitidine), single-dose intravenous pharmacokinetic profiles in patients with spinal cord injury are indistinguishable from the drug disposition profiles characteristic of healthy control populations. It may be inferred, then that the influence of the pathophysiology of spinal cord injury on drug disposition is greatest on those drugs which are the least biotransformed and most likely to be distributed into the increased extracellular fluid volume which is characteristic of patients with this disability.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

Impact of the intragastric location of extended release tablets on food interactions.

Gastrointestinal motility and transport as well as concomitant food intake are factors that are known to influence pharmacokinetics derived after intake of extended release dosage forms. However, the mechanisms behind these influencing factors are mostly unknown. In this study the gastrointestinal transit and the in vivo drug release of magnetically labelled extended release tablets containing felodipine were monitored together with the drug absorption phase of pharmacokinetics under fasting and fed conditions in six healthy volunteers using Magnetic Marker Monitoring. It was found that the in vivo drug release profiles of the tablets compared well under fasting and fed conditions. However, the plasma concentration profiles were strongly influenced by concomitant food intake. This could be attributed to elongated residence of the tablets in proximal parts of the stomach, resulting in delayed drug absorption and the occurrence of late high plasma peak concentrations. The lag time until the first appearance of felodipine in plasma and the residence time of the tablets in the proximal stomach, were found to be directly correlated. The study shows that increased plasma peak drug concentrations after intake of extended release formulations together with food can be explained by poor mixing in the proximal part of the stomach and are not necessarily due to failure of the formulation to control drug release (dose dumping).

Adult↗

[The effect of intravenous prostaglandin F 2 alpha on the motility of the gastrointestinal tracts after major abdominal surgery (author's transl)].

TThe effect of prostaglandin F 2 alpha was studied clinically and electromyographically on the motility of the gastric antrum, duodenum, jejunum, ileum and transverse colon in 20 patients by giving 2 hours intravenous drip infusion at 0.3 approximately 0.5 microgram/kg/min for 2 hours after major abdominal surgery. Folling results were obtained. 1. The motility of stomach and colon was least active than any other site of alimentary tract during 48 hours after surgery. This seems to be one of the most important causes of so called postoperative ileus. 2. Recovery from reflex inhibition of motility of the alimentary tract after surgery was seen in duodenum at first, and then in jejunum and ileum in order. It was proved that intravenous drip infusion of PGF 2 alpha at 0.3 approximately 0.5 microgram/kg/min for 2 hours had produced the increase of electrical activity in any site of gastrointestinal tract and subsequently brought about increasing of propulsive movement. The effect of PGF 2 alpha is proportional to its concentration. 4. tit was concluded that PGF 2 alpha could be administered most effectively by intravvenous drip infusion at 0.5 microgram/kg/min 3 times daily for 3 days after surgery for the satisfactory recovery from the postoperative ileus, and no appreciable side effect was observed.

Abdomen↗

Factors affecting esophageal motility in gastroesophageal reflux disease.

BACKGROUND: There are conflicting data concerning the effect of gastroesophageal reflux disease (GERD) on esophageal motor function. HYPOTHESIS: Duration of GERD might affect severity of symptoms, grade of esophageal mucosal injury, and esophageal motor behavior. DESIGN: Retrospective study of a defined cohort. SETTINGS: Two referral centers, one of them academic, for esophageal gastrointestinal motility disorders. PATIENTS: One hundred forty-seven patients with documented GERD. MAIN OUTCOME MEASURES: Symptoms, grade of mucosal injury on esophagoscopy, esophageal manometry, ambulatory esophageal pH monitoring, and esophagogram. RESULTS: Patients with GERD had significantly decreased lower esophageal sphincter resting pressure (P =.02), lower amplitude of esophageal peristalsis at all levels of measurement (P<.001), and more delayed esophageal transit (P =.007) compared with control subjects. Patients with dysphagia, severe esophagitis, and Barrett esophagus presented with a longer history of the disease, significantly worse esophageal motor function (P<.01), and more prolonged esophageal transit than patients without the above features of the disease. Impairment of esophageal peristalsis and lower esophageal sphincter resting pressure were significantly inversely related to the duration of the disease (P<.001). Also, delay of esophageal transit was significantly related to the duration of the disease (P =.002) and inversely related to the amplitude of esophageal peristalsis (P<.001). Unlike the manometric variables, the extent of reflux, as assessed by ambulatory 24-hour esophageal pH monitoring, was not related to the duration of the disease. CONCLUSION: A long history of GERD is more commonly associated with presence of dysphagia, delayed esophageal transit, severe esophagitis, presence of Barrett esophagus, and impaired esophageal motility.

Adult↗

Chronic idiopathic slow transit constipation: pathophysiology and management.

OBJECTIVE: Patients with idiopathic slow-transit constipation comprise a small proportion of the total population complaining of constipation. The purpose of this review is to present an update of pathophysiology of this disorder and its application in clinical management. METHODS: Medline was used to search English language articles published up to the end of September 2002 on the subject of slow-transit constipation. RESULTS AND CONCLUSIONS: Patients with idiopathic slow-transit constipation can be divided into 2 subgroups: 1. patients with normal proximal gastrointestinal motility and with onset of constipation in connection with childbirth or pelvic surgery. This subgroup may benefit from consideration of surgical treatment; 2. patients who have a dysfunctional enteric nervous/neuroendocrine system and exhibit colonic dysmotility as part of a generalised gastrointestinal dysmotility. Surgical approach in this subgroup seems to be unhelpful and medical treatment appears to be a better approach.

Autonomic Nervous System↗

Periodic fluctuations of gut regulatory peptides in phase with the duodenal migrating myoelectric complex in preruminant calves: effect of different sources of dietary protein.

Four preruminant calves with implanted electrodes in the duodenum and a catheter in the external jugular vein were used for investigation of plasma gut regulatory peptide profiles during different phases of migrating myoelectric complex (MMC) in the small intestine. The effects of different dietary proteins on the rhythmic activity of gut peptides and gastrointestinal motility were compared. In particular, the effects of skimmed-milk protein (retaining physiological patterns of abomasal clotting, and abomaso-intestinal digesta flow) v. fish protein (devoid of clotting activity and modifying the digesta flow) were studied. In calves fed on the milk diet, plasma concentrations of pancreatic polypeptide, motilin, secretin, cholecystokinin (CCK) and somatostatin, but not vasoactive intestinal polypeptide or gastrin, fluctuated in phase with the duodenal MMC in the preprandial period. Feeding transiently affected the intestinal MMC and abolished the peptide fluctuations in a specimen-specific manner. In contrast, calves fed on the fish-protein diet showed more profound changes in intestinal MMC. In these animals the MMC-related fluctuations were significant only for plasma CCK. In conclusion, the source of dietary protein has an impact on the physiological endocrine function of the small intestine. Observed fluctuations of plasma gut regulatory peptides seem to be secondary to duodenal motility cycles.

Animals↗

The role of metoclopramide in peroral jejunal biopsy: a controlled randomized trial.

Metoclopramide is known to enhance gastric emptying and stimulate duodenal and small-intestinal peristaltic activity. The effect of the drug on peroral jejunal biopsy was examined in a controlled, double-blind, randomized trial. Forty-nine patients (24 females and 25 males) who required jejunal biopsy for diagnostic purposes were admitted to the study. All the biopsies were performed by the same operator using the Quinton multipurpose suction biopsy tube and applying the same technique. Twenty-four patients ranging in age from 18 to 67 years (mean 44.5) received placebo intravenously (sodium metabisulfite), and 25 patients from 16 to 73 years old (mean 39.9) received 10 mg of metoclopramide intravenously prior to the jejunal intubation. Objective parameters of the study were (1) time in minutes required for the intubation at the biopsy site, ie, the area at the ligament of Treitz, and (2) fluoroscopy time. Intubation time in the placebo group was 22.3 +/- 1.9 min (mean +/- SEM) vs 11.3 +/- 1.4 min in the metoclopramide group (P less than 0.001). Fluoroscopy exposure time was 2.47 +/- 0.25 in the placebo group vs 1.40 +/- 0.12 min in the metoclopramide group (P less than 0.001). Subjective clinical evaluation of the operator's assessment of the procedure was based on a 0-4 scale (much easier = 0, easier = 1, average = 2, harder = 3, and much harder = 4). Metoclopramide administration resulted in a significantly easier performance of the procedure (P less than 0.001) but did not influence patient tolerance. Three patients who received metoclopramide and one receiving placebo developed mild to moderate drowsiness of short duration. The results of this controlled trial indicate that metoclopramide significantly shortens the time required for jejunal biopsy and reduces fluoroscopy exposure. Its regulatory action on gastrointestinal motility contributes to the easier performance of a valuable diagnostic procedure.

Adolescent↗

Kappa-opiate agonist-induced inhibition of gastrointestinal transit in different strains of mice.

The effects of kappa-opiate agonists on gastrointestinal motility was assessed in Swiss Webster, C57BL/6, BALB/c and DBA/2 strains of mice. The kappa-agonists, PD 117302, U-69593 and U-50488H (3 mg kg-1), were injected subcutaneously and the distance travelled by a charcoal meal in the gastrointestinal tract was measured. All kappa-agonists induced significant inhibition of charcoal meal transit; however, there were significant strain differences in the antitransit effect. It is concluded that kappa-receptors are involved in the inhibition of gastrointestinal transit and that the negative data reported in the literature may be due to a genotype-dependent effect of kappa-agonists.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

Scintigraphy of the whole gut: clinical evaluation of transit disorders.

OBJECTIVE: To describe an initial clinical experience with a noninvasive scintigraphic technique for assessing gastrointestinal motility. DESIGN: We studied gastric, small bowel, and colonic transit in 109 unselected patients encountered between June and December 1992 at the Mayo Clinic. MATERIAL AND METHODS: The study patients were categorized on the basis of major complaint (constipation in 46, upper gastrointestinal symptoms in 45, and diarrhea in 18) and presence or absence of an underlying organic disease. Radioscintigraphy was used to analyze various regions of the gastrointestinal tract; scans were obtained at 2, 4, 6, and 24 hours after ingestion of a radiolabeled test meal. RESULTS: Overall, patients with a main complaint of constipation usually had slow or normal gastric, small bowel, and colonic transit, whereas those with diarrhea as the major symptom usually had normal or fast results of these studies. In the 65 patients with no underlying organic disease, inconsistent patterns of gastric emptying and small bowel and colonic transit were noted. CONCLUSION: Our results suggest that this 24-hour scintigraphic test may be clinically useful in screening for dysmotility syndromes in patients with nausea, vomiting, diarrhea, or constipation.

Adolescent↗

KIT (CD117): a review on expression in normal and neoplastic tissues, and mutations and their clinicopathologic correlation.

CD117 (KIT) is a type III receptor tyrosine kinase operating in cell signal transduction in several cell types. Normally KIT is activated (phosphorylated) by binding of its ligand, the stem cell factor. This leads to a phosphorylation cascade ultimately activating various transcription factors in different cell types. Such activation regulates apoptosis, cell differentiation, proliferation, chemotaxis, and cell adhesion. KIT-dependent cell types include mast cells, some hematopoietic stem cells, germ cells, melanocytes, and Cajal cells of the gastrointestinal tract, and neoplasms of these cells are examples of KIT-positive tumors. Other KIT-positive normal cells include epithelial cells in skin adnexa, breast, and subsets of cerebellar neurons. KIT positivity has been variably reported in sarcomas such as angiosarcoma, Ewing sarcoma, synovial sarcoma, leiomyosarcoma, and MFH; results of the last three are controversial. The variations in published data may result from incomplete specificity of some polyclonal antibodies, possibly contributed by too high dilutions. Also, KIT is expressed in pulmonary and other small cell carcinomas, adenoid cystic carcinoma, renal chromophobe carcinoma, thymic, and some ovarian and few breast carcinomas. A good KIT antibody reacts with known KIT positive cells, and smooth muscle cells and fibroblasts are negative. KIT deficiency due to hereditary nonsense/missense mutations leads to disruption of KIT-dependent functions such as erythropoiesis, skin pigmentation, fertility, and gastrointestinal motility. Conversely, pathologic activation of KIT through gain-of-function mutations leads to neoplasia of KIT-dependent and KIT-positive cell types at least in three different systems: mast cells/myeloid cells--mastocytosis/acute myeloid leukemia, germ cells--seminoma, and Cajal cells--gastrointestinal stromal tumors (GISTs). KIT tyrosine kinase inhibitors such as imatinib mesylate are the generally accepted treatment of metastatic GISTs, and their availability has prompted an active search for other treatment targets among KIT-positive tumors such as myeloid leukemias and small cell carcinoma of the lung, with variable and often nonconvincing results.

Gene Expression Regulation, Neoplastic↗

Stereospecific inhibition of gastrointestinal transit by kappa opioid agonists in mice.

Systemic administration of highly selective kappa opiate agonists, U-50488H and U-69593 (3, 10 and 30 mg/kg i.p.) produced significant inhibition of the gastrointestinal transit in mice as assessed by charcoal meal test. In contrast, the (+) stereoisomer of U-50488H, U-53455E did not inhibit the gastrointestinal motility. Furthermore, the kappa-selective antagonist, Mr 2266 (3 mg/kg) when administered along with the agonists, reversed the effects of the agonists. These results suggest that stereospecific kappa opiate receptors are involved in inhibition of gut motility in mice.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

Pharmacological effects of oxytocin on gastric emptying and intestinal transit of a non-nutritive liquid meal in female rats.

The effects of oxytocin (OT) on gastric emptying, gastrointestinal transit, and plasma levels of cholecystokinin (CCK) were studied in female rats. Gastrointestinal motility was assessed in rats 15 min after intragastric instillation of a test meal containing charcoal and Na(2)(51)CrO(4). Gastric emptying was determined by measuring the amount of radiolabeled chromium contained in the small intestine as a percentage of the initial amount received. Gastrointestinal transit was evaluated by calculating the geometric center of distribution of the radiolabeled marker. Blood samples were collected for CCK radioimmunoassay. After administration of OT (0.2-0.8 mg/kg), gastric emptying and gastrointestinal transit were inhibited, whereas the plasma concentration of CCK was increased in a dose-dependent manner. Atosiban, an oxytocin receptor antagonist, effectively attenuated the OT- induced inhibition of gastric emptying and gastrointestinal transit. However, administration of atosiban alone had no effect on gastric emptying and gastrointestinal transit. The selective CCK(1) receptor antagonists, devazepide and lorglumide, effectively attenuated the OT-induced inhibition of gastric emptying and gastrointestinal transit. L-365, 260, a selective CCK(2) receptor antagonist, did not alter the OT-induced inhibition of gastric emptying and gastrointestinal transit. These results suggest that OT inhibits gastric emptying and gastrointestinal transit in female rats via a mechanism involving CCK stimulation and CCK(1) receptor activation.

Animals↗

Plasma acylated ghrelin levels correlate with subjective symptoms of functional dyspepsia in female patients.

OBJECTIVE: Ghrelin is a brain-gut peptide that is mainly secreted from gastric endocrine cells (X/A like cells). In addition to promoting growth-hormone release and appetite, ghrelin also affects gastric motility and secretion. Circulating ghrelin levels are related to appetite and energy balance. Functional dyspepsia (FD) is a disorder characterized by the presence of chronic or recurrent symptoms of upper abdominal pain or discomfort. Although no known specific organic abnormalities are present in FD, abnormalities in gastrointestinal motility and sensitivity are thought to play a role in a substantial subgroup of patients. In addition, some patients also suffer from anorexia and body-weight loss. To investigate the role of ghrelin in the pathophysiology of FD, circulating ghrelin levels in affected patients were measured. MATERIAL AND METHODS: Eighteen Japanese female patients with functional dyspepsia and 18 healthy volunteers were recruited for the study. Acylated and desacyl forms of ghrelin were measured using commercially available enzyme-linked immunosorbent assay kits. RESULTS: Although plasma levels of acylated or desacyl ghrelin were not significantly different between healthy subjects and FD patients, plasma acylated, but not desacyl ghrelin, levels were correlated with a subjective symptom score in FD patients. In addition, the ratio of acylated to desacyl ghrelin (A/D ratio) was correlated strongly with acylated, but not desacyl, ghrelin levels. CONCLUSIONS: The correlation of circulating acylated ghrelin levels with the subjective symptom score and the A/D ratio in FD patients suggest that acylated ghrelin may play a role in the pathophysiology of FD.

Adult↗