Gastrointestinal Tract In Response Research Articles

Activation of cholecystokinin (CCK 1) and serotonin (5-HT 3) receptors increases the discharge of pancreatic vagal afferents

Cholecystokinin and serotonin are released from the gastrointestinal tract in response to the products of digestion and play critical roles in mediating pancreatic secretion via vago-vagal reflex pathways. This study was designed to investigate the effects of activation of cholecystokinin CCK 1 and serotonin (5-hydroxytryptamine, 5-HT) 5-HT 3 receptors on pancreatic vagal afferent discharge and to determine whether there is an interaction between these receptors. Male Sprague Dawley rats anaesthetised with isoflurane (1.5%/100% O 2) were used in all experiments. The effects of systemic administration of cholecystokinin and the serotonin 5-HT 3 receptor agonist phenylbiguanide on pancreatic vagal afferent discharge were recorded before and after administration of cholecystokinin CCK 1 and serotonin 5-HT 3 receptor antagonists. Cholecystokinin (0.1–10 µg/kg, i.v.) and phenylbiguanide (1 and 10 µg/kg, i.v.) increased pancreatic vagal afferent discharge dose-dependently. Cholecystokinin CCK 1 receptor antagonists, lorglumide (10 mg/kg, i.v.) and devazepide (0.5 mg/kg, i.v.), reduced cholecystokinin- and phenylbiguanide-induced increases in pancreatic vagal afferent discharge significantly ( n = 5, P < 0.05). On the other hand, serotonin 5-HT 3 receptor blockade with granisetron (1 mg/kg, i.v.) or MDL72222 ([(1S,5R)-8-methyl-8-azabicyclo[3.2.1]octan-3-yl] 3,5-dichlorobenzoate; 0.1 mg/kg, i.v.) inhibited the pancreatic vagal afferent discharge responses to phenylbiguanide but not those to cholecystokinin. This study has confirmed that cholecystokinin and phenylbiguanide activate pancreatic vagal afferent discharge via activation of cholecystokinin CCK 1 and serotonin 5-HT 3 receptors, respectively. In addition, it has demonstrated that (i) the serotonin 5-HT 3 agonist phenylbiguanide acts partly via an interaction with cholecystokinin CCK 1 receptors, and (ii) the actions of cholecystokinin are not dependent on serotonin 5-HT 3 receptor activation.

Gastrointestinal Satiety Signals

The increasing prevalence of obesity worldwide has imparted renewed impetus to the study of the mechanisms of appetite regulation. Digestion and nutrient absorption take place in the gastrointestinal (GI) tract, whereas food intake is controlled by neuronal circuits in the central nervous system. The need for gut-brain cross talk is therefore clear. It is now recognized that hormones released into the circulation from the GI tract in response to nutritional stimuli form a key component of this gut-brain axis. Peptides such as glucagon-like peptide-1, oxyntomodulin, pancreatic polypeptide, and peptide YY3-36 reduce food intake in both animal models and in humans. Physiologically, such peptides are thought to act as satiety signals and meal terminators. Here, we review the current state of the field of the effects of gut hormone action on appetite control.

Regulation of Ingestive Behavior, the Upper Gastrointestinal Motility and Gastric Acid Secretion by Ghrelin in Mammals

Ghrelin, a novel 28-amino acid peptide, was recently identified as the first endogenous ligand for growthhormone secretagogue receptors (previously known as orphan receptors), and discovered by “reverse pharmacology”. The ghrelin peptide features a unique post-translational modification of O-n-octanoylation at serine 3, and is secreted from X/A cells in gastric oxyntic glands into the blood circulation. Two major molecular forms of ghrelin are found in the stomach and plasma: acyl ghrelin with O-n-octanoylated serine in the position 3, and des-acyl ghrelin. Among dozens of enzymes, hormones and other factors secreted by the gastrointestinal tract in response to food in the lumen, acyl ghrelin is the only gastrointestinal signal to increase meal size. Acyl ghrelin stimulates food intake both in free-feeding (naturally fed) and food-deprived (fasted) rodents, and induces adiposity. Also, acyl ghrelin ameliorates cancer cachexia in nude mice, and alleviates ingestive behavior induced by cancer chemotherapy-related dyspepsia in normal rats. However, des-acyl ghrelin counteracts the metabolic but not the neuroendocrine response to acyl ghrelin. Transgenic mice overexpressing des-acyl ghrelin have been shown small phenotype. In addition, des-acyl ghrelin inhibits food intake in food-deprived mice and rats. Acyl ghrelin stimulates gastrointestinal motor activity and accelerates gastric emptying in rats, but not in dogs. On the contrary, des-acyl ghrelin has been shown to disrupt gastric motility in rats, and delay gastric emptying in mice and rats. For the majority of experiments, acyl ghrelin stimulates gastric acid secretion in rats, however, different results exist.

β-Cell Failure in Diabetes and Preservation by Clinical Treatment

There is a progressive deterioration in beta-cell function and mass in type 2 diabetics. It was found that islet function was about 50% of normal at the time of diagnosis, and a reduction in beta-cell mass of about 60% was shown at necropsy. The reduction of beta-cell mass is attributable to accelerated apoptosis. The major factors for progressive loss of beta-cell function and mass are glucotoxicity, lipotoxicity, proinflammatory cytokines, leptin, and islet cell amyloid. Impaired beta-cell function and possibly beta-cell mass appear to be reversible, particularly at early stages of the disease where the limiting threshold for reversibility of decreased beta-cell mass has probably not been passed. Among the interventions to preserve or "rejuvenate" beta-cells, short-term intensive insulin therapy of newly diagnosed type 2 diabetes will improve beta-cell function, usually leading to a temporary remission time. Another intervention is the induction of beta-cell "rest" by selective activation of ATP-sensitive K+ (K(ATP)) channels, using drugs such as diazoxide. A third type of intervention is the use of antiapoptotic drugs, such as the thiazolidinediones (TZDs), and incretin mimetics and enhancers, which have demonstrated significant clinical evidence of effects on human beta-cell function. The TZDs improve insulin secretory capacity, decrease beta-cell apoptosis, and reduce islet cell amyloid with maintenance of neogenesis. The TZDs have indirect effects on beta-cells by being insulin sensitizers. The direct effects are via peroxisome proliferator-activated receptor gamma activation in pancreatic islets, with TZDs consistently improving basal beta-cell function. These beneficial effects are sustained in some individuals with time. There are several trials on prevention of diabetes with TZDs. Incretin hormones, which are released from the gastrointestinal tract in response to nutrient ingestion to enhance glucose-dependent insulin secretion from the pancreas, aid the overall maintenance of glucose homeostasis through slowing of gastric emptying, inhibition of glucagon secretion, and control of body weight. From the two major incretins, glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), only the first one or its mimetics or enhancers can be used for treatment because the diabetic beta-cell is resistant to GIP action. Because of the rapid inactivation of GLP-1 by dipeptidyl peptidase (DPP)-IV, several incretin analogs were developed: GLP-1 receptor agonists (incretin mimetics) exenatide (synthetic exendin-4) and liraglutide, by conjugation of GLP-1 to circulating albumin. The acute effect of GLP-1 and GLP-1 receptor agonists on beta-cells is stimulation of glucose-dependent insulin release, followed by enhancement of insulin biosynthesis and stimulation of insulin gene transcription. The chronic action is stimulating beta-cell proliferation, induction of islet neogenesis, and inhibition of beta-cell apoptosis, thus promoting expansion of beta-cell mass, as observed in rodent diabetes and in cultured beta-cells. Exenatide and liraglutide enhanced postprandial beta-cell function. The inhibition of the activity of the DPP-IV enzyme enhances endogenous GLP-1 action in vivo, mediated not only by GLP-1 but also by other mediators. In preclinical studies, oral active DPP-IV inhibitors (sitagliptin and vildagliptin) also promoted beta-cell proliferation, neogenesis, and inhibition of apoptosis in rodents. Meal tolerance tests showed improvement in postprandial beta-cell function. Obviously, it is difficult to estimate the protective effects of incretin mimetics and enhancers on beta-cells in humans, and there is no clinical evidence that these drugs really have protective effects on beta-cells.

Beneficial effects of sub-chronic activation of glucagon-like peptide-1 (GLP-1) receptors on deterioration of glucose homeostasis and insulin secretion in aging mice

Aging is associated with an increased incidence of glucose intolerance and type 2 diabetes. Glucagon-like peptide-1 (GLP-1) is an important insulinotropic peptide secreted from the gastrointestinal tract in response to nutrient absorption. The present study was designed to assess the sub-chronic glucose regulatory effects of the potent long-acting GLP-1 receptor agonist, (Val 8)GLP-1, in aging 45–49 week old mice. Daily injection of (Val 8)GLP-1 (25 nmol/kg body weight) for 12 days had no significant effect on food intake, body weight, non-fasting plasma glucose and insulin concentrations. However, after 12 days, the glycaemic response to intraperitoneal glucose was improved ( P < 0.05) in (Val 8)GLP-1 treated mice. In keeping with this, glucose-mediated insulin secretion was enhanced ( P < 0.05) and insulin sensitivity improved ( P < 0.05) compared to controls. These data indicate that sub-chronic activation of the GLP-1 receptor by daily treatment with (Val 8)GLP-1 counters aspects of the age-related impairment of pancreatic β-cell function and insulin sensitivity.

Application of 16S rRNA gene-targetted fluorescence in situ hybridization and restriction fragment length polymorphism to study porcine microbiota along the gastrointestinal tract in response to different sources of dietary fibre

A total of 32 pigs of 15+/-0.38 kg body weight were fed for 6 weeks one of four diets differing in their source of dietary fibre. FISH was used to quantify the main bacterial groups in the pig gut using the following probes: Eub338, Bac303, Rfla729, Rbro730, Erec482, Fprau645, Prop853, Str493 and Lab158. FISH counts revealed important differences at four sites along the pig gastrointestinal tract, but we were unable to show differences related to diets. Stomach and jejunal samples gave total bacterial counts of 0.1-5.3 x 10(8) g(-1) of contents. In the stomach, streptococci and lactobacilli were predominant, and the clostridial cluster IX group was abundant (14-41% of total bacterial count). Clostridial cluster IX bacteria were present elsewhere in the gastrointestinal tract at 1-8%. The other groups were generally more abundant in the proximal colon and rectum: Bacteroides/Prevotella (5-10%), clostridial cluster XIVa (10-19%), and cluster IV relatives of Faecalibacterium prausnitzii (1-4%) and ruminococcus (4-10%). Restriction fragment length polymorphism profiles showed changes related to diet, with pigs fed wheat bran having the lowest richness of all diets (P=0.008).

Oro-Facial Granulomatosis: Crohnʼs Disease or a New Inflammatory Bowel Disease?

Oro-facial granulomatosis (OFG) is a rare chronic inflammatory disorder presenting characteristically with lip swelling but also affecting gingivae, buccal mucosa, floor of mouth, and a number of other sites in the oral cavity. Histologically, OFG resembles Crohn's disease (CD), and a number of patients with CD have oral involvement identical to OFG. However, the exact relationship between OFG and CD remains unknown. Thirty-five patients with OFG and no gut symptoms were identified from a combined oral medicine/gastroenterology clinic. All underwent a standardized assessment of the oral cavity and oral mucosal biopsy to characterize the number of sites affected and the type of inflammation involved. Hematological and biochemical parameters were also recorded. All 35 patients underwent ileocolonoscopy and biopsy to assess the presence of coexistent intestinal inflammation. Ileal or colonic abnormalities were detected in 19/35 (54%) cases. From gut biopsies, granulomas were present in 13/19 cases (64%). An intestinal abnormality was significantly more likely if the age of OFG onset was less than 30 years (P=0.01). Those with more severe oral inflammation were also more likely to have intestinal inflammation (P=0.025), and there was also a correlation between the histologic severity of oral inflammation and the histologic severity of gut inflammation (P=0.047). No relationship was found between any blood parameter and intestinal involvement. Endoscopic and histologic intestinal abnormalities are common in patients with OFG with no gastrointestinal symptoms. Younger patients with OFG are more likely to have concomitant intestinal involvement. In these patients, granulomas are more frequent in endoscopic biopsies than reported in patients with documented CD. OFG with associated intestinal inflammation may represent a separate entity in which granulomatous inflammation occurs throughout the gastrointestinal tract in response to an unknown antigen or antigens.

Enhancing Central Nervous System Endogenous GLP-1 Receptor Pathways for Intervention in Alzheimers Disease

Glucagon-like peptide-1 (7-36)--amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet beta-cell proliferation, glucose-dependent insulin secretion, and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, are coupled to the cyclic AMP second messenger pathway, and are expressed throughout the brain of rodents and humans. We previously reported that GLP-1 and exendin-4, a naturally occurring, long-acting analogue of GLP-1 that binds the GLP-1 receptor (GLP-1R), possess neurotrophic properties. GLP-1R agonists protect neurons against amyloid-beta peptide (Abeta) and glutamate-induced apoptosis in cell culture studies and attenuate cholinergic neuron atrophy in the basal forebrain of the rat following an excitotoxic lesion. The biochemical cascades activated by neural GLP-1R stimulation are discussed in comparison to those activated by pancreatic receptors, and, additionally, are compared to signaling pathways associated with the classical neurotrophins. GLP-1R stimulation promotes pathways that favour cell survival over apoptosis. GLP-1 readily enters brain, and its diverse physiological actions, which include insulinotropic, cardiovascular as well as neurotrophic ones, may prove beneficial in a variety of diseases prevalent in aging, including Alzheimer's disease (AD). Its ability to lower brain levels of Abeta in mice would appear to be particularly pertinent in this regard. Furthermore, the ready availability of clinical material and the clinical history of its long term use in subjects with type 2 diabetes would support testing the value of GLP-1R agonists in AD trials.

Studies of the peptide YY and neuropeptide Y2 receptor genes in relation to human obesity and obesity-related traits.

Peptide-YY (PYY) is secreted from endocrine L-cells of the gastrointestinal tract in response to caloric ingestion and may mediate postprandial satiety through the hypothalamic neuropeptide Y2 receptor (Y2R). We examined whether variants in the genes encoding PYY and Y2R might be associated with obesity-related phenotypes in humans. Among 101 subjects with severe early-onset obesity and a history of hyperphagia, we found two rare sequence variants-L73P and IVS2 + 32delG-in PYY and three rare missense mutations-L40F, F87I, and A172T-in Y2R. Although none of these were found in 100 normal-weight white control subjects, L73P in PYY and F87I and A172T in Y2R did not segregate with obesity in family studies, and family data were unavailable for IVS2 + 32delG in PYY and L40F in Y2R. Two common single nucleotide polymorphisms (SNPs), R72T and IVS3 + 68C>T, in PYY were in tight linkage disequilibrium but showed no association with BMI in a large white population. In the Y2R, two SNPs, 585T>C and 936T>C, were found and were in tight linkage disequilibrium. Men, homozygous for the rarer variant, had significantly lower BMI (P = 0.017), waist-to-hip ratio (P = 0.013), and, surprisingly, higher nonesterified fatty acid levels (P = 0.01). In conclusion, mutations in PYY and Y2R are not commonly found in humans with severe early-onset obesity. The relationship between common variants in Y2R and obesity-related traits deserves further exploration in other populations.

Gastrointestinal satiety signals I. An overview of gastrointestinal signals that influence food intake.

An overview is presented of those signals generated by the gastrointestinal (GI) tract during meals that interact with the central nervous system to create a sensation of fullness and satiety. Although dozens of enzymes, hormones, and other factors are secreted by the GI tract in response to food in the lumen, only a handful are able to influence food intake directly. Most of these cause meals to terminate and hence are called satiety signals, with CCK being the most investigated. Only one GI signal, ghrelin, that increases meal size has been identified. The administration of exogenous CCK or other satiety signals causes smaller meals to be consumed, whereas blocking the action of endogenous CCK or other satiety signals causes larger meals to be consumed. Satiety signals are relayed to the hindbrain, either indirectly via nerves such as the vagus from the GI tract or else directly via the blood. Most factors that influence how much food is eaten during individual meals act by changing the sensitivity to satiety signals. This includes adiposity signals as well as habits and learning, the social situation, and stressors.

Selective expression of glutathione S-transferase genes in the murine gastrointestinal tract in response to dietary organosulfur compounds.

A short-term feeding regimen was designed to analyze the effects of compounds such as diallyl disulfide (DADS), diallylthiosulfinate (allicin) from garlic and butylated hydroxyanisole (BHA) on glutathione S-transferase (GST) expression in the gastrointestinal tract and liver of male mice. After animals were force-fed these compounds, tissue GSTs were purified and individual subunits resolved by HPLC and identified on the basis of mass spectrometry (ESI MS) and immunoreactivity data. The effects of DADS and allicin on GST expression were especially prominent in stomach and small intestine, where there were major coordinate changes in GST subunit profiles. In particular, the transcripts of the mGSTM1 and mGSTM4 genes, which share large segments of common 5'-flanking sequences, and their corresponding subunits were selectively induced. Levels of alpha class subunits also increased, whereas mGSTM3 and mGSTP1 were not affected. The inducible mGSTA5 and non-responsive mGSTM3 subunits had not been identified previously. Liver and colon GSTs were also affected to a lesser extent, but this short-term feeding regimen had no effect on GST subunit patterns from other organs, including heart, brain and testis. Real-time PCR (TaqMan) methods were used for quantitative estimations of relative amounts of the mRNAs encoding the GSTs. Effects on the transcripts generally paralleled changes at the protein level, for the most part, however, the greatest relative increases were observed for those mRNAs that were expressed at low abundance constituitively. Mechanisms by which the organosulfur compounds operate to affect GST transcription could involve reversible modification of certain protein sulfhydryl groups, shifts in reduced glutathione/oxidized glutathione ratios and resultant changes in cellular redox status.

Glucagon-like peptide-1 decreases endogenous amyloid-beta peptide (Abeta) levels and protects hippocampal neurons from death induced by Abeta and iron.

Glucagon-like peptide-1(7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. It was recently reported that GLP-1 and exendin-4, a naturally occurring, more stable analogue of GLP-1 that binds at the GLP-1 receptor, possess neurotrophic properties and can protect neurons against glutamate-induced apoptosis. We report here that GLP-1 can reduce the levels of amyloid-beta peptide (Abeta) in the brain in vivo and can reduce levels of amyloid precursor protein (APP) in cultured neuronal cells. Moreover, GLP-1 and exendin-4 protect cultured hippocampal neurons against death induced by Abeta and iron, an oxidative insult. Collectively, these data suggest that GLP-1 can modify APP processing and protect against oxidative injury, two actions that suggest a novel therapeutic target for intervention in Alzheimer's disease.

Gastrointestinal physiology and functions.

While the health benefit of a functional food may be a metabolic response that lowers risk for disease, the actual target for the food or food component may be on the functioning of the gastrointestinal tract (GIT). For example, slowing absorption from the intestine, as measured by examining the appearance of the nutrient or food component in the blood, the hormone response associated with absorption of the compound or excretion of the compound, may provide a health benefit. However, the food component may slow absorption by delaying gastric emptying, altering the mixing within the intestinal contents or decreasing the availability of digestive enzymes in the intestine. These measures of GIT function provide validation of the mechanisms by which the functional food or food components affect metabolism. Bioavailability of physiologically active compounds from foods will be determined by the digestibility of foods that contain these compounds, their subsequent absorption and utilization by tissues. The physical structure of foods contributes to the functional effects of foods as well as to the availability of compounds from foods. For example, recent studies have demonstrated that changing the viscosity of the gut contents alters absorption and GIT response. Additionally, food structures such as the plant cell wall change the availability of absorbable compounds along the gastrointestinal contents. The areas of probiotics and prebiotics have highlighted the potential importance of gut microflora in health. While evidence suggests biological activity relevant to disease risk reduction, the long-term implications of the microbial activity have yet to be established.

Protection and reversal of excitotoxic neuronal damage by glucagon-like peptide-1 and exendin-4.

Glucagon-like peptide-1 (7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the L cells of the gastrointestinal tract in response to food. It has potent effects on glucose-dependent insulin secretion, insulin gene expression, and pancreatic islet cell formation. In type 2 diabetes, GLP-1, by continuous infusion, can normalize blood glucose and is presently being tested in clinical trials as a therapy for this disease. More recently, GLP-1 has been found to have central nervous system (CNS) effects and to stimulate neurite outgrowth in cultured cells. We now report that GLP-1, and its longer-acting analog exendin-4, can completely protect cultured rat hippocampal neurons against glutamate-induced apoptosis. Extrapolating these effects to a well defined rodent model of neurodegeneration, GLP-1 and exendin-4 greatly reduced ibotenic acid-induced depletion of choline acetyltransferase immunoreactivity in basal forebrain cholinergic neurons. These findings identify a novel neuroprotective/neurotrophic function of GLP-1 and suggest that such peptides may have potential for halting or reversing neurodegenerative processes in CNS disorders, such as Alzheimer's disease, and in neuropathies associated with type 2 diabetes mellitus.

Endocrine and neuroendocrine signals of energy stores: view from the chair.

Feeding behaviour and energy homeostasis are fundamental processes that are critical for survival. As such they represent important elements of the mechanism whereby fuel, stored in the form of adipose tissue is held constant. The adipostatic (or lipostatic) model, originally suggested by Kennedy in 1953, hypothesizes that signals proportional to the size of fat stores are integrated into a complex regulatory system that includes signals generated by substrate depletion and replenishment, as well as biological rhythms, habits and learned associations. Key components of the adipostatic model are hormones whose circulating concentrations are proportional to adipose tissue mass, which act as tonic signals to the brain for regulating food intake and serve to maintain a constant body weight. A second set of signals, related to the quantity and quality of ingested food, consists of neural afferents and peptides released from the gastrointestinal tract in response to specific nutrients. The papers in this symposium cover recent work on both types of signals. The first two papers examine the evidence that leptin and insulin fulfill the role of adiposity signals. Leptin, being the new hormone in town, has gained most recent attention, and is the subject of the first paper in this symposium.

Signal Transduction Pathways Mediating Neurotensin-stimulated Interleukin-8 Expression in Human Colonocytes

Neurotensin (NT), a neuropeptide released in the gastrointestinal tract in response to several stimuli, is involved in the pathophysiology of colonic inflammation. However, the molecular mechanism(s) mediating this proinflammatory response remains unclear. We found that NCM460, non-transformed human colonocytes, express a functional high affinity NT receptor that mediates NT-induced Erk activation. By using NCM460 cells stably transfected with NTR1, we show that NTR1 activation leads to interleukin (IL)-8 secretion that is mediated via both NF-kappaB- and Erk-dependent pathways. In addition, NT-stimulated NF-kappaB activation is dependent on intracellular calcium release. NT-stimulated Erk activity requires Ras activation because overexpression of the dominant negative Ras mutant Ras-17N almost completely inhibits the Erk activation. Furthermore, NT directly stimulates Ras-GTP formation as shown by a Ras-GTP pull-down assay. By using reporter gene constructs containing targeted substitutions in the IL-8 promoter, we show that the NF-kappaB, AP-1, and to a lesser degree the C/EBP sites in the IL-8 promoter region are required for IL-8 gene expression induced by NT. In summary, our results demonstrate that NT stimulates calcium-dependent NF-kappaB and Ras-dependent Erk pathways that mediate the release of IL-8 from non-transformed human colonocytes. We speculate that these NT-related proinflammatory pathways are important in the pathophysiology of colonic inflammation.

TREK-1 regulation by nitric oxide and cGMP-dependent protein kinase. An essential role in smooth muscle inhibitory neurotransmission.

Potassium channels activated by membrane stretch may contribute to maintenance of relaxation of smooth muscle cells in visceral hollow organs. Previous work has identified K(+) channels in murine colon that are activated by stretch and further regulated by NO-dependent mechanisms. We have screened murine gastrointestinal, vascular, bladder, and uterine smooth muscles for the expression of TREK and TRAAK mRNA. Although TREK-1 was expressed in many of these smooth muscles, TREK-2 was expressed only in murine antrum and pulmonary artery. TRAAK was not expressed in any smooth muscle cells tested. Whole cell currents from TREK-1 expressed in mammalian COS cells were activated by stretch, and single channel recordings showed that the stretch-dependent conductance was due to 90 pS channels. Sodium nitroprusside (10(-6) or 10(-5) m) and 8-Br-cGMP (10(-4) or 10(-3) m) increased TREK-1 currents in perforated whole cell and single channel recordings. Mutation of the PKG consensus sequence at serine 351 blocked the stimulatory effects of sodium nitroprusside and 8-Br-cGMP on open probability without affecting the inhibitory effects of 8-Br-cAMP. TREK-1 encodes a component of the stretch-activated K(+) conductance in smooth muscles and may contribute to nitrergic inhibition of gastrointestinal muscles.

Alternate mucosal immune system: organized Peyer's patches are not required for IgA responses in the gastrointestinal tract.

The progeny of mice treated with lymphotoxin (LT)-beta receptor (LTbetaR) and Ig (LTbetaR-Ig) lack Peyer's patches but not mesenteric lymph nodes (MLN). In this study, we used this approach to determine the importance of Peyer's patches for induction of mucosal IgA Ab responses in the murine gastrointestinal tract. Immunohistochemical analysis revealed that LTbetaR-Ig-treated, Peyer's patch null (PP null) mice possessed significant numbers of IgA-positive (IgA+) plasma cells in the intestinal lamina propria. Further, oral immunization of PP null mice with OVA plus cholera toxin as mucosal adjuvant resulted in Ag-specific mucosal IgA and serum IgG Ab responses. OVA-specific CD4+ T cells of the Th2 type were induced in MLN and spleen of PP null mice. In contrast, when TNF and LT-alpha double knockout (TNF/LT-alpha-/-) mice, which lack both Peyer's patches and MLN, were orally immunized with OVA plus cholera toxin, neither mucosal IgA nor serum IgG anti-OVA Abs were induced. On the other hand, LTbetaR-Ig- and TNF receptor 55-Ig-treated normal adult mice elicited OVA- and cholera toxin B subunit-specific mucosal IgA responses, indicating that both LT-alphabeta and TNF/LT-alpha pathways do not contribute for class switching for IgA Ab responses. These results show that the MLN plays a more important role than had been appreciated until now for the induction of both mucosal and systemic Ab responses after oral immunization. Further, organized Peyer's patches are not a strict requirement for induction of mucosal IgA Ab responses in the gastrointestinal tract.

Effect of gastric inhibitory polypeptide on bovine fat metabolism

Gastric inhibitory polypeptide (GIP), a hormone secreted by the gastrointestinal tract in response to nutrient absorption, exerts anabolic effects on adipose tissue in some species. Cattle fed on grass silage diets tend to deposit more fat than animals fed on dried forages. We investigated the effect of diet on blood GIP concentrations in cattle. Plasma concentrations tended to be higher in cattle fed grass silage alone or supplemented with fishmeal (0.61 ng/ml) compared with animals fed dried grass/barley (0.43 ng/ml, P>0.1) and were inversely correlated with plasma insulin concentrations ( r=−0.727, P<0.01). The effects of increasing concentrations (0, 0.1, 1.0, 10.0 nM) of GIP and glucagon-like peptide-1 (GLP-1) on basal and insulin-stimulated lipogenesis in bovine adipose tissue in vitro were investigated after 4 and 24 h of incubation. No conclusive effects were obtained with either peptide. Subsequently, the effect of exogenous administration of GIP (10 or 50 ng/kg liveweight per min) on whole-body fat metabolism was investigated in two steers in vivo. Plasma concentration and flux rate of palmitate was increased by GIP only at the higher infusion level suggesting lipolysis and possibly fatty acid re-esterification was stimulated at high concentration. We conclude that although gut peptides may regulate nutrient utilisation, it is unlikely that they play a major role in promoting fat accretion in cattle. However, the small number of animals used in these studies indicates the need for caution and further studies are warranted.

Action of FMRFamide-like Peptides on Porcine Gastrointestinal Motility In Vitro

Decker, B., B. Vadokas, U. Kutschenreuter, K. Golenhofen, K. Voigt, G. P. Mcgregor and K. Mandrek. Action of FMRFamide-like peptides on porcine gastrointestinal motility in vitro. Peptides 18(10) 1531–1537, 1997.—Mechanical activity was recorded in circular and longitudinal smooth muscle preparations isolated from extensive regions of the porcine gastrointestinal tract in response to the FMRFamide-like neuropeptides F8Famide and A18Famide. In all preparations, the peptides were about equipotent in producing phasic contractions or enhancing spontaneous activity. The most prominent responses were observed in jejunal longitudinal strips which were on the average 91% (±4% SEM, n = 15; 10 −6 M) of the histamine (10 −5 M) responses. The peptide-induced phasic activity was completely abolished by nifedipine but was unaffected by tetrodotoxin, atropine, phentolamine, yohimbine, phenoxybenzamine, propranolol, methysergide, cimetidine, indomethacin, levallorphane or naloxone. Both peptides enhanced acetylcholine-induced contractions. However, bovine ileum and guinea-pig taenia coli was not affected by these peptides. The results indicate that F8F- and A18F-amide contract porcine gastrointestinal smooth muscle by acting directly via non-opioid receptors on L-type calcium channels. In addition an increase of the sensitivity to cholinergic stimulation occurs.