Several receptors mediate the antisecretory effect of peptide YY, neuropeptide Y, and pancreatic polypeptide on VIP-induced fluid secretion in the rat jejunum in vivo

Lack of peptide YY signaling in mice disturbs gut microbiome composition in response to high-fat diet

Peptide YY (PYY), produced by endocrine L cells in the gut, is known for its critical role in regulating gastrointestinal functions as well as satiety. However, how these processes are integrated with maintaining a healthy gut microbiome composition is unknown. Here, we show that lack of PYY in mice leads to distinct changes in gut microbiome composition that are diet‐dependent. While under chow diet only slight differences in gut microbiome composition could be observed, high‐fat diet (HFD) aggravated these differences. Specifically an increased abundance of the Bacteroidetes phylum with a corresponding decrease of the Firmicutes/Bacteroidetes ratio could be detected in Pyy‐knockout (KO) mice in response to HFD. Detailed analysis of the Bacteroidetes phylum further revealed that the Alistipes genus belonging to the Rikenellaceae family, the Parabacteroides belonging to the Tannerellaceae family, as well as Muribaculum were increased in Pyy‐KO mice. In order to investigate whether these changes are associated with changed markers of gut barrier and immunity, we analyzed the colonic expression of various pro‐inflammatory cytokines, as well as tight junction proteins and mucin 2, and identified increased mRNA expression of the tight junction proteins Cldn2 and Ocel1 in Pyy‐KO mice, while pro‐inflammatory cytokine expression was not significantly altered. Together these results highlight a critical gene‐environment interaction between diet and the gut microbiome and its impact on homeostasis of the intestinal epithelium under conditions of reduced PYY signaling which is commonly seen under obese conditions.

Abnormalities in ileal stem, neurogenin 3, and enteroendocrine cells in patients with irritable bowel syndrome

Background

This study examined whether the densities of stem- and enteroendocrine cell progenitors are abnormal in the ileum of patients with irritable bowel syndrome (IBS), and whether any abnormalities in ileal enteroendocrine cells are correlated with abnormalities in stem cells and enteroendocrine cell progenitors.

Methods

One hundred and one IBS patients covering all IBS subtypes were recruited, and 39 non-IBS subjects were included as a control group. The patients and controls underwent standard colonoscopies, during which biopsy specimens were obtained from the ileum. The biopsy specimens were stained with hematoxylin-eosin and immunostained for Musashi-1 (Msi-1), neurogenin 3 (NEUROG3), chromogranin A (CgA), serotonin, peptide YY (PYY), oxyntomodulin (enteroglucagon), pancreatic polypeptide, and somatostatin. The immunoreactive cells were quantified by computerized image analysis.

Results

The densities of Msi-1, NEUROG3, CgA, and serotonin cells were reduced in all IBS patients and in patients with diarrhea-predominant IBS (IBS-D), mixed-diarrhea-and-constipation IBS (IBS-M), and constipation-predominant (IBS-C) relative to the control subjects. While the PYY cell density was increased in IBS-C relative to controls, it did not differ between control subjects and IBS-D and IBS-M patients. The densities of Msi-1 and NEUROG3 cells were strongly correlated with that of CgA cells.

Conclusions

The abnormalities in the ileal enteroendocrine cells appear to be caused by two mechanisms: (1) decreases in the clonogenic activity of the stem cells and in the endocrine-cell progenitors differentiating into enteroendocrine cells, and (2) switching on the expression of PYY and switching off the expression of certain other hormones in other types of the enteroendocrine cells.

Dietary fiber in irritable bowel syndrome (Review)

Irritable bowel syndrome (IBS) is a common chronic gastrointestinal disorder. It is widely believed that IBS is caused by a deficient intake of dietary fiber, and most physicians recommend that patients with IBS increase their intake of dietary fiber in order to relieve their symptoms. However, different types of dietary fiber exhibit marked differences in physical and chemical properties, and the associated health benefits are specific for each fiber type. Short-chain soluble and highly fermentable dietary fiber, such as oligosaccharides results in rapid gas production that can cause abdominal pain/discomfort, abdominal bloating/distension and flatulence in patients with IBS. By contrast, long-chain, intermediate viscous, soluble and moderately fermentable dietary fiber, such as psyllium results in a low gas production and the absence of the symptoms related to excessive gas production. The effects of type of fiber have been documented in the management of IBS, and it is known to improve the overall symptoms in patients with IBS. Dietary fiber acts on the gastrointestinal tract through several mechanisms, including increased fecal mass with mechanical stimulation/irritation of the colonic mucosa with increasing secretion and peristalsis, and the actions of fermentation byproducts, particularly short-chain fatty acids, on the intestinal microbiota, immune system and the neuroendocrine system of the gastrointestinal tract. Fiber supplementation, particularly psyllium, is both safe and effective in improving IBS symptoms globally. Dietary fiber also has other health benefits, such as lowering blood cholesterol levels, improving glycemic control and body weight management.

Endocrine cells in the ileum of patients with irritable bowel syndrome

AIM

To study the ileal endocrine cell types in irritable bowel syndrome (IBS) patients.

METHODS

Ninety-eight patients with IBS (77 females and 21 males; mean age 35 years, range 18-66 years) were included, of which 35 patients had diarrhea (IBS-D), 31 patients had a mixture of both diarrhea and constipation (IBS-M), and 32 patients had constipation (IBS-C) as the predominant symptoms. The controls were 38 subjects (26 females and 12 males; mean age 40 years, range 18-65 years) who had submitted to colonoscopy for the following reasons: gastrointestinal bleeding, where the source of bleeding was identified as hemorrhoids (n = 24) or angiodysplasia (n = 3), and health worries resulting from a relative being diagnosed with colon carcinoma (n = 11). The patients were asked to complete the: Birmingham IBS symptom questionnaire. Ileal biopsy specimens from all subjects were immunostained using the avidin-biotin-complex method for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), enteroglucagon, and somatostatin cells. The cell densities were quantified by computerized image analysis, using Olympus cellSens imaging software.

RESULTS

The gender and age distributions did not differ significantly between the patients and the controls (P = 0.27 and P = 0.18, respectively). The total score of Birmingham IBS symptom questionnaire was 21 ± 0.8, and the three underlying dimensions: pain, diarrhea, and constipation were 7.2 ± 0.4, 6.6 ± 0.4, and 7.2 ± 0.4, respectively. The density of serotonin cells in the ileum was 40.6 ± 3.6 cells/mm² in the controls, and 11.5 ± 1.2, 10.7 ± 5.6, 10.0 ± 1.9, and 13.9 ± 1.4 cells/mm² in the all IBS patients (IBS-total), IBS-D, IBS-M, and IBS-C patients, respectively. The density in the controls differed significantly from those in the IBS-total, IBS-D, IBS-M, and IBS-C groups (P < 0.0001, P = 0.0001, P = 0.0001, and P < 0.0001, respectively). There was a significant inverse correlation between the serotonin cell density and the pain dimension of Birmingham IBS symptom questionnaire (r = -0.6, P = 0.0002). The density of PYY cells was 26.7 ± 1.6 cells/mm(2) in the controls, and 33.1 ± 1.4, 27.5 ± 1.4, 34.1 ± 2.5, and 41.7 ± 3.1 cells/mm² in the IBS-total, IBS-D, IBS-M, and IBS-C patients, respectively. This density differed significantly between patients with IBS-total and IBS-C and the controls (P = 0.03 and < 0.0001, respectively), but not between controls and, IBS-D, and IBS-M patients (P = 0.8, and P = 0.1, respectively). The density of PYY cells correlated significantly with the degree of constipation as recorded by the Birmingham IBS symptom questionnaire (r = 0.6, P = 0.0002). There were few PP-, enteroglucagon-, and somatostatin-immunoreactive cells in the biopsy material examined, which made it impossible to reliably quantify these cells.

CONCLUSION

The decrease of ileal serotonin cells is associated with the visceral hypersensitivity seen in all IBS subtypes. The increased density of PYY cells in IBS-C might contribute to the constipation experienced by these patients.

Abnormal rectal endocrine cells in patients with irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common gastrointestinal disorder. In a previous study the total number of endocrine cells in the rectum of IBS patients, as detected by chromogranin A, did not differ from that of healthy controls. While the total endocrine cell content of the rectum appears to be unchanged in IBS patients, changes in particular endocrine cells cannot be excluded. This study was undertaken, therefore, to investigate the cell density of different rectal endocrine cell types in (IBS) patients. Fifty patients with IBS (41 females and 9 males) were included in the study. Thirty patients had diarrhoea (IBS-D) and 20 had constipation (IBS-C) as the predominant symptom. Twenty-seven subjects were included as controls (19 females and 8 males). Rectal biopsy specimens were immunostained using the avidin-biotin-complex method for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), and oxyntomodulin and somatostatin cells. The cell densities were quantified by computerised image analysis. The serotonin cell density did not differ significantly, although a type II statistical error cannot be excluded, due to the small size of the sample. The densities of PYY and Oxyntomodulin cells were significantly lower and that of somatostatin were significantly higher in IBS patients than controls. These abnormalities were observed in both IBS-D and IBS-C patients. The abnormalities in the endocrine cells observed in this study in the rectum differed considerably from those seen in the colon of IBS patients. This indicates that caution in using the rectum to represent the large intestine in these patients. These abnormalities could be primary (genetic) or secondary to changes in the gut hormones found in other segments of the gut and/or other pathological processes. Although the-cause-and effect relationship of the abnormalities found in rectal endocrine cells is difficult to elucidate, they might contribute to the symptoms associated with IBS. The densities of PYY and somatostatin cells are potential biomarkers with good sensitivity and specificity for the diagnosis of IBS.

Changes in the symptom pattern and the densities of large-intestinal endocrine cells following Campylobacter infection in irritable bowel syndrome: a case report

Background

Irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder. Post-infectious IBS (PI-IBS) is a subset of IBS that accounts for a large proportion of IBS patients. The PI-IBS symptoms meet the Rome criteria for IBS with diarrhoea (IBS-D) or IBS with mixed bowel habits (IBS-M). A low-grade inflammation has been reported to occur in PI-IBS. Abnormalities in intestinal endocrine cells have been reported in both sporadic IBS and PI-IBS.

Case presentation

A 20-year-old female with a diagnosis of IBS with constipation (IBS-C), according to Rome III criteria, contracted Campylobacter-induced gastroenteritis, after which her symptom pattern changed to IBS-M. She showed an intestinal low-grade inflammation that was manifested by an increase in the number of intraepithelial and lamina propria leucocytes and lymphocytes and an increase in the density of mast cells in lamina propria. There was also an increase in the density of intestinal serotonin and peptide YY (PYY) cells and a decrease in the density of rectal somatostatin cells. Follow-up of the patient at 4-months post-infection revealed reduction of IBS symptoms and an improvement in her quality of life. However, 6 months following the Campylobacter infection, the patient switched back from IBS-M to IBS-C, probably due to recovery from PI-IBS. The patient was treated with prucalopride, which is serotonin 5HT₄ receptor agonist. Six months later following this treatment, the symptoms were reduced and the quality of life improved in the reported patient.

Conclusions

Gastroenteritis in patients with IBS-C causes a post-infectious, low-grade inflammation. Interaction between immune-cells and intestinal endocrine cells increases the density of certain endocrine cells, which in turn might be responsible for the change in the symptom pattern, the milder symptoms and the improvement in the quality of life seen in the reported patient. The findings in this case raise the question as to whether intestinal infections are responsible for the previously reported switching of IBS from one subtype to another over time.

Clinical presentation, diagnosis, pathogenesis and treatment options for lymphocytic colitis (Review)

Lymphocytic colitis (LC) is characterized by chronic or relapsing non-bloody watery diarrhea and a macroscopically normal colon. However, histopathological examination of colonic biopsy samples reveals an increased intraepithelial infiltration of lymphocytes (≥20/100 enterocytes), and increased inflammatory cells within the lamina propria, but with a normal mucosal architecture. The reported prevalence of LC varies from 14.2 to 45 per 100,000 individuals, while its reported incidence is between 0.6 and 16 per 100,000 individuals. LC has a high rate of spontaneous symptomatic remission and is not associated with an increased risk of colon cancer or inflammatory bowel disease. The diagnosis is based on the histopathological findings. The density of colonic chromogranin A-positive cells provides an effective diagnostic tool with high sensitivity and specificity in both the right and left colon. Gastrointestinal infections, drugs, and/or autoimmunity may trigger chronic colonic low-grade inflammation. Colonic nitric oxide, serotonin and peptide YY (PYY) cell densities are markedly increased in patients with LC. It has been hypothesized that the low-grade inflammation in LC through the endocrine-immune axis causes this increase. It has been postulated further that these abnormalities in the neuroendocrine system of the colon are responsible for the diarrhea observed in patients with LC. The benign course and rate of spontaneous remission of LC denotes that drugs with severe side-effects should be avoided if possible. The drug cost and drug coverage may also be limiting factors for some patients. These aspects should be taken into account when making decisions regarding treatment options.

Low densities of serotonin and peptide YY cells in the colon of patients with irritable bowel syndrome

BACKGROUND

The gut hormones are important in regulating gastrointestinal motility. Disturbances in gastrointestinal motility have been reported in patients with irritable bowel syndrome (IBS). Reduced endocrine cell density, as revealed by chromogranin A, has been reported in the colon of IBS patients.

AIMS

To investigate a possible abnormality in the colonic endocrine cells of IBS patients.

METHODS

A total of 41 patients with IBS according to Rome Criteria III and 20 controls were included in the study. Biopsies from the right and left colon were obtained from both patients and controls during colonoscopy. The biopsies were immunostained for serotonin, peptide YY (PYY), pancreatic polypeptide (PP), entroglucagon, and somatostatin cells. Cell densities were quantified by computerized image analysis.

RESULTS

Serotonin and PYY cell densities were reduced in the colon of IBS patients. PP, entroglucagon, and somatostatin-immunoreactive cells were too few to enable reliable quantification.

CONCLUSION

The cause of these observations could be primary genetic defect(s), secondary to altered serotonin and/or PYY signaling systems and/or subclinical inflammation. Serotonin activates the submucosal sensory branch of the enteric nervous system and controls gastrointestinal motility and chloride secretion via interneurons and motor neurons. PYY stimulates absorption of water and electrolytes, and inhibits prostaglandin (PG) E2, and vasoactive intestinal peptide, which stimulates intestinal fluid secretion and is a major regulator of the "ileal brake". Although the cause and effect relationship of these findings is difficult to elucidate, the abnormalities reported here might contribute to the symptoms associated with IBS.

Enteroendocrine and neuronal mechanisms in pathophysiology of acute infectious diarrhea

BACKGROUND

While enterocyte secretion is the predominant mechanism considered responsible for secretory diarrhea in response to acute enteric infections, there are several lines of evidence that support alternative mechanisms controlling fluid and electrolyte secretion in diarrhea.

AIM

To review enteroendocrine and neuronal mechanisms that participate in the development of acute infectious diarrhea.

RECENT ADVANCES

Acute infectious diarrheas due to bacterial toxins (e.g., cholera, E. coli heat-stable enterotoxin, C. difficile) and rotavirus are all associated with secretion of transmitters from enteroendocrine cells (e.g., 5-HT) and activation of afferent neurons that stimulate submucosal secretomotor neurons. The latter secrete acetylcholine (which binds to muscarinic receptors on epithelial cells) and VIP. Involvement of nerves was demonstrated by inhibition of bacterial toxin-induced secretion by hexamethonium (nicotinic), tetrodotoxin (Na(+) channel blocker), and lidocaine (visceral/mucosal afferents). Nicotinic receptors are present on secretomotoneurons and these are activated by release of acetylcholine from enteric interneurons or extrinsic efferent fibers. Specific organisms also modify other mechanisms that may contribute to development of acute diarrhea. Thus, mucin secretion, activation of motor mechanisms, increased mucosal permeability and inhibition of bile acid absorption have been reported in specific types of acute infectious diarrhea.

CONCLUSION

New therapies targeting neural and transmitter mediation including 5-HT, VIP, NPY, as well as toxin receptors and channels activated during acute infectious diarrhea could usher in a novel approach to enhancing glucose-electrolyte solutions used in the treatment of acute diarrhea.

Regulatory effects of Y4 receptor agonist (BVD-74D) on food intake

The objective of this study was to clarify the role of a novel agonist with high selectivity and affinity for Y4 receptors in the regulation of food intake. The Y4 receptor agonist BVD-74D was administered to C57BL/6J mice that were fed with a normal or high-fat diet, and to fatty liver Shionogi (FLS)-ob/ob mice; the food intake, water intake, and body weight gain were measured in these mice. In the mice fed with a normal diet, the cumulative food intake significantly decreased at 20 min and 1 h after the administration of 1 mg/kg of BVD-74D and at 1, 2, 4, 8, and 24 h after the administration of 10 mg/kg of BVD-74D. Moreover, the cumulative water intake and body weight gain significantly decreased in these mice. Among the mice that were fed with a high-fat diet, the cumulative food intake and water intake significantly decreased 1, 2, and 4 h after BVD-74D (10 mg/kg) administration. Furthermore, the cumulative food intake significantly decreased 2 and 4 h after BVD-74D (10 mg/kg) administration in the FLS-ob/ob mice. Thus, we propose that the novel Y4 receptor agonist BVD-74D has suppressive effects on food intake, water intake, and weight gain in normal mice fed with normal diets and on food intake in normal mice fed with high-fat diets and in FLS-ob/ob mice. These findings indicate that the Y4 receptor and its agonist would be promising targets for obesity.

NPY Y2 receptor agonist PYY(3-36) inhibits diarrhea by reducing intestinal fluid secretion and slowing colonic transit in mice

Peptide YY (PYY)(3-36), a neuropeptide Y (NPY) Y2 receptor agonist, is a powerful inhibitor of intestinal secretion. Based on this anti-secretory effect, NPY Y2 receptor agonists may be useful as novel anti-diarrheal agents, but anti-diarrheal efficacy has yet to be determined. We therefore examined the anti-diarrheal efficacy of PYY(3-36) and a selective Y2 receptor agonist, N-acetyl-[Leu28, Leu31]-NPY(24-36), in experimental mouse models of diarrhea. Intraperitoneal administration of PYY(3-36) (0.01-1mg/kg) and N-acetyl-[Leu28, Leu31]-NPY(24-36) (10mg/kg) significantly inhibited diarrhea (increase in wet fecal weight and diarrhea score) induced by dimethyl-prostaglandin E2, 5-hydroxytryptamine, and castor oil. Anti-diarrheal activities of PYY(3-36) and N-acetyl-[Leu28, Leu31]-NPY(24-36) were comparable to the effects of loperamide (1mg/kg), a widely used anti-diarrheal drug. To clarify the anti-diarrheal mechanisms of NPY Y2 receptor agonists, we investigated the effects of PYY(3-36) and N-acetyl-[Leu28, Leu31]-NPY(24-36) on intestinal fluid secretion and colonic transit. PYY(3-36) (1mg/kg) and N-acetyl-[Leu28, Leu31]-NPY(24-36) (10mg/kg) significantly reduced dimethyl-prostaglandin E2-induced intestinal fluid accumulation in conscious mice, suggesting that NPY Y2 receptor agonists inhibit diarrhea, at least in part, by reducing intestinal secretion. In addition, PYY(3-36) (0.01-1mg/kg) and N-acetyl-[Leu28, Leu31]-NPY(24-36) (10mg/kg) potently inhibited normal fecal output, suggesting that NPY Y2 receptor activation inhibits colonic motor function and NPY Y2 receptor agonists inhibit diarrhea partly by slowing colonic transit. These results indicate that NPY Y2 receptor agonists inhibit diarrhea in mice by not only reducing intestinal fluid secretion, but also slowing colonic transit, and illustrate the therapeutic potential of NPY Y2 receptor agonists as effective treatments for diarrhea.

Neuropeptide Y Y2 receptor in health and disease

We briefly survey the current knowledge and concepts regarding structure and function of the neuropeptide Y Y2 receptor and its agonists, especially as related to pharmacology of the receptor and its roles in pathological processes. Specific structural features are considered that could be responsible for the known compartmentalization and participation of the receptor in cell and tissue organization. This is further discussed in relation to changes of levels of the Y2 receptor in pathological conditions (especially in epilepsy and drug abuse), to endocytosis and recycling, and to participation in wound healing, retinopathy and angiogenesis. Properties of the receptor and of Y2 agonists are considered and reviewed in connection to the negative regulation of transmitter release, feeding, mood and social behavior. The possible involvement of the Y2 receptor in diabetes, carcinogenesis and bone formation is also reviewed.

Attenuation of acute experimental colitis by preventing NPY Y1 receptor signaling

Neuropeptide Y (NPY), a 36-amino acid peptide, is widely expressed in the central and peripheral nervous system. NPY is involved in the regulation of several physiological processes, including energy balance, food intake, and nociception. Recently, we showed that activation of the NPY Y1 receptor is required for cutaneous neurogenic inflammation. Because neurogenic inflammation could participate in colitis, the aim of this study was to investigate the role of the NPY Y1 receptor in acute colitis using mice genetically deficient of NPY Y1 receptor. In addition, the Y1 receptor antagonist H409/22, was also investigated. Animals received 5% dextran sulfate sodium (DSS) in drinking water for 7 days. One group of animals also received the Y1 receptor antagonist, administered intraperitoneally twice daily. Disease activity was assessed daily for 7 days in all groups. DSS induced colitis in all animals resulting in weight loss, diarrhea, epithelial damage, crypt shortening, and inflammatory infiltration. However, clinical manifestation of the disease was markedly attenuated in Y1 null mutant mice as well as in mice receiving the Y1 antagonist. Histological analysis showed that tissue damage and ulceration were less severe in Y1-deficient animals. Consistent with the clinical and histological data, capsaicin-induced plasma extravasation was significantly reduced in the gut of Y1 null mutant animals compared with treated wild-type animals. These data indicate that NPY and Y1 receptor are involved in intestinal inflammation and suggest that inhibition of NPY Y1 receptor signaling may provide a novel therapeutic approach in the treatment of colonic inflammation.

In vivo absorption of water and electrolytes in mouse intestine. Application to villin -/- mice

This study was done to establish and validate a single-pass perfusion method for measuring the absorption of water and electrolytes by the mouse small intestine. The method was then used to study intestinal absorption in mice whose villin gene had been invalidated (v-/-). The single-pass perfusion of the jejunum measures the absorption of water, Cl(-), Na(+), K(+), HCO, and glucose in anesthetized wild-type and v-/- mice in vivo. We measured absorption under basal and stimulated conditions (carbachol, vasoactive intestinal polypeptide, intralumen PGE(2)). Basal absorption and stimulated secretions were similar to those previously obtained in rats. There was no difference between wild-type and v-/- mice in animals with mixed genetic background or in pure C57BL6 mice. We conclude that this in vivo perfusion method is suitable for studying the absorption/secretion of electrolytes in the mouse intestine and that a lack of villin does not significantly alter basal and secretagogue-stimulated electrolyte movements across the epithelium of the mouse jejunum in vivo.

Structure and receptor binding of PYY analogs

Differences in the structure of PYY and two important analogs, PYY [3-36] and [Pro34]PYY, are evaluated. Y-receptor subtype ligand binding data are used in conjunction with structural data to develop a model for receptor subtype selective agonists. For PYY it is proposed that potent binding to Y1, Y4 and Y5 receptors requires the juxtaposition of the two termini while Y2 binding only requires the C-terminal helix. Further experiments that delineate between primary and tertiary structure contributions for receptor binding and activation are required to support the hypothesis that tertiary structure is stable enough to influence the expression of PYY's bioactivity.

PepT1-mediated epithelial transport of dipeptides and cephalexin is enhanced by luminal leptin in the small intestine

Dietary proteins are mostly absorbed as di- and tripeptides by the intestinal proton-dependent transporter PepT1. We have examined the effects of leptin on PepT1 function in rat jejunum and in monolayers of the human enterocyte-like 2 cell Caco-2. Leptin is produced by the stomach and secreted in the gut lumen. We show here that PepT1 and leptin receptors are expressed in Caco-2 and rat intestinal mucosal cells. Apical (but not basolateral) leptin increased Caco-2 cell transport of cephalexin (CFX) and glycylsarcosine (Gly-Sar), an effect that was associated with increased Gly-Sar uptake, increased membrane PepT1 protein, decreased intracellular PepT1 content, and no change in PepT1 mRNA levels. The maximal velocity (Vmax) for Gly-Sar transport was significantly increased by leptin, whereas the apparent Michaelis-Menten constant (Km) did not change. Furthermore, leptin-stimulated Gly-Sar transport was completely suppressed by colchicine, which disrupts cellular translocation of proteins to plasma membranes. Intrajejunal leptin also induced a rapid twofold increase in plasma CFX after jejunal perfusion with CFX in the rat, indicating enhanced intestinal absorption of CFX. These data revealed an unexpected action of gastric leptin in controlling ingestion of dietary proteins.

Structure-activity studies including a Psi(CH(2)-NH) scan of peptide YY (PYY) active site, PYY(22-36), for interaction with rat intestinal PYY receptors: development of analogues with potent in vivo activity in the intestine

Peptide YY (PYY) is a gut hormone that inhibits secretion and promotes absorption and growth in the intestinal epithelium. We have performed structure-activity studies with the active site, N-alpha-Ac-PYY(22-36)-NH(2), for interaction with intestinal PYY receptors. Investigation of aromatic substitutions at position 27 resulted in analogues that exhibited potent in vitro antisecretory potencies with N-alpha-Ac-[Trp(27)]PYY(22-36)-NH(2) exhibiting even greater potency than intact PYY. In vivo studies in dogs revealed that this analogue also promoted intestinal absorption of water and electrolytes during continuous intravenous and intraluminal infusion. Investigations carried out to identify features that would enhance stability revealed that incorporation of Trp(30) increased affinity for PYY receptors. A "CH(2)-NH" scan revealed that incorporation of reduced bonds at position 28-29 or 35-36 imparted greater receptor affinity. In general, disubstituted analogues designed based on the results of single substitutions exhibited good receptor affinity with N-alpha-Ac-[Trp(27),CH(2)-NH(35-36)]PYY(22-36)-NH(2) having the greatest affinity (IC(50) = 0.28 nM). Conservative multiple substitutions with Nle-->Leu and Nva-->Val also imparted good affinity. An analogue designed to encompass most of the favored substitutions, N-alpha-Ac-[Nle(24,28),Trp(30),Nva(31), CH(2)-NH(35-36)]PYY(22-36)-NH(2), exhibited a proabsorptive effect in dogs comparable to, but longer lasting than, that of intact hormone. Selected analogues also exhibited good antisecretory potencies in rats with N-alpha-Ac-[Trp(30)]PYY(22-36)-NH(2) being even more potent than PYY. However, the potencies did not correlate well with the PYY receptor affinity or the proabsorptive potencies in dogs. These differences could be due to species effects and/or the involvement of multiple receptors and neuronal elements in controlling the in vivo activity of PYY compounds. PYY(22-36) analogues exhibited good affinity for neuronal Y2 receptors but poor affinity for Y1 receptors. Also, crucial analogues in this series hardly bound to Y4 and Y5 receptors. In summary, we have developed PYY(22-36) analogues which, via interacting with intestinal PYY receptors, promoted potent and long-lasting proabsorptive and antisecretory effects in in vivo models. These compounds or analogues based on them may have useful clinical application in treating malabsorptive disorders observed under a variety of conditions.

Neural mechanism of the antisecretory effect of peptide YY in the rat colon in vivo

The purpose of this work was to determine the mechanism of the antisecretory effect of peptide YY in the rat colon and whether this effect is physiological. In this prospect, doses of exogenous peptide YY producing physiological and supraphysiological plasma levels were intravenously infused in rats provided with colonic and jejunal ligated loops in vivo, under secretory stimulation by vasoactive intestinal peptide. Peptide YY decreased the secretory effect of VIP in a dose-related fashion. The effect of peptide YY was blocked or strongly decreased by tetrodotoxin, hexamethonium, idazoxan, haloperidol, and the sigma antagonist BMY 14, 802 in both the colon and jejunum. We conclude that peptide YY decreases water and electrolyte secretion in the colonic mucosa by a complex neural mechanism involving at least two neurons connected through a nicotinic synapse, alpha-2 adrenoceptors and sigma receptors, and that this effect can occur with physiological doses of peptide YY.

Antisecretory effect of peptide YY through neural receptors in the rat jejunum in vitro

Basal short circuit current (Isc) was measured in stripped rat jejunum after addition of neural antagonists and of peptide YY (PYY). Basal Isc was slightly (by 10-21%) but significantly inhibited by tetrodotoxin, hexamethonium, idazoxan, and the sigma antagonist BMY 14,802. PYY (10(-7) M) reduced basal Isc by approximately 54%. This inhibition was unchanged by hexamethonium but reduced by 44-68% in the presence of tetrodotoxin, idazoxan, haloperidol, BMY 14,802, and atropine. The Y2 agonist pYY(3-36) was more potent than the Y1 agonist (Leu31,Pro34)PYY. In conclusion, PYY reduces basal Isc in rat jejunum in part through a neural mechanism involving muscarinic receptors, alpha2 adrenoceptors, and sigma receptors and, in part, through a direct effect on enterocytes. The PYY effect seems mainly carried out through Y2-receptor activation.

Pharmacological profile of the rat intestinal crypt peptide YY receptor vs. the recombinant rat Y5 receptor

Peptide YY and neuropeptide Y have potent antisecretory effects in rat small intestine. Scatchard analysis of [125I]peptide YY binding revealed a 10-fold higher concentration of receptors in rat jejunal crypt cells than in villus cells and no detectable receptors in colonic epithelium. Reverse transcription polymerase chain reaction analysis of neuropeptide Y Y5 receptor mRNA indicated that they are mainly expressed in rat jejunal crypts with very few or no expression in villus cells and colon epithelium, respectively. In order to determine whether neuropeptide Y Y5 receptors could represent the intestinal crypt receptor for peptide YY and neuropeptide Y, the ability of peptide YY, neuropeptide Y, pancreatic polypeptide and analogues to inhibit [125I]peptide YY binding to membrane prepared from rat crypt cells and COS-7 cells (African green monkey kidney cells) transfected with the rat neuropeptide Y Y5 receptor cDNA was tested. It appeared that several analogues displayed different inhibition constants (Ki) in the two binding assays, more especially N-alpha-acetyl-peptide YY-(22-36) which was 1200 x more potent in the crypt cell binding assay than in the recombinant neuropeptide Y Y5 receptor binding assay. These data support that the intestinal crypt peptide YY receptor is not a Y5 receptor. reserved.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Identification and distribution of mRNA encoding the Y1, Y2, Y4, and Y5 receptors for peptides of the PP-fold family in the rat intestine and colon

Peptide YY (PYY), neuropeptide Y (NPY) and pancreatic polypeptide (PP) are structurally related peptides which have potent antisecretory effects in small and/or large intestines. Receptors mediating these effects are still unknown with the exception of a PYY-preferring receptor expressed in small intestinal crypts. In the present study, expression of recently cloned Y1, Y2, and Y5 receptors which have similar affinity for PYY and NPY and Y4 receptors which have a high affinity for PP was investigated in gut by RT-PCR analysis. The data show that all Y receptors are expressed in small intestine and/or colon but with specific distributions. Y1 receptors are only expressed in nonepithelial colonic tissue, whereas Y2 and Y4 receptors are present in both epithelial and nonepithelial tissue of the small or large intestine. In contrast, Y5 receptor expression appears to be restricted to epithelial crypts of the small intestine and nonepithelial tissue of colon. Sequencing of PCR products showed 100% identity with the corresponding sequences of the cloned Y1, Y4, or Y5 receptors. The PCR product obtained with Y2 primers from rat crypt cells showed 84% identity with the cloned human Y2 receptor. These data indicate a wide distribution of Y receptors in small intestine and colon. They also suggest that Y1, Y2, Y4, and Y5 receptors may be responsible for still unexplained effects of PYY, NPY, or PP on secretion in small and large intestines.

Inhibitory effects of peptide YY on basal and VIP-stimulated short-circuit current in the rat jejunum: influence of technical conditions on observed results

The interaction of PYY and VIP was studied in stripped and intact rat jejunum preparations mounted in Ussing chambers. PYY decreased basal Isc in intact as well as in stripped jejunum. Stripping was necessary to evidence a stimulation of basal Isc by VIP. When PYY and VIP were administered at the same time in the serosal bath, their effects seemed additive; VIP stimulation took over when VIP was present in ten times larger amounts than PYY, while PYY inhibition predominated at isomolar concentrations (10(-7) M) of both peptides. However, when PYY was administered three to six minutes before isomolar amounts of VIP, the VIP stimulation developed without being notably hampered. At this time, however, the amount of radioimmunoassayable PYY in the serosal compartment represented still 60% of the added amount. In conclusion, the experimental conditions can significantly change the results: stripping the longitudinal muscle/myenteric plexus impairs the effect of PYY and VIP in a different fashion, while the timing and order of administration of the peptides may change the apparent interaction between VIP stimulation and PYY inhibition.

Neural modulation of the antisecretory effect of peptide YY in the rat jejunum

The endocrine and neural peptide, peptide YY, inhibits intestinal secretion of water and electrolytes in several animal species and in man. Peptide YY receptors have been evidenced on isolated rat jejunal crypt cells, but neural receptors are also likely to participate in the antisecretory effect of peptide YY in vivo. The aim of the present study was to investigate the mechanisms of the peptide YY effect on vasoactive intestinal peptide (VIP)-stimulated jejunal net water flux in the rat. Antagonist experiments using several drugs affecting neurally mediated processes were done for the purpose. A small peptide YY dose (10 pmol/kg) inhibited significantly (P < 0.005) the jejunal net water flux produced by 30 microg/kg per h of VIP. The inhibitory effect of peptide YY was suppressed, or strongly and significantly reduced, by tetrodotoxin, hexamethonium, lidocaine, idazoxan and BMY14,802 (51-(4-fluorophenyl)-4-(-4-(5-fluoro-2pyrimidinyl)-1-piperazinyl)- 1-butanol), whereas devazepide and L-NAME (L-omega-N-arginine methyl ester) had no effect. These results suggest that peptide YY inhibits VIP-stimulated jejunal net water flux in vivo through a neural mechanism implicating the participation of nicotinic synapses, alpha2-adrenoceptors and sigma receptors.