Enteric nerves in diabetic rats: increase in vasoactive intestinal polypeptide but not substance P

The distribution of vasoactive intestinal polypeptide (VIP) and substance P-like immunoreactivities was studied by immunohistochemistry in the myenteric plexus and circular muscle layer of the ileum and proximal colon of rats 8 wk after induction of diabetes with streptozotocin. A consistent increase was observed in fluorescence intensity of VIP-like immunoreactivity in the nerve fibers, and intensely stained cell bodies were significantly more frequent in the myenteric plexus of the ileum (p less than 0.001) from diabetic animals. Some varicosities of VIP-like immunoreactive fibers in the myenteric plexus appeared to be enlarged. Vasoactive intestinal polypeptide-like immunoreactivity was increased and VIP-like immunoreactive nerves appeared thicker in the circular muscle layer of both diabetic ileum and proximal colon. The VIP levels were measured biochemically in tissue consisting of the smooth muscle layers and myenteric plexus. A significant increase in the VIP content per centimeter of intestine was found in both the ileum (p less than and proximal colon (p less than 0.01) from diabetic rats. In contrast, no apparent change in substance P innervation was observed immunohistochemically in the myenteric plexus and circular muscle layer of either diabetic ileum or proximal colon when compared with controls. The results are discussed in relation to the symptoms of autonomic neuropathy of the gut in diabetes.     

Exaggeration of the cholecystokinin-induced motor response in the cat gastrointestinal tract

A stimulation of distal colonic motor activity was produced in anesthetized cats following intravenous administration of cholecystokinin. The contractile response elicited by cholecystokinin was not reduced following pretreatment with atropine. However, when animals were treated with agents which increased the net cholinergic input to the colon, a marked exaggeration of the subsequent cholecystokinin-induced response occurred. This cholinergically mediated exaggeration was produced following administration of the cholinergic agonist bethanechol, or after removal of tonic inhibitory systems mediated by prostaglandin or alpha-adrenergic input, whose blockade results in atropine-sensitive colonic stimulation. Cholecystokinin was also found to produce stimulation of motor activity in the pylorus, jejunum, proximal colon and gallbladder. Cholinergically mediated exaggeration of the cholecystokinin response was also present in the pylorus and proximal colon, but not gallbladder or jejunum. An inhibition of spontaneous motor activity was produced in the ileum or duodenum following cholecystokinin administration.     

Human distribution and release of a putative new gut hormone, peptide YY

A radioimmunoassay has been developed for the new intestinal hormonal peptide tyrosine tyrosine [peptide YY (PYY)]. Peptide YY concentrations were measured in separated layers of the human gastrointestinal tract, where PYY was found exclusively in the mucosal epithelium which contained the endocrine cells. Peptide YY was found throughout the small intestine, in very low concentrations (5 pmol/g) in duodenum (6 pmol/g) and jejunum (5 pmol/g), but in higher concentrations in the terminal ileum (84 pmol/g). High concentrations were found throughout the colon (ascending 82 pmol/g, sigmoid 196 pmol/g), being maximum in the rectum (480 pmol/g). The major molecular form of PYY-like immunoreactivity in human intestine appeared to be identical to pure porcine hormone, both as judged by gel permeation chromatography and by reverse-phase high-pressure liquid chromatography. Basal plasma concentrations of PYY were low but rose in response to food, remaining elevated for several hours postprandially. The known potent biologic actions of PYY, its high concentrations in gut endocrine cells, and its release into the circulation after a normal meal suggest that this peptide may function physiologically as a circulating gut hormone.     

替加色罗对肝硬化大鼠肠传输功能的影响

目的研究替加色罗对肝硬化大鼠肠道传输功能的影响,探讨其可能的作用机制。方法24只Wister大鼠随机分为肝硬化模型组、肝硬化替加色罗组和正常对照组,采用葡聚糖蓝-2000为胃肠内标记物,观察大鼠肠道传输的变化,同时放射免疫测定大鼠血浆：肠道组织中胃动素（MTL）、血管活性肠肽（VIP）及P物质（SP）含量的变化,乙酰胆碱酯酶（Ache）组织化学染色,观察肝硬化大鼠小肠肌间神经丛胆碱能神经的变化,并对其分布进行定量分析。结果与对照组比较,肝硬化模型组大鼠小肠动力显著减弱（P〈0.01）,血浆及空肠组织中MTL、VIP的含量明显增加,SP的含量则显著减少（P〈0.01）,小肠肌间神经丛胆碱能神经的分布明显减少（P〈0.01）;肝硬化替加色罗组大鼠小肠动力与对照组比较无明显差异,血浆及空肠组织中MTL、VIP的含量与模型组比较无明显差异,SP的含量及肠肌间神经丛胆碱能神经的分布则与肝硬化模型组差异显著（P〈0.01）。结论替加色罗对肝硬化大鼠小肠运动功能减退有明显改善作用,其机制可能与SP及肌间神经丛胆碱能神经的分布变化有关,而MTL、VIP可能未参与其作用。     

Time course of adaptive regulatory peptide changes following massive small bowel resection in the dog

Basal and postprandial concentrations of gastrointestinal hormones were measured in 12 dogs before and at one and three months after a 75% small bowel resection. Five animals were studied again at six months. Concentrations of enteric hormones and neuropeptides, measured in the proximal jejunum and distal ileum adjacent to the anastomotic site at the time of euthanasia, were compared with concentrations in control tissues taken from each animal at the time of resection. Increased basal and postprandial levels of gastrin (P<0.05), cholecystokinin (CCK,P<0.05), glucose-dependent insulinotropic peptide (GIP,P<0.01), peptide YY (PYY,P<0.001), and enteroglucagon (P<0.001), were seen at one month after small bowel resection. In contrast, no significant changes were seen in concentrations of secretin, motilin, neurotensin, somatostatin, PP, or glucagon. Concentrations of enteroglucagon, GIP, and PYY remained high throughout the six-month study period. In contrast, gastrin and CCK had normalized by three months. Thus, only enteroglucagon, PYY, and GIP showed sustained elevations following enterectomy; the gastrin and CCK changes were transient. Following enterectomy, concentrations of vasoactive intestinal polypeptide (VIP) were reduced by about 50% in mucosal (P<0.001) and muscle (P<0.05) layers of proximal and distal gut. In contrast, calcitonin gene-related peptide (CGRP) was increased by about twofold in jejunal and ileal mucosa (P<0.05), and CGRP elevations were even more marked in the muscle layers (P<0.001). Somatostatin and neuropeptide Y (NPY) concentrations were similar to controls in all areas except for a small decrease in NPY in ileal mucosa (P<0.05). These findings suggest that the increased motilin and PP concentrations previously reported after bowel resection in man are more likely to reflect underlying inflammatory bowel disease rather than enterectomy. The normalization of hypergastrinemia explains why the increased acid secretion after small bowel resection is transient. These results provide evidence for independent secretory control of enteroglucagon and PYY, which are both products of intestinal L cells. In addition, these studies reveal marked changes in enteric neuropeptide concentrations following bowel resection. VIP, which is thought to be a major inhibitory transmitter in the gut, is markedly reduced, while CGRP, which is mainly localized in sensory afferent fibers, is increased. These major neuropeptide changes are likely to be of importance in the adaptive responses to massive small bowel resection.Presented at the annual Meeting of the American Gastroenterological Association in Boston, May 1993, and published in abstract form inGastroenterolgy 104:A232 and A468, 1993.     

Distribution of the gut hormones in the primate intestinal tract.

Reliable and specific radioimmunoassays have been developed for the gut hormones secretin, gastrin, cholecystokinin, pancreatic glucagon, VIP, GIP, motilin, and enteroglucagon. Using these assays, the relative pattern of distribution of the gut hormones has been determined using the same bowel extracts for all measurements. VIP occurred in high concentration in all regions of the bowel, whereas secretin, GIP, motilin, and CCK were predominantly localised in the proximal small intestine. Pancreatic glucagon was almost exclusively confined to the pancreas. Like VIP, enteroglucagon also exhibited a wide pattern of distribution but was maximal in the ileum. The acid ethanol extraction method that was used was found to be unsuitable for gastrin. On gel chromatography of the extracts, motilin and VIP eluted as single molecular species in identical position to the pure porcine peptides. CCK, pancreatic glucagon, enteroglucagon and GIP were all multiform.     

Neuroendocrine peptides of the gastrointestinal tract of an animal model of human type 2 diabetes mellitus

We studied ten obese diabetic mice (Umeå/ Bom-ob) and 10 homozygous lean controls aged 21 weeks. The concentration of several neuroendocrine peptides was determined by radioimmunoassay of tissue extracts of antrum, duodenum and distal colon. The neuroendocrine peptides that we investigated were: secretin, gastric inhibitory polypeptide (GIP), gastrin, motilin, peptide YY (PYY), somatostatin, vasoactive intestinal polypeptide (VIP), substance P, neurotensin, neuropeptide Y (NPY) and galanin. In the antrum, gastrin, somatostatin, VIP, substance P and NPY concentrations were significantly lower in obese diabetic mice than in the lean controls. There was no statistical difference between the obese mice and lean controls for neurotensin and galanin content. In the duodenum, the concentration of substance P was lower in the obese diabetic mice than in lean mice. There was no statistical difference between obese diabetic mice and lean controls regarding the concentration of secretin, GIP, motilin, gastrin, somatostatin, VIP, neurotensin, NPY or galanin. In the colon, the levels of PYY, somatostatin, VIP, substance P, NPY and galanin were significantly lower in the obese diabetic mice than the lean controls. The concentration of neurotensin in the obese mice did not differ from that in the lean controls. The present study showed that the neuroendocrine system is disturbed in an animal model of human type 2 diabetes and that this disturbance differs from that observed in other animal models of human type 1 diabetes. The present findings may have some implications for the gastrointestinal dysfunction observed in patients with type 2 diabetes.     

Abnormal levels of neuropeptide Y and peptide YY in the colon in irritable bowel syndrome

OBJECTIVE: To assess the levels of gut peptides involved in gastrointestinal motor, secretory and sensory function in colonic biopsies in irritable bowel syndrome (IBS) patients and healthy controls. METHODS: We studied 34 patients with IBS and 15 subjects without gastrointestinal symptoms. The predominant bowel pattern in the IBS patients was constipation in 17 patients (IBS-C) and diarrhoea in 17 patients (IBS-D). With radioimmunoassay, the levels of vasoactive intestinal peptide (VIP), substance P, neuropeptide Y (NPY) and peptide YY (PYY) were analysed in biopsies from the descending colon and ascending colon obtained during colonoscopy. RESULTS: The IBS patients had lower levels of PYY in the descending colon than the controls, but the levels in the ascending colon did not differ. The NPY levels were lower in IBS-D than in IBS-C, both in the ascending colon and in the descending colon. Low levels of VIP were more common in IBS patients, but mean levels did not differ between groups. No group differences were observed for substance P. The levels of VIP, substance P and NPY were higher in the ascending colon than in the descending colon, whereas the opposite pattern was seen for PYY. CONCLUSION: IBS patients demonstrate lower levels of PYY in the descending colon than controls. Colonic NPY levels differ between IBS subgroups based on the predominant bowel pattern. These findings may reflect the pathophysiology of IBS and the symptom variation within the IBS population.     

Myenteric plexus in streptozotocin-treated rats. Neurochemical and histochemical evidence for diabetic neuropathy in the gut

Adrenergic, cholinergic, and serotoninergic nerves were studied in the myenteric plexus of ileum and colon from streptozotocin-treated rats, an animal model of juvenile-onset diabetes. In view of clinical reports implicating diabetic autonomic neuropathy as the cause of gastrointestinal dysfunction in diabetes mellitus, neurochemical and histochemical techniques were used to study changes in the innervation of the gut. In the myenteric plexus of the ileum from diabetic animals, adrenergic nerves displayed signs of degeneration and the brightness of fluorescence in serotoninlike immunoreactive nerves was lower. Cholinergic nerves, however, did not display any signs of reduction in the ileum, and both choline acetyltransferase and acetylcholinesterase activities per centimeter were increased. In contrast, in the proximal colon 8 wk after induction of diabetes, neurochemical assays revealed significant increases in noradrenaline and serotonin levels as well as choline acetyltransferase activity, although no obvious changes in the pattern of innervation could be detected histochemically. The results indicate that changes do occur in the innervation of the gut of the streptozotocin-diabetic model shortly after the induction of diabetes, although they differ significantly in the ileum and colon; these may be of relevance to the types of gastrointestinal dysfunction displayed in human diabetes.     

Human gut hormone profiles in patients with short bowel syndrome

We have studied gut hormone profiles in a small number of patients on treatment with home parenteral nutrition following near-total enterectomy who had no evidence of Inflammatory bowel disease and who were otherwise healthy. These and age- and sex-matched controls had gut hormone profiles measured after an overnight fast and a standard test meal. Circulating pancreatic glucagon concentrations and profiles were the same in both groups as were the Neurotensin and VIP. Peptide YY (PYY) concentrations and profiles were markedly raised in the short bowel group. It is suggested that the normal glucagon responses reflect the integrity of the remaining duodenum and pancreas. Circulating neurotensin and VIP originate largely from outside the bowel and so the removal of the gut source does not significantly affect their profiles. Enteroglucagon and PYY are secreted from terminal ileum and colon in response to unabsorbed food residues. The elevated circulating levels and profiles are consistent with those observed by others in patients with jejunoileal bypass or major resections in whom unabsorbed nutrients reach the colon.     

Intraduodenal and Intrajejunal Administration of the Herbal Medicine, Dai-Kenchu-Tou, Stimulates Small Intestinal Motility via Cholinergic Receptors in Conscious Dogs

The aim of the present study was to study the effect and mechanism of action of intraduodenal and intrajejunal dai-kenchu-to, an herbal medicine clinically effective for uncomplicated postoperative adhesive intestinal obstruction, on upper gastrointestinal motility. Five mongrel dogs were equipped with four strain-gauge force transducers on the antrum, duodenum, and proximal and distal jejunum to measure contractile activity. Dai-kenchu-to (0.5, 1.5, and 3.0 g) was administered into the duodenal or proximal jejunal lumen. The effect of atropine, hexamethonium, phentolamine, propranolol, and ondansetron on intraduodenal and intrajejunal dai-kenchu-to-induced contractions was studied. Plasma motilin was measured by specific radioimmunoassay. Intraduodenal and intrajejunal dai-kenchu-to induced phasic contractions in the duodenum and proximal jejunum, respectively, and those contractions migrated distally. Phasic contractions induced by intraduodenal and intrajejunal dai-kenchu-to were inhibited by atropine and hexamethonium at all sites. Plasma motilin was not affected by dai-kenchu-to. Intraduodenal and intrajejunal dai-kenchu-to stimulates upper gastrointestinal motility at and distal to the administration sites through cholinergic receptors.     

Somatostatin inhibits motilin-induced interdigestive contractile activity in the dog

The interaction between motilin and somatostatin on gastrointestinal motor activity was studied in fasted, unanesthetized dogs. Contractions of the stomach, duodenum, jejunum, and ileum were recorded with extraluminal strain gage force transducers. Motilin initiated a pattern of contractile activity which closely resembled phase III of the interdigestive motor complex. Somatostatin delayed the onset of the motilin response and reduced motor activity in the stomach and the jejunum. During somatstatin infusion the motilin-induced contractile pattern did not migrate to the jejunum. The cycle of natural interdigestive motor complexes was also interrupted by somatostatin. Somatostatin alters natural and motilin-induced interdigestive migrating motor complexes of the canine gastrointestinal tract.     

Measurement of gut hormonal peptides in biopsies from human stomach and proximal small intestine.

Using sensitive and specific radioimmunoassays, concentrations of hormonal peptides have been measured in small biopsies taken from the human stomach, duodenum, and proximal jejunum. Comparison is made of these hormone concentrations and the number of respective endocrine cells present determined by quantitative immunocytochemistry. Immunoreactive somatostatin, VIP, motilin, and gastrin were detected in all regions examined, whereas secretin and GIP were undetectable in antral extracts. Enteroglucagon-like immunoreactivity was present only at and beyond the ligament of Treitz, although a few enteroglucagon-producing cells were shown by immunocytochemistry in the duodenum. The variation of hormone concentration was found to be small in these biopsies of normal tissue within each region of the gut examined, indicating that representative hormone concentrations may be reliably obtained from small biopsy tissues. An attempt has been made to establish reference values for gut hormone concentrations in such biopsies; this may allow future study of any changes in concentration that may occur in pathological conditions.     

Glucagon, secretin and vasoactive intestinal polypeptide immunoreactivities in rat gut after jejuno-ileal bypass and resection

Jejuno-ileal bypass (JIB) and resection are associated with hyperplastic and other changes in residual functional gut. In studies on endocrine changes, circulating hormone levels are usually measured. In this study with Sprague-Dawley rats, glucagon, secretin and vasoactive intestinal polypeptide (VIP), immunoreactivities were measured in extracts of gut tissues including formerly adjacent segments of functional and bypassed jejunum and ileum. Young adult (200-220 g) and mature (404-440 g) rats received greater than 90% JIB. Though slight differences were observed in the response of the young and old rats to the operations, and between the effects of JIB and resection, the results do not indicate major involvement of secretin, VIP or gut glucagon-like immunoreactivity in the effects of surgery. Changes include increased immunoreactivity of secretin in the upper and of VIP in the lower functional gut following JIB. N-terminal-to central glucagon immunoreactivity in the functional ileum did not change substantially after operations, but was significantly lower in the non-functional than functional ileum after bypass. Plasma levels of this immunoreactivity were higher following operations and highest following resection.     

Contractile responses to natural tachykinins and selective tachykinin analogs in normal and inflamed ileal and colonic muscle

BACKGROUND: Tachykinins and acetylcholine are main physiological motility stimulators in the gut by their effects exerted through neurokinin and muscarinic receptors. METHODS: Longitudinal and circular muscle strips from normal ileum and colon or corresponding tissues from patients with inflammatory bowel disease were studied in organ baths. Contractile responses to the tachykinins substance P, neurokinin A, neurokinin B and neuropeptide gamma and specific analogs for their respective receptors were compared to acetylcholine. RESULTS: Acetylcholine caused concentration-dependent phasic contractions in longitudinal and circular muscle of normal ileum and colon (both P < 0.01). In inflamed tissues, contractile responses were reduced to 17%-33% in ileum (P < 0.05) and 3%-26% in colon (P < 0.01). Both natural tachykinins and their specific analogs caused concentration-dependent phasic, tonic and rhythmic contractions (each P < 0.01). Neuropeptide gamma was most potent in contracting the ileum and colon, followed by neurokinin A, substance P and neurokinin B, let alone longitudinal muscle of the ileum where neuropeptide gamma and neurokinin A were equipotent. Of the tachykinin analogs, Nle10-NKA(4-10) was more potent than substance P methyl ester and senktide, indicating neurokinin 2 receptors are predominant for contractile effects of tachykinins. In inflamed tissues, contractile responses to tachykinins were reduced to 0%-42% in ileum (P < 0.05) and 0%-17% in colon (P < 0.01) compared to controls. CONCLUSION: In humans, tachykinins exert gut contractile effects, of similar strength as acetylcholine, predominantly through activation of neurokinin 2 receptors. These responses are greatly reduced in inflamed tissues of ulcerative colitis and Crohn disease.     

Effects of vasoactive intestinal peptide and pancreatic polypeptide in rabbit intestine.

The effects of porcine vasoactive intestinal peptide (VIP) and bovine pancreatic polypeptide (PP) on jejunal, ileal, and colonic fluid transport were studied in the rabbit. VIP produced secretion in the small intestine (jejunum greater than ileum) but did not affect absorption in the colon. PP had no secretory effects in jejunum, ileum, or colon. The small intestinal secretion induced by VIP was not associated with raised cAMP concentrations in the mucosa; this suggests that the secretory effects of VIP in vivo are mediated by a mechanism other than stimulation of adenylate cyclase.     

Peptide YY kinetics and effects on blood pressure and circulating pancreatic and gastrointestinal hormones and metabolites in man

Peptide YY (PYY) is a 36 amino acid peptide produced by mucosal endocrine cells of the ileum and colon which inhibits acid secretion and intestinal transit in man. To assess its effects on metabolites and digestive hormones PYY was infused into 18 fasting normal subjects at three dose levels (0.06, 0.19, and 0.57 pmol kg-1 min-1), each for a period of 1 h. During the infusions mean plasma PYY levels increased by 8, 25, and 73 pmol/liter, respectively. The mean disappearance half-time on stopping the infusions was 9.2 +/- 0.4 (SEM) min. The mean MCR was 7.3 +/- 0.7 ml kg-1 min-1 and the apparent volume of distribution was calculated to be 94 +/- 9 ml kg-1. During the highest dose infusion there was a significant increase in both systolic and diastolic blood pressure, of 8.6 +/- 3.7 mmHg (P less than 0.05) and 10.9 +/- 3.0 mmHg (P less than 0.01), respectively. PYY caused a significant 50% reduction in plasma pancreatic polypeptide concentrations (P less than 0.05) and a 55% reduction in circulating motilin levels (P less than 0.05). PYY had no significant effect on circulating concentrations of insulin, glucagon, gastrin, gastric inhibitory peptide, neurotensin, enteroglucagon, or vasoactive intestinal peptide. PYY also had no significant effect on circulating concentrations of glucose, lactate, glycerol, or nonesterified fatty acids. This recently discovered human intestinal hormonal peptide thus has significant effects both on gastrointestinal hormones (motilin and pancreatic polypeptide) and blood pressure in man, but appears not to influence glucose or lipid metabolism.     

Intragastric Capsaicin Stimulates Motility of Upper Gut and Proximal Colon via Distinct Pathways in Conscious Dogs

The aim of the present study was to investigatethe effect and mechanism of action of intragastric andintraduodenal capsaicin on gastrointestinal motility.Five mongrel dogs were equipped with eight strain gauge force transducers on the stomach, smallintestine, and proximal colon. In the interdigestivestate, capsaicin was administered into the gastric orduodenal lumen. The effects of atropine, hexamethonium, ondansetron, and FK888 on capsaicin-inducedcontractions were studied. Intragastric capsaicininduced contractions within 15 min in the gastricantrum, duodenum, proximal jejunum, and proximal colon.These stimulatory effects were inhibited by atropineat all sites; by hexamethonium in the small intestineand colon; by ondansetron in the antrum, duodenum, andcolon; and by FK888 in the antrum and colon,respectively. Intraduodenal capsaicin had no effect oncontractility. Stimulation of afferent fibers bycapsaicin in the stomach but not in the duodenumaugments contractile activity in local and distantregions of the gut via distinct pathways.     

Distribution and development of peptidergic nerves and gut endocrine cells in mice with congenital aganglionic colon, and their normal littermates

Studies were made of the distribution of gut hormones and neuropeptides in the gastrointestinal tract of mice with hereditary aganglionic colon (s1/s1) and their normal littermates. Antisera to substance P, vasoactive intestinal polypeptide, and enkephalins demonstrated markedly diminished numbers of immunofluorescent nerve fibers in the aganglionic segment of colon; in contrast, in proximal colon and small intestine the distribution of peptidergic nerve fibers was essentially normal. Mucosal endocrine cells were demonstrated in the colon by antisera to substance P, somatostatin, glucagon, and cholecystokinin; in each case there were similar numbers of cells in s1/s1 and normal mice. Radioimmunoassays for vasoactive intestinal polypeptide and bombesin showed diminished concentrations of immunoreactive material in the aganglionic segment of colon of 16-17-day-old animals. However, assays for CCK--which is predominantly located in endocrine cells--showed similar concentrations of immunoreactive material throughout the gut of s1/s1 and normal mice. It was of interest that the concentrations of immunoreactive substance P were lower than normal not only in the aganglionic segment of colon, but also in proximal colon and distal small intestine, and that at all ages the development of substance P in the intestine was delayed in the s1/s1 mice. The results are consistent with the idea that the constriction of the aganglionic segment of colon develops as a consequence of lack of intrinsic inhibitory neurons, possibly those containing vasoactive intestinal polypeptide. The presence of an aganglionic segment is attributable to delayed migration of the neuroblasts from the neural crest. Thus the findings of normal populations of gut endocrine cells in the aganglionic segment is further support for the view that the embryologic origin of gut endocrine cells is different to that of gut neurons.