Neural somatostatin, vasoactive intestinal polypeptide and substance P in canine and human jejunum

The human enteric nervous system. Historical and modern advances. Collaboration between science and surgery

BACKGROUND

There are considerable advantages and opportunities for surgeons and trainee surgeons in conducting a period of research allied with basic scientists. Such clinicians are well placed to define relevant clinical questions, provide human material (tissue, biopsy and blood) and translate the techniques derived in experimental animals to human subjects.

METHODS

This small review explores research conducted on the nervous system of the intestines, with an emphasis on the translation of findings from animal to human.

RESULTS

This work shows that new techniques of immunohistochemistry and retrograde tracing, developed in animal tissue, have greatly expanded our knowledge of the structure of the human enteric nervous system.

CONCLUSIONS

Such findings have sparked therapeutic trials for the treatment of gastrointestinal disorders in patients.

5-HT containing enteroendocrine cells characterised by morphologies, patterns of hormone co-expression, and relationships with nerve fibres in the mouse gastrointestinal tract

5-HT containing enteroendocrine cells (EEC), the most abundant type of EEC in the gut, regulate many functions including motility, secretion and inflammatory responses. We examined the morphologies of 5-HT cells from stomach to rectum, patterns of hormone co-expression in the stomach and colon, and the relationship of 5-HT cells with nerve fibres. We also reviewed some of the relevant literature. The morphologies of 5-HT cells were distinct, depending on their location in the gut. A noticeable feature of some 5-HT cells in the antrum and colon was their long basal processes, which resembled processes of neurons, whereas 5-HT cells in the small intestinal mucosa lacked basal processes. In the stomach, numerous 5-HT cells, including cells with basal processes, were identified as enterochromaffin-like cells by their expression of histidine decarboxylase. In the colon, we observed a small number of 5-HT cells that were in close contact with, but distinct from, oxyntomodulin (OXM) and PYY immunoreactive EEC. We did not find specific relationships between nerve fibres and the processes of colonic 5-HT cells. We conclude that five major features, i.e., gut region, morphology, hormone content, receptor repertoire and cell lineage, can be used to define 5-HT cells.

Vasoactive Intestinal Polypeptide (VIP) in the Intestinal Mucosal Nerve Fibers in Dogs with Inflammatory Bowel Disease

Simple Summary

Canine inflammatory bowel disease (IBD)—a group of gastrointestinal disorders—is a serious problem in veterinary medicine. The etiology of IBD remains unknown, and its diagnosis and effective treatment are difficult. One of the less-known aspects of IBD pathology is the influence of this disease on the enteric nervous system, which is located in the intestinal wall and regulates most of the gastrointestinal functions. Therefore, the aim of the present study was to evaluate the influence of IBD on the intramucosal nerve fibers containing vasoactive intestinal polypeptide (VIP). VIP is one of the most important substances produced by the enteric nervous structures that is involved in many regulatory processes in the gastrointestinal tract. The obtained results show that IBD induces changes in the density of intramucosal VIP-positive nerve fibers in the canine gastrointestinal tract. It suggests that VIP is involved in the pathological processes occurring during this disease. Observed changes may be a result of neuroprotective and/or adaptive processes regulated by VIP, aimed at the homeostasis maintenance in the inflamed gastrointestinal (GI) tract and induced by proinflammatory factors.

Abstract

Canine inflammatory bowel disease (IBD) is a group of enteropathies with nonspecific chronic symptoms and poorly understood etiology. Many aspects connected with IBD are not understood. One of them is the participation of the intestinal nervous system in the development of pathological processes. Thus, this study aimed to demonstrate changes in the density of intramucosal nerve fibers containing vasoactive intestinal polypeptide (VIP)—one of the most important intestinal nervous factors caused by the various stages of IBD development. Mucosal biopsy specimens collected from the duodenum, jejunum and descending colon of healthy dogs and dogs with varied severity of IBD were included in the experiment. The density of VIP-like immunoreactive (VIP-LI) nerves was determined by a single immunofluorescence technique and a semi-quantitative method consisting in VIP-LI fiber counts in the field of view (0.1 mm²). The obtained results indicate that IBD induces changes in the density of mucosal VIP-LI nerve fibers in the canine gastrointestinal tract. The initial decrease is followed by an increase in VIP-like immunoreactivity in successive stages of the disease. These observations show that VIP is a neuronal factor that participates in the pathological processes connected with canine IBD. The observed changes probably result from the neuroprotective and/or adaptive properties of VIP. Protective and adaptive reactions induced by inflammation aim to protect the GI tract against damage by proinflammatory factors and ensure the homeostasis in the enteric nervous system (ENS) under the conditions changed by the disease process.

Distributions and relationships of chemically defined enteroendocrine cells in the rat gastric mucosa

This paper provides quantitative data on the distributions of enteroendocrine cells (EEC), defined by the hormones they contain, patterns of colocalisation between hormones and EEC relations to nerve fibres in the rat gastric mucosa. The rat stomach has three mucosal types: non-glandular stratified squamous epithelium of the fundus and esophageal groove, a region of oxyntic glands in the corpus, and pyloric glands of the antrum and pylorus. Ghrelin and histamine were both contained in closed cells, not contacting the lumen, and were most numerous in the corpus. Gastrin cells were confined to the antrum, and 5-hydroxytryptamine (5-HT) and somatostatin cells were more frequent in the antrum than the corpus. Most somatostatin cells had basal processes that in the antrum commonly contacted gastrin cells. Peptide YY (PYY) cells were rare and mainly in the antrum. The only numerous colocalisations were 5-HT and histamine, PYY and gastrin and gastrin and histamine in the antrum, but each of these populations was small. Peptide-containing nerve fibres were found in the mucosa. One of the most common types was vasoactive intestinal peptide (VIP) fibres. High-resolution analysis showed that ghrelin cells were closely and selectively approached by VIP fibres. In contrast, gastrin cells were not selectively innervated by VIP or CGRP fibres. The study indicates that there are distinct populations of gastric EEC and selective innervation of ghrelin cells. It also shows that, in contrast to EEC of the small intestine, the majority of EEC within the stomach contained only a single hormone.

What neurons hide behind calretinin immunoreactivity in the human gut?

Calretinin (CALR) is often used as an immunohistochemical marker for the histopathological diagnosis of human intestinal neuropathies. However, little is known about its distribution pattern with respect to specific human enteric neuron types. Prior studies revealed CALR in both myenteric and submucosal neurons, most of which colabel with choline acetyl transferase (ChAT). Here, we specified the chemical code of CALR-positive neurons in small and large intestinal wholemounts in a series of 28 patients. Besides other markers, we evaluated the labeling pattern of CALR in combination with vasoactive intestinal peptide (VIP). In colonic submucosa, CALR and VIP were almost completely colocalized in about three-quarters of all submucosal neurons. In the small intestinal submucosa, both the colocalization rate of CALR and VIP as well as the proportion of these neurons were lower (about one-third). In the myenteric plexus of both small intestine and colon, CALR amounted to 11 and 10 %, respectively, whereas VIP to 5 and 4 % of the whole neuron population, respectively. Colocalization of both markers was found in only 2 and 3 % of myenteric neurons, respectively. In section specimens, nerve fibers coreactive for CALR and VIP were found in the mucosa but not in the muscle coat. Summarizing the present and earlier results, CALR was found in at least one submucosal and two myenteric neuron populations. Submucosal CALR+/VIP+/ChAT± neurons innervate mucosal structures. Furthermore, CALR immunoreactivity in the myenteric plexus was observed in morphological type II (supposed primary afferent) and spiny type I (supposed inter- or motor-) neurons.

Substance P- and choline acetyltransferase immunoreactivities in somatostatin-containing, human submucosal neurons

The submucous layers of human small and large intestines contain at least two separate neuron populations. Besides morphological features, they differ in their immunoreactivities for calretinin (CALR) and somatostatin (SOM), respectively. In this study, submucosal wholemounts of 23 patients or body donors (including all segments of small intestine and colon) were immunohistochemically quadruple stained for CALR and SOM as well as for substance P (SP) and choline acetyltransferase (ChAT). We found that all SOM-positive neurons co-stained for ChAT and the majority for SP [between 50% in the small intestinal external submucosal plexus (ESP) and 75% in the colonic ESP]. In contrast, a majority of CALR-neurons contained ChAT (between 77% in the small intestinal ESP and 92% in the large intestinal ESP) whereas less than 4% of CALR-neurons were co-immunoreactive for SP. Another set of wholemounts was co-stained for peripherin, a marker enabling morphological analysis. Where identifiable, both SOM alone- and SOM/SP-neurons displayed a uniaxonal (supposed pseudouniaxonal) morphology. We suggest that the chemical code of SOM-immunoreactive, human submucosal neurons may be "ChAT+/SOM+/SP±". In additional sections double stained for SOM and SP, we regularly found double-labelled nerve fibres only in the mucosa. In contrast, around submucosal arteries mostly SOM alone- fibres were found and the muscularis propria contained numerous SP-alone fibres. We conclude that the main target of submucosal SOM(/SP)-neurons may be the mucosa. Due to their morpho-chemical similarity to human myenteric type II neurons, we further suggest that one function of human submucosal SOM-neurons may be a primary afferent one.

Somatostatin in inflammatory bowel disease

Intestinal inflammation is controlled by various immunomodulating cells, interacting by molecular mediators. Neuropeptides, released by enteric nerve cells and neuroendocrine mucosa cells, are able to affect several aspects of the general and intestinal immune system, with both pro- as well as anti-inflammatory activities. In inflammatory bowel disease (IBD) there is both morphological as well as experimental evidence for involvement of neuropeptides in the pathogenesis. Somatostatin is the main inhibitory peptide in inflammatory processes, and its possible role in IBD is discussed.

Calretinin and somatostatin immunoreactivities label different human submucosal neuron populations

In human myenteric plexus, calretinin (CALR) and somatostatin (SOM) coexist in Dogiel Type II neurons, which were considered as intrinsic primary afferent neurons in the guinea pig. The aims of this study were to test if also human submucosal neurons costain immunohistochemically for CALR and SOM and whether these or other neurons display Type II morphology. Two sets of submucosal wholemounts of small and large intestine from 29 patients (median age 65 years) were triple stained for CALR, SOM, and human neuronal protein Hu C/D (HU, a pan-neuronal marker) as well as for CALR, SOM, and peripherin (PER), respectively. Only exceptionally, neurons coreactive for both CALR and SOM were found. The three major groups of neurons were CALR-/HU-coreactive (CALR-neurons), SOM-/HU-coreactive (SOM-neurons), and HU-alone-positive neurons. We observed significantly more CALR-neurons in the external submucosal plexus (ESP) of all regions and more SOM-neurons in the internal submucosal plexus (ISP), although with substantial interindividual variations. Comparisons of small vs. large intestine revealed more SOM-neurons (ESP: 29% vs. 4%, ISP: 40% vs. 13%) but fewer CALR-neurons (ESP: 37% vs. 77%, ISP: 21% vs. 67%) in small intestine. Morphologically, CALR-neurons had multiple processes; in some cases, we identified multidendritic/uniaxonal neurons. In contrast, SOM-neurons had mostly only one process. The functions of both populations as possible primary afferent neurons, interneurons, secretomotor neurons, or vasomotor neurons are discussed. Future morphochemical distinction of these groups may reveal different subgroups.

Identification of neuron types in the submucosal ganglia of the mouse ileum

The continuing and even expanding use of genetically modified mice to investigate the normal physiology and development of the enteric nervous system and for the study of pathophysiology in mouse models emphasises the need to identify all the neuron types and their functional roles in mice. An investigation that chemically and morphologically defined all the major neuron types with cell bodies in myenteric ganglia of the mouse small intestine was recently completed. The present study was aimed at the submucosal ganglia, with the purpose of similarly identifying the major neuron types with cell bodies in these ganglia. We found that the submucosal neurons could be divided into three major groups: neurons with vasoactive intestinal peptide (VIP) immunoreactivity (51% of neurons), neurons with choline acetyltransferase (ChAT) immunoreactivity (41% of neurons) and neurons that expressed neither of these markers. Most VIP neurons contained neuropeptide Y (NPY) and about 40% were immunoreactive for tyrosine hydroxylase (TH); 22% of all submucosal neurons were TH/VIP. VIP-immunoreactive nerve terminals in the mucosa were weakly immunoreactive for TH but separate populations of TH- and VIP-immunoreactive axons innervated the arterioles in the submucosa. Of the ChAT neurons, about half were immunoreactive for both somatostatin and calcitonin gene-related peptide (CGRP). Calretinin immunoreactivity occurred in over 90% of neurons, including the VIP neurons. The submucosal ganglia and submucosal arterioles were innervated by sympathetic noradrenergic neurons that were immunoreactive for TH and NPY; no VIP and few calretinin fibres innervated submucosal neurons. We conclude that the submucosal ganglia contain cell bodies of VIP/NPY/TH/calretinin non-cholinergic secretomotor neurons, VIP/NPY/calretinin vasodilator neurons, ChAT/CGRP/somatostatin/calretinin cholinergic secretomotor neurons and small populations of cholinergic and non-cholinergic neurons whose targets have yet to be identified. No evidence for the presence of type-II putative intrinsic primary afferent neurons was found.

Therapeutic targets in pulmonary arterial hypertension

Pulmonary arterial hypertension is a progressive, fatal disease. Current treatments including prostanoids, endothelin-1 (ET-1) antagonists, and phosphodiesterase (PDE) inhibitors, have sought to address the pulmonary vascular endothelial dysfunction and vasoconstriction associated with the condition. These treatments may slow the progression of the disease but do not afford a cure. Future treatments must target more directly the structural vascular changes that impair blood flow through the pulmonary circulation. Several novel therapeutic targets have been proposed and are under active investigation, including soluble guanylyl cyclase, phosphodiesterases, tetrahydrobiopterin, 5-HT2B receptors, vasoactive intestinal peptide, receptor tyrosine kinases, adrenomedullin, Rho kinase, elastases, endogenous steroids, endothelial progenitor cells, immune cells, bone morphogenetic protein and its receptors, potassium channels, metabolic pathways, and nuclear factor of activated T cells. Tyrosine kinase inhibitors, statins, 5-HT2B receptor antagonists, EPCs and soluble guanylyl cyclase activators are among the most advanced, having produced encouraging results in animal models, and human trials are underway. This review summarises the current research in this area and speculates on their likely success.

Inflammation and inflammatory agents activate protein kinase C epsilon translocation and excite guinea-pig submucosal neurons

BACKGROUND & AIMS

Properties of enteric neurons are transformed by inflammation and protein kinase C (PKC) isoforms are involved both in long-term changes in enteric neurons, and in transducing the effects of substances released during inflammation. We investigated roles of PKCepsilon in submucosal neurons by studying translocation in response to inflammatory mediators, effects on neuron excitability, and the changes in PKCepsilon distribution in a trinitrobenzene sulphonate model of ileitis.

METHODS

Immunohistochemical detection and analysis of association with membrane and cytosolic fractions, and Western blot analysis of cytosolic and particulate fractions were used to quantify translocation. Electrophysiology methods were used to measure effects on neuron excitability.

RESULTS

All submucosal neurons were immunoreactive for the novel PKC, PKCepsilon, and direct PKC activators, phorbol 12,13-dibutyrate, ingenol 3,20-dibenzoate, and the PKCepsilon-specific activator, transactivator of transduction-Psiepsilon receptor for activated C kinase, all caused PKCepsilon translocation from cytoplasm to surfaces of the neurons. Electrophysiologic studies showed that the stimulant of novel PKCs, ingenol (1 micromol/L), increased excitability of all neurons. Stimulation of protease-activated receptors caused PKCepsilon translocation selectively in vasoactive intestinal peptide secretomotor neurons, whereas a neurokinin 3 tachykinin receptor agonist caused translocation in neuropeptide Y and calretinin neurons. In all cases translocation was reduced significantly by a PKCepsilon-specific translocation inhibitor peptide. Increased PKCepsilon at the plasma membrane occurred in all neurons 6-7 days after an inflammatory stimulus.

CONCLUSIONS

Major targets for PKCepsilon include ion channels near the plasma membrane. PKCepsilon is likely to have a significant role in controlling the excitability of submucosal neurons and is probably an intermediate in causing hyperexcitability after inflammation.

Identification of neurons that express 5-hydroxytryptamine4 receptors in intestine

5-Hydroxytryptamine (5-HT) is an endogenous stimulant of intestinal propulsive reflexes. It exerts its effects partly through 5-HT4 receptors; 5-HT4 receptor agonists that are stimulants of intestinal transit are in clinical use. Both pharmacological and recent immunohistochemical studies indicate that 5-HT4 receptors are present on enteric neurons but the specific neurons that express the receptors have not been determined. In the present work, we describe the characterization of an anti-5-HT4 receptor antiserum that reveals immunoreactivity for enteric neurons and other cell types in the gastrointestinal tract. With this antiserum, 5-HT4 receptor immunoreactivity has been found in the muscularis mucosae of the rat oesophagus, a standard assay tissue for 5-HT4 receptors. It is also present in the muscularis mucosae of the guinea-pig and mouse oesophagus. In guinea-pig small intestine and rat and mouse colon, 5-HT4 receptor immunoreactivity occurs in subpopulations of enteric neurons, including prominent large neurons. Double-staining has shown that these large neurons in the guinea-pig small intestine are also immunoreactive for two markers of intrinsic primary afferent neurons, cytoplasmic NeuN and calbindin. Some muscle motor neurons in the myenteric ganglia are immunoreactive for this receptor, whereas it is rarely expressed by secretomotor neurons. Immunoreactivity also occurs in the interstitial cells of Cajal but is faint in the external muscle. Expression of the protein and mRNA has been confirmed in extracts containing enteric neurons. The observations suggest that one site of action of 5-HT4 receptor agonists is the intrinsic primary afferent neurons.

Tachykinins and tachykinin receptors in the gut, with special reference to NK2 receptors in human

Tachykinins (TKs), substance P (SP), neurokinin A (NKA) and B (NKB) are important peptide modulators of intestinal motility in animal species studied so far, including humans. Modulation of motility by TKs can occur at various levels, since these peptides are expressed in cholinergic excitatory motor neurons projecting to both circular and longitudinal muscle, interneurons, and intramural and extramural sensory neurons. The effects of SP, NKA and NKB are preferentially mediated through the stimulation of NK1, NK2 and NK3 receptors, respectively; however, the selectivity of natural TKs for their preferred receptors is relative. In addition, SP and NKA are expressed in similar quantities in the human intestine and adequate stimuli can release similar amount of these TKs from enteric nerves. Furthermore, a single anatomical substrate can express more than one TK receptor type, so that the blockade of a single receptor type may not reveal functional effects in integrated models of motility. In isolated human small intestine and colon circular muscle strips, both NK1 and NK2 receptors mediate contractile effects. Indeed, in the human small intestine, smooth muscle electrical and motor events induced by electrical field stimulation (EFS) can involve either or both NK1 and NK2 receptors or these latter receptors predominantly, depending on the experimental conditions. In contrast, in the human colonic smooth muscle, only the NK2 receptor-mediated component of the response to EFS is prominent and some evidence would suggest that this component is the main excitatory motor mechanism at this level. Furthermore, a NK2 receptor-mediated secretory component in the human colonic mucosa has been recently demonstrated. Thus, it could be speculated that the blockade of both NK1 and NK2 receptors will be necessary to antagonise motor effects induced by exogenous administration or endogenous release of TKs in the small intestine, whereas the blockade of the NK2 receptors would be sufficient to disrupt physiological motor and, possibly, secretory activity at the colonic level. Available evidence indicates that, in healthy volunteers, the infusion of NKA (25 pmol/kg/min i.v.) stimulated small intestine motility and precipitated a series of intestinal and non-intestinal adverse events. Nepadutant (8 mg i.v.), a selective NK2 receptor antagonist, antagonised small intestine motility induced by NKA and prevented associated intestinal adverse events. In another study, the same dose of nepadutant increased colo-rectal compliance during isobaric balloon distension in healthy volunteers pretreated with a glycerol enema, disclosing a NK2 receptor-mediated component in the regulation of colonic smooth muscle tone. However, the prolonged blockade of NK2 receptors by nepadutant (16 mg i.v. b.i.d. for 8 days) did not affect bowel habits, neither in term of movements nor of stool consistency. Altogether, these results indicate that, even when there is a significant redundance in the effects of TKs and in the role of their receptors, the selective blockade of tachykinin NK2 receptors can have functional consequences on human intestinal motility and perception, but this can occur without the disruption of the physiological functions.

Immunohistochemical characterization of putative primary afferent (sensory) myenteric neurons in human small intestine

Pseudouni- or multiaxonal Dogiel type II neurons are the intrinsic primary afferent (sensory) neurons (IPANs) in the guinea pig small intestine. Our aim was to decipher the chemical code of human myenteric type II neurons and to establish their putative vertical projections, i.e., from the myenteric plexus to the submucosa/mucosa. Additionally, we tried to distinguish them chemically from uniaxonal, dendritic type V neurons displaying, at first glance, similar shapes, i.e., smoothly contoured cell bodies with several long processes. Wholemount preparations of the myenteric plexus were immunohistochemically double or triple stained for neurofilaments (NF) and one or two of the following peptides: calbindin, calretinin (CR), calcitonin gene-related peptide (CGRP), somatostatin (SOM) and substance P (SP). In each triple stained wholemount three counts were conducted: (1) NF-positive pseudouni- or multiaxonal (type II) neurons including their reactivities for the above peptides, (2) uniaxonal or NF-negative neurons displaying coreactivities for the above peptides and (3) NF-reactive type V neurons taking into account their reactivities for the above markers. Additionally, type II neurons, which had an axon leading into (disrupted) interconnecting strands towards the submucosa were counted and somal areas of types II and V neurons were measured. The majority of myenteric type II neurons displayed coreactivities for SOM/CR (89.6%), SOM/SP (86.6%) and SP/CR (81.6%), respectively. A minority of type II neurons was positive for CGRP or calbindin. A small population with type III morphology (uniaxonal, long and slender dendrites) displayed the same coreactivities as type II neurons. In contrast, not one single type V neuron was coreactive for SOM/CR, SOM/SP or SP/CR. Out of 627 type II neurons counted in six wholemounts, 84 type II neurons displayed an axon which could be followed into disrupted interconnecting strands indicating a vertical projection pattern. Somal areas of type II neurons were twice as big as those of type V neurons (904+/-210 versus 449+/-110 microm(2)). In conclusion, most human myenteric type II neurons contain SOM, SP and CR. We suggest they are the human IPANs. Type V neurons are both morphologically and chemically distinctly different from type II neurons and may represent descending interneurons. Further studies have to decipher the type-specific chemical code of type II neurons distinguishing them also from type III neurons.

MEK inhibits secretin release and pancreatic secretion: roles of secretin-releasing peptide and somatostatin

We investigated the mechanism of action of methionine enkephalin (MEK) on HCl-stimulated secretin release and pancreatic exocrine secretion. Anesthetized rats with pancreatobiliary cannulas and isolated upper small intestinal loops were perfused intraduodenally with 0.01 N HCl while bile and pancreatic juice were diverted. The effect of intravenous MEK on acid-stimulated secretin release and pancreatic exocrine secretion was then studied with or without coinfusion of naloxone, an anti-somatostatin (SS) serum, or normal rabbit serum. Duodenal acid perfusate, which contains secretin-releasing peptide (SRP) activity, was collected from donor rats with or without pretreatment with MEK, MEK + naloxone, or MEK + anti-SS serum, concentrated by ultrafiltration, and neutralized. The concentrated acid perfusate (CAP), which contains SRP bioactivity, was infused intraduodenally into recipient rats. MEK increased plasma SS concentration and inhibited secretin release and pancreatic fluid and bicarbonate secretion dose-dependently. The inhibition was partially reversed by naloxone and anti-SS serum but not by normal rabbit serum. In recipient rats, CAP increased plasma secretin level and pancreatic secretion. CAP SRP bioactivity decreased when it was collected from MEK-treated donor rats; this was partially reversed by coinfusion with naloxone or anti-SS serum. These results suggest that in the rat, MEK inhibition of acid-stimulated pancreatic secretion and secretin release involves suppression of SRP activity release. Thus the MEK inhibitory effect appears to be mediated in part by endogenous SS.

Intestinal intraepithelial lymphocytes influence the production of somatostatin

BACKGROUND

We have previously demonstrated that intestinal intraepithelial lymphocytes (iIELs) inhibit lymphocyte proliferation. Because somatostatin also prevents lymphocyte proliferation, we hypothesized that iIELs may influence production of somatostatin.

METHODS

Isolates of intestinal epithelium that were obtained from Brown Norway (BN) rats and contained an iIEL-enriched population (defined as CD45+) were incubated with irradiated Lewis splenocytes for allogeneic stimulation. BN rat splenocytes incubated with irradiated Lewis splenocytes served as a control. Supernatants were harvested after 4 days and assayed for somatostatin by using a radioimmunoassay.

RESULTS

The somatostatin level in the intestinal epithelium-conditioned supernatant was significantly higher than that of the control group (176 +/- 60 versus 10 +/- 2 fmol/ml; p < 0.05). Removal of the CD45+ cell subset resulted in a fifteenfold reduction in somatostatin levels. The CD45+ cell lysates had significantly higher levels of somatostatin than did CD45+ depleted cells (1304 +/- 531 versus 128 +/- 41 fmol/ml; p < 0.05).

CONCLUSIONS

The isolates of intestinal epithelium produced significant amounts of somatostatin. Removal of the CD45+ cells caused a significant loss of somatostatin production. Intracellular levels of somatostatin appeared to be highest in the CD45+ subpopulation. These data suggest that iIELs (that is, CD45+ cells) may have a significant influence on the production of somatostatin and may be a source of somatostatin production. Production of somatostatin by iIELs may help modulate immune responses in gut-associated lymphoid tissue.