Gut hormone secreting cells--unsolved problems

The gut endocrine cells generally are bipolar paraneurons, extending from the epithelial base to the luminal surface. The cells, also known as the basal-granulated cells, produce peptidic and amine ++ signal substances to release them in response to the luminal stimuli. The substances are released not only in an endocrine fashion, but also, and more importantly, in a paracrine way, thus stimulating nervous, muscular, secretory and other elements in the vicinity. Attention should be paid also to other secretions of the gut endocrine cells, ATP and chromogranins (acidic carrier proteins) which are co-released with the peptides and amines. Various gut hormones have been demonstrated to be released into the gut lumen, besides into the blood and tissue spaces. The possible mechanism of this partial exocrine function of the endocrine cells remains to be explored.     

Neurotransmitters, neuromodulators, and neurotrophin receptors in the gut of pantex, a hybrid sparid fish (Pagrus major x Dentex dentex). Localizations in the enteric nervous and endocrine systems

The gut of Pantex, a sparid hybrid fish (Pagrus major x Dentex dentex) with a great potential importance for the Italian aquaculture, was histochemically and immunohistochemically investigated in order to evidence components of the intramural nervous and diffuse endocrine systems. The general structural aspects of the intramural nervous system were shown by the Nissl-thionin staining. As in most other fish, it was only organized in the myenteric plexus. Acetylcholinesterase (AChE) activity was observed in both nerve cell bodies and terminals all along the gut. The NADPH-diaphorase reactivity too, possibly linked to the synthesis and release of nitric oxide, was present in nerve cell bodies and nerve terminals of the oesophagus, stomach and intestine. In addition, the intramural nervous system was shown to contain Trk (tyrosinekinase) receptors for neurotrophin, as evidenced by Trk A-, Trk B- and Trk C-like immunoreactivities, thus suggesting an involvement of neurotrophin in the function of this system. Trk B- and Trk C-like immunoreactivities were detected in epithelial endocrine cells, too. The additional presence of serotonin- and metenkephalin-like immunoreactivities in numerous endocrine cells in the epithelial layers of the stomach and intestine was showed.     

Apelin cells in the rat stomach

Apelin is a recently discovered peptide that is the endogenous ligand for the APJ receptor. Apelin is produced in the central nervous system, heart, lung, mammary gland and gastrointestinal (GI) tract. The aim of this study was to identify by immunohistochemistry (IHC) cell types in the rat stomach that produce apelin peptide. IHC revealed abundant apelin-positive cells, primarily in the neck and upper base regions of the gastric glands in the mucosal epithelium. Apelin is not detected in the muscle layer. Apelin-positive cells were identified as mucous neck, parietal cells, and chief cells. Apelin is also identified in gastric epithelial cells that produce chromogranin A (CGA), a marker of enteroendocrine cells. The findings that apelin is expressed in gastric exocrine and endocrine cells agrees with and extends other data showing that apelin peptide is measurable in the gut lumen and in the systemic circulation by immunoassay.     

Calbindin 28 kDa in endocrine cells of known or putative calcium-regulating function. Thyro-parathyroid C cells, gastric ECL cells, intestinal secretin and enteroglucagon cells, pancreatic glucagon, insulin and PP cells, adrenal medullary NA cells and some pituitary (TSH?) cells

The distribution of calbindin in some endocrine glands (thyroid, parathyroid, ultimobranchial body, pituitary and adrenals) and in the diffuse endocrine cells of the gut and pancreas has been investigated immunohistochemically using an antiserum raised against the 28 kDa calbindin from chicken duodenum. The identity of calbindin-immunoreactive cells in a number of avian and mammalian species was ascertained by comparison with hormone-reactive cells in consecutive sections or by double immunostaining of the same section with both calbindin and hormone antibodies. Calcitonin-producing C cells of the mammalian and avian thyroid, parathyroid or ultimobranchial body, PP, glucagon and insulin cells of the mammalian and avian pancreas, enteroglucagon cells of the avian intestine, secretin cells of the mammalian duodenum, histamine-producing ECL cells of the mammalian stomach, as well as noradrenaline-producing cells of the adrenal medulla and some (TSH?) cells of the adenohypophysis were among the calbindin-immunoreactive cells. Although some species variability has been observed in the intensity and distribution of the immunoreactivity, especially in the pancreas and the gut, a role for calbindin in the mechanisms of calcium-mediated endocrine cell stimulation or of intracellular and extracellular calcium homeostasis is suggested.     

Cellular bases for interactions between immunocytes and enteroendocrine cells in the intestinal mucosal barrier of rhesus macaques

The roles of the interactions between nervous, endocrine, and immune systems have been well established in human health and diseases. At present, little is known about the cellular bases for neural-endocrine-immune networks in the gastrointestinal mucosa. In the current study, duodenum, jejunum, ileum, cecum, colon, and rectum autopsies from 15 rhesus macaques and endoscopic duodenal biopsies from 12 rhesus macaques were collected, and the spatial relationships between the endocrine cells and immune cells in the intestinal mucosa were examined by transmission electron microscopy. Eight types of enteroendocrine cells similar to human enterochromaffin cells (EC), D1, G, I, K, L, N, and S cells were found to lie within a one-cell-size distance from immunocytes, in particular the eosinophils in the epithelia or lamina propria. Close apposition of large areas of plasma membranes between many types of enteroendocrine cells and immunocytes, especially between EC, K, S cells and eosinophils, were observed in the epithelia for the first time. These data indicate that complex interactions occur between diverse types of enteroendocrine cells and various immune cells through paracrine mechanisms or via mechanisms dependent on cell-to-cell contact; such interactions might play key roles in maintaining the gut mucosal barrier integrity of rhesus macaques.     

Mast cells: the immune gate to the brain

Mast cells were originally considered wandering histiocytes, but are now known to derive from the bone marrow and enter the tissues as immature or precursor cells which then differentiate under micro-environmental influences such as interleukin-3. At least three types of mature mast cells have been identified as serosal (lung, peritoneal, skin), mucosal (nasal, gastrointestinal) and brain (dural, perivascular, parenchymal) with their own distinct biochemical, morphological and functional characteristics. Mast cells are necessary for immediate hypersensitivity reactions where they release numerous biologically powerful mediators in response to immunoglobulin E (IgE) and antigen (Ag), and appear to be required for delayed reactions. Anaphylatoxins, basic peptides and drugs, as well as certain neuropeptides and hormones, can also trigger mast cell secretion. Recent evidence indicates that mast cells are found in close proximity to neurons, an association which may be regulated by nerve growth factor. Moreover, mast cells may be capable of selective release of mediators which could, in turn, regulate further secretion. This information suggests that mast cells may serve as a link between the immune, endocrine and nervous systems and could have an important role in the access of lymphocytes and pathogens to the brain. The possible role of such interactions in the pathophysiology of specific neuroinflammatory conditions is also discussed.     

The distribution of GAWK-like immunoreactivity in neuroendocrine cells of the human gut, pancreas, adrenal and pituitary glands and its co-localisation with chromogranin B

GAWK is a recently discovered peptide isolated from extracts of human pituitary gland and subsequently shown to be identical to sequence 420-493 of human chromogranin B. The distribution of this peptide was studied in human gut, pancreas, adrenal and pituitary glands using antisera to two portions of the 74 amino acid peptide (sequences 1-17 and 20-38). In addition, the co-existence of GAWK immunoreactivity with other peptides and chromogranin B was investigated using comparative immunocytochemistry. In the gut, GAWK was localised mainly to serotonin-containing cells of the mucosal epithelium, where electron microscopy showed it to be stored in typical electron-dense (250 nm diameter) granules, and to a moderate population of nerve fibres in the gut wall. Considerable quantities of GAWK-like immunoreactivity were measured in the gut, up to 36.3 +/- 18 pmol GAWK 1-17/g wet weight of tissue (mean +/- SEM) and 12.4 +/- 2.9 pmol GAWK 20-38/g. Chromatography of gut extracts revealed several GAWK-like immunoreactive peaks. GAWK-like immunoreactivity was also detected in endocrine cells of pancreas, pituitary gland and adrenal medulla, where the highest concentrations of GAWK-like immunoreactivity were measured (GAWK 1-17 2071.8 +/- 873.2 and GAWK 20-38 1292.7 +/- 542.7 pmol/g). Endocrine cells containing GAWK-like immunoreactivity were found also to be immunoreactive for chromogranin B. Our results define a discrete distribution of GAWK immunoreactivity in human endocrine cells and nerves and provide morphological support for the postulated precursor-product relationship between chromogranin B and GAWK. Details of the functions of this peptide are awaited.     

Ultrastructure and immunocytochemistry of endocrine cells in the midgut of the desert locust,Schistocerca gregaria (Forskal)

Summary The endocrine cells of the midgut epithelium of the desert locust are found dispersed among the digestive cells and are similar to those of the vertebrate gut. According to their reactivity to silver impregnation techniques and the ultrastructural features of the secretory granules (shape, electron-density, size, and structure) 10 types of endocrine cell have been identified, of which seven are located in the main segment of the midgut or in the enteric caeca, and the other three seem to be present only in the ampullae through which the Malpighian tubules drain into the gut. The endocrine cells have a slender cytoplasmic process that reaches the gut lumen, a feature that supports the receptosecretory nature postulated for this cellular type in insects as well as vertebrates. Antisera directed against mammalian gastrin, CCK, insulin, pancreatic polypeptide and bombesin reacted with some of the endocrine cells. This is the first time that insulin- and bombesin-like immunoreactive cells have been described in the midgut of an insect.     

Laryngeal endocrine cells: topographic distribution and adaptation to chronic hypercapnic hypoxia

The morphology, topographic distribution, effects of denervation, and exposure to hypercapnic hypoxia of endocrine cells were examined in rat larynx. The endocrine cells, which were immunoreactive for protein gene product 9.5 (PGP 9.5) and calcitonin gene-related peptide (CGRP), were observed within the epithelial layer of the laryngeal cavity and in the laryngeal gland, while solitary endocrine cells with apical and/or basal cytoplasmic processes appeared near the glottis. After denervation of the left cervical vagosympathetic trunk and the superior laryngeal nerve, the number of mucosal endocrine cells in the denervated side was not significantly different from that in the intact side. After exposure to hypercapnic hypoxia for 3 months, the number of endocrine cells with PGP 9.5 and CGRP was markedly increased. In conclusion, the secretion of laryngeal endocrine cells may be stimulated by CO2 rather than O2. Furthermore, the endocrine cells and the sensory and autonomic nervous system may regulate each other by an axon reflex mechanism. Endocrine cells appear to play a very important role in the local regulation of the laryngeal mucosa.     

Consequences of Citrobacter rodentium infection on enteroendocrine cells and the enteric nervous system in the mouse colon

We tested the hypothesis that Citrobacter rodentium infection leads to changes in the mucosal enteroendocrine signalling and the enteric nervous system and that the host's immune response contributes to these changes. Enteroendocrine cells, serotonin (5-HT) reuptake transporter (SERT), 5-HT release, and inducible nitric oxide synthase (iNOS) expression were assessed in the colon of infected wild-type or severe combined immunodeficient (SCID) mice. Immunoreactivity for iNOS and neuropeptides were examined in the submucosal and myenteric plexuses. Mice were orogastrically infected with C. rodentium and experiments were conducted during the injury phase (10 days) and the recovery phase (30 days). 5-HT and somatostatin enteroendocrine cells and SERT were significantly reduced 10 days after infection, with numbers returning to control values at 30 days. 5-HT release was increased at 10 days. Changes to the mucosal serotonin signalling system were not observed in SCID mice. iNOS immunoreactivity was increased in the submucosa and mucosa at 10 days and returned to baseline levels by 30 days. No differences were observed in neuropeptide or iNOS immunoreactivity in the enteric plexuses following infection. The host's immune response underlies changes to enteroendocrine cells, SERT expression and 5-HT release in C. rodentium infection. These changes could contribute to disturbances in gut function arising from enteric infection.     

Gastric endocrine cells share a clonal origin with other gut cell lineages

There has been considerable debate about the ontological origin of gut endocrine cells as being either from the neural crest (or primitive epiblast) or from the endodermal stem cell. We have attempted to define the ontological origin of endocrine cells by applying an experimental system that uses a marker to identify one of the two phenotypes present in chimaeric mice as suggested by Ponder et al. (1985). This study involved two separate experiments. The first made use of the unique staining properties of Dolichos biflorus agglutinin (DBA), a lectin that binds to the N-acetyl galactosamine sugar residues present on the surface of C57Bl mouse gut, but absent from RoRIII mouse gut, in C57Bl----RoIII mouse chimaeras at the ultrastructural level. A four-stage procedure for staining at the EM level was developed. Although mature villous endocrine cells stained for DBA, immature endocrine cells did not, either in the positive crypts of chimaeric mouse gut or in gut from C57Bl positive controls. Thus a second marker was chosen. This experiment combined immunocytochemistry (to identify gastric antral gastrin cells chosen as a representative neuroendocrine cell) with in situ DNA hybridization for the mouse male chromosome repeat sequence PY 353 (to identify XY cells) in XX----XY chimaeric mice. This study showed that the sex chromosomal pattern in the gastrin cells parallels that of other cells in the same gastric gland and therefore are clonal with them. This suggests that gut endocrine cells share a common stem cell with other epithelial cell lineages in the antrum and are endodermally derived.     

The distribution of GAWK-like immunoreactivity in neuroendocrine cells of the human gut,pancreas, adrenal and pituitary glands and its co-localisation with chromogranin B

Summary GAWK is a recently discovered peptide isolated from extracts of human pituitary gland and subsequently shown to be identical to sequence 420–493 of human chromogranin B. The distribution of this peptide was studied in human gut, pancreas, adrenal and pituitary glands using antisera to two portions of the 74 amino acid peptide (sequences 1–17 and 20–38). In addition, the co-existence of GAWK immunoreactivity with other peptides and chromogranin B was investigated using comparative immunocytochemistry.In the gut, GAWK was localised mainly to serotonin-containing cells of the mucosal epithelium, where electron microscopy showed it to be stored in typical electron-dense (250 nm diameter) granules, and to a moderate population of nerve fibres in the gut wall. Considerable quantities of GAWK-like immunoreactivity were measured in the gut, up to 36.3±18 pmol GAWK 1–17/g wet weight of tissue (mean±SEM) and 12.4±2.9 pmol GAWK 20–38/g. Chromatography of gut extracts revealed several GAWK-like immunoreactive peaks. GAWK-like immunoreactivity was also detected in endocrine cells of pancreas, pituitary gland and adrenal medulla, where the highest concentrations of GAWK-like immunoreactivity were measured (GAWK 1–17 2071.8±873.2 and GAWK 20–38 1292.7±542.7 pmol/g). Endocrine cells containing GAWK-like immunoreactivity were found also to be immunoreactive for chromogranin B.Our results define a discrete distribution of GAWK immunoreactivity in human endocrine cells and nerves and provide morphological support for the postulated precursor-product relationship between chromogranin B and GAWK. Details of the functions of this peptide are awaited.     

Glucagon-like peptides: regulators of cell proliferation,differentiation, and apoptosis

Peptide hormones are secreted from endocrine cells and neurons and exert their actions through activation of G protein-coupled receptors to regulate a diverse number of physiological systems including control of energy homeostasis, gastrointestinal motility, neuroendocrine circuits, and hormone secretion. The glucagon-like peptides, GLP-1 and GLP-2 are prototype peptide hormones released from gut endocrine cells in response to nutrient ingestion that regulate not only energy absorption and disposal, but also cell proliferation and survival. GLP-1 expands islet mass by stimulating pancreatic beta-cell proliferation and induction of islet neogenesis. GLP-1 also promotes cell differentiation, from exocrine cells or immature islet progenitors, toward a more differentiated beta-cell phenotype. GLP-2 stimulates cell proliferation in the gastrointestinal mucosa, leading to expansion of the normal mucosal epithelium, or attenuation of intestinal injury in experimental models of intestinal disease. Both GLP-1 and GLP-2 exert antiapoptotic actions in vivo, resulting in preservation of beta-cell mass and gut epithelium, respectively. Furthermore, GLP-1 and GLP-2 promote direct resistance to apoptosis in cells expressing GLP-1 or GLP-2 receptors. Moreover, an increasing number of structurally related peptide hormones and neuropeptides exert cytoprotective effects through G protein-coupled receptor activation in diverse cell types. Hence, peptide hormones, as exemplified by GLP-1 and GLP-2, may prove to be useful adjunctive tools for enhancement of cell differentiation, tissue regeneration, and cytoprotection for the treatment of human disease.     

Ontogeny of endocrine cells in the gut of the insect Periplaneta americana

Summary The ontogeny of the endocrine cells of the gut of the cockroach Periplaneta americana was studied by immunohistochemistry. During embryogenesis, the midgut begins to be formed as an outgrowth of the foregut and hindgut invaginations. Gut endocrine cells with pancreatic polypeptide (PP)-like immunoreactivity begin to appear at the anterior and posterior ends of the forming midgut. These cells are restricted to the midgut epithelium, and no mitotic cells with PP-like immunoreactivity are observed. These results strongly suggest that the gut endocrine cells, at least those with PP-like immunoreactivity, are derived from precursor cells they have in common with other epithelial cells of the midgut.     

Human uterine mast cells. Isolation, purification, characterization, ultrastructure, and pharmacology.

As part of an ongoing investigation of human mast cell heterogeneity, we have isolated, partially purified, and characterized the uterine mast cell and compared it with mast cells isolated from other organs. The average histamine content of myometrium and leiomyofibroma obtained from hysterectomies was 2.1 +/- 0.3 (mean +/- SEM) microgram/g of tissue (n = 10), and the histamine content of the two tissues did not differ significantly. A mild collagenase, hyaluronidase, and DNase digestion was used to disperse the uterine mast cells, with an average yield of 9.5% (range, 0 to 21%). The average histamine/uterine mast cell was 2.1 +/- 0.2 pg (n = 3), and 61 +/- 7% (n= 3) of the uterine mast cells survived overnight culture. Early purification efforts with Percoll gradients have yielded up to 80% pure uterine mast cells, with an average of 27 +/- 10% (n = 5). Uterine mast cells released histamine in response to the secretogogues anti-IgE and A23187 but did not respond to substance P or to the basophil secretogogues FMLP, C5a, and 12-O-tetradecanoylphorbol-13-acetate. After 1 microgram/ml anti-IgE stimulation, the uterine mast cell appeared to make significant quantities of PGD2 (89 +/- 26 ng/10(6) cells, n = 6) (p less than 0.05), as assayed by RIA. Simultaneously, leukotriene C4 release was 45 +/- 15 ng/10(6) cells, (n = 6) (p less than 0.05), as assayed by RIA. Combined gas-chromatography mass spectroscopy analysis of anti-IgE-stimulated cell supernatants confirmed the production of PGD2. In pharmacologic studies, isobutyl-methylxanthine and isoproterenol blocked anti-IgE-induced histamine release. The uterine mast cell is similar to the lung mast cell in terms of response to secretogogues and release of arachidonic acid metabolites. Ultrastructurally, the uterine mast cell contains scroll granules, crystal granules, combined granules, homogeneously dense granules, and large lipid bodies, many with focal lucencies within them. Particle granules, most frequently present in gut mast cells of mucosal origin, were absent from uterine mast cells. Although certain features are analogous to the ultrastructure of skin or lung mast cells, the combination of structures is distinctive for uterine mast cells.     

The presence of a galanin-like peptide in the gut neuroendocrine system of Lampetra fluviatilis and Acipenser transmontanus: an immunohistochemical study

Galanin is a brain-gut neuropeptide present in the central and peripheral nervous systems of vertebrates. In the present survey, the galaninergic and the diffuse endocrine systems of the alimentary canal of the river lamprey, Lampetra fluviatilis, and the white sturgeon, Acipenser transmontanus, were studied by immunohistochemistry. The results show the presence of galanin-like immunoreactive endocrine cells in the gut of L. fluviatilis. In addition, a galanin-like immunoreactivity was detected in enteric intramural neurons of both species. It is conceivable that the galaninergic system plays in both species a role in the regulation of the gut muscle contractility and in the modulation of mucosal secretive/absorptive processes. In A. transmontanus, the presence of galanin-like immunoreactive nerve fibres associated with components of the gut associated-lymphoid tissue is possibly correlated with a control of the defensive events at this site. The presence of a galanin-like immunoreactivity in the neuroendocrine system of these two ancient fishes confirms the hypothesis on the early occurrence of this regulative molecule in the gastro-enteric system of vertebrates.     

A soluble factor produced by lamina propria mononuclear cells is required for TNF-alpha enhancement of IFN-gamma production by T cells.

The role of TNF-alpha in the mucosal inflammation of Crohn's disease has been demonstrated by the prolonged clinical responses and/or remissions among patients receiving i.v. infusion of anti-TNF-alpha. A correlation between TNF-alpha and elevated IFN-gamma production is suggested by the reduction in the number of IFN-gamma producing lamina propria mononuclear cells (LPMC) found in colonic biopsies from anti-TNF-alpha-treated patients. The aim of this study was to define the mechanism of TNF-alpha-augmented mucosal T cell IFN-gamma production. In this paper we present evidence that cultured LPMC secrete a factor which acts on preactivated T cells in concert with TNF-alpha to augment IFN-gamma production. This activity is independent of IL-12 and IL-18, the well-documented potentiators of IFN-gamma expression, and is not produced by PBMC. Peripheral blood PHA-activated T cells incubated in supernatants from LPMC became responsive to TNF-alpha by increasing IFN-gamma output upon stimulation. These results are consistent with a model in which LPMC, but not PBMC, release an unidentified substance when cultured in vitro with low dose IL-2. This substance can act on preactivated peripheral T cells, as well as on lamina propria T cells, conditioning them to respond to TNF-alpha by increased IFN-gamma secretion upon stimulation. Expression of this factor in the gut mucosa could contribute to up-regulation of the Th1 response in the presence of TNF-alpha, and could be important for mucosal immunoregulation.     

Microscopic organization of epithelial endocrine cells of the gastrointestinal tract mucosa in lower vertebrates. I. Epithelial endocrine cells of the stomach of the common frog

The quantity, histotopography and submicroscopic organization of endocrine cells in various mucosal epithelium sections of frog were studied using light and electron microscopy. It is shown that the majority of endocrine cells per square millimetre is located in the proximal part of the stomach. Eight types of endocrine cells depending on the submicroscopic structure of secretory granules are defined.     

Regulation of secretion and synthesis of gastrointestinal hormones: studies with cultured gut endocrine cells

Small number of endocrine cells are diffusely distributed in the gut mucosa. Studies on their secretory mechanisms have been further complicated by numerous neural, paracrine, and endocrine factors affecting their response. Recent technical development for isolation and culture of gut endocrine cells has circumvented these problems and enabled to study their receptors, signal transduction mechanism, and biosynthesis of gut hormones. In this review, current progress made in the cellular physiology of gut endocrine cells is summarized.