Peptides and epithelial growth regulation

Influence of enteric helminths on the distribution of intestinal endocrine cells belonging to the diffuse endocrine system in brown trout, Salmo trutta L

The presence of intestinal helminths in the alimentary canal of brown trout, Salmo trutta L., can alter the number of cells that synthesize modulatory peptides. A total of 167 brown trout were collected from tributaries of the River Brenta (northern Italy), of which 119 (71.3%) specimens were infected with enteric helminths, 28 with the acanthocephalan Pomphorhynchus laevis Müller, 1776 with intensity of infection ranging from 1 to 162 (18.57 +/- 30.79) worms per host and 67 fish with the cestode Cyathocephalus truncatus Pallas, 1781. Intensity of infection with C. truncatus ranged from 1 to 85 (6.87 +/- 12.59) per fish. In 24 fish there were concurrent infections of both species of helminths. The caecal and middle regions of the intestine were the most heavily parasitized. Immunohistochemical tests showed a decrease in endocrine cells (ECs) of the diffuse endocrine system (DES) positive to gastrin, cholecystokinin-8, bombesin and secretin antisera in the intestine of the infected trout. The number of ECs immunoreactive to anti-glucagon serum did not show differences in the digestive tract of uninfected brown trout and in conspecifics parasitized with P. laevis. The density of cells containing glucagon-like material was low in the fish parasitized with C. truncatus. The results suggest that endoparasitic helminths induce alterations in the DES of infected S. trutta.

Aging alters gastric mucosal responses to epidermal growth factor and transforming growth factor-alpha

Administration of pharmacological doses of epidermal growth factor (EGF) or transforming growth factor-alpha (TGF-alpha) in young rats stimulates gastric mucosal proliferation, but, in aged rats, the same treatment inhibits proliferation. This may be due to enhanced ligand-induced internalization of EGF receptor (EGFR). In support of this, we demonstrated that although a single injection of EGF (10 microg/kg) or TGF-alpha (5 microg/kg) in young (4-6 mo old) rats greatly increased membrane-associated EGFR tyrosine kinase activity, the same treatment slightly inhibited the enzyme activity in aged (24 mo old) rats. This treatment also produced a greater abundance of punctate cytoplasmic EGFR staining in gastric epithelium of aged rats, consistent with EGFR internalization. In vitro analyses demonstrated that exposure of isolated gastric mucosal cells from aged but not young rats to 100 pM TGF-alpha resulted in marked increases in intracellular EGFR tyrosine kinase activity and that induction of EGFR tyrosine kinase activity in mucosal membranes from aged rats occurred at doses 1,000-fold less than those required in young rats. Our data suggest that aging enhances sensitivity of the gastric mucosa to EGFR ligands. This may partly explain EGFR-mediated inhibition of gastric mucosal proliferation in aged rats.

Effect of gum arabic in an oral rehydration solution on recovery from diarrhea in rats

BACKGROUND

It has been shown that gum arabic, a soluble fiber, enhances water, electrolyte, and glucose absorption from oral rehydration solutions in jejunal perfusion of healthy rats and in animals with theophylline-induced secretion or chronic osmotic-secretory diarrhea. This report concerns a study of the effectiveness of an oral rehydration solution supplemented with gum arabic, during recovery from chronic osmotic secretory diarrhea in free-living rats.

METHODS

Chronic diarrhea was induced in 60- to 80-g juvenile rats by providing a magnesium citrate-phenolphthalein solution as the sole fluid source for 7 days. This led to diarrhea characterized by dehydration, soft stools, increased cecal volume, decreased food and fluid intake and failure to gain weight. After 7 days of diarrhea, rats recovered for 24 hours with either tap water or an oral rehydration solution (90 mM Na, 111 mM glucose, 20 mM K, 80 mM chloride, 20 mM citrate) with or without 2.5 g/l gum arabic.

RESULTS

Although all three solutions improved the diarrhea, optimal recovery from diarrhea was achieved with the gum arabic-supplemented oral rehydration solution. After 4 hours and 24 hours, rats drinking the gum arabic-supplemented solution gained more weight and had lower fecal output than rats receiving water or the rehydration solution without gum arabic. All three solutions normalized plasma osmolality after 24 hours.

CONCLUSIONS

The positive effects of the gum arabic-supplemented rehydration solution on fluid and electrolyte absorption seen during jejunal perfusion also occurred during recovery from chronic osmotic secretory diarrhea, when free-living animals drank the solution ad libitum.

A role for the enteric nervous system in the response to helminth infections

The enteric nervous system (ENS) in the gut contains a particularly high concentration of nerve cells, and effectively functions as an independent 'minibrain'. Interactions between nerve, endocrine, immune and other cell types allow the sophisticated regulation of normal gut physiology. They can also bring about a co-ordinated response to parasitic infection, possibly leading to expulsion of the parasite. In this review, Derek McKay and Ian Fairweather will consider, in brief, data pertaining to changes in the ENS following intestinal helminth infections and speculate on the role that these alterations may have in the expulsion of the parasite burden and the putative ability of the parasite to modulate these events.

Development of morphological changes and ileal glucagon gene expression in the small intestine of lambs infected with Trichostrongylus colubriformis

To investigate the consequences of subclinical Trichostrongylus colubriformis infection on the intestinal mucosa and the associated changes in entero-glucagon gene expression, sheep were infected with 30000 larvae and killed 5, 10, 15 or 20 days after infection. Histological and cytological changes were examined. In the main site of infection, the upper duodenum, villous atrophy associated with crypt hyperplasia developed gradually. Cytological changes in the enterocytes appeared concurrently, characterized by a progressive reduction in brush border and in the number of ribosomes in the cytoplasm, changes in the internal structure of mitochondria, and enlargement of the intercellular spaces. Neither histological nor cytological modifications were found before day 15. At the same time, villous hypertrophy developed distally, beyond the main site of infection; this was interpreted as an adaptive response to parasitism. Enteroglucagon gene expression in the ileum was measured in parallel with the mucosal changes but did not reveal any difference between infected and control sheep. The results indicate that this gastrointestinal hormone does not have a major role in the response to nematode parasitism.

Tissue hypertrophy and epithelial proliferation rate in the gut of rats fed on bread and haricot beans (Phaseolus vulgaris)

The present study was designed to test the hypothesis that increasing short-chain fatty acid (SCFA) production in the large bowel increases gut epithelial proliferation rate (EPR). Two experiments were carried out in which rats were fed on bread (wholemeal or white)-based diets containing graded amounts of cooked haricot (Phaseolus vulgaris) beans; the latter are a rich source of fermentable carbohydrates. Consumption of beans was associated with several-fold increases in SCFA production with the greatest relative increase being for butyrate. Despite the very large increase in SCFA production, there was no evidence that this had any effect on EPR in the duodenum. Where the basal diet contained wholemeal bread (Expt 1) there was no effect of enhanced SCFA supply on EPR in either the caecum or colon, but with the white bread-based diet (Expt 2) adding beans produced increments in both SCFA supply and EPR in the caecum. Evidence that SCFA are responsible for enhanced EPR above normal levels is not convincing. In those instances where enhanced SCFA supply is associated with increased EPR, the increase may be (1) from a hypoproliferative state towards normal, (2) a transient phenomenon accompanying tissue hypertrophy or (3) a homeostatic response to increased cell loss by cell sloughing or apoptosis. It is not likely that there is any direct link with risk of colon cancer.

The long-term effect of pinealectomy on the crypts of the rat gastrointestinal tract

Previously it has been found that rat small bowel crypt cell hyperplasia occurred several weeks after pinealectomy. To determine if this effect was longer-lasting (because of the possible role of the pineal in bowel malignancy) the crypt cell proliferation rate was determined in rat small bowel and colon 6 months after pinealectomy, using a stathmokinetic technique. Although the hyperproliferative effect of pinealectomy was well maintained in the small bowel crypts after 6 months, the hyperproliferative effect in the colonic crypts was much less marked. There is no obvious explanation for these findings, although it is possible that regional differences in levels of gut neuropeptides or melatonin are involved. The mechanism of the effect of pinealectomy on the crypts remains unexplained--in particular, why the effect is so prolonged.

Mediation of the trophic effects of short-chain fatty acids on the rat jejunum and colon

BACKGROUND/AIMS

Short-chain fatty acids (SCFAs) are trophic to small intestinal and colonic mucosa. This study determined whether SCFAs infused into the cecum out of continuity stimulated jejunal and colonic cellularity and whether these effects were mediated by the autonomic nervous system and/or enterotrophic hormones.

METHODS

To eliminate direct trophic effects of SCFAs in contact with mucosa, 60 rats underwent cecal isolation with placement of an infusion catheter into the proximal cecum, formation of distal cecocutaneous stoma, and restoration of intestinal continuity with ileocolonic anastomosis. Rats underwent cecal denervation or remained normally innervated and received 1 of 3 infusions for 10 days: SCFAs, saline, or no infusion. Twenty-four additional rats were assigned to the same groups but underwent infusion into the proximal colon (in circuit).

RESULTS

Cecal infusion of SCFAs into innervated rats increased (P < 0.05) jejunal DNA, villous height, surface area, crypt depth, and gastrin without increasing colonic variables. In denervated rats, SCFAs did not significantly affect these variables. However, direct intracolonic infusions of SCFAs increased (P < 0.05) colonic mucosal DNA and crypt depth.

CONCLUSIONS

Jejunotrophic effects of cecally infused SCFAs are mediated afferently by the autonomic nervous system and are associated with increased jejunal gastrin. SCFAs have local trophic effects on the colon.

Gut hormones, growth and malignancy

There is now clear-cut evidence that polypeptide growth factors control the proliferation of the normal gastrointestinal mucosa. Epidermal growth factor (EGF) stimulates normal growth throughout the gastrointestinal tract, and accelerates the healing of ulcerated epithelium. While the effects of gastrin were at first thought to be similarly widespread, the gastrin target now appears to be restricted to the enterochromaffin-like cells in the stomach. Isolated reports suggest that several other hormones, including fibroblast growth factor and the insulin-like growth factors, have similar proliferative effects. In contrast, indirect evidence suggests that somatostatin and transforming growth factor-beta inhibit the growth of the gastrointestinal mucosa. The same growth factors profoundly affect the growth of some gastrointestinal carcinomas. Prolonged hypergastrinaemia increases the risk of development of gastric endocrine tumours, but has no effect on the incidence of gastric adenocarcinoma. Gastrin also stimulates the in vivo growth of 50% of gastric and colorectal carcinoma xenografts, but has no consistent effect on the growth of carcinoma cell lines in vitro. EGF, on the other hand, significantly stimulates proliferation of many gastrointestinal cell lines in culture. Interest has recently focused on autocrine stimulation of gastrointestinal carcinoma growth. Elevated levels of EGF receptor, and of EGF or related mRNAs, have been demonstrated in gastric carcinomas, and the growth of some gastrointestinal cell lines is inhibited by antibodies against EGF, and by antisense oligonucleotides based on EGF mRNA. Similarly gastrin/cholecystokinin antagonists inhibit the growth of several colon carcinoma cell lines, although the spectrum of antagonist potencies suggests that classical gastrin and cholecystokinin receptors are not necessarily involved. Continued research on antagonists may therefore lead to novel therapies for gastrointestinal cancers.

Oat bran, rye bran, and soybean hull increase goblet cell volume density in the small intestine of the golden hamster. A histochemical and stereologic light-microscopic study

Small-intestinal morphology, particularly the amount of goblet cells, was studied in Syrian golden hamsters fed either a low-fibre (0.5% fibre) diet or the same diet supplemented with oat bran, rye bran, or soybean hull (12% fibre) during 6 weeks. All fibre diets increased the density of goblet cell volume to epithelial volume and to villus volume in the ileum and to some extent in the jejunum and also the number of goblet cells related to surface traces of villi both in the proximal and distal small intestine. The weight of the small intestine and the circumference and the volume of the intestinal wall in the ileum were greater in the rye bran diet group as compared with all the other groups, suggesting hyperplasia. These results suggest that oat bran, rye bran, and soybean hull supplementation might result in higher goblet cell secretory activity in both the proximal and distal small intestine of hamsters. The various fibre sources influenced the small-intestinal wall differently.

Characterization of superior cervical ganglion neurons that project to the submandibular glands, the eyes, and the pineal gland in rats

These studies sought to determine whether the cell bodies of rat superior cervical ganglion neurons projecting to three very different target organs differ in terms of their size, number, location within the ganglion and/or neuropeptide content, and whether these features are altered in response to neonatal deafferentiation of the ganglion. A series of retrograde tracer, immunocytochemical, and double-labeling studies revealed differences in the size, number, location and neuropeptide content of superior cervical ganglion neurons that project to the submandibular salivary glands, eyes, or pineal gland. The mean areas of the cell bodies of neurons projecting to the submandibular gland are largest, those projecting to the eye are smallest, and those projecting to the pineal are intermediate in size. Submandibular gland projecting neurons are found throughout the ganglion, while the eye and pineal projecting populations are localized to the rostral quadrants. The different subpopulations of target organ specific superior cervical ganglion neurons are heterogeneous in their content of vasoactive intestinal peptide-, neuropeptide Y- and somatostatin-like immunoreactivity. A greater percentage of submandibular gland than of pineal projecting neurons display vasoactive intestinal peptide-like immunoreactivity, but there are no differences in the percentage of neurons displaying neuropeptide Y- or somatostatin-like immunoreactivity between the target organ specific groups. Neonatal deafferentiation does not result in changes in the size, number or distribution of target organ specific neurons, or in the percentage of immunoreactive neurons in these populations. In conclusion, these studies provide evidence that the size and distribution of neurons and percentage of peptide-containing neurons in the superior cervical ganglion is related to the target organ innervated, but provides no evidence of exclusive target organ-peptide relationships.

Pre- and post-natal ontogeny of neutral endopeptidase 24-11 ('enkephalinase') studied by in vitro autoradiography in the rat

Neutral endopeptidase (NEP, enkephalinase, CALLA) which is present in various neural and non-neural tissues, is able to cleave a variety of regulatory peptides. The distribution of NEP has been studied during rat pre- and post-natal development by autoradiography after in vitro binding of the tritiated inhibitor [3H]HACBO-Gly to whole-body and organ sections. In the central nervous system (CNS), where the presence of NEP has been related to the termination of the action of enkephalins, the external layer of the olfactory bulbs is the only structure prominently labeled before birth. Other CNS structures rich in NEP in the adult, such as the nigrostriatal tract, are progressively labeled after birth. Outside the CNS, the progressive appearance of NEP in the kidney, the lungs and the salivary glands suggests its concomitant involvement in adult physiological functions, including fluid balance control, possibly by cleaving the atrial natriuretic peptide (ANP) and other peptides. On the other hand, transient or enhanced expression of NEP is observed during the development of several organs such as the sensory organs, the heart and the major blood vessels, the intestine, the bones and the genital tubercle. In addition to the still incompletely known physiological functions of the enzyme, the developmental pattern of its expression in several tissues strongly suggests a modulatory role for NEP in the ontogeny of a large number of organs.

Role of salivary epidermal growth factor in the pathogenesis of Barrett's columnar lined oesophagus

Epidermal growth factor (EGF) is implicated in the regeneration of epithelial cells at the site of inflammation or ulceration in the gastrointestinal tract. Single parotid EGF concentration and production was studied in 64 patients with Barrett's columnar lined oesophagus (CLO), in 22 patients with severe reflux oesophagitis without columnar metaplasia and in 51 normal controls. In control patients, mean salivary EGF concentration was 2790 pg/ml (median 1450 pg/ml; range 450-16,500 pg/ml) and mean single parotid EGF production was 2550 pg/min (median 1750 pg/min; range 790-18,000 pg/min). Patients with severe reflux oesophagitis had a similar EGF concentration (mean 3112 pg/ml; median 1500 pg/ml; range 300-16,000 pg/ml) and production (mean 3100 pg/min; median 2200 pg/min; range 790-17,950 pg/min) to controls. Patients with CLO had a 62 per cent lower mean EGF concentration (mean 1197 pg/ml; median 640 pg/ml; range 233-4500 pg/ml) (P less than 0.001, Mann-Whitney U test) and a 60 per cent lower EGF production (mean 1254 pg/min; median 800 pg/min; range 170-3125 pg/min) (P less than 0.001, Mann-Whitney U test) than patients with severe reflux oesophagitis. A subpopulation with malignant change in CLO (n = 16) had a similar EGF concentration and production to the CLO group as a whole (mean 1240 and 1300 pg/min, respectively). Low salivary EGF levels are associated with Barrett's CLO but not with severe oesophagitis without columnar metaplasia. EGF levels do not identify those patients who will subsequently develop malignant change.

Hymenolepis diminuta: changes in the levels of certain intestinal regulatory peptides in infected C57 mice

The levels of 10 regulatory peptides in acid-alcohol extracts of three regions of the small intestine (0-20%, 30-60%, and 70-100%, with respect to distance from the pylorus) have been monitored radioimmunometrically in sham-infected male (6-8 week old) C57 mice and mice given a 5-cysticercoid infection of the rat tapeworm Hymenolepis diminuta and autopsied 10 days postprimary infection and 5 days postsecondary infection (administered 28 days postprimary infection). The regulatory peptides examined were gastrin, gastrin-releasing peptide (GRP), glucagon (= enteroglucagon), motilin, neurotensin (NT), pancreatic polypeptide (PP), peptide histidine isoleucine (PHI), somatostatin (SRIF), substance P (SP), and vasoactive intestinal peptide (VIP). Statistical analyses revealed significant deviations from control values of five of the peptides (enteroglucagon and SP, both elevated; NT, PHI and VIP, all lowered) in intestinal tissue from infected mice; measurement of the same peptides in colonic extracts revealed no significant differences between infected and sham-infected mice. Parallel changes in peptide levels between normal infected and immunosuppressed infected mice were not evident, although elevations in the tissue levels of enteroglucagon and SP were found in infected Wistar rats (normal host). Results are discussed with respect to a peptidergic involvement in the pathology and host immune response to an intestinal tapeworm.

Short chain fatty acids dilate isolated human colonic resistance arteries

Colonic biopsy specimens were obtained from patients undergoing surgery for carcinoma of the rectum. Colonic resistance arteries (internal diameter 178-345 microns) were dissected out under the microscope and mounted in a microvascular myograph capable of measuring isometric tension development. Experiments were designed to test compounds trophic to the gastrointestinal tract--namely, glutamine and the three short chain fatty acids, acetic, propionic, and butyric acid, for effects on vascular tone. Glutamine in concentrations up to 30 mM neither constricted nor dilated the resistance arteries. The three short chain fatty acids alone and in combination, however, caused a concentration-dependent (range 0.1-30 mM) dilatation of resistance arteries preconstricted with 50 mM K+, and this relaxant effect was unaffected by removal of the endothelium, presence of indomethacin, and preconstriction with vasopressin. These data suggest that the trophic effect of glutamine on intestinal mucosa cannot be explained through actions of this compound on the resistance vasculature. In contrast, the relaxant effect of short chain fatty acids on resistance arteries in vitro suggests that these compounds may be able to improve the colonic microcirculation in vivo, thereby providing an explanation for their trophic effect on intestinal mucosa.

Does dietary fibre stimulate intestinal epithelial cell proliferation in germ free rats?

The aim of the present experiment was to investigate the role of hind gut fermentation in the proliferative response of the intestinal epithelium to dietary fibre. We have previously shown that refeeding starved rats with an elemental diet supplemented with fermentable dietary fibre (but not inert bulk) is capable of stimulating intestinal epithelial cell proliferation throughout the gastrointestinal tract. Three groups of 10 germ free (GF) rats and three groups of 10 conventional (CV) rats, were used. All groups were starved for three days and then refed for two days with either an elemental diet (Flexical); Flexical plus 30% kaolin; or Flexical plus 30% of a fibre mixture. Cell production was determined by the accumulation of vincristine arrested metaphases in microdissected crypts. There was no significant difference between refeeding the rats with an elemental diet alone or with kaolin supplementation, however, the addition of fibre in CV rats was associated with a significant increase in intestinal crypt cell production rate in both the small intestine (p less than 0.01) and the colon (p less than 0.001). This marked proliferative effects of fibre was abolished in the GF rats. It can be concluded that it is the products of hind gut fermentation, not fibre per se that stimulate intestinal epithelial cell proliferation in the colon and small intestine.

Plasma enteroglucagon, peptide YY and gastrin in rats deprived of luminal nutrition, and after urogastrone-EGF administration. A proliferative role for PYY in the intestinal epithelium?

Intestinal tissue mass was significantly reduced throughout the gastrointestinal tract (p less than 0.001) of intravenously fed (TPN) rats. Urogastrone-epidermal growth factor, (URO-EGF), reversed these changes. Although plasma enteroglucagon and gastrin levels showed a small increase with URO-EGF, this was far less than the gut tissue weight change, suggesting that it was unlikely that they were involved in modulating the proliferative response of the intestine to URO-EGF. Peptide tyrosine tyrosine (PYY) levels were however significantly increased by URO-EGF, indicating that PYY may possibly have a role in the modulation of intestinal cell proliferation.

Bombesin-like peptides: neuropeptides with mitogenic activity

In recent years, a remarkable advance has been made in identifying the extracellular factors that control cell proliferation in a variety of cells. Bombesin-like peptides (BN-LP) are neuropeptides involved in the regulation of many important functions, including sensory transmission, regulation of central autonomic pathways, thermoregulation, pituitary, gastric, and pancreatic secretion, food intake, and satiety. They also may stimulate cellular proliferation in a developmental and tissue-specific manner. Their role in pathogenesis appears to be related to their properties as growth factors, especially in the lung, where BN-LP are proposed to induce growth of normal and neoplastic epithelial cells. The formulated hypothesis of control of SCLC growth by BN-LP will be tested using specific synthetic BN antagonists. Neuronal modulation of the release of BN-LP from neuroepithelial bodies and paracrine effects of BN-LP as sensory neurotransmitters indicate possible pathways of nervous system involvement in tissue development, proliferation, and differentiation, as well as repair processes and wound healing.

Role of salivary epidermal growth factor in the maintenance of physicochemical characteristics of oral and gastric mucosal mucus coat

The involvement of salivary epidermal growth factor (EGF) in the maintenance of oral and gastric mucosal mucus coat dimension and chemical characteristics was investigated using sialoadenectomized rats. Examination of the oral and gastric mucosal surface by phase contrast microscopy and Alcian blue uptake revealed that deprivation of salivary EGF caused a 31-36% reduction in mucus coat thickness and a 38-43% reduction in adherent mucin content. Chemical analyses indicated that the mucus coat of sialoadenectomized group exhibited a 21-28% increase in protein and a 67% decrease in covalently bound fatty acids, a 30% decrease in carbohydrates, and a 32-37% decrease in lipids. Sialoadenectomy also evoked changes in the chemical composition of mucus glycoprotein component of oral and gastric mucus coat reflected in the lower content of sulfate (25-26%), associated lipids (24-25%), and covalently bound fatty acids (67-75%). Intragastric supplementation of EGF had no effect on the physicochemical changes caused by sialoadenectomy in the oral mucosal mucus coat, while nearly complete restoration to normal characteristics occurred in the gastric mucosal mucus coat. The results suggest that salivary EGF is essential for the maintenance of mucus coat dimension and quality needed in the protection of alimentary tract epithelium.