Fluorescence and electron microscopic histochemistry of endocrine-like cells in gastric mucosa and argyrophil tumor of Praomys (Mastomys) natalensis. Analysis of 5-hydroxytryptamine, histamine, Histidine decarboxylase, and aromatic amino acid decarboxylase

Effects of gastrin on the histamine-secretory and proliferative activity of cultured carcinoid cells derived from the stomach of the rodent Mastomys natalensis

The effects of gastrin on the synthesis and release of histamine and on cellular proliferation were investigated in a homotransplantable carcinoid tumor implanted in the rodent Mastomys natalensis and in cultured cells derived from the tumor. The homotransplanted tumor was immunopositive for histamine, synaptophysin and protein gene product 9.5, and its cells contained numerous secretory granules that were visualized by electron microscopy. When carcinoid cells were cultured in a medium with a high concentration of gastrin-I (10(4) pg/mL) for 7 days, large electron-dense secretory granules were characteristically observed in the cytoplasm. By contrast, only a few such granules and numerous secondary lysosomes were seen in cells that had been cultured in the same medium without gastrin-I. A high concentration of gastrin-I (10(4) pg/mL) significantly increased the release of histamine into the culture medium from the carcinoid cells compared with the control (P < 0.05). Cellular proliferation, as determined by monitoring the incorporation of [methyl-3H]-thymidine into the carcinoid cells increased significantly at lower concentrations of gastrin-I (10(2) and 10(3) pg/mL), (P < 0.05). At higher concentrations (10(4) pg/mL or more), gastrin-I had no effect on proliferation. These findings indicate that gastrin stimulates the synthesis and release of histamine by carcinoid cells, as well as their proliferation.

Implications of sustained suppression of gastric acid secretion

The implications of profound and sustained suppression of acid secretion are of increasing concern. Short-term inhibition of acid secretion by H2-receptor blockade or proton pump inhibition alters the gastric luminal flora and increases the risk of nosocomial pneumonia in critically ill patients who are receiving prophylaxis for stress gastritis. Long-term suppression alters gut flora, carcinogen levels in the gastric lumen, and the hormonal milieu, leading to proliferative changes in the fundic mucosa. Previous reports have noted a significant incidence of gastric malignancies in the achlorhydric environment of atrophic gastritis and pernicious anemia. Concern has also been expressed regarding the possibility of gastric neoplasia that arises after vagotomy and distal gastrectomy. The exact risk of gastric epithelial and endocrine hyperplasia or neoplasia in patients receiving potent antisecretory agents is not yet known, but such risks cannot be dismissed until long-term follow-up studies are available. The relationship between sustained suppression of acid secretion and the proliferation of epithelial and endocrine elements may provide insight into processes that regulate replication and growth of cells in the gastric mucosa.

The effect of omeprazole-induced hypergastrinemia on the oxyntic mucosa of mastomys

Mastomys is a rodent with a high incidence of spontaneous carcinoids in the acid-producing part of the stomach. The present study was conducted to examine whether hypergastrinemia could promote tumor formation in this species. Mastomys, 4 months of age, were treated for 5 months with omeprazole subcutaneously, 100 mumol/kg body weight daily, and compared with mastomys given the vehicle only. The plasma gastrin concentration and the number of antral gastrin cells were increased in the omeprazole-treated group. The hypergastrinemia was associated with elevated histidine decarboxylase activity and histamine content in the oxyntic mucosa and with a trophic effect on the oxyntic mucosa and the enterochromaffin-like cells. However, no carcinoid tumors were observed, possibly because the strain of mastomys studied does not produce carcinoids spontaneously.

Intra-ocular transplantation of carcinoid tumours from mastomys and humans

Carcinoid tumours from man and Mastomys (Praomys) natalensis produce a variety of peptide hormones. The study of these peptide-secreting tumours has been difficult because of the small amount of tissue available and because of limitations with present cell culture systems. The aim of this study was to establish an experimental model where carcinoid tumours could be maintained and their hormone secretion studied. The intra-ocular transplantation technique was chosen for its simplicity and high rate of success. Gastric carcinoid tumours from mastomys (n = 4) and human carcinoids (n = 2) (one bronchial and one ileal) were transplanted to the anterior eye chamber of Sprague-Dawley rats. Pieces of fresh tumour tissue were injected into the anterior eye chamber of rats and allowed to grow for 4-8 weeks. Rats transplanted with human tissue were immunosuppressed by daily injections with cyclosporin A (20 mg/kg). Eye chambers were inspected regularly and plasma from transplanted rats was collected for assay of peptide YY (PYY) and glucagon. Vascularization of transplants occurred within 1-2 days after transplantation in 70-80 per cent of all experiments. Microscopic analysis of transplants demonstrated a rich supply of blood vessels to tumour cells which contained characteristic neurosecretory granules. Transplanted rats had significantly (P less than 0.05) elevated levels of PYY (44-165 pmol/l) and glucagon (67-162 pmol/l) in plasma as compared with sham-operated rats (PYY 28-40 pmol/l, glucagon 33-40 pmol/l), indicating that hormone secretion by tumour cells in oculo was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of gastric endocrine tumor and age-related gut peptide alterations in Mastomys

The Mastomys (Praomys natalensis) species are a unique natural model in which the bioactivity of gastric carcinoids may be studied. Several investigators have previously demonstrated that these tumors contain large amounts of histamine. In this study we investigated the presence of peptides associated with the neoplasm. The levels and location of gastrin, gastric inhibitory peptide (GIP), neurotensin, peptide YY (PYY), pancreatic polypeptide (PP), glucagon, bombesin, vasoactive intestinal peptide (VIP) and somatostatin (SRIF) were investigated by radioimmunoassay and immunocytochemistry. In addition the distribution of these peptides were evaluated in the gastrointestinal tract of young and old animals to investigate possible age-related changes. PYY and enteroglucagon (EG) were significantly (P less than 0.001) elevated in both tumor tissue (676 +/- 152, 551 +/- 164 pmol/g) and plasma (620 +/- 160, 500 +/- 147 pmol/l) of tumor-bearing animals. Immunocytochemistry revealed PYY- and EG-like immunoreactivity in 20-30% of tumor cells. A significant decrease (P less than 0.05) in bombesin was noted in older animals, but no changes in gastric tissue content of PYY or EG could be detected between young and old animals. Gastrin was not detected in tumors and there were no significant changes in tissue or plasma levels with age. Small bowel concentrations of VIP and PYY were higher in the older mastomys (P less than 0.05). In contrast, colonic levels of bombesin, VIP, somatostatin and PYY were significantly lower (P less than 0.05) in older mastomys compared with young. The age-related changes in several peptides may reflect an adaptive response to acid hypersecretion. The multi-hormonal character of these neoplasms suggests that these tumors develop from a pluripotential stem cell.

Histamine in endocrine cells in the stomach. A survey of several species using a panel of histamine antibodies

Antibodies to histamine were used to examine the localization of the amine in cells of the stomach and upper small intestine of a great variety of species, including cartilaginous and bony fish, amphibia, reptiles (lizard), birds (chicken) and a large number of mammals. In all species gastric histamine was localized in endocrine cells (invariably found in the epithelium) and mast cells (usually with an extra-epithelial localization). The endocrine cells were identified as such by immunostaining with antibodies to chromogranin A and the mast cells were identified by toluidine blue staining. Histamine-immunoreactive endocrine cells were found almost exclusively in the acid-producing part of the stomach; only rarely were such cells observed in the pyloric gland area. They were fairly numerous in the gastric mucosa of the two subclasses of fish as well as in the amphibia and reptile species studied. Here, the majority of the histamine-immunoreactive endocrine cells seemed to have contact with the gastric lumen (open type cells) and were located in the surface epithelium (certain fish only) or together with mucous neck cells at the bottom of the pits. In the chicken, histamine-immunoreactive endocrine cells were numerous and located peripherally in the deep compound glands. They were without contact with the lumen (closed type) and had long basal extensions ("paracrine" appearance), running close to the base of the oxyntic-peptic cells. In mammals, the number of histamine-immunoreactive endocrine cells in the stomach varied greatly. They were particularly numerous in the rat and notably few in the dog, monkey and man. In all mammals, the histamine-immunoreactive endocrine cells were of the closed type and located basally in the oxyntic glands. They often had a "paracrine" appearance with long basal processes. Histamine-storing mast cells, finally, were few in both subclasses of fish as well as in the amphibian species and in the lizard. They were fairly numerous in chicken proventriculus (beneath the surface epithelium), few in the oxyntic mucosa of mouse, rat and hamster, moderate in number in hedgehog, guinea-pig, rabbit, pig and monkey, and numerous in cat, dog and man.(ABSTRACT TRUNCATED AT 400 WORDS)

Gastrin and the trophic control of gastric mucosa

Gastrin is a trophic stimulant of the acid producing gastric mucosa. Experiments have been carried out in rats, in which chronic states of either low or high serum gastrin levels were induced by surgical manipulation or drug treatment. A relationship between circulating gastrin and a trophic effect could be demonstrated in the oxyntic mucosa, but not in the pancreas and small intestine. Endocrine cells in the oxyntic mucosa (the ECL cells and A-like cells) are among the target cells for the trophic action of gastrin. The functional significance of these two cell populations is unknown. There is much experimental evidence indicating that they are under functional as well as tropic control of gastrin. The vagus nerve also exerts trophic control on the oxyntic mucosa, including the endocrine cells within it. This could be demonstrated by one-sided truncal vagotomy which caused atrophy of the mucosa and hypoplasia of endocrine cells (notably the ECL cells) on the denervated side of the stomach. Conversely, portacaval shunt greatly increased the number of ECL cells. There was no hypergastrinaemia after portacaval shunt, and no trophic effect on other cell types in the oxyntic mucosa. The factors responsible for the ECL cell proliferation after portacaval shunting remain unknown. Tumours may arise spontaneously from the ECL cells. Such neoplasias have been described in Mastomys (Praomys natalensis) and in man. ECL cell hyperplasia and neoplasia in man, but not in Mastomys, are usually associated with hypergastrinaemia either as a result of a gastrin producing tumour or as a result of achylia (sometimes associated with pernicious anaemia). It is unlikely that gastrin alone is responsible for the neoplasia, though it is quite likely that long-standing hypergastrinaemia triggers or facilitates a sequence of events that ultimately leads to tumour formation, via diffuse ECL cell hyperplasia.

Localization of histamine and histamine H2-receptor antagonists in the gastric mucosa

Histamine stimulates acid secretion by the parietal cell and this secretion is inhibited by the histamine H2-receptor antagonists. Whole body autoradiography showed that radioactivity from 14C-histamine was localized in the artery walls of the stomach and in the muscularis mucosae, but that the level in the fundic mucosa was the same as the blood. When the H2-receptor antagonists burimamide, metiamide and cimetidine were labelled with 35S, 14C or 3H and dosed to rats, whole body autoradiography showed that the stomach was predominantly labelled in the glandular mucosa from 5 to 120 min after administration. Microautoradiography in the rat and dog after intravenous injection of [3H]metiamide or [3H]cimetidine demonstrated an uptake of tritium in the parietal cell cytoplasm that was 3- to 4-times greater than that found in adjacent peptic cells or areas of muscularis mucosa. The preferential labelling persisted at a low level up to 6h after injection in the rat. The localization of radioactivity from the H2-antagonists in the parietal cell cytoplasm correlates well with their pharmacological activity in preventing acid secretion from this cell.

Gastric carcinoids of argyrophil ECL cells

Histochemical and ultrastructural studies were carried out in four gastric carcinoids, two of which were associated with atrophic gastritis and pernicious anemia. All tumors showed intense argyrophilia and vesicular granules resembling those of endocrine enterochromaffinlike (ECL) cells in normal human gastric mucosa. Tumor cells were found to be unreactive to all the 18 available antiserums to gut hormones, including gastrin, somatostatin, glucagon, and pancreatic polypeptides. The tumors were interpreted as ECL cell argyrophil carcinoids with the various degrees of differentiation and atypia.