An immunohistochemical study on the distribution of endocrine cells in the gastrointestinal tract of the musk shrew, Suncus murinus

The endocrine cells in the gastrointestinal tract of the musk shrew were studied immunohistochemically. Eleven kinds of endocrine cells, immunoreactive for serotonin, somatostatin, gastrin, cholecistokinin, gastric inhibitory polypeptide, motilin, secretin, neurotensin, pancreatic glucagon, enteroglucagon and bovine pancreatic polypeptide, were revealed. In the stomach, serotonin-, somatostatin-, gastrin-, pancreatic glucagon- and enteroglucagon-immunoreactive cells were detected. The first three types of cells predominated and were more abundant in the pyloric glands than in the other stomach regions. In the small intestine, all types of endocrine cells were found, each having different distributions and relative frequencies. In the large intestine, 10 types of endocrine cells except cholecystokinin-immunoreactive cells were detected. Serotonin- and bovine pancreatic polypeptide-immunoreactive cells were more numerous in the large intestine than in the small intestine.     

An immunocytochemical investigation with monoclonal antibodies to somatostatin

Summary Four monoclonal antibodies specific for somatostatin have been produced and characterized. These antibodies were used to assess the anatomical relationship of somatostatin-containing cells in the pancreas and gastrointestinal tract of man, baboon and rat with ten other peptide-containing endocrine cells. The peptides investigated were gastrin, cholecystokinin, motilin, secretin, neurotensin, gastric inhibitory polypeptide, gut-glucagon, pancreatic glucagon, pancreatic polypeptide and insulin.The only regions in which somatostatin cells were seen in close contact with another endocrine cell were in the pancreas and the gastric antrum. In the pancreas somatostatin cells were commonly seen in close contact with insulin, glucagon and pancreatic polypeptide cells and infrequent contact was demonstrable with the gastrin-immunoreactive cells in the antrum of both rat and man. In all other cases no evidence was obtained for a close anatomical relationship between somatostatin cells and the other enteroendocrine cells.     

An immunocytochemical investigation with monoclonal antibodies to somatostatin

Four monoclonal antibodies specific for somatostatin have been produced and characterized. These antibodies were used to assess the anatomical relationship of somatostatin-containing cells in the pancreas and gastrointestinal tract of man, baboon and rat with ten other peptide-containing endocrine cells. The peptides investigated were gastrin, cholecystokinin, motilin, secretin, neurotensin, gastric inhibitory polypeptide, gut-glucagon, pancreatic glucagon, pancreatic polypeptide and insulin. The only regions in which somatostatin cells were seen in close contact with another endocrine cell were in the pancreas and the gastric antrum. In the pancreas somatostatin cells were commonly seen in close contact with insulin, glucagon and pancreatic polypeptide cells and infrequent contact was demonstrable with the gastrin-immunoreactive cells in the antrum of both rat and man. In all other cases no evidence was obtained for a close anatomical relationship between somatostatin cells and the other enteroendocrine cells.     

An immunohistochemical study of gut endocrine cells in two species of insectivorous vespertilinid bats (Chiroptera: Pipistrellus abramus and Plecotus auritus sacrimontis)

11 endocrine cell types immunoreactive for either 5-hydroxytryptamine (5-HT), somatostatin, gastrin, cholecystokinin (CCK), gastric inhibitory peptide (GIP), motilin, secretin, neurotensin, pancreatic glucagon, enteroglucagon or bovine pancreatic polypeptide (BPP) were found in gastrointestinal tract of 2 species of insectivorous bats. 5 of these 11 types of endocrine cells were located in the stomach and all 11 types of endocrine cells were found in the intestine. However, the distribution and relative frequency of each immunoreactive endocrine cell varied among the cell types and between the 2 species of bats examined. In Brunner's glands, gastrin- and 5-HT-immunoreactive cells were detected very rarely in Pipistrellus and only occasionally in Plecotus. The present results obtained from the insectivorous bats were compared with those of the sanguivorous vampire bats.     

Histological and immunohistochemical studies of the endocrine cells of the gastrointestinal mucosa of the toad (Bufo regularis)

Summary Using histological and immunhistochemical techniques, nine endocrine cell types were observed in the mucosa of the gastrointestinal tract of the toad,Bufo regularis, viz. enterochromaffin, somatostatin, glucagon, pancreatic polypeptide (PP), secretin, gastric inhibitory peptide (GIP), gastrin-C-terminal pentapeptide (GTPP), neurotensin and bombesin cells. The enterochromaffin cells were distributed throughout the gastrointestinal tract except the rectum. Somatostatin, glucagon, PP, secretin, GIP and GTPP cells were observed both in the ileum and bombesin cells only in the pyloric and antral parts of the stomach. Immunostaining of consecutive sections did not reveal more than one polypeptide hormone in any of these cell types. It is concluded from the present results that the toad gastrointestinal mucosa contains endocrine cell types that are more or less homologous to those in the mammal alimentary tract, though some of them exhibit a different topographic distribution.     

The effect of neurotensin and secretin on gastric acid secretion and mucosal blood flow in man

Neurotensin stimulates pancreatic secretion directly and by potentiating the effect of secretin. Neurotensin also inhibits gastric secretion. Secretin inhibits gastric secretion as well, but whether it also interacts with neurotensin is not known. Secretin is known to inhibit gastric mucosal blood flow (GMBF). The effect of neurotensin on GMBF is not known. Acid secretion (triple lumen perfused orogastric tube) and GMBF ([14C]aminopyrine clearance) were therefore measured in 6 subjects during neurotensin, secretin and neurotensin plus secretin infusions. Neurotensin plus secretin reduced acid secretion by a median 130 (range 34-394) mumol/min which was significantly greater than either neurotensin at 36 (7-67) mumol/min or secretin 54 (20-347) mumol/min alone (P less than 0.05). This effect appeared independent of GMBF. Neurotensin plus secretin reduced GMBF by 14 (12-27) ml/min but not significantly more than neurotensin at 11 (3-20) ml/min or secretin 18 (2-27) ml/min alone. Further, there was no correlation between changes in acid output and GMBF during infusion of the peptides. We conclude that the inhibitory effects of neurotensin and secretin on gastric secretion are at least additive and together they may function as an 'enterogastrone'.     

Histological and immunohistochemical studies of the endocrine cells of the gastrointestinal mucosa of the toad (Bufo regularis)

Using histological and immunhistochemical techniques, nine endocrine cell types were observed in the mucosa of the gastrointestinal tract of the toad, Bufo regularis, viz. enterochromaffin, somatostatin, glucagon, pancreatic polypeptide (PP), secretin, gastric inhibitory peptide (GIP), gastrin-C-terminal pentapeptide (GTPP), neurotensin and bombesin cells. The enterochromaffin cells were distributed throughout the gastrointestinal tract except the rectum. Somatostatin, glucagon, PP, secretin, GIP and GTPP cells were observed both in the stomach and in the small intestine. Neurotensin cells were seen only in the ileum and bombesin cells only in the pyloric and antral parts of the stomach. Immunostaining of consecutive sections did not reveal more than one polypeptide hormone in any of these cell types. It is concluded from the present results that the toad gastrointestinal mucosa contains endocrine cell types that are more or less homologous to those in the mammal alimentary tract, though some of them exhibit a different topographic distribution.     

Different actions of secretin and Gly-extended secretin predict secretin receptor subtypes

Only one secretin receptor has been cloned and its properties characterized in native and transfected cells. To test the hypothesis that stimulatory and inhibitory effects of secretin are mediated by different secretin receptor subtypes, pancreatic and gastric secretory responses to secretin and secretin-Gly were determined in rats. Pancreatic fluid secretion was increased equipotently by secretin and secretin-Gly, but secretin was markedly more potent for inhibition of basal and gastrin-induced acid secretion. In Chinese hamster ovary cells stably transfected with the rat secretin receptor, secretin and secretin-Gly equipotently displaced (125)I-labeled secretin (IC(50) values 5.3 +/- 0.5 and 6.4 +/- 0.6 nM, respectively). Secretin, but not secretin-Gly, caused release of somatostatin from rat gastric mucosal D cells. Thus the equipotent actions of secretin and secretin-Gly on pancreatic secretion appear to result from equal binding and activation of the pancreatic secretin receptor. Conversely, secretin more potently inhibited gastric acid secretion in vivo, and only secretin released somatostatin from D cells in vitro. These results support the existence of a secretin receptor subtype mediating inhibition of gastric acid secretion that is distinct from the previously characterized pancreatic secretin receptor.     

Regulatory peptides in the gastrointestinal tract of Alligator mississipiensis

Summary The gastrointestinal tract of the alligator Alligator mississipiensis has been investigated for the presence of immunoreactivity to fourteen regulatory peptides all known to occur in the mammalian gut system.Mucosal endocrine cells reacting specifically with the antisera to neurotensin, C-terminal gastrin, somatostatin, bombesin, secretin, pancreatic glucagon and enteroglucagon were detectable, the distribution of these cells being, in general, similar to the mammalian pattern. Peripheral nerve cell bodies and nerve fibres were detected with the antisera to vasoactive intestinal polypeptide, substance P, bombesin and somatostatin again with a distribution similar to that seen in mammals.No immunoreactivity was observed with the available antisera to glicentin, motilin, gastric inhibitory polypeptide, gastrin 34, cholecystokinin 9–20 and met-enkephalin.     

Cardiac output and regional blood flows during hypoxaemia in unanaesthetized newborn lambs

There is limited information available regarding the effects of hypoxemia on cardiac output and the distribution of blood flow and oxygen delivery in unanaesthetized newborns of any species. We measured these variables in 12 unanaesthetized newborn lambs during a control period and during 50% and 75% reductions in aortic blood oxygen content which were produced by placing each lamb in an environment of 8-10% and 5-6% oxygen, respectively. 1-2% carbon dioxide was added to the gas mixture and there were no significant changes in aortic blood PCO2 or pH. Hypoxaemia was associated with a 15-20% increase in cardiac output but total somatic oxygen delivery decreased. Cerebral, myocardial, adrenal and diaphragmatic blood flows increased and their oxygen deliveries were not diminished. Oxygen deliveries to the spleen, kidneys, gastrointestinal tract and carcass decreased when aortic blood oxygen content was reduced. This study demonstrates that the newborn lamb has a limited ability to increase its cardiac output during hypoaxemia, but that oxygen deliveries to the heart, brain, adrenals and diaphragm are maintained in association with a redistribution of blood flow.     

Acute stimulation of ganglionic tyrosine hydroxylase activity by secretin,VIP and PHI

We have examined the ability of a number of neuropeptides to increase tyrosine hydroxylase (TH) activity in the superior cervical ganglion in vitro. Secretin and vasoactive intestinal peptide (VIP) both increased TH activity, whereas angiotensin II, bombesin, bradykinin, cholecystokinin octapeptide, insulin, luteinizing hormone-releasing hormone, [D-Ala², Met³]enkephalinamide, motilin, neurotensin, somatostatin, and substance P produced no effects. Secretin and VIP increased TH activity with an EC₅₀ of 5 nM and 0.5 μM, respectively. The effects of these peptides were not altered by prior decentralization of the ganglia, by addition of hexamethonium (3 mM) and atropine (6 μM), or by lowering the concentration of calcium in the medium to 0.1 mM. Addition of carbachol (3 μM) potentiated the effects of both secretin and VIP on TH activity. Several gastrointestinal peptides with structural similarities to secretin and VIP were examined for their ability to increase TH activity. Glucagon, gastric inhibitory peptide and human pancreatic tumor growth hormone-releasing factor produced no effect at a concentration of 10 μM, while PHI increased enzyme activity.     

Gastrointestinal secretory, motor and circulatory effects of corticotropin releasing factor (CRF)

This study was designed to determine the effects of CRF on the gastrointestinal functions such as secretion, motility and circulation in dogs. CRF was found to inhibit dose-dependently gastric acid response to pentagastrin but not to histamine. CRF stimulated pancreatic bicarbonate and protein secretion under basal conditions and in response to secretin or cholecystokinin (CCK). This stimulation was accompanied by an increase in plasma levels of pancreatic polypeptide (PP), but not of secretin or gastrin. CRF caused a partial inhibition of the migrating motor complexes in fasted dogs and increased spike activity of the small bowel. These motor effects of CRF probably resulted from the action of the released PP on the intestinal smooth muscle. CRF is also a potent and selective stimulant of the mesenteric blood flow. This effect may be secondary to the stimulation of intestinal motility and metabolism.     

The distribution of endocrine cells in the mucosa of the gastrointestinal tract of the house musk shrew,Suncus murinus (Insectivora)

Summary The distribution of endocrine cells in the gastrointestinal tract of the house musk shrew, Suncus murinus (Family Soricidae, Order Insectivora) was studied immunohistochemically. The hormones investigated were gastrin, cholecystokinin (CCK), somatostatin, secretin, glucagon, gastric inhibitory polypeptide (GIP), motilin and neurotensin. In the gastric mucosa, gastrin and somatostatin cells were only found in the pyloric regions, and no other hormonal cell-types were observed. In the intestinal mucosa, the largest number of endocrine cells belonged to the gastrin and glucagon/glicentin cell-types, whereas CCK-33/39 and secretin cells were the least numerous. Numbers of other cell-types were intermediate between these two groups. The gastrin and GIP cells were mostly localized in the proximal portion of the intestine, decreasing in number towards the distal portion. The motilin and CCK-33/39 cells were restricted to the proximal half. The glucagon/glicentin and neurotensin cells were most abundant in the middle portion. The somatostatin and secretin cells, although only present in small numbers, were randomly distributed throughout the intestine. This characteristic distribution of gastrointestinal endocrine cells is discussed in comparison with the distribution patterns of other mammals.Dr. Munemitsu Hoshino, who was Professor of the Department of Pathology and directed this study, passed away on May 23rd 1988     

Hepatic bile and pancreatic exocrine secretions evoked by gastrointestinal peptides in sheep

The secretory response of hepatic bile and exocrine pancreas to gastrointestinal peptides has been studied in chronically cannulated sheep. Pancreatic juice flow and protein output were evoked dose dependently by intraportal injection of secretin, CCK-8, caerulein, VIP and neurotensin. However, biliary secretion was evoked by only secretin. Biliary and pancreatic exocrine secretions were enhanced by delivered gastric juice into the duodenum as followed by the increased plasma concentration of immunoreactive secretin (IRS). Results suggest that secretin is the major peptide that regulates pancreatic exocrine secretion and hepatic bile production in the sheep.     

Up- and down-regulation of membrane receptors as possible mechanisms related to the antiulcer actions of milk in rat gastric mucosa

The effects of a cow's milk diet on receptor activity and histamine metabolism in gastric glands and mucosa isolated from adult rats were examined. The milk diet was associated with (1) a decreased mobilization of H₂ receptors by histamine and (2) an increased mobilization of PGE₂ (prostaglandin E₂) receptors in mucous cells (cytoprotective effect) and parietal cells (antiacid effect). These changes are not observed for the receptors reducing pentagastrin- and histamine-induced gastric acid secretion (pancreatic/enteroglucagons, somatostatin) and stimulating mucus, bicarbonate and pepsin secretions in the rat (secretin). Cimetidine produced a parallel displacement of the histamine dose-response curve, suggesting competitive inhibition between this classical H₂ receptor antagonist and histamine in the two experimental groups. Prostaglandins and other components in milk such as EGF (epidermal growth factor) and somatostatin might therefore protect gastric mucosa by a differential control of PGE₂ and histamine H₂ receptor activity eitherdirectly (PGE₂ in milk) orindirectly (inhibition of endogeneous histamine synthesis/release and stimulation of PGE-I synthesis/release).     

Actions of various gastrointestinal peptides on the isolated amphibian spinal cord.

The effects of a number of peptides which are found in the gastrointestinal tract have been ascertained on the direct current recorded dorsal and ventral root responses of the isolated hemisected toad spinal cord. Motilin, substance P, bombesin, neurotensin, and thyrotropin releasing hormone had potent depolarizing actions on dorsal root terminals and motoneurons. These substances evoked discernable effects at concentrations as low as 10--7 M, or even lower with motilin. The effects of motilin, neurotensin, and thyrotropin-releasing hormone were greatly reduced or abolished by perfusion of the preparation with tetrodotoxin. Adrenocorticotrophic hormone, secretin, and pancreozymin (cholecystokinin) also depolarized dorsal root terminals and motoneurons. The effects of secretin and cholecystokinin were not abolished by tetrodotoxin. Leu- and Met-enkephalin had weak hyperpolarizing actions on the dorsal and ventral root potentials of repetitively stimulated preparations. Gastrin, gastric inhibitory peptide, glucagon, and somatostatin had no apparent effects on the responses of the preparation. Angiotensin and vasopressin both had rather weak depolarizing effects on the dorsal and ventral roots.     

Functional and structural characterization of the secretin receptors in rat gastric glands: Desensitization and glycoprotein nature

We have documented and characterized the down-regulation of the¹²⁵I-secretin binding sites and the associated desensitization of the secretin receptor-cAMP system in rat gastric glands. Secretin induced a rapid decrease of the high-affinity¹²⁵I-secretin binding sites with t^1/2=30 min at 37°C. Half-maximal down-regulation and desensitization occurred at 10^–9 M secretin, a physiological concentration corresponding to the half-maximal activation of the secretin receptor. The Scatchard parameters of the low-affinity¹²⁵I-secretin binding sites were unaffected by the pretreatment. This desensitization is heterologous in view of the loss of responsiveness to the truncated glucagon-like peptide 1 (TGLP-1), and pharmacologically selective since the sectetin-related analogue VIP (10^–7 M) does not alter the secretin-induced cAMP generation in rat gastric glands. The glycoprotein nature of the secretin receptor has also been demonstrated using WGA-agarose affinity chromatography of the solubilized¹²⁵I-secretin receptor complex.     

Effect of thyrotropin-releasing hormone on gastro-intestinal secretions in dogs

Thyrotropin-releasing hormone (TRH) immunoreactivity has been shown previously to be distributed throughout the gastrointestinal tract and the pancreas. This study demonstrated that TRH given intravenously suppresses, in a dose-related manner, sham-feeding induced food intake and inhibits gastric secretion provoked by infusion of pentagastrin or instillation of 10% liver extract into the stomach. TRH also reduces pancreatic response to secretin, caerulein, feeding a meat meal or duodenal acidification. The findings that TRH inhibits gastric and pancreatic secretions induced by exogenous and endogenous stimulants, and that the inhibition by TRH of post-prandial secretion is not accompanied by any change in serum gastrin, indicate that TRH probably acts directly on the exocrine stomach and pancreas.     

Neuroendocrine peptide levels in the gastrointestinal tract of mice after unilateral cervical vagotomy

The effects of left and right unilateral cervical vagotomy on the content of several neuroendocrine peptides were studied in different parts of the murine gastrointestinal tract, known to receive vagal innervation. The neuroendocrine peptides investigated were secretin, gastric inhibitory peptide (GIP), gastrin, motilin, peptide YY (PYY), somatostatin, substance P, VIP, neurotensin, neuropeptide Y (NPY), and galanin. The neuroendocrine peptide concentration was affected after both left and right vagotomy, and that the changes in the concentrations of the neuroendocrine peptide levels occurred in all the gastrointestinal segments investigated, namely antrum, small and large intestine. However, these changes varied, depending on which side was vagotomized and the interval after vagotomy. It is concluded that the vagus nerve had an important impact on the neuroendocrine system in the murine gut. It is suggested, furthermore that the contradictory results obtained earlier on the effect of vagotomy on the gastrointestinal peptides may depend on differences in the vagotomy methods used and on differences in observation time after vagotomy.     

Effect of atropine and somatostatin on bombesin-stimulated plasma gastrin,cholecystokinin and pancreatic polypeptide in man

Infusion of the neuropeptide bombesin stimulates the secretion of several gastrointestinal hormones by an unknown mechanism. We have investigated the effects of atropine (15 ng/kg as bolus followed by 2.5 ng/kg · 30 min) and somatostatin (125 μg as i.v. bolus followed by 62.5 μg/30 min) on the stimulation of 3 hormones (gastrin, cholecystokinin and pancreatic polypeptide) by 60 pmol/kg · 20 min bombesin in 6 healthy volunteers. Plasma samples for measurement of hormones by sensitive and specific radioimmunoassays were obtained at − 5, 0, 2.5, 5, 7.5, 10, 15, 20, 25 and 30 min. Bombesin induced significant increases in plasma gastrin (12 ± 2 to 34 ± 3 pM; P < 0.0005), cholecystokinin (1.2 ± 0.2 to 8.9 ± 0.7 pM; P < 0.0001) and pancreatic polypeptide (22 ± 4 to 72 ± 19 pM; P < 0.05). There were great differences between the effects of atropine and somatostatin on the hormonal responses to bombesin. Atropine slightly increased the response of gastrin by 19% and that of cholecystokinin by 15%, but strongly inhibited the bombesin-stimulated pancreatic polypeptide secretion by 97%. On the other hand, somatostatin inhibited the bombesin-induced secretion of gastrin by 48%, cholecystokinin by 82% and pancreatic polypeptide by 107%. These results point to considerable qualitative and quantitative differences in the stimulatory mechanisms of bombesin on the hormones studied.