Somatostatin effectively prevents ethanol- and NSAID-induced gastric mucosal damage in rats

Gastric protection by α-melanocyte-stimulating hormone against ethanol in rats: Involvement of somatostatin

The proopiomelanocortin-derived tridecapeptide alpha-melanocyte-stimulating hormone (alpha-MSH) is a neuropeptide that exerts broad anti-inflammatory actions in mammals. This study aimed to investigate the effect of alpha-MSH on ethanol-induced gastric ulcer in rats and to evaluate the involvement of endogenous somatostatin in the actions of the peptide. The rats received 1 mL 75% ethanol or saline orally. alpha-MSH was given (25 micro g/rat; i.p.) alone or following the somatostatin antagonist cyclo-(7-aminoheptanoyl-PH-E-d-Trp-Lys-THR) (10 microM/kg; i.p.) administration. Gastric lesions were scored macroscopically and microscopically following decapitation at 30 min after ethanol challenge. Gastric malondialdehyde (MDA) level, myeloperoxidase (MPO) activity and mast cell counts were assessed. Ethanol-induced gastric hemorrhagic lesions were characterized by increased gastric MDA level, MPO activity and mast cell counts. alpha-MSH treatment decreased the extent of tissue injury and reversed tissue MDA level, MPO activity and mast cell counts. The effect of the peptide on the severity of gastric lesions, MDA level and MPO activity was reversed by the somatostatin antagonist. In conclusion, alpha-MSH is beneficial in a rat model of gastric ulcer via mechanisms which partly involve the endogenous somatostatin.

Effect of acid secretion blockade on acute gastric mucosal lesions induced by Tityus serrulatus scorpion toxin in anaesthetized rats

Scorpion venom (TX) promotes gastric acid and pepsin secretion leading to acute gastric mucosal lesions (AGML), when injected in animals. The goal of the present study was to observe the effects of acid gastric secretion blockers over the incidence of TX-induced AGML in vivo. To verify this model, we used male albino rats, fasted 18-20 h (n=122) and anaesthetized with urethane (1.4 g/kg, i.p.). Their trachea and left femoral vein were both cannulated; the first to avoid airway obstructions during scorpion intoxication and the second for administration of saline, TX and acid blockers. Following the surgical procedure, the animals were divided in 10 groups of at least 10 animals each. Control groups were injected with NaCl 0.9% 1 ml/kg (n=10) or TX 375 microg/kg (n=32). Test groups (n=10, each) received atropine 5 mg/kg, cimetidine 10mg/kg, ranitidine 2.5mg/kg, ranitidine 5mg/kg, omeprazol 1 mg/kg, omeprazol 4 mg/kg, octreotide 80 and octreotide 100 microg/kg 10 min before the TX was injected. After 1h of intoxication, the stomach was resected for macroscopic study and the gastric secretion was collected for volume, pH and acid output assessment. We observed that all blockers were able to completely or partially prevent the TX-induced acid secretion as well as the AGML (p<0.05). Our data suggest the TX-induced AGML can be prevented by different class of acid blockers injected before the intoxication.

The efficacy of octreotide in pancreatic and intestinal changes: radiation-induced enteritis in animals

Radiation enteritis occurs during the radiotherapy of many intraabdominal malignancies. Radiation induces cellular injury directly and through the generation of free radicals. In the present study we aimed to investigate the effect of octreotide (OCT) pretreatment in irradiation-induced enteritis. For this aim, rats were injected with 50 microg/kg OCT 4 days before irradiation and continued for 3 more days, until sacrifice. Then intestinal and pancreatic myeloperoxidase (MPO) activities and intestinal malondialdehyde (MDA) levels of the rats were measured. Irradiation significantly increased intestinal and pancreatic MPO activities and MDA levels of intestinal tissues in comparison to those of the sham group. OCT treatment improved this elevation. The histopathologic evaluation of the mucosal structure was also preserved in the OCT-treated group. Inflammation of pancreatic tissue was also confirmed with histopathological examinations. In the irradiation group, NFkappa-B overexpression was detected. OCT treatment decreased the end organ damage and inflammation of the small intestine. In conclusion, OCT appears to have beneficial effects on intestinal and pancreatic damage in abdominal irradiation through the inflammatory process.

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Octreotide ameliorates alendronate-induced gastric injury

Alendronate causes serious gastrointestinal adverse effects. The aim of this study was to investigate whether octreotide, a synthetic somatostatin analogue, improves the alendronate-induced gastric injury. Rats were administered 20mg/kg alendronate by gavage for 4 days, either alone or following treatment with octreotide (0.1 ng/kg, i.p.). On the last day, following drug administration, pilor ligation was performed and 2h later, rats were killed and stomachs were removed. Gastric acidity and tissue ulcer index values, lipid peroxidation (as assessed by malondialdehyde, MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity as well as the histologic appearance of the stomach tissues were determined. Chronic oral administration of alendronate induced significant gastric damage, increasing lipid peroxidation (37.1+/-3.2 nmol/g) and myeloperoxidase activity (57.6+/-3.7 U/g), while tissue glutathione levels (09.+/-0.1 micromol/g) decreased. Treatment with octreotide prevented this damage as well as the changes in biochemical parameters (MDA: 23.4+/-1.3 nmol/g; MPO: 31.68 U/g; GSH: 15.+/-0.1 micromol/g). Findings of the present study suggest that alendronate induces oxidative gastric damage by a local irritant effect, and that octreotide ameliorates this damage by inhibiting neutrophil infiltration and reducing lipid peroxidation. Therefore, its therapeutic role as a "ulcer healing" agent must be further elucidated in alendronate-induced gastric mucosal injury.

Role of acute elevation of portal venous pressure by exogenous glucagon on gastric mucosal injury in rats with portal hypertension

Time-course studies revealed the increased susceptibility of the gastric mucosa to noxious injury in portal hypertension correlates with the level of elevated portal venous pressure and hyperglucagonemia. Whether acute elevation of portal venous pressure by exogenous glucagon aggravates such injury is not known. We tested the hypothesis that glucagon in a dose sufficient to acutely elevate portal venous pressure aggravates noxious injury of the gastric mucosa in rats with portal hypertension. Infusion of a portal hypotensive dose of somatostatin should reverse these changes. In anesthetized rats with portal vein ligation, glucagon, somatostatin or the combination was administered intravenously in a randomized, coded fashion. Acidified ethanol-induced gastric mucosal injury was determined. Portal venous pressure and gastric mucosal perfusion and oxygenation (reflectance spectrophotometry) were monitored to confirm the effects of the respective intravenous treatments. Exogenous glucagon exacerbated acidified ethanol-induced gastric mucosal injury. The exacerbation was attenuated by somatostatin. These changes paralleled the portal hypertensive and hypotensive effects of glucagon and somatostatin, respectively. Our data suggest that a unique mechanism is triggered with the onset of portal hypertension. In an antagonistic manner, glucagon and somatostatin modulate this novel mechanism that controls portal venous pressure and susceptibility of the gastric mucosa to noxious injury.

Somatostatin-induced gastric protection against ethanol: involvement of nitric oxide and effects on gastric mucosal blood flow

BACKGROUND/AIMS

The mechanisms of somatostatin-mediated gastroprotection are not fully understood. Aims of this study were to determine in the rat the role of nitric oxide (NO) in somatostatin-induced effects on gastric mucosal protection and blood flow (GMBF) in the absence and in the presence of intraluminal ethanol.

METHODS

Ethanol (70% v/v)-induced gastric mucosal injury after orogastric dosing was quantitated at 30 min and GMBF determined in an ex vivo gastric chamber preparation.

RESULTS

Somatostatin (4 microg/kg; i.p.) protection against ethanol-induced ulceration was prevented by the NO inhibitor L-NNA and restored by L-arginine, but not D-arginine. Somatostatin (1-8 microg/kg; i.p.) did not effect basal GMBF. The gastroprotective dose of somatostatin (4 microg/kg; i.p.) prevented the decrease in GMBF caused by ethanol. L-NNA reversed this vascular effect of somatostatin.

CONCLUSION

Somatostatin-induced gastroprotection and restoration of GMBF during ethanol exposure involve mechanisms which are dependent on NO generation.

Beta(beta)3-adrenergic receptors in human pancreatic islet and duodenal somatostatin neuroendocrine cells

BACKGROUND

We previously localized beta3-adrenergic receptors immunohistochemically in human gastrointestinal smooth muscle and incidently found a population of human pancreatic islet cells and duodenal epithelial neuroendocrine cells that also expressed beta3-adrenergic receptors.

AIM

To identify the nature of the islet and duodenal cells that stained positive for beta3-adrenergic receptors.

METHODS

Paraffin sections of human pancreas and duodenum and Chinese hamster ovary cells transfected with the human beta3-adrenergic receptor were immuno-stained for beta3-adrenergic receptors using an affinity-purified rabbit polyclonal antibody (anti-P12) raised against a 15 amino acid sequence (P12) of the human receptor. Immunohistochemical staining for the receptor was carried out in the presence and absence of P12 peptide and both somatostatin 14 and 18 peptides. beta3-adrenergic receptor-stained sections were also double-immunostained with anti-insulin, -glucagon, -somatostatin and -pancreatic polypeptide antibodies.

RESULTS

A subpopulation of human pancreatic islet cells and duodenal epithelial cells expressed positive cytoplasmic beta3-adrenergic receptor immunostaining. Using distribution and double-staining techniques, these cells were found to be somatostatin-positive D cells but not A or B cells. The positive staining of D cells with anti-P12 antibody was inhibited by prior incubation of the antibody with P12 peptide but not somatostatin-14 or -28 peptides. Pancreatic vascular smooth muscle and duodenal vascular and non-vascular smooth muscle also stained with anti-P12 antibody. Transfected Chinese hamster ovary cells showed positive membrane staining.

CONCLUSION

We have identified a population of neuroendocrine cells in the human pancreas and duodenum that express beta3-adrenergic receptors. These cells appear to be somatostatin D cells.

Dual effects of somatostatin analog octreotide on gastric emptying during and after intragastric fill

The effect of the somatostatin analog agonist octreotide (Oct) on gastric emptying of 12.5% glucose during and after intragastric fill was examined in nondeprived rats equipped with stainless steel gastric fistulas. The rate of intragastric infusion (1.0 ml/min) and the volumes delivered (6 or 12 ml) were within the ranges typically observed in rats normally ingesting the same stimulus. In experiment 1, a dose-related suppression of glucose emptying during 12-min infusions was obtained in response to Oct (0, 0.0014, 0.014, 0.14, and 1.4 nmol/kg sc) injected 60 min before the test. The highest dose tested yielded a 37% suppression of glucose solute emptying during fill. In experiment 2, the suppression of emptying during fill induced by Oct (1.4 nmol/kg) was reversed by 10 or 40 microgram/kg of the somatostatin antagonist cyclo(7-aminoheptanoyl-Phe-D-Trp-Lys-Thr[Bzl]). The antagonist did not by itself affect emptying. Experiment 3 showed that the suppression of emptying obtained with 0.14 and 1.4 nmol/kg Oct had disappeared when the gastric sample was withdrawn 36 min after the termination of 12-min glucose infusions. Experiment 4 showed that the Oct-induced reductions in emptying during 6- and 12-min infusions, in fact, were reversed within 6 min after infusion offset. The point of transition between suppressed and increased emptying did not depend on time from injection or from infusion onset but was linked to the offset of the intragastric infusion regardless of its duration. The present findings support the notion that separable mechanisms govern gastric emptying during vs. after gastric fill.

Corticotropin-releasing factor-induced suppression of gastric emptying in the rat is blocked by cyclo(7-aminoheptanoyl-phe-D-TRP-LYS-THR[BZL], an in vivo somatostatin antagonist

Corticotropin-releasing factor (CRF) acts centrally to suppress gastric emptying and increase plasma levels of somatostatin in rats. The experiments were conducted to examine whether cyclo(7-aminoheptanoyl-phe-D-TRP-LYS-THR[BZL]), which acts as a somatostatin antagonist in vivo, blocks the effect of CRF on gastric emptying of glucose. Sprague-Dawley rats were implanted with chronic intragastric fistulas and guide cannulas for fourth intracerebroventricular (4th i.c.v.) delivery. The stomach was evacuated after the offset of a 12-min intragastric glucose infusion (12.5%, 1.0 ml/min). CRF, (1000 pmol) injected 4th i.c.v. suppressed solute emptying by 44% as compared to vehicle (P < 0.001). Pretreatment with cyclo(7-aminoheptanoyl-phe-D-TRP-LYS-THR[BZL]), 40 microg/kg, s.c., having no effect when delivered alone, blocked the effect of CRF on emptying. The results suggest that endogenously released somatostatin participates in CRF-induced suppression of gastric emptying during gastric fill.

Involvement of endogenous cholecystokinin and somatostatin in gastroprotection induced by intraduodenal fat

Duodenal fat such as oleate is known to influence gut functions by release of cholecystokinin (CCK), but the contribution of CCK endogenously released by duodenal fat or by diversion of pancreatic juice from the duodenum in the mechanism of mucosal integrity and gastroprotection has been little studied. This study was designed to compare the effect of CCK-8 and intraduodenal (i.d.) instillation of sodium oleate, or diversion of the pancreatic biliary secretions that are known to release CCK, on the gastric mucosal lesions induced by topical application of 100% ethanol or acidified aspirin (ASA) in rats with or without the pretreatment with a CCK-A receptor antagonist, loxiglumide, or with L-365,260 to block CCK-B receptors. In addition, the effect of suppression of prostaglandin (PG) biosynthesis by indomethacin (5 mg/kg i.p.), inhibition of nitric oxide (NO)-synthase by L-NAME (5 mg/kg i.v.), or blockade of sensory nerves by capsaicin (125 mg/kg s.c.) on the protective activity of sodium oleate was determined. Sodium oleate (50-200 mM i.d.), or diversion of pancreatic juice from the duodenum for 3 h that produced significant rise in plasma CCK levels, significantly reduced gastric lesions induced by 100% ethanol to an extent similar to that induced by exogenous CCK-8 (5 nmol/kg s.c.). The protective effect of oleate or diversion of pancreatic juice was accompanied by an increase in gastric blood flow (GBF). Both protection and accompanying hyperemia were completely abolished by blockade of CCK-A receptors with loxiglumide, whereas L-365,260, an antagonist of CCK-B receptors, had no effect. Oleate given i.d. significantly attenuated acidified ASA-induced gastric lesions and gastric secretion while increasing the luminal concentration of somatostatin. These effects were significantly reduced by loxiglumide but not by L-365,260. In contrast, CCK-8, which stimulated gastric acid secretion, failed to affect the lesions induced by acidified ASA and the decrease in the GBF produced by this ulcerogen. Indomethacin, which suppressed PG generation by approximately 90%, failed to influence the protective activity of oleate or CCK-8 against ethanol-induced lesions, whereas L-NAME, vagotomy, or sensory denervation significantly attenuated this protection and accompanying hyperemia. Addition to L-NAME of L-arginine, but not D-arginine, restored the protective and hyperemic effects of CCK-8 and duodenal oleate against gastric lesions induced by ethanol or acidified ASA. We conclude that endogenous CCK released by oleate or diversion of pancreatic secretion exerts a potent gastroprotective action on the stomach involving predominantly CCK-A receptors and depending on vagal activity, and hyperemia mediated by NO and sensory nerves but unrelated to acid secretory effects and endogenous PG.

Physiological role of cholecystokinin in gastroprotection in humans

OBJECTIVE

Cholecystokinin (CCK) is able to protect gastric mucosa against acute injury in experimental animals but little is known about the role of this hormone in maintaining mucosal integrity in humans. This double-blind, placebo controlled study was performed in 16 healthy volunteers. It describes the effects of CCK-8 infused intravenously (i.v.) at physiological doses and endogenous CCK released by intraduodenal (i.d.) oleate on gastric mucosal damage, as brought about by ethanol without or with pretreatment with loxiglumide, a selective CCK-A receptor antagonist.

METHODS

CCK-8 was infused i.v. 30 min before and throughout the study or i.d. oleate was instilled through a separate duodenal tube. Thirty minutes after the start of i.v. infusion of CCK or i.d. oleate instillation, 100 ml of 50% ethanol spray was applied to the gastric mucosa using an endoscope. Gastroscopy was performed and mucosal lesions were quantified using modified Lanza score. Gastric biopsies were taken from oxyntic mucosa for histological evaluation and gastric content was aspirated for radioimmunoassay of somatostatin.

RESULTS

In placebo-treated subjects ethanol caused endoscopic damage, with an average score of 2.8+/-0.2. Histologically, a widespread disruption of surface epithelium and deep hemorrhagic necrotic lesions were observed. Pretreatment with CCK or i.d. oleate markedly reduced the endoscopic lesion score to 0.7+/-0.1 and 0.3+/-0.1, respectively, and in both cases this reduction was accompanied by a significant rise in plasma CCK. Histologically, surface epithelium was still disrupted but deep necrotic lesions were absent. Gastric content collected before and after CCK or oleate showed a several-fold increase of luminally released somatostatin.

CONCLUSIONS

Pretreatment with loxiglumide abolished the protective effects of i.v. CCK-8 and i.d. oleate on mucosal lesions induced by ethanol and prevented the rise in intragastric somatostatin, but failed to affect the increments in plasma CCK. Endogenous CCK plays a physiological role in the maintenance of mucosal integrity. This occurs through activation of CCK-A receptors and is associated with an increased gastric luminal release of somatostatin.

Peptidergic and cholinergic neurons and mediators in peptone-induced gastroprotection: role of cyclooxygenase-2

This study investigates the neural pathways, mediators, and cyclooxygenase isoenzymes involved in the gastroprotection conferred by peptone in rats. Intragastric perfusion with 8% peptone protected against gross and histological damage induced by subsequent perfusion with 50% ethanol. The gastroprotective effect of peptone was near maximally inhibited by gastrin immunoneutralization, inactivation of capsaicin-sensitive afferent neurons, calcitonin gene-related peptide (CGRP) immunoneutralization, blockade of gastrin receptors, CGRP, bombesin/gastrin-releasing peptide (GRP), or somatostatin receptors, and by the nitric oxide (NO) synthase inhibitor NG-nitro-L-arginine methyl ester and was partially (46%) counteracted by atropine. Indomethacin and the selective cyclooxygenase-2 inhibitors NS-398 and L-745,337 dose dependently (50% inhibitory dose, 4.2, 0.8, and 1.5 mg/kg, respectively) attenuated the peptone-induced protection. Dexamethasone was ineffective. These results indicate that protective effects of peptone involve endogenous gastrin and possibly somatostatin and are mediated by capsaicin-sensitive afferent, cholinergic, and bombesin/GRP neurons. CGRP, NO, and prostaglandins participate as essential mediators. The study provides evidence that prostaglandins derived from a constitutive cyclooxygenase-2 contribute to mucosal defense in the presence of ulcerogens and thus participate in homeostatic functions of the stomach.

Effect of cigarette smoke on ethanol-induced gastric mucosal lesions: the role of nitric oxide and neutrophils

The roles of neutrophil aggregation, inducible nitric oxide synthase activation and chemoattractant, leukotriene B4, in potentiation of the cigarette smoke effect on ethanol-induced gastric mucosal damage were studied. Smoke exposure markedly increased gastric lesion formation following ethanol administration and this was accompanied by substantial increase in gastric mucosal leukotriene B4 concentration, myeloperoxidase and inducible nitric oxide synthase activities. Antineutrophil serum or aminoguanidine pretreatment significantly attenuated both gastric mucosal lesion formation and inducible nitric oxide synthase activity. The increased myeloperoxidase activity was abolished by antineutrophil serum but not by aminoguanidine. These data indicated that both neutrophil mobilization and inducible nitric oxide synthase activation in the gastric mucosa play an important role in the potentiating action of cigarette smoke on ethanol-induced gastric mucosal lesion formation. Increased synthesis of nitric oxide from inducible nitric oxide synthase during gastric damage may be secondary to neutrophil infiltration in the gastric mucosa. Chemoattractant leukotriene B4 could also contribute to neutrophil recruitment in the tissue.

Effect of octreotide, a somatostatin analogue, on release of inflammatory mediators from isolated guinea pig bladder

OBJECTIVE

Somatostatin has been demonstrated to inhibit inflammation under certain circumstances. We hypothesized that in vivo treatment with octreotide, a long-acting analogue of somatostatin analogue, would diminish the capacity of inflammatory peptides to stimulate in vitro release of inflammatory mediators by the bladder.

METHODS

Female guinea pigs were injected with octreotide (20 mg./kg. i.m.) prior to euthanasia. Control guinea pigs received no treatment prior to euthanasia. Urinary bladders were removed and incubated with substance P (SP, 10 microM), neurokinin A (NKA, 10 microM), or bradykinin (BK, 10 microM) in the presence or absence of indomethacin (50 microM), and release of histamine, prostaglandins (PGE2 and PGF2 alpha), and leukotriene (LTB4) was determined.

RESULTS

Sensory peptides and BK induced time-dependent release of histamine and eicosanoids from isolated urinary bladder. Blockade of cyclooxygenase with indomethacin (50 microM) abolished peptide-induced prostaglandin release but enhanced LTB4 release. In vivo octreotide pretreatment decreased peptide-induced histamine release, had no effect on PGE2 or PGF2 alpha release, and LTB4 release. However, octreotide prevented the increase in LTB4 release in tissues incubated with indomethacin.

CONCLUSIONS

These results indicate that somatostatin has the capacity to suppress the release of histamine and prevents potentiation of LTB4 release by indomethacin by the guinea pig bladder in response to pro-inflammatory peptides, indicating that somatostatin may be useful in preventing or treating some forms of cystitis.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.

Comparison of cholecystokinin, pentagastrin, and duodenal oleate in gastroprotection in rats

BACKGROUND

Cholecystokinin (CCK) and gastrin show a potent influence on gastric secretion and motility, but their role in mucosal integrity has been little studied.

METHODS

In this study the effects of CCK-8, pentagastrin, and duodenal oleate on acute gastric lesions induced by 100% ethanol were studied in rats.

RESULTS

CCK-8 was about 13 times more potent than pentagastrin in protecting the gastric mucosa against ethanol damage. CCK released by duodenal oleate also protected gastric mucosa against this damage. The protective effects of CCK-8 were almost completely abolished by the blockage of CCK-A receptors with loxiglumide, whereas the protective effect of pentagastrin was completely abolished by L-365,260. The protective effects of CCK, pentagastrin, or duodenal oleate against ethanol injury were accompanied by a marked increase in luminal content of somatostatin, suggesting that this peptide is implicated in this protection. The protective activity of CCK and pentagastrin against ethanol injury was accompanied by a significant increase in gastric blood flow. Inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine methyl ester abolished almost completely both gastric protection and hyperemia induced by CCK and pentagastrin. Addition of L-arginine, but not D-arginine, restored the protective and hyperemic effects of CCK and pentagastrin. Pretreatment with the sulfhydryl blocking agent N-ethylmaleimide also abolished the protective and hyperemic effects of CCK and pentagastrin. The hyperemia, but not the protection, afforded by CCK and pentagastrin was reduced after sensory nerve deactivation with capsaicin.

CONCLUSIONS

Both exogenous and endogenous CCK and pentagastrin exert protective activity against ethanol damage, and this effect is mediated through separate receptors, NO, and sulfhydryl-sensitive pathway.