Increase In Gastric Blood Flow Research Articles

Peripheral administration of Neuropeptide-W protects against stress-induced gastric injury in rats

AimsNeuropeptide W (NPW) participates in the regulation of neuroendocrine response to stress, but the possible protective effects of NPW against stress-induced gastric ulcers have not yet been evaluated. The purpose of the present study was to investigate whether peripherally administered NPW could have gastroprotective effects in water-immersion restraint stress (WIRS)-induced gastric injury. Main methodsSprague-Dawley rats were subjected to WIRS for 6 h, and treated with NPW (0.1, 0.3, 1 and 5 μg/kg) or saline at 30 min before WIRS application. Under anesthesia, capsaicin (1 %) was applied perivagally for degeneration of vagal afferent fibers (VAD) at two weeks before WIRS protocol. Blood, gastric and brain tissues were obtained for biochemical, molecular and histological assessments. Key findingsNPW treatment given immediately before WIRS application attenuated stress-induced gastric oxidant damage along with an increase in gastric blood flow, while similar gastroprotective effects were observed in NPW-treated rats with denervated vagal afferents. NPW prevented elevations in serum IL-6 and TNF-α levels, and increased cycloxygenase-1 mRNA, but suppressed cycloxygenase-2 mRNA levels. In addition, WIRS-induced downregulation of NPW expression in the brain tissue was reversed in NPW-treated rats having less severe ulcers, suggesting that cerebral NPW production could be critical in the central regulation of stress-induced ulcerogenesis. SignificanceOur results demonstrate for the first time that the peripheral administration of NPW offers an anti-ulcer activity in stress-induced gastric ulcer by regulating gastric blood flow, suppressing oxidant damage and inflammation via the modulation of COX-induced gastroprotection and without the contribution of vagal afferent fibers.

УЧАСТИЕ TRPV1 В РЕГУЛЯЦИИ ПРОДУКЦИИ БИКАРБОНАТОВ И КРОВОТОКА В ЖЕЛУДКЕ ПРИ УВЕЛИЧЕНИИ ПОЛОСТНОЙ КИСЛОТНОСТИ, "Российский физиологический журнал им. И.М. Сеченова"

Целью работы было выяснить, как влияет взаимодействие ванилоидных рецепторов переменного потенциала 1-го типа TRPV1 с эндотелиальной (eNOS) и нейрональной (nNOS) изоформами синтазы оксида азота на секрецию бикарбонатов (HCO) и кровоток в теле желудка на фоне аппликации кислоты на слизистую оболочку желудка (СОЖ). У наркотизированных крыс концентрация HCO3 в полостном перфузате желудка рассчитывалась на основе измеренных значений pH/PCO2, а объемный кровоток в стенке органа регистрировался с помощью лазерной допплеровской флоуметрии. Раздражение СОЖ подкисленным гипертоническим раствором (1 M NaCl, pH 2.0) значительно усиливало секрецию HCO3. Деструкция капсаицин-чувствительных первичных афферентов большими дозами капсаицина устраняла эту реакцию. Блокада TRPV1 не влияла на продукцию HCO и увеличение кровотока, вызванные внутрижелудочной аппликацией кислоты. Тем не менее было показано, что TRPV1 активируют eNOS, что приводит к усилению желудочного кровотока и ослаблению транспорта HCO3 на поверхность СОЖ. На активность nNOS, усиливающую продукцию HCO3, TRPV1 влияния не оказывали.

Carbon monoxide released from its pharmacological donor, tricarbonyldichlororuthenium (II) dimer, accelerates the healing of pre-existing gastric ulcers.

Carbon monoxide (CO), a gaseous mediator produced by haem oxygenases (HOs), has been shown to prevent stress-, ethanol-, aspirin- and alendronate-induced gastric damage; however, its role in gastric ulcer healing has not been fully elucidated. We investigated whether CO released from tricarbonyldichlororuthenium (II) dimer (CORM-2) can affect gastric ulcer healing and determined the mechanisms involved in this healing action. Gastric ulcers were induced in Wistar rats by serosal application of acetic acid. Animals received 9days of treatment with RuCl3 [2.5mg·kg-1 intragastrically (i.g.)], haemin (5mg·kg-1 i.g.), CORM-2 (0.1-10mg·kg-1 i.g.) administered alone or with zinc protoporphyrin IX (ZnPP, 10mg·kg-1 i.g.), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5mg·kg-1 i.g.), NG -nitro-l-arginine (l-NNA, 15mg·kg-1 i.g.), indomethacin (5mg·kg-1 i.g.) or glibenclamide (10mg·kg-1 i.g.). Gastric ulcer area and gastric blood flow (GBF) were assessed planimetrically, microscopically and by laser flowmeter respectively. Gastric mRNA/protein expressions of EGF, EGF receptors, VEGFA, HOs, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), COX-2, hypoxia-inducible factor (HIF)-1α and pro-inflammatory iNOS, IL-1β and TNF-α were determined by real-time PCR or Western blots. CORM-2 and haemin but not RuCl3 or ZnPP decreased ulcer size while increasing GBF. These effects were reduced by ODQ, indomethacin, l-NNA and glibenclamide. CORM-2 significantly decreased the expression of pro-inflammatory markers, Nrf2/HO1 and HIF-1α, and up-regulated EGF. CO released from CORM-2 or endogenously produced by the HO1/Nrf2 pathway accelerates gastric ulcer healing via an increase in GBF, an up-regulation in EGF expression and down-regulation of the inflammatory response.

Mechanisms of Esophageal Protection, Gastroprotection and Ulcer Healing by Melatonin. Implications for the Therapeutic use of Melatonin in Gastroesophageal Reflux Disease (GERD) and Peptic Ulcer Disease

Melatonin is a potent reactive oxygen metabolite scavenger and antioxidant that has been shown to influence many physiological functions of the gastrointestinal (GI) tract including secretion, motility, digestion and absorption of nutrients. The role of melatonin in gastroduodenal defense and ulcer healing has been the subject of recent investigations. Melatonin produced in the GI mucosa plays an important role in protection against noxious agents thus contributing to the maintenance of GI integrity and to esophageal protection, gastroprotection and ulcer healing. This review was designed to summarize the involvement of melatonin, conventionally considered as a major hormone of the pineal gland, in the maintenance of gastric mucosal integrity, gastroprotection, ulcer healing and intestinal disorders. Melatonin was originally shown to attenuate gastric mucosal lesions but controversy exists in the literature as to whether melatonin derived from the pineal gland, considered as the major source of this indole, or rather gastrointestinal melatonin plays predominant role in gastroprotection. Intragastric and central administration of exogenous melatonin and L-tryptophan, this indoleamine precursor, affords protection against gastric hemorrhagic damage caused by the exposure of gastric mucosa to variety of non-topical and topical ulcerogens such as stress, ethanol and ischemia-reperfusion. The speed of ulcer healing in experimental animals and humans is accelerated by melatonin. This indoleamine could be also effective against the esophageal lesions provoked by reflux esophagitis in animal models and prevents the incidence of GERD in humans. The melatonin-induced gastroprotection is accompanied by an increase in gastric blood flow, plasma melatonin concentration, enhancement in mucosal generation of PGE2, luminal NO content and plasma gastrin levels. Melatonin scavenges reactive oxygen metabolites, exerts anti-oxidizing and anti-inflammatory actions and inhibits the formation of metalloproteinases- 3 and -9; both implicated in the pathogenesis of gastrointestinal injury and formation of gastric ulcers. Blockade of MT2 receptors by luzindole, significantly attenuated melatonin- and L-tryptophan-induced protection and increased the speed of ulcer healing and these effects were accompanied by an increase in the GBF and luminal content of NO suggesting that melatonin exhibits gastroprotection and hyperemia via activation of MT2 receptors and release of NO. The accumulated evidence indicates that the melatonin-induced gastroprotection and the enhancement in healing rate of gastric ulcers may involve the gastroprotective factors derived from the activation of PG/COX and NO/NOS systems as well as gastrin which also was shown to exhibit protective and trophic effects in the upper GItract. Interestingly, pinealectomy, which suppressed plasma melatonin levels, markedly exacerbated gastric lesions induced by topical and non-topical ulcerogens and these effects are counteracted by a concurrent supplementation with melatonin. Evidence is provided that exogenous melatonin and that converted from its precursor, L-tryptophan, attenuates acute gastric lesions and accelerates ulcer healing via interaction with MT2 receptors due to an enhancement of gastric microcirculation, probably mediated by NO and PG derived from NOS and COX-1 and COX-2 overexpression and activity. The pineal gland plays an important role in the limitation of gastric mucosal injury and the acceleration of ulcer healing via releasing endogenous melatonin, which attenuates oxidative stress and exerts anti-inflammatory action.

P47 Exogenous and endogenous hydrogen sulfide (H2S) in gastroprotection against ischemia/reperfusion lesions progressing into chronic ulcers. Role of endogenous prostaglandins, sensory neuropeptides and vanilloid receptors

H 2 S is an endogenous gasotransmitter which exerts vasodilatatory, neuromodulatory and anti-inflammatory activities but little is known whether this gaseous mediator affects ischemia–reperfusion (I/R)-induced gastric erosions. We studied the effect of H 2 S precursor, l -cysteine and H 2 S-donor, NaHS on I/R lesions induced by 30 min of I followed by 3 h of R and their progression into chronic gastric ulcers at 12–72 h after the end of I. Rats exposed to I/R received once daily (1) l -cysteine (2–40 mg/kg) and (2) NaHS (0.1–10 mg/kg i.g.) combined or not with the inhibitor of CSE, d , l -propargylglycine (PAG 30 mg/kg i.g.); (3) the non-selective (indomethacin; 5 mg/kg i.p.) or selective COX-1 (SC-560, 5 mg/kg i.p.) and COX-2 inhibitors (celecoxib 30 mg/kg i.g.); (4) blockade of sensory nerves by capsaicin (125 mg/kg s.c.) and the inhibition of vanilloid receptor (VR-1) by capsazepine (10 mg/kg i.g.). The number of gastric lesions was measured by planimetry, the gastric blood flow (GBF) determined by H 2 -gas clearance technique, the mucosal concentration of H 2 S was determined spectrophotometrically, the plasma IL-1beta and TNF-alpha were determined by ELISA and mRNA expressions for CSE, COX-1-, COX-2-, CGRP, IL-1beta-, and TNF-alpha were assessed by RT-PCR. I/R-induced gastric mucosal lesions progressed into gastric ulcers at 72 h following the end of I. The significant fall in the H 2 S concentration and GBF were observed in gastric mucosa of I/R and these effects persisted up to 72 h upon standard I/R. NaHS (5 mg/kg i.g.) and l -cysteine (20 mg/kg i.g.) which significantly increased H 2 S content in the gastric mucosa and GBF, significantly reduced I/R-induced gastric lesions area at 24 h and 72 h following end of I. Capsaicin denervation, capsazepine and treatment with COXs inhibitors exacerbated I/R injury and significantly reduced the GBF and these effects were reversed by co-treatment with CGRP (10 μg/kg s.c.) or dimethyl PGE 2 (5 μg/kg i.g.) in the presence of NaHS and cysteine in capsaicin-denervated or COX-1- and COX-2-inhibited animals. The mRNA expression for CSE and CBS was increased in I/R gastric mucosa and this was inhibited by NaHS and cysteine. We conclude that (1) pathogenesis of I/R injury involves the fall in the generation of H 2 S and (2) NaHS and cysteine protect the gastric mucosa against I/R lesions and accelerate the healing of these lesions progressing into gastric ulcers via an increase in GBF mediated by endogenous H 2 S, PG pathway and CGRP.

RETRACTION: Role of Angiotensin-(1–7) in Gastroprotection against Stress-Induced Ulcerogenesis. The Involvement of Mas Receptor, Nitric Oxide, Prostaglandins, and Sensory Neuropeptides

Angiotensin-(1-7) [Ang-(1-7)] is a major vasoactive metabolite of angiotensin I (Ang I), both being important components of the renin-angiotensin system (RAS). Ang-(1-7) acting via Mas receptor was documented in kidneys, heart, brain, and gastrointestinal (GI)-tract. We studied the gastroprotective activity of exogenous Ang-(1-7) in rats exposed to water immersion and restraint stress (WRS) without or with A-779 [d-Ala7-Ang-(1-7), an antagonist of Ang-(1-7) Mas receptors], AVE 0991 (5-formyl-4-methoxy-2-phenyl-1[[4-[2-(ethylaminocarbonylsulfonamido)-5-isobutyl-3-thienyl]-phenyl]-methyl]-imidazole), the agonist of Ang-(1-7) receptor, as well as the inhibition of nitric-oxide (NO) synthase, the suppression of cyclo-oxygenase (COX)-1 (indomethacin, SC-560 [5-(4-chloro-phenyl)-1-(4-methoxyphenyl)-3-trifluoromethyl-pyrazole]), the activity COX-2 (rofecoxib), and denervation with capsaicin. The mRNA expression of constitutively expressed nitric-oxide synthase (cNOS), inducible nitric-oxide synthase (iNOS), interleukin (IL)-1β, and tumor necrosis factor (TNF)-α was analyzed by reverse transcription polymerase chain reaction. The WRS lesions were dose-dependently reduced by pretreatment with Ang-(1-7), which also caused an increase in gastric blood flow (GBF) and luminal content of NO. COX-1 and COX-2 inhibitors or L-NNA (N5-[imino(nitroamino)methyl]-L-ornithine) reversed the reduction in lesion number and the rise in GBF evoked by Ang-(1-7). Ang II augmented the WRS lesions, decreased GBF and increased the plasma IL-1β and TNF-α levels. Capsaicin denervation attenuated the reduction of Ang-(1-7)-induced gastric lesions and the rise in GBF; these effects were restored by supplementation with calcitonin gene-related peptide (CGRP). The cNOS mRNA was upregulated while iNOS, IL-1β and TNF-α mRNAs were downregulated in Ang-(1-7)-pretreated rats. We conclude that Ang-(1-7), in contrast to Ang II, which worsened WRS ulcerogenesis, affords potent gastroprotection against WRS ulcerogenesis via an increase in GBF mediated by NO, endogenous prostaglandins, sensory neuropeptides, and anti-inflammatory action involving the inhibition of proinflammatory markers iNOS, IL-1β, and TNF-α.

Metabolic fate of S-nitrosoglutathione after oral administration: Where does NO go?

Increasing the gastric mucosal perfusion by nitric oxide (NO) action can reduce the gastric injuries caused by non-steroidal anti-inflammatory drugs (NSAIDs). We have shown previously that topical administration of the NO donor S-nitrosoglutathione (GSNO) on the gastric mucosa of rats increases gastric blood flow, pointing to a possible oral therapeutic approach for treating NSAIDs side effects. In the present study, we found that oral administration of GSNO solutions (7–365 μmol/kg) to Swiss mice leads to a significant dose–response increase in the plasmatic levels of nitrite and nitrate (NOx) measured by chemiluminescence, with peak levels (160 mM) achieved after 1 h. At the same time, intact GSNO could not be detected in the plasma of the GSNO-treated animals by high-sensitivity Ultra Performance Liquid Chromatography (UPLC), 1 h after oral administration. These results indicate that gastric vasodilatation is not associated with a direct action of GSNO molecules, what is in accordance with the fact that GSNO vanishes completely 1 h after incubation in human plasma, as shown by UPLC analysis. In addition, no signal of free NO could be detected after incubation of human plasma with GSNO 50 μM by using a nanomolar-sensitive NO selective electrode (ISO-NOP and APOLLO 4000), over a 1 h period. These findings strongly suggest that the fate of GSNO after contact with the biological milieu involves its primary reaction with proteins by S-nitrosation or/and S-nitrosylation with the transfer of its NO moiety to other effector molecules, which are ultimately responsible for the observed increase in gastric blood flow.

Gastric blood flow responses to autonomic nerve stimulation and related pharmacological studies in rats.

The effects of autonomic nerve stimulation on rat gastric blood flow (GBF) were studied using a cross thermocouple method. Stimulation of the periarterial nerve bundles along the left gastric artery produced a decrease in GBF which was antagonized by phenoxybenzamine (0.05 mg kg-1 i.v.), but not by propranolol (1 mg kg-1 i.v.). Stimulation of the vagus nerves elicited an increase in GBF, within a latency of 20 s, which was not apparently affected by atropine (0.15 and 1.5 mg kg-1 i.v.) but was completely blocked by hexamethonium (10 mg kg-1 i.v.). The GBF increase due to acetylcholine (0.25 micrograms rat-1 i.a.), was markedly blocked by atropine (0.15 mg kg-1 i.v.). Vagal stimulation also produced both the cholinergic excitation and non-cholinergic inhibition of gastric motility. The vagally induced GBF increase was little affected by any pretreatment with phentolamine, propranolol, indomethacin or aprotinin. These results suggest that sympathetic nerve stimulation creases GBF through alpha-adrenoceptors and parasympathetic nerve stimulation increases GBF through a non-cholinergic mechanism in rats and that the GBF increase may result from a primary dilator effect of vagal stimulation on the blood vessels because of the immediate initiation of the response.

Involvement of capsaicin-sensitive afferent nerves and cholecystokinin 2/gastrin receptors in gastroprotection and adaptation of gastric mucosa to Helicobacter pylori-lipopolysaccharide.

Lipopolysaccharide (LPS) is one of the virulence factors in the Helicobacter pylori (Hp)-infected stomach, but it remains unknown whether single and prolonged pretreatment with Hp-LPS can affect the course of gastric damage induced by aspirin (ASA). We compared the effects of Hp-LPS with those induced by LPSs isolated from intestinal Bacteroides fragilis, Yersinia enterocolitica, and Campylobacter jejuni applied for 4 days on acute ASA-induced gastric lesions in rats. The area of ASA-induced gastric lesions, gastric blood flow (GBF), expression of mRNA and protein of leptin and plasma leptin, gastrin, interleukin-1beta, and tumor necrosis factor-alpha levels were examined. Single (once) or repeated (five times) i.p. injections of Hp-LPS (1 mg/kg) or intestinal LPSs failed to produce macroscopic gastric damage and did not affect the GBF when compared with vehicle. Hp-LPS injected repeatedly suppressed the gastric acid secretion, up-regulated leptin mRNA and protein, and increased plasma leptin and gastrin levels. Hp-LPS significantly reduced the ASA-induced gastric damage and the accompanying decline in the GBF, and these effects were significantly attenuated by capsaicin denervation and selective antagonism of cholecystokinin-B (CCK2) receptors by RPR-102681 [N-(metoxy-3 phenyl) N-(N-methyl N-phenyl-carbamylmethyl) carbamoylmethyl]-3 ureido]-3 phenyl]-2 propronique] but not by loxiglumide, an antagonist of CCK1 receptors. We conclude that 1) daily application of Hp-LPS enhances gastric mucosal resistance against ASA damage due to the increase of GBF and the expression and release of leptin and gastrin exerting trophic and gastroprotective effects, and 2) this enhanced resistance to ASA damage in Hp-LPS-adapted stomach is mediated by the sensory afferents and specific CCK2/gastrin receptors.

Gastric mucosal blood flow changes in Helicobacter pylori infection and NSAID-induced gastric injury.

The impact of H. pylori infection on gastric mucosal blood flow and NSAID-induced gastric damage is unclear. To study the effects of H. pylori infection on gastric mucosal blood flow, both at basal conditions and after NSAID exposure, and its relation with mucosal damage and nitric oxide production. Gastric mucosal blood flow, nitric oxide production and gastric damage were assessed in time after H. pylori SS1 or E. coli inoculation in mice. Experiments were conducted in basal conditions or after oral exposure to indomethacin (20 mg/kg). H. pylori infected mice exhibited a significant increase in gastric blood flow and gastric nitric oxide production 1 week after infection, but those parameters returned to basal levels by 4 weeks. NSAID challenge elicited a similar reduction in gastric blood flow [25-35%] in H. pylori-infected and control animals. However, only 1 week H. pylori-infected mice, which exhibited a significant baseline hyperemia, were able to maintain gastric blood flow values within the normal range after NSAID exposure. NSAID-induced gastric damage was increased in H. pylori-infected mice by 4 weeks, but not 1 week after infection. Underlying H. pylori infection aggravates acute NSAID-induced gastric damage. However, at early phases, gastric hyperemia associated with increased nitric oxide production may exert some protective role.

Histamine is involved in gastric vasodilation during acid back diffusion via activation of sensory neurons.

Protective vasodilation during acid back diffusion into the rat gastric mucosa depends on activation of sensory neurons and mast cell degranulation with histamine release. We hypothesized that these two mediator systems interact and that histamine partly exerts its effect via sensory nerves. Gastric blood flow (GBF) and luminal histamine were measured in chambered stomachs, and mast cell numbers were assessed by morphometry. Ablation of sensory neurons and depletion of mast cells were produced by pretreatment with capsaicin or dexamethasone, respectively. Mucosal exposure to 1.5 M NaCl and then to pH 1.0 saline in ablated and control rats caused increased luminal histamine and reduced numbers of mast cells. Enterochromaffin-like cell marker pancreastatin remained unchanged. Only control rats responded with an increase in GBF. Capsaicin stimulation (640 microM) of the undamaged mucosa induced identical increase in GBF and unchanged mast cell mass in normal and dexamethasone-treated rats. Increase in GBF after topical exposure to histamine (30 mM) in rats pretreated with capsaicin or a calcitonin gene-related peptide (CGRP)(1) antagonist human CGRP(8-37) or exposed to the calcium pore blocker ruthenium red was less than one-half of that in control rats. These data suggest that mast cell-derived histamine is involved in gastric vasodilatation during acid back diffusion partly via sensory neurons.

Gastroprotective Effect of Histamine and Acid Secretion on Ammonia-Induced Gastric Lesions in Rats

Background: Previous studies have shown that ammonia produced by Helicobacter pylori urease or administrated intragastrically exhibits a toxic effect on the gastric mucosa. In the present study we investigated the influence of histamine and gastric acid secretion on ammonia (NH4OH)-induced gastric lesions. Methods: The gastric mucosa in rats was exposed to NH4OH (1.5 ml of 250 mM solution) under basal conditions, after administration of histamine (1 mg/kg), urea with urease, and ranitidine (40 mg/kg subcutaneously) given alone or in combination. We measured the area of gastric lesions, gastric blood flow (GBF), plasma gastrin concentration, DNA synthesis, gastric acid secretion and gastric luminal concentration of PGE2. Results: Application of NH4OH resulted in the formation of acute gastric lesions. This effect was accompanied by a fall in GBF, a rise in gastric pH, and a reduction in mucosal DNA synthesis. Administration of histamine 30 min prior to NH4OH reduced the area of gastric lesions. This was accompanied by an increase in GBF, DNA synthesis, and prostaglandin E2 (PGE2) production. Ranitidine given prior to NH4OH enhanced gastric mucosa damage, and reduced GBF and DNA synthesis. This effect was accompanied by a reduction in gastric acid secretion. Ranitidine given prior to histamine abolished gastric acid secretion and the protective effect of histamine against NH4OH-induced damage; these effects were accompanied by a decrease in GBF, DNA synthesis, and concentration of PGE2. Pretreatment with 2% urea with urease given prior to NH4OH reduced NH4OH lesions. This effect was associated with an increase in gastric acid secretion, gastric generation of PGE2, GBF, and DNA synthesis. Ranitidine given prior to urea with urease inhibited gastric acid secretion and the gastroprotective effect of urea-urease gastroprotection. Conclusions: Histamine and gastric secretion exhibit a protective effect against ammonia-induced gastric lesions. This effect appears to depend upon the stimulation of gastric acid secretion and PGE2 production, and the improvement of gastric microcirculation.

Hyperammonemia Reduces Water Immersion–Restraint Stress Gastric Ulcers in Rats

1. The influence of hyperammonemia (produced by the continuous intraperitoneal infusion of ammonium acetate for 6 days) on stress-induced gastric ulcer formation was investigated in conscious rats. 2. Continuous ammonium acetate infusion significantly reduced stress-induced gastric ulceration concomitant with an increase in gastric blood flow, as determined using radioactive microspheres. The serum levels of L-arginine as well as nitrite and nitrate (oxidative byproducts of nitric oxide) were increased by ammonium acetate infusion. 3. Prior administration of N ω-nitro-L-arginine methyl ester, a competitive nitric oxide synthase inhibitor, substantially attenuated the increase in gastric blood flow caused by ammonium acetate infusion and diminished the protective effect on gastric ulceration. 4. These findings suggest that the synthesis of endogenous nitric oxide from L-arginine is accelerated by continuous ammonium acetate infusion when the urea cycle remains intact and has a substantial cytoprotective effect on the stomach, probably through maintaining the gastric mucosal microcirculation.

Polyamines and epidermal growth factor in the recovery of gastric mucosa from stress-induced gastric lesions.

Polyamines such as spermine or putrescine, resulting from increased activity of ornithine decarboxylase (ODC), are known for gastroprotective and mucosal growth-promoting effects. EGF exhibits similar effects, but little is known about the involvement of polyamines in acceleration of the healing of stress-induced gastric lesions by epidermal growth factor (EGF). In this study, rats with intact or suppressed ODC activity by alpha-difluoromethy-ornithine (DFMO, 400 mg/kg i.p.) were subjected to 3.5 h of water immersion and restraint stress (WRS) without or with addition of spermine or EGF. At 0, 2, 6, 12, or 24 h after stress, rats were sacrificed. The number of gastric lesions was determined and gastric blood flow (GBF) was recorded by the H2 gas clearance technique. Stress produced gastric lesions (mean number 18+/-2 per stomach) and decreased GBF (by approximately 43%), but at 2, 6, 12, and 24 h after stress, these lesions and the decrease in GBF were gradually attenuated. Pretreatment with DFMO or removal of an endogenous source of EGF by salivectomy resulted in a marked decrease in mucosal DNA synthesis and significantly delayed the healing of stress lesions. EGF or spermine significantly accelerated ulcer healing and increased the GBF in rats with intact or removed salivary glands. DFMO significantly reduced the enhancement of healing and the increase in GBF induced by EGF, but failed to influence those induced by exogenous spermine. We conclude that polyamines play an important role in mucosal recovery from stress lesions due to acceleration of mucosal repair and increase in gastric microcirculation and that increased ODC activity and resulting excessive polyamine release appear to act as primary mediators of EGF-induced acceleration of the healing of stress lesions.

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.

Gastroprotective Activity of Melatonin and Its Precursor, L-Tryptophan, against Stress-induced and Ischaemia-induced Lesions Is Mediated by Scavenge of Oxygen Radicals

Background: Melatonin, a pineal hormone that is biosynthesized from L-tryptophan, is known to scavenge oxygen free radicals and to be present in the gut, but little is known about the role of this hormone and its precursor, L-tryptophan, in protecting the gastric mucosa from damage accompanied by increase in the generation of oxygen radicals. Methods: This study was designed to determine the effects of melatonin and L-tryptophan on the formation of acute gastric lesions induced by stress and ischaemia reperfusion and, for comparison, by topical irritants such as 100% ethanol or acidified acetylsalicylic acid. Results: It was found that pretreatment with melatonin in doses ranging from 1.2 to lOmg/kg dose-dependently reduced the stress-induced gastric lesions and was accompanied by a reduction in blood-free radicals and by attenuation of the fall in gastric blood flow. L-tryptophan applied intragastrically in doses ranging from 1 to lOOmg/kg also reduced dose-dependently the lesions induced by stress; this effect too was accompanied by a rise in gastric blood flow. Pretreatment with indomethacin, to block the biosynthesis of prostaglandins, significantly augmented the lesions produced by stress and completely abolished the protective effects of melatonin or L-tryptophan. Both melatonin and tryptophan reduced the formation of acute gastric lesions provoked by ischaemia reperfusion; this was accompanied by an increase in gastric blood flow. In contrast, melatonin and L-tryptophan failed to influence acute gastric lesions induced by topical irritants such as 100% ethanol or acidified aspirin. Conclusions: Melatonin and L-tryptophan protect the gastric mucosa from damage by stress and ischaemia reperfusion, and this action is mediated, at least in part, by the limitation in the free radicals, the stimulation of mucosal generation of PG and by the increase in gastric blood flow.

Effect of capsaicin and resiniferatoxin on gastrointestinal blood flow in rats

The effect of capsaicin and resiniferatoxin on gastrointestinal blood flow was studied in anaesthetized rats by laser Doppler flowmetry. Resiniferatoxin injected into the jugular vein (0.08–1.6 nmol/kg) produced a marked and dose-dependent increase in gastric blood flow, while the effect of capsaicin (0.33–19.6 nmol/kg) was transient, variable and accompanied by profound systemic blood pressure changes. After acute bilateral cervical vagotomy combined with sympathetic neurone blockade (guanethidine 16 μmol/kg) or α-adrenoceptor blockade (phentolamine 1.6 μmol/kg), the vasodilator response to injected resiniferatoxin was more pronounced, indicating that the resiniferatoxin-induced gastric vasodilatation is not due to reflexes via parasympathetic or sympathetic efferent fibres. Resiniferatoxin given i.v. (0.08–0.64 nmol/kg) evoked a similar increase in the blood flow of the jejunum. Capsaicin (0.33–33 μM) or resiniferatoxin (0.16–1.6 μM) applied topically to the serosal surface of the stomach or jejunum produced a pronounced and long-lasting increase in blood flow after vagotomy and guanethidine treatment. The blood flow and blood pressure responses to capsaicin and resiniferatoxin were absent in rats desensitized with systemic capsaicin pretreatment. These laser Doppler data provide the first evidence for the effect of resiniferatoxin on gastrointestinal microcirculation and indicate the advantages of this agent and technique to study the sensory-efferent function of capsaicin-sensitive fibres.

Differences in action of topical and systemic cysteamine on gastric blood flow, gastric acid secretion and gastric ulceration in the rat

The effect of cysteamine on gastric blood flow and on the indomethacin-induced gastric mucosal damage was studied. In anesthetized rats, cysteamine (280 mg/kg) given subcutaneously (sc) decreased gastric blood flow measured by the laser Doppler flowmetry technique. In contrast, cysteamine (1–60 mg/ml) applied topically to the serosal surface of the stomach evoked a concentration-dependent and long-lasting increase in gastric blood flow. At 60 mg/ml, cysteamine increased blood flow by 166.8 ± 26.1% of predrug control value. Pretreatment with indomethacin (20 mg/kg, sc), intravenous (iv) atropine (1 mg/kg), propranolol (1 mg/kg, iv), combined H 1 and H 2-blockade or bilateral cervical vagotomy alone or combined with iv guanethidine (8 mg/kg), or pretreatment with the capsaicin analogue resiniferatoxin did not reduce the vasodilator response to cysteamine. The vasodilator response to topical capsaicin, was not reduced after sc cysteamine (280 mg/kg) pretreatment. In conscious pylorus-ligated rats, sc cysteamine (100 or 280 mg/kg) given simultaneously with indomethacin inhibited gastric acid output but had variable effects on the indomethacin-induced gastric mucosal damage. Cysteamine (100 or 280 mg/kg) administered sc 4 h prior to indomethacin enhanced gastric injury by sc indomethacin, but did not prevent the gastroprotective action of capsaicin. In contrast, orally administered cysteamine (60 mg/ml) reduced gastric injury induced by sc indomethacin plus intragastric HCl. These data provide the first evidence for the effect of cysteamine on gastric microcirculation in the rat and suggest a direct vasodilator effect for topical cysteamine. The microvascular effects of cysteamine are largely responsible for the different effects of this agent on experimental gastric injury.

Age-Related Changes in Gastric Blood Flow in Rats

The present study was designed to examine the influence of aging on the gastric blood flow, a major mucosal protective mechanism against experimental gastric mucosal injury, basally and after treatment with acid, a known stimulant of gastric blood flow. Our data demonstrated that aging was associated with a significant decline in basal gastric blood flow (both mucosal and serosal). However, there were no significant differences in acid-induced increases in gastric blood flow between the young and aged animals. These findings suggest that aging is associated with selective and specific reductions in mucosal protective mechanisms that may predispose aged animals to gastric mucosal injury.

Gastric adaptation to aspirin and stress enhances gastric mucosal resistance against the damage by strong irritants.

Gastric mucosal adaptation to injury induced by repeated application of aspirin (ASA) or stress is a well-documented phenomenon, but it is known whether such adaptation affects the mucosal tolerance to other strong irritants. In this study gastric adaptation was induced by repeated daily administration of acidified ASA for 4 consecutive days (Series A) or by 3.5H of water immersion and restraint stress (WRS) applied every other day for up to 8 days (series B). When the adaptation to ASA or WRS was fully developed, rats of series A and B were challenged with strong irritants such as 100% ethanol, 200 mM acidified taurocholate (TC), or 25% NaCl for 1 h or with WRS for 3.5 h. ASA or WRS applied once produced numerous gastric lesions and deep histologic necrosis accompanied by a decrease in gastric blood flow. With repeated application of ASA or stress the mucosal adaptation to ASA and WRS developed; the area of gastric lesions was reduced by 86% and 56%, respectively, and this was accompanied by a marked decrease of superficial and deep necrosis, and increase in gastric blood flow (GBF) and the enhancement of mucosal regeneration. An increase in mucosal and luminal contents of epidermal growth factor (EGF) and in mucosal expression of EGF receptors was also observed in the mucosa adapted to ASA or stress. In rats adapted to ASA or stress and then challenged with 100% ethanol, 200 mm TC, 25% NaCl, stress or ASA, the areas of macroscopic gastric lesions and deep histologic necrosis were remarkable reduced as compared with those in non-adapted vehicle-treated rats. This was also accompanied by a significant decrease in (GBF), a marked increase of mucosal and luminal contents of EGF and expression of its receptors, and enhanced mucosal cell proliferation. Gastric adaptation to ASA or stress enhances mucosal resistance to the injury induced by strong irritants, and this appears to be mediated by mucosal regeneration, probably resulting from increased luminal and mucosal contents of EGF and excessive expression of its receptors.