Peripheral GLP-1 gastroprotection against ethanol: the role of exendin, NO, CGRP, prostaglandins and blood flow

The aim of this study was to investigate the effects of peripherally injected glucagon like peptide-1 (GLP-1) on ethanol-induced gastric mucosal damage and the mechanisms included in the effect. Absolute ethanol was administered through an orogastric cannula right after the injection of GLP-1 (1, 10, 100, 1000 or 10,000 ng/kg; i.p.). The rats were decapitated an hour later, the stomachs removed and the gastric mucosal damage scored. 1000 ng GLP-1 inhibited gastric mucosal damage by 45% and 10,000 ng GLP-1 by 60%. The specific receptor antagonist exendin-(9-39) (2500 ng/kg; i.p.), calcitonin gene related peptide (CGRP) receptor antagonist CGRP-(8-37) (10 microg/kg; i.p.), nitric oxide (NO) synthase inhibitor l-NAME (30 mg/kg; s.c.) and cyclooxygenase inhibitor indomethacin (5 mg/kg; i.p.) inhibited the preventive effect of GLP-1 on ethanol-induced gastric mucosal damage. GLP-1 also prevented the decrease in gastric mucosal blood flow caused by ethanol when administered at gastroprotective doses (1000 and 10,000 ng/kg; i.p.). In conclusion, GLP-1 administered peripherally prevents the gastric mucosal damage caused by ethanol in rats. CGRP, NO, prostaglandin and gastric mucosal blood flow are thought to play a role in this effect, mediated through receptors specific to GLP-1.     

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.     

Investigation of the mechanisms involved in the central effects of glucagon-like peptide-1 on ethanol-induced gastric mucosal lesions

The aim of this study was to investigate the effects of intracerebroventricularly injected glucagon-like peptide-1 (GLP-1) on ethanol-induced gastric mucosal damage and to elucidate the mechanisms involved. Absolute ethanol was administered through an orogastric cannula 5 min before GLP-1 (1 microg/10 microl) injection. One hour later, the rats were decapitated, their stomachs were removed and scored for mucosal damage. GLP-1 inhibited the ethanol-induced gastric mucosal damage by 92%. Centrally injected atropine sulphate, a muscarinic receptor antagonist (5 microg/10 microl), prevented the gastroprotective effect of GLP-1, while mecamylamine, a nicotinic receptor antagonist (25 microg/10 microl), was ineffective. Peripherally injected atropine methyl nitrate (1 mg/kg) did not change the effect of GLP-1, but mecamylamine (5 mg/kg) blocked it. Cysteamine, a somatostatin depletor (280 mg/kg, s.c.), did not affect the protective activity of GLP-1, while inhibition of nitric oxide (NO) synthesis by L-NAME (3 mg/kg, i.v.) significantly abolished the protective effect of GLP-1 on ethanol-induced gastric mucosal lesions. We conclude that central muscarinic and peripheral nicotinic cholinergic receptors and NO, but not somatostatin, contribute to the protective effect of intracerebroventricularly injected GLP-1 on ethanol-induced gastric mucosal damage.     

Studies on gastroprotection induced by capsaicin and papaverine.

Capsaicin and papaverine are potent vasorelaxants with strong gastroprotective activity against damage induced by absolute ethanol. This protection was originally attributed to the increase in gastric mucosal blood flow (GBF) but the possibility that NO mediates the protective and hyperemic effects of capsaicin and papaverine has been little studied. Using N-nitro-L-arginine (L-NNA), a selective blocker of NO synthase, and L-arginine as a substrate for NO, we investigated the role of NO in protective action of capsaicin and papaverine against ethanol-induced gastric damage and in GBF. Pretreatment with capsaicin (0.1-0.5 mg/kg i.g.) or papaverine (0.1-2 mg/kg i.g.) reduced dose-dependently the area of ethanol-induced lesions, the LD50 being 0.3 and 1 mg/kg, respectively. This protection was accompanied by a gradual increase in the GBF. Intravenous (i.v.) injection of L-NNA (1.2-5 mg/kg), which by itself caused only a small increase in ethanol lesions, reversed dose-dependently the protective and hyperemic effects of capsaicin and papaverine against ethanol-induced damage and attenuated the increase in GBF induced by each of these agents alone. This deleterious effect of L-NNA on the gastric mucosa and the GBF was fully antagonized by L-arginine (200 mg/kg i.v.) but not by D-arginine. L-arginine partly restored the decrease in GBF induced by L-NNA. Pretreatment with indomethacin (5 mg/kg i.p.), which suppressed the generation of PG by 85%, slightly enhanced the mucosal lesions induced by ethanol but failed to affect the fall in GBF induced by this irritant. Gastroprotective and hyperemic effects of capsaicin and papaverine were partly reversed by indomethacin suggesting that endogenous PG are also implicated in these effects. Addition of L-NNA to indomethacin completely eliminated both the protective and hyperemic effects of capsaicin and papaverine. We conclude that both NO and PG contribute to the gastroprotective and hyperemic effects of capsaicin and papaverine on the gastric mucosa.     

Quebrachitol-induced gastroprotection against acute gastric lesions: Role of prostaglandins, nitric oxide and KATP channels

The effect of Quebrachitol (2-O-methyl-l-inositol), a bioactive component from Magonia glabrata fruit extract was investigated against gastric damage induced by absolute ethanol (96%, 0.2 ml/animal) and indomethacin (30 mg/kg, p.o.), in mice. Quebrachitol at oral doses of 12.5, 25, and 50 mg/kg markedly attenuated the gastric lesions induced by ethanol to the extent of 69%, 64%, and 53% and against indomethacin by 55%, 59%, and 26%, respectively. While pretreatment with TRPV1 antagonist capsazepine (5 mg/kg, i.p.) failed to block effectively the gastroprotective effect of quebrachitol (25 mg/kg) against ethanol damage, the non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg, p.o.), almost abolished it. Furthermore, quebrachitol effect was significantly reduced in mice pretreated with l-NAME, or glibenclamide, the respective inhibitors of nitric oxide synthase and K⁺_ATP channel activation. Thus we provide the first evidence that quebrachitol reduces the gastric damage induced by ethanol and indomethacin, at least in part, by mechanisms that involve endogenous prostaglandins, nitric oxide release, and or the activation of K⁺_ATP channels.     

Body temperature dependency in baclofen-induced gastric acid secretion in rats relation to capsaicin-sensitive afferent neurons

Body temperature dependency in gastric functional responses to baclofen, a GABA(B) agonist, such as acid secretion, mucosal blood flow (GMBF) and motor activity, was examined in urethane-anesthetized rats under normal (37+/-1 degrees C) and hypothermic (31+/-1 degrees C) conditions. A rat stomach was mounted in an ex-vivo chamber, perfused with saline, and the acid secretion was measured using a pH-stat method, simultaneously with GMBF by a laser Doppler flowmeter. Gastric motility was measured using a miniature balloon as intraluminal pressure recordings. Intravenous administration of baclofen significantly increased acid secretion at the doses > 0.3 mg/kg under hypothermic conditions, yet it caused a significant stimulation only at doses > 10 mg/kg under normothermic conditions. The increases in gastric motility and GMBF were similarly induced by baclofen, irrespective of whether the animals were subjected to normothermic or hypothermic conditions. These functional responses to baclofen under hypothermic conditions were totally attenuated by either bilateral vagotomy or atropine (3 mg/kg, s.c.). Baclofen at a lower dose (1 mg/kg i.v.) significantly increased the acid secretion even under normothermic conditions when the animals were subjected to chemical deafferenation of capsaicin-sensitive neurons or pretreatment with intracisternal injection of CGRP8-37 (30 ng/rat). These results suggest that 1) gastric effects of baclofen are dependent on body temperature in stimulating acid secretion but not GMBF or motor activity, 2) the acid stimulatory action of baclofen is enhanced under hypothermic conditions, and 3) the suppression of baclofen-induced acid response under normothermic conditions may be related to capsaicin-sensitive afferent neuronal activity, probably mediated by central release     

Stimulatory effects of endogenous and exogenous nitric oxide on gastric acid secretion in anesthetized rats

We previously reported the stimulatory effect of endogenous nitric oxide (NO) on gastric acid secretion in the isolated mouse whole stomach and histamine release from gastric histamine-containing cells. In the present study, we investigated the effects of endogenous and exogenous NO on gastric acid secretion in urethane-anesthetized rats. Acid secretion was studied in gastric-cannulated rats stimulated with several secretagogues under urethane anesthesia. The acid secretory response to the muscarinic receptor agonist bethanechol (2 mg/kg, s.c.), the cholecystokinin(2) receptor agonist pentagastrin (20 microg/kg, s.c.) or the centrally acting secretagogue 2-deoxy-D-glucose (200 mg/kg, i.v.) was dose-dependently inhibited by the NO synthase inhibitor N(omega)-nitro-L-arginine (L-NNA, 10 or 50 mg/kg, i.v.). This inhibitory effect of L-NNA was reversed by a substrate of NO synthase, L-arginine (200 mg/kg, i.v.), but not by D-arginine. The histamine H(2) receptor antagonist famotidine (1 mg/kg, i.v.) completely inhibited the acid secretory response to bethanechol, pentagastrin or 2-deoxy-D-glucose, showing that all of these secretagogues induced gastric acid secretion mainly through histamine release from gastric enterochromaffin-like cells (ECL cells). On the other hand, histamine (10 mg/kg, s.c.)-induced gastric acid secretion was not inhibited by pretreatment with L-NNA. The NO donor sodium nitroprusside (0.3-3 mg/kg, i.v.) also dose-dependently induced an increase in acid secretion. The sodium nitroprusside-induced gastric acid secretion was significantly inhibited by famotidine or by the soluble guanylate cyclase inhibitor methylene blue (50 mg/kg, i.v.). These results suggest that NO is involved in the gastric acid secretion mediated by histamine release from gastric ECL cells.     

Gastroprotective action of orexin-A against stress-induced gastric damage is mediated by endogenous prostaglandins, sensory afferent neuropeptides and nitric oxide

Orexin-A, identified in the neurons and endocrine cells in the gut, has been implicated in control of food intake and sleep behavior but little is known about its influence on gastric secretion and mucosal integrity. The effects of orexin-A on gastric secretion and gastric lesions induced in rats by 3.5 h of water immersion and restraint stress (WRS) or 75% ethanol were determined. Orexin-A (5-80 microg/kg i.p.) increased gastric acid secretion and attenuated gastric lesions induced by WRS and this was accompanied by the significant rise in plasma orexin-A, CGRP and gastrin levels, the gastric mucosal blood flow (GBF), luminal NO concentration and an increase in mRNA for CGRP and overexpression of COX-2 protein and the generation of PGE(2) in the gastric mucosa. Orexin-A-induced protection was abolished by selective OX-1 receptor antagonist, vagotomy and attenuated by suppression of COX-1 and COX-2, deactivation of afferent nerves with neurotoxic dose of capsaicin, pretreatment with CCK(2)/gastrin antagonist, CGRP(8-37) or capsazepine and by inhibition of NOS with L-NNA. This study shows for the first time that orexin-A exerts a potent protective action on the stomach of rats exposed to non-topical ulcerogens such as WRS or topical noxious agents such as ethanol and these effects depend upon hyperemia mediated by COX-PG and NOS-NO systems, activation of vagal nerves and sensory neuropeptides such as CGRP released from sensory nerves probably triggered by an increase in gastric acid secretion induced by this peptide.     

Exogenous and endogenous ghrelin in gastroprotection against stress-induced gastric damage

Ghrelin, identified in the gastric mucosa has been involved in control of food intake and growth hormone (GH) release but little is known about its influence on gastric secretion and mucosal integrity. The effects of ghrelin on gastric secretion, plasma gastrin and gastric lesions induced in rats by 75% ethanol or 3.5 h of water immersion and restraint stress (WRS) were determined. Exogenous ghrelin (5, 10, 20, 40 and 80 microg/kg i.p.) increased gastric acid secretion and attenuated gastric lesions induced by ethanol and WRS and this was accompanied by the significant rise in plasma ghrelin level, gastric mucosal blood flow (GBF) and luminal NO concentrations. Ghrelin-induced protection was abolished by vagotomy and attenuated by suppression of COX, deactivation of afferent nerves with neurotoxic dose of capsaicin or CGRP(8-37) and by inhibition of NOS with L-NNA but not influenced by medullectomy and administration of 6-hydroxydopamine. We conclude that ghrelin exerts a potent protective action on the stomach of rats exposed to ethanol and WRS, and these effects depend upon vagal activity, sensory nerves and hyperemia mediated by NOS-NO and COX-PG systems.     

Involvement of gastrin in gastric secretory and protective actions of N-alpha-methyl histamine

N alpha-methylhistamine (N alpha-MH) is one of an unusual metabolite of histamine that was found in Helicobacter pylori-infected stomachs and is believed to interact with specific histamine H(1), H(2) and H(3)-receptors to stimulate gastric acid secretion and gastrin release from isolated G-cells but the effects of N alpha-MH on gastric mucosal integrity have been little studied. This study was designed; (1) to compare the effect of exogenous N alpha-MH with that of standard histamine on gastric secretion and plasma gastrin levels in rats equipped with gastric fistula (series A); and (2) to assess the action of N alpha-MH on gastric lesions induced by 100% ethanol (series B) in rats with or without removal of antral portion of the stomach (antrectomy). Rats of series B were pretreated intragastrically (i.g.) or intraperitoneally (i.p.) with N alpha-MH or histamine (0.1-2 mg/kg) 30 min prior to 100% ethanol (1.5 ml, i.g.) with or without: (1) vehicle (saline); (2) RPR 102681 (30 mg/kg i.p.), to block CCK-B/gastrin receptors; and (3) ranitidine (40 mg/kg s.c.) to inhibit histamine H(2)-receptors. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H(2)-gas clearance method and venous blood was collected for determination of plasma gastrin levels by radioimmunoassay (RIA). N alpha-MH and histamine dose-dependently increased gastric acid output (series A); the dose increasing this secretion by 50% (ED(50)) being 2 and 5 mg/kg i.g or i.p., respectively, and this effect was accompanied by a significant rise in plasma gastrin levels. Both, N alpha-MH and histamine attenuated dose-dependently the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. These secretory, protective, hipergastrinemic and hyperemic effects of N alpha-MH and histamine were completely abolished by antrectomy, whereas pretreatment with RPR 102681 attenuated significantly the N alpha-MH and histamine-induced protection against ethanol damage and accompanying hyperemia. Ranitidine, that produced achlorhydria and a further increase in plasma gastrin levels, failed to influence the N alpha-MH- and histamine-induced protection and accompanying rise in the GBF. We conclude that (1) N alpha-MH stimulates gastric acid secretion and exhibit gastroprotective activity against acid-independent noxious agents in the manner similar to that afforded by histamine; and (2) this protection involves an enhancement in the gastric microcirculation and release of gastrin acting via specific CCK-B/gastrin receptors but unexpectedly, appears to be unrelated to histamine H(2)-receptors.     

Effect of Concomitant Administration of L-Glutamine and Cycloart-23-ene-3β, 25-diol (B2) with Sitagliptin in GLP-1 (7–36) Amide Secretion,Biochemical and Oxidative Stress in Streptozotocin - Nicotinamide Induced Diabetic Sprague Dawley Rats

Previously we have reported that, cycloart-23-ene-3β, 25-diol (called as B2) and L-glutamine stimulated glucagon like peptide-1 (GLP-1) (7–36) amide secretion diabetic rats. The objective of present investigation was to investigate the concomitant administration of cycloart-23-ene-3β, 25-diol+sitagliptin and L-glutamine+sitagliptin in streptozotocin - nicotinamide induced diabetic Sprague Dawley. Type 2 diabetes was induced in overnight fasted male Sprague Dawley rats pre-treated with nicotinamide (100 mg/kg, i.p.) followed by administration of streptozotocin (55 mg/kg, i.p.) 20 min after. The rats were divided into; I- non-diabetic, II- diabetic control, III- Sitagliptin (5 mg/kg, p.o.)+cycloart-23-ene-3β, 25-diol (1 mg/kg, p.o.), IV- Sitagliptin (5 mg/kg, p.o.)+L-glutamine (1000 mg/kg, p.o.). The concomitant treatment of cycloart-23-ene-3β, 25-diol and L-glutamine with sitagliptin was 8 weeks. Plasma glucose, body weight, food and water intake were determined every week. Glycosylated haemoglobin, lipid profile, plasma and colonic active (GLP-1) (7–36) amide, plasma and pancreatic insulin, histology of pancreata and biomarkers of oxidative stress were measured after 8^th week treatment. Concomitant administration of cycloart-23-ene-3β, 25-diol and L-glutamine with sitagliptin significantly (p<0.001) reduced plasma glucose, glyoxylated haemoglobin, lipid profile and oxidative stress parameters compared to diabetic control groups. Both concomitant treatment increased plasma and pancreatic insulin as well as plasma and colonic active (GLP-1) (7–36) amide secretion. Histological analysis by Gomori staining observed less destruction of pancreatic β cells. The result obtained from this study; it is concluded that concomitant administration of cycloart-23-ene-3β, 25-diol+sitagliptin and L-glutamine+sitagliptin showed additive antihyperglycaemic effect in diabetic rats.     

Mechanisms involved in the gastroprotective activity of esculin on acute gastric lesions in mice

This work describes the gastroprotective actions of esculin (6,7-dihydroxycoumarin-6-o-glucoside) against indomethacin- or ethanol-induced lesions and verifies the role of nitric oxide, ATP-dependent K⁺ channels, prostaglandins, transient receptor potential vanilloid 1 and antioxidant effects in the gastroprotective mechanism of esculin in the ethanol-induced gastric lesion model. The intragastric administration of esculin at doses of 12.5, 25 and 50 mg/kg was able to protect the gastric mucosa against ethanol (0.2 mL/animal p.o.), and esculin at doses of 25 and 50 mg/kg protected against indomethacin-induced lesions (20 mg/kg p.o.). Administration of l-NAME (10 mg/kg i.p.), glibenclamide (10 mg/kg i.p.) or indomethacin (10 mg/kg p.o.), but not capsazepine (5 mg/kg p.o.), was able to reduce the gastroprotection promoted by esculin (25 mg/kg) on the ethanol-induced lesions. Measurements of nitrite, a NO metabolite, were increased in the group that was pretreated with esculin. In terms of antioxidant activity as a gastroprotective mechanism of esculin, the results show that pre-treatment with esculin decreased the amount of GSH, increased SOD activity, did not interfere with the CAT activity and decreased both the MPO activity and the MDA amount. In conclusion, pre-treatment with esculin confers significant gastroprotective and antioxidant activity and leads to a reduction in gastric injury; the mechanisms underlying these effects include stimulation of endogenous prostaglandins, nitric oxide synthesis, opening of K_ATP channels and reduction of free radicals or modulation of antioxidant enzyme systems.     

表皮生长因子和降钙素基因相关肽在高频电磁场 治疗急性胃损伤中作用研究

目的：探讨高频电磁场（high-frequency electromagnetic fields,HEMFs）曝露治疗急性胃损伤的作用机制。方法：选用健康SD大鼠,以Indomethacin灌胃法复制胃粘膜急性损伤模型,观察40．68MHz HEMFs（波长为7．3m）曝露（微热量,30—50mA,15min,1／d）治疗1或6次后,大鼠胃粘膜损伤程度（胃损伤指数和病理损伤积分）、胃粘膜血流量、血浆表皮生长因子（epidermal growth factor,EGF）和降钙素基因相关肽（calcitonin gene—related peptide,CGRP）水平。结果：HEMFs曝露1次后,胃粘膜血流量较对照组明显升高（P〈0．05）,大鼠胃粘膜损伤程度、血浆EGF和CGRP水平较对照组均无显著性差异（P均〉0．05）;HEMFs曝露6次后,胃粘膜损伤程度较对照组明显改善（P均〈0．05）,胃粘膜血流量显著升高（P〈0．05）,血浆EGF和CGRP水平较对照组无显著性差异（P均〉0.05）。结论：HEMFs曝露治疗大鼠胃粘膜急性损伤可能与其增加胃粘膜血流量有关,与血EGF和CGRP无关。     

Role of prostaglandins and nitric oxide in the lipopolysaccharide-induced ACTH and corticosterone response.

This study was designed to determine the role of endogenous prostaglandins (PG) and nitric oxide (NO) in the lipopolysaccharide (LPS)-induced ACTH and corticosterone secretion in conscious rats. LPS (0.5 and 1 mg/kg) given i.p. stimulated the hypothalamic-pituitary-adrenocortical (HPA) activity measured 2 h later. A non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg i.p.), piroxicam (2 mg/kg i.p.), a more potent antagonist of constitutive cyclooxygenase (COX-1) and compound NS-398 (2 mg/kg i.p.), a selective inhibitor of inducible cyclooxygenase (COX-2) given 30 min before LPS (1 mg/kg i.p.) significantly diminished both the LPS-induced ACTH and corticosterone secretion. COX-2 blocker was the most potent inhibitor of ACTH secretion (72.3%). Nomega-nitro-L-arginine methyl ester (L-NAME 2 and 10 mg/kg i.p.), a non-selective nitric oxide synthase (NOS) blocker given 15 min before LPS did not substantially alter plasma ACTH and corticosterone levels 2 h later. Aminoguanidine (AG 100 mg/kg i.p.), a selective inducible nitric oxide synthase (iNOS) inhibitor, considerably enhanced ACTH and corticosterone secretion induced by a lower dose (0.5 mg/kg) of LPS and did not significantly alter this secretion after a larger dose (1 mg/kg) of LPS. L-NAME did not markedly affect the indomethacin-induced inhibition of ACTH and corticosterone response. By contrast, aminoguanidine abolished the indomethacin-induced reduction of ACTH and corticosterone secretion after LPS. These results indicate an opposite action of PG generated by cyclooxygenase and NO synthesized by iNOS in the LPS-induced HPA-response.     

Reduction of asymmetric dimethylarginine in the protective effects of rutaecarpine on gastric mucosal injury

Our recent study has shown that asymmetric dimethylarginine (ADMA) plays an important role in facilitating gastric mucosal injury by multiple factors. To explore whether the protection of rutaecarpine against gastric mucosal injury is related to reduction of ADMA content, a model of ethanol-induced gastric mucosal injury in rats was selected for this study. The ulcer index, the content of ADMA and NO, and the activity of dimethylarginine dimethylaminohydrolase (DDAH) in gastric tissues were measured in vivo after pretreatment with rutaecarpine. The in vitro effect of rutaecarpine on the release of calcitonin gene-related peptide (CGRP) and NO from isolated gastric tissues was also determined. The results showed that ethanol significantly increased the ulcer index, decreased the DDAH activity and the NO level, and elevated the ADMA level, which was attenuated by pretreatment with rutaecarpine (0.6 mg/kg or 1.2 mg/kg). In the isolated gastric tissues, rutaecarpine significantly increased the release of both CGRP and NO; the release of NO, but not CGRP, was abolished in the presence of l-NAME (10(-4) mol/L). The present results suggest that rutaecarpine protects the gastric mucosa against injury induced by ethanol and that the gastroprotection of rutaecarpine is related to reduction of ADMA levels through stimulating the release of CGRP.     

Endothelin-induced sudden death and the possible involvement of platelet activating factor (PAF)

Endothelin (5 nmol/kg, i.v.) caused a transient hypotension followed by a lasting hypertension in rats. However, an abrupt fall in the blood pressure was observed in most rats 6 to 30 min after the injection of endothelin and sudden death followed with lethality noted over 60 min. An abnormal electrocardiogram (ECG) (ventricular arrhythmias) was observed in rats injected with endothelin. Endothelin (i.v.) also caused sudden death in mice. Pretreatment (5 or 60 min) with specific PAF antagonists, CV-6209 (0.1-3 mg/kg, i.v.) and WEB 2086 (30 mg/kg, p.o.), and a calcium channel blocker, diltiazem (60 mg/kg, p.o.) prevented death and attenuated the ECG changes induced by endothelin, but CV-6209 did not prevent the blood pressure changes induced by endothelin. CV-6209 (0.5-3 mg/kg, i.v.), WEB 2086, diltiazem and dexamethasone (5 mg/kg, i.v.) protected mice against the death induced by endothelin. On the other hand, aspirin (cyclooxygenase inhibitor, 100 mg/kg, p.o.) did not protect mice from the death. Thus, endothelin is a highly toxic peptide with cardiotoxic effects, and PAF may be involved in the pathogenesis of the sudden death.     

Effects of centrally injected GLP-1 in various experimental models of gastric mucosal damage

Glucagon-like peptide-1 (GLP-1) is accepted to be a peptide involved in the central regulation of gastrointestinal function, but its potential gastroprotective effect is not clear. The aim of this study was to investigate whether intracerebroventricularly injected GLP-1 has protective effects on gastric mucosal lesions induced by several models, and if yes, whether these effects are due to the gastric antisecretory effect of the peptide. GLP-1 which was injected in three different doses (1, 10, 100 ng/10 microl; i.c.v.) to conscious rats prevented the mucosal lesions induced by reserpine and ethanol, but did not prevent the gastric mucosal lesions induced by pyloric ligation. In addition, 1 ng/10 microl dose of centrally injected GLP-1 inhibited gastric acid secretion in pylorus-ligated rats. As a result, we conclude that intracerebroventricularly injected GLP-1 may play a role in the prevention of gastric mucosal lesions induced by certain experimental models and this gastroprotective effect may be independent from its antisecretory effect.     

Sensory nerves in central and peripheral control of pancreatic integrity by leptin and melatonin.

Central nervous system affects pancreatic secretion of enzymes however, the neural modulation of acute pancreatitis has not been investigated. Leptin and melatonin have been recently reported to affect the inflammatory response of various tissues. The identification of specific receptors for both peptides in the pancreas suggests that leptin and melatonin could contribute to the pancreatic protection against inflammation. The aim of this study was: 1/ to compare the effect of intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) administration of leptin or melatonin on the course of caerulein-induced pancreatitis (CIP) in the rat, 2/ to examine the involvement of sensory nerves (SN) and calcitonin gene-related peptide (CGRP) in pancreatic protection afforded by leptin or melatonin, 3/ to assess the effect of tested peptides on lipid peroxidation products (MDA + 4-HNE) in the pancreas of CIP rats, 4/ to investigate the influence of leptin or melatonin on nitric oxide (NO) release from isolated pancreatic acini and 5/ to determine the effects of caerulein and leptin on leptin receptor gene expression in these acini by RT-PCR. CIP was induced by subcutaneous (s.c.) infusion of caerulein (25 microg/kg) to the conscious rats, confirmed by the significant increases of pancreatic weight and plasma amylase and by histological examination. This was accompanied in marked reduction of pancreatic blood flow and significant rise of MDA + 4-HNE in the pancreas. Leptin or melatonin were administered i.p. or i.c.v. 30 min prior to the start of CIP. Deactivation of SN was produced by s.c. capsaicin (100 mg/kg). An antagonist of CGRP, CGRP 8-37 (100 microg/kg i.p.), was given together with leptin or melatonin to the CIP rats. MDA + 4-HNE was measured using LPO commercial kit. NO was determined using the Griess reaction. Pretreatment of CIP rats with i.p. leptin (2 or 10 microg/kg) or melatonin (10 or 50 mg/kg) significantly attenuated the severity of CIP. Similar protective effects were observed following i.c.v. application of leptin (0.4 or 2 microg/rat) but not melatonin (10 or 40 microg/rat) to the CIP rats. Capsaicin deactivation of SN oradministration of CGRP 8-37 abolished above beneficial effects of leptin on CIP, whereas melatonin-induced protection of pancreas was unaffected. Pretreatment with i.p. melatonin (10 or 50 mg/kg), but not leptin, significantly reduced MDA + 4-HNE in the pancreas of CIP rats. Leptin (10(-10) - 10(-6) M) but not melatonin (10(-8) - 10(-5) M) significantly stimulated NO release from isolated pancreatic acini. Leptin receptor gene expression in these acini was significantly increased by caerulein and leptin. We conclude that 1/ central or peripheral pretreatment with leptin protects the pancreas against its damage induced by CIP, whereas melatonin exerts its protective effect only when given i.p., but not following its i.c.v. adminstration, 2/ activation of leptin receptor in the pancreatic acini appears to be involved in the beneficial effects of leptin on acute pancreatitis, 3/ the protective effects of leptin involve sensory nerves, CGRP and increased generation of NO whereas melatonin-induced protection of the pancreas depends mainly on the antioxidant local effect of this indole, and scavenging of the radical oxygen species in the pancreatic tissue.     

Gastroprotective and vasodilatory effects of epidermal growth factor: the role of sensory afferent neurons

Epidermal growth factor (EGF) has been shown to exert gastric hyperemic and gastroprotective effects via capsaicin-sensitive afferent neurons, including the release of calcitonin gene-related peptide (CGRP). We examined the protective and vasodilatory effects of EGF on the gastric mucosa and its interaction with sensory nerves, CGRP, and nitric oxide (NO) in anesthetized rats. Intragastric EGF (10 or 30 microg) significantly reduced gastric mucosal lesions induced by intragastric 60% ethanol (50.6% by 10 microg EGF and 70.0% by 30 microg EGF). The protective effect of EGF was significantly inhibited by pretreatment with capsaicin desensitization, human CGRP1 antagonist hCGRP-(8-37), or N(omega)-nitro-L-arginine methyl ester (L-NAME). Intravital microscopy showed that topically applied EGF (10-1,000 microg/ml) dilated the gastric mucosal arterioles dose dependently and that this vasodilatory effect was significantly inhibited by equivalent pretreatments. These findings suggest that EGF plays a protective role against ethanol-induced gastric mucosal injury, possibly by dilating the gastric mucosal arterioles via capsaicin-sensitive afferent neurons involving CGRP and NO mechanisms.     

Vagus-mediated activation of mucosal mast cells in the stomach: effect of ketotifen on gastric mucosal lesion formation and acid secretion induced by a high dose of intracisternal TRH analogue.

TRH analogue, RX 77368, injected intracisternally (i.c.) at high dose (3 microg/rat) produces gastric mucosal lesion formation through vagal-dependent pathway. The gastric mucosal hyperemia induced by i.c. RX 77368 was shown to be mediated by muscarinic vagal efferent fibres and mast cells. Furthermore, electrical vagal stimulation was observed to induce gastric mucosal mast cell degranulation. The aim of the study was to assess the influence of ketotifen, a mast cell stabilizer, on RX 77368-induced gastric lesion formation and gastric acid secretion. RX 77368 (3 microg, i.c.) or vehicle (10 microL, i.c.) was delivered 240 min prior to the sacrifice of the animals. Ketotifen or vehicle (0.9% NaCl, 0.5 mL) was injected intraperitoneally (i.p.) at a dose of 10 mg x kg(-1) 30 min before RX 77368 injection. The extent of mucosal damage was planimetrically measured by a video image analyzer (ASK Ltd., Budapest) device. In the gastric acid secretion studies, the rats were pretreated with ketotifen (10 mg x kg(-1), i.p.) or vehicle (0.9% NaCl, 0.5 mL, i.p.), 30 min later pylorus-ligation was performed and RX 77368 (3 microg, i.c.) or vehicle (0.9% NaCl, 10 microL, i.c.) was injected. The rats were killed 240 min after i.c. injection, and the gastric acid secretion was measured through the titration of gastric contents with 0.1 N NaOH to pH 7.0. RX 77368 (3 microg, i.c.) resulted in a gastric mucosal lesion formation involving 8.2% of the corpus mucosa (n = 7). Ketotifen elicited an 85% inhibition on the development of mucosal lesions (n = 7, P < 0.001) whereas ketotifen alone had no effect on the lesion formation in the mucosa (n = 7). The RX 77368 induced increase of gastric acid secretion was not influenced by ketotifen pretreatment in 4-h pylorus-ligated animals. Central vagal activation induced mucosal lesion formation is mediated by the activation of mucosal mast cells in the stomach. Mast cell inhibition by ketotifen does not influence gastric acid secretion induced by i.c. TRH analogue in 4-h pylorus-ligated rats.