Pawlik Mw

Role of central and peripheral ghrelin in the mechanism of gastric mucosal defence.

Ghrelin, identified in the gastric mucosa, has been involved in the control of food intake and growth hormone (GH) release, but whether this hormone influences the gastric secretion and gastric mucosal integrity has been little elucidated. We compared the effects of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of ghrelin on gastric secretion and gastric lesions induced in rats by 75% ethanol or 3.5 h of water immersion and restraint stress (WRS) with or without suppression of nitric oxide (NO)-synthase or functional ablation of afferent sensory nerves by capsaicin. The number and the area of gastric lesions was measured by planimetry, the GBF was assessed by the H2-gas clearance method and blood was withdrawn for the determination of the plasma ghrelin and gastrin levels. In addition, the gastric mucosal expression of mRNA for CGRP, the most potent neuropeptide released from the sensory afferent nerves, was analyzed in rats exposed to WRS with or without ghrelin pre-treatment. Ghrelin (5–80 µg/kg i.p. or 0.6–5 µg/kg i.c.v.) increased gastric acid secretion and attenuated gastric lesions induced by ethanol and WRS. This protective effect was accompanied by a significant rise in the gastric mucosal blood flow (GBF), luminal NO concentration and plasma ghrelin and gastrin levels. Ghrelin-induced protection was abolished by vagotomy and significantly attenuated by L-NNA and deactivation of afferent nerves with neurotoxic dose of capsaicin. The signal for CGRP mRNA was significantly increased in gastric mucosa exposed to WRS as compared to that in the intact gastric mucosa and this was further enhanced in animals treated with ghrelin. We conclude that central and peripheral ghrelin exerts a potent protective action on the stomach of rats exposed to ethanol or WRS, and these effects depend upon vagal activity and hyperemia mediated by the NOS-NO system and CGRP released from sensory afferent nerves.

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.

Importance of the pineal gland, endogenous prostaglandins and sensory nerves in the gastroprotective actions of central and peripheral melatonin against stress-induced damage

Abstract:   Melatonin attenuates acute gastric lesions induced by topical strong irritants because of scavenging of free radicals, but its role in the pathogenesis of stress‐induced gastric lesions has been sparingly investigated. In this study we compared the effects of intragastric (i.g.) or intracerebroventricular (i.c.v.) administration of melatonin and its precursor, l‐tryptophan, with or without concurrent treatment with luzindole, a selective antagonist of melatonin MT2 receptors, on gastric lesions induced by water immersion and restraint stress (WRS). The involvement of pineal gland, endogenous prostaglandins (PG) and sensory nerves in gastroprotective action of melatonin and l‐tryptophan against WRS was studied in intact or pinealectomized rats or those treated with indomethacin or rofecoxib to suppress cyclooxygenase (COX)‐1 and COX‐2, respectively, and with capsaicin to induce functional ablation of the sensory nerves. In addition, the influence of i.c.v. and i.g. melatonin on gastric secretion was tested in a separate group of rats equipped with gastric fistulas. At 3.5 hr after the end of WRS, the number of gastric lesions was counted, the gastric blood flow (GBF) was determined by H2‐gas clearance technique and plasma melatonin and gastrin levels were measured by specific radioimmunoassay (RIA). Biopsy mucosal samples were taken for determination of expression of mRNA for COX‐1 and COX‐2 by reverse transcriptase‐polymerase chain reaction (RT‐PCR) and of the mucosal generation of prostaglandin E2 (PGE2) by RIA. Melatonin applied i.g. (1.25–10 mg/kg) or i.c.v. (1.25–10 μg/kg) dose‐dependently inhibited gastric acid secretion and significantly attenuated the WRS‐induced gastric damage. This protective effect of melatonin was accompanied by a significant rise in the GBF and plasma melatonin and gastrin levels and in mucosal generation of PGE2. Pinealectomy, which suppressed plasma melatonin levels, aggravated the gastric lesions induced by WRS and these effects were counteracted by i.g. or i.c.v. application of melatonin. Luzindole abolished completely the gastroprotective effects of melatonin and l‐tryptophan and attenuated significantly the rise in GBF evoked by the indoleamine and its precursor. Indomethacin and rofecoxib, which diminished PGE2 biosynthesis by c. 90 and 75% or capsaicin denervation, attenuated significantly melatonin‐ and l‐tryptophan‐induced protection and the rise in the GBF. Both the protection and the hyperemia were restored by addition of exogenous CGRP to capsaicin‐denervated animals. COX‐1 mRNA was detected by RT‐PCR in the intact and melatonin‐treated gastric mucosa, while COX‐2 mRNA, which was undetectable in the intact gastric mucosa, appeared in WRS‐exposed mucosa, especially in the melatonin‐treated animals and this was accompanied by increased generation of PGE2 in gastric mucosa. Pinealectomy downregulated COX‐2 mRNA and this effect was reversed by supplementation of pinealectomized animals with melatonin. We conclude that, (a) exogenous melatonin and its precursor, l‐tryptophan, attenuates WRS‐induced gastric lesions via interaction with MT2 receptors, (b) this protective action of melatonin is because of an enhancement of gastric microcirculation, probably mediated by PGE2 derived from COX‐2 overexpression and activity, the activation of brain‐gut axis involving CGRP released from sensory nerves, and the release of gastrin and (c) the pineal plays an important role in the limitation of WRS‐induced gastric lesions via releasing melatonin, which exerts gastroprotective and hyperemic activities against stress ulcerogenesis.

Gastric secretion, proinflammatory cytokines and epidermal growth factor (EGF) in the delayed healing of lingual and gastric ulcerations by testosterone

Abstract.Hormonal fluctuations are known to predispose ulceration of the upper gastrointestinal tract, but to date no comparative study of their effects on the healing of pre-existing ulcers in the oral cavity and stomach has been made. We studied the effects of depletion of testosterone and of EGF on the healing of acetic acid-induced ulcers using rats having undergone bilateral orchidectomy and/or salivectomy respectively. We measured alterations in gastric acid secretion and blood flow at ulcer margins, as well as plasma levels of testosterone, gastrin and the proinflammatory cytokines IL-1β and TNF-α. Testosterone (0.01–10 mg/kg/day i. m.) dose-dependently delayed oral and gastric ulcer healing. When applied in an optimal dose of 1 mg/kg/day, this hormone significantly raised gastric acid secretion and plasma IL-1β and TNF-α levels. Attenuation of plasma testosterone levels via bilateral orchidectomy inhibited gastric acid secretion and accelerated the healing of oral and gastric ulcers, while increasing plasma gastrin levels and these effects were reversed by testosterone. Salivectomy raised plasma testosterone levels, and delayed oral and gastric ulcer healing. Treatment of salivectomised animals with testosterone further inhibited ulcer healing, and this effect was counteracted by EGF. We propose that testosterone delays ulcer healing via a fall in blood flow at the ulcer margin, a rise in plasma levels of IL-1β and TNF-α and, in the case of gastric ulcers, an increase in gastric acid secretion. EGF released from the salivary glands plays an important role in limitation of the deleterious effects of testosterone on ulcer healing.

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.

Ghrelin and Stress Protection

Ghrelin, identified in the gastric mucosa, is involved in control of food intake and growth hormone (GH) release. Besides being an appetite hormone, central and peripheral ghrelin exerts a potent protective action against gastric mucosal experimental injury induced by stress, an effect dependant on vagal activity and hyperemia mediated by nitric oxide synthase (NOS)-nitric acid (NO) and cyclo-oxygenase (COX)-prostaglandin (PG) systems and calcitonin gene related peptide (CGRP) released from sensory afferent nerves.