Adaptation of the gastric mucosa to stress. Role of prostaglandin and epidermal growth factor

Carbon Monoxide (CO) Released from Tricarbonyldichlororuthenium (II) Dimer (CORM-2) in Gastroprotection against Experimental Ethanol-Induced Gastric Damage

The physiological gaseous molecule, carbon monoxide (CO) becomes a subject of extensive investigation due to its vasoactive activity throughout the body but its role in gastroprotection has been little investigated. We determined the mechanism of CO released from its donor tricarbonyldichlororuthenium (II) dimer (CORM-2) in protection of gastric mucosa against 75% ethanol-induced injury. Rats were pretreated with CORM-2 30 min prior to 75% ethanol with or without 1) non-selective (indomethacin) or selective cyclooxygenase (COX)-1 (SC-560) and COX-2 (celecoxib) inhibitors, 2) nitric oxide (NO) synthase inhibitor L-NNA, 3) ODQ, a soluble guanylyl cyclase (sGC) inhibitor, hemin, a heme oxygenase (HO)-1 inductor or zinc protoporphyrin IX (ZnPPIX), an inhibitor of HO-1 activity. The CO content in gastric mucosa and carboxyhemoglobin (COHb) level in blood was analyzed by gas chromatography. The gastric mucosal mRNA expression for HO-1, COX-1, COX-2, iNOS, IL-4, IL-1β was analyzed by real-time PCR while HO-1, HO-2 and Nrf2 protein expression was determined by Western Blot. Pretreatment with CORM-2 (0.5-10 mg/kg) dose-dependently attenuated ethanol-induced lesions and raised gastric blood flow (GBF) but large dose of 100 mg/kg was ineffective. CORM-2 (5 mg/kg and 50 mg/kg i.g.) significantly increased gastric mucosal CO content and whole blood COHb level. CORM-2-induced protection was reversed by indomethacin, SC-560 and significantly attenuated by celecoxib, ODQ and L-NNA. Hemin significantly reduced ethanol damage and raised GBF while ZnPPIX which exacerbated ethanol-induced injury inhibited CORM-2- and hemin-induced gastroprotection and the accompanying rise in GBF. CORM-2 significantly increased gastric mucosal HO-1 mRNA expression and decreased mRNA expression for iNOS, IL-1β, COX-1 and COX-2 but failed to affect HO-1 and Nrf2 protein expression decreased by ethanol. We conclude that CORM-2 released CO exerts gastroprotection against ethanol-induced gastric lesions involving an increase in gastric microcirculation mediated by sGC/cGMP, prostaglandins derived from COX-1, NO-NOS system and its anti-inflammatory properties.

PROSTAGLANDINS, CAPSAICIN-SENSITIVE SENSORY NERVES AND NEUTROPHIL INFILTRATION, BUT NOT NITRIC OXIDE, CONTRIBUTE TO COLD RESTRAINT STRESS-INDUCED GASTRIC ADAPTATION IN RATS

The aim of the present study was to determine the role of prostaglandins (PG), nitric oxide (NO) and capsaicin-sensitive sensory nerves in neutrophil infiltration in gastric adaptation to cold restraint stress in rats. Wistar rats were exposed to single or repeated cold restraint stress for 3.5 h every other day for up to 4 days. Prior to repeated stress, rats were pretreated with NG-nitro-L-arginine methyl ester (L-NAME; 10 mg/kg, s.c.), indomethacin (10 mg/kg, s.c.) or capsaicin (125 mg/kg, s.c.). The extent of gastric mucosal lesions was evaluated histologically and myeloproxidase (MPO) activity, PGE2, NO and calcitonin gene-related peptide (CGRP) levels were measured in gastric tissue. Cold restraint stress produced haemorrhagic lesions and reduced PGE2 and CGRP levels in the stomach, with an increase in MPO activity and NO levels. Repeated stress insults reduced stress-induced gastric damage, NO production and MPO activity, with an increase in PGE2 and CGRP levels compared with rats exposed to single cold restraint stress. Adaptation to cold restraint stress was prevented by indomethacin and capsaicin pretreatment, but not by L-NAME. We conclude that the stomach has the ability to adapt to repeated exposure to cold restraint stress and that the adaptation, via inhibition of neutrophil infiltration, is mediated, at least in part, by endogenous PG and CGRP.

Effect of psychogenic stress on gastrointestinal function

This review summarizes the studies published over the last twenty years on the effects of psychogenic stress on gastrointestinal function, using animal models. The effects of stress on gastric ulceration have received wide attention and the central and local mechanisms of mucosal damage have been, for the most part, clearly delineated. In comparison, relatively few studies have focused on the impact of stress on intestinal and colonic physiology, even though its influence on intestinal motility, mucosal permeability and inflammation has been established. More work is necessary in this field, especially considering the importance of irritable bowel syndrome in modern society.

Rodent submandibular gland peptide hormones and other biologically active peptides

The cervical sympathetic trunk-submandibular gland neuroendocrine axis plays an integral role in physiological adaptations and contributes to the maintenance of systemic homeostasis, particularly under the 'stress conditions' seen with tissue damage, inflammation, and aggressive behavior. The variety of polypeptides, whose release from acinar and ductal cells is under sympathetic nervous system control, offers coordinated and progressive levels of endocrine communication. Proteolytic enzymes (e.g. the kallikreins and furin maturases) are involved in the conversion of inactive precursors (e. g. Pro-EGF and SMR1) into biologically active molecules (e.g. EGF, SMR1-pentapeptide), which act on local or distant targets and thereby modulate the homeostatic process.

Activation of genes for spasmolytic peptide, transforming growth factor alpha and for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to aspirin damage in rats

BACKGROUND

NSAIDs, such as aspirin (ASA), cause widespread mucosal damage, but repeated ASA insults appear to induce mucosal tolerance (adaptation) to this injury. The mechanism of the gastric adaptation to the damage induced by ASA has not been fully explained.

AIM

To determine the role of the mucosal gene expression for spasmolitic peptide (SP) (a member of trefoil peptides) and transforming growth factor alpha (TGF alpha) as well as for cyclooxygenase (COX)-1 and COX-2 during gastric adaptation to ASA in rats.

METHODS

Gastric lesions were produced by ASA (100 mg/kg in 1.5 mL of 0.2 M HCl) applied intragastrically (i.g.) as a single dose. every day for 5 days. Control rats were given 1.5 mL of vehicle (0.2 M HCl i.g.) as a single dose, during 5 consecutive days. Gastric blood flow (GBF) was measured by H2-gas clearance technique and gastric mucosal specimens were taken for the assessment of cell proliferation rate in gastric mucosa by bromodeoxyuridine (BrdU) uptake, mucosal generation of prostaglandin E2 measured by radioimmunoassay, and for expression of SP, TGF alpha COX-1 and COX-2 mRNA as determined by RT-PCR. To quantify the relative amounts of mRNA for SP and TGF alpha, southern blotting analysis of the PCR products was performed and the intensity of PCR products was compared with that of beta-actin used as a standard.

RESULTS

ASA applied once produced numerous gastric erosions, but with repeated ASA doses the adaptation to this NSAID developed, the area of gastric lesions being reduced by 86% after six consecutive ASA insults. This adaptation to ASA was accompanied by approximately a 90% reduction in prostaglandin E2 biosynthesis, by a significant rise in BrdU uptake by glandular cells predominantly in the neck region of gastric glands and by expression of SP (SP/beta-actin ratio; 0.96 +/- 0.08 in ASA-adapted mucosa vs. 0.38 +/- 0.05 in the control mucosa) and TGF alpha (TGF alpha/beta-actin ratio: 0.97 +/- 0.07 in ASA-adapted mucosa vs. 0.77 +/- 0.06 in the control mucosa). COX-1 expression was detected in vehicle-control gastric mucosa and after single exposure to ASA or after six consecutive ASA insults, while COX-2 mRNA was not detected in vehicle-control gastric mucosa, but appeared after single ASA insult and was sustained after subsequent ASA doses.

CONCLUSIONS

(i) Gastric adaptation to aspirin injury involves enhanced cell proliferation which appears to be mediated by increased expression of SP and TGF alpha, and (ii) rapid upregulation of COX-2 expression following single and repeated ASA insults may represent a compensatory response to suppression of prostaglandin generation by this NSAID.

Growth markers in the human gastric mucosa during adaptation to continued aspirin administration

The mechanism of gastric mucosal adaptation to continued aspirin (ASA) administration is unknown. We have investigated growth and proliferation markers in healthy subjects under prolonged ASA treatment. In eight healthy volunteers, ASA treatment (2 g/day) was continued for 14 days. Endoscopy was performed before medication; at days 3, 7, and 14 of ASA treatment; and at days 16 and 18 (2 and 4 days, respectively, after medication was ceased). Gastric biopsies from oxyntic and antral mucosa were studied by histology and by histochemistry for proliferating cell nuclear antigen (PCNA), epidermal growth factor (EGF), transforming growth factor-alpha (TGF-alpha), and epidermal growth factor receptor (EGFr). ASA treatment did not change the expression of EGF and EGFr significantly. The PCNA index showed local inconsistent variations. However, increased TGF-alpha expression after ASA was noted, particularly in hyperplastic surface epithelium. Edema and teleangiectases were common in gastric mucosa after ASA. An increasing incidence of foveolar hyperplasia was also noted in the antral mucosa. Healthy subjects on prolonged ASA treatment gradually develop parameters of chronic reactive gastritis accompanied by increased TGF-alpha expression in gastric surface epithelial cells, especially in hyperplastic areas.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Gastric mucosal adaptation to diclofenac injury

Adaptation occurs to the gastric injury produced by nonsteroidal antiinflammatory drugs during continued dosing. The aim of this study was to identify characteristics of this phenomenon that might help in the search for underlying mechanisms. The time frame for onset and offset of adaptation of diclofenac (damage assessed planimetrically) was examined in rats. Adaptation to oral diclofenac took three to five days to develop, and persisted for up to five days after the last dose. It was also demonstrable after subcutaneous dosing or when injury was measured by a change in mucosal potential difference. Diclofenac-adapted rats were protected against injury induced by subsequent exposure to ethanol, indomethacin, aspirin, or piroxicam, indicating that adaptation is not specific to injury by the adapting agent. This cross-adaptation was dose-dependent and characterized histologically by a reduction in deep damage. In conclusion, gastric adaptation to diclofenac is mediated by mechanisms that take several days to develop and be lost. The route of administration appears to be unimportant, but the development of both adaptation and cross-adaptation is influenced by dosage size.

Gastric microbleeding following single and repeated dosing with naproxen

BACKGROUND

Adaptation to gastric damage from nonsteroidal anti-inflammatory drugs (NSAID) has been observed during ongoing dosage in rats and humans. However, this does not always occur, and our previous data suggest that NSAID half-life may be a determining factor.

AIM

To investigate whether adaptation occurs during 1 week of naproxen administration in humans.

SUBJECTS

Thirteen healthy volunteers were studied at baseline, and after one or seven daily doses of naproxen 750 mg. Gastric microbleeding was measured 4 h after naproxen in gastric washings collected during a 30-min period. Serum thromboxane B concentrations were also assayed, as a marker of cyclo-oxygenase inhibition.

RESULTS

Mean blood loss after placebo was 0.60 microL/10 min (95% CI: 0.21-0.98). This rose to 2.15 (0.73-3.57) and 1.75 (0.74-2.76) microL/10 min after one and seven daily doses of naproxen, respectively (P < 0.05 vs. baseline; day 1 vs. 7 not significant). Thromboxane B concentrations were < 10% of control at both day 1 and 7 of dosing.

CONCLUSION

In accord with our findings in rats, adaptation to this moderately long acting NSAID in humans was not apparent. We conclude that any adaptation to naproxen is unlikely to be clinically important.

Gastric adaptation to stress: role of sensory nerves, salivary glands, and adrenal glands

BACKGROUND

Single exposure to water immersion and restraint stress (WRS) in rats produces acute gastric mucosal damage, but repetitive WRS insults lead to gastric adaptation to stress ulcerogenesis. This study was designed to assess the mechanism of this adaptation, particularly the role of sensory nerves, salivary glands, adrenal glands, and gastric acid secretion.

METHODS

WRS was applied for a standard period of 3.5 h, either once or repeated every other day for up to 8 days in intact rats and in animals with capsaicin-induced deactivation of sensory nerves, vagotomy, salivectomy, adrenalectomy, and inhibition of gastric acid secretion by H2-blocker.

RESULTS

WRS applied once produced multiple gastric erosions accompanied by a significant increase in gastric acid secretion and a decrease in gastric blood flow (GBF) and DNA synthesis. Repeated WRS insults resulted in a significant decrease in the number of gastric lesions, reaching a maximum after four consecutive exposures to WRS. This adaptation to stress ulcerogenesis was accompanied by a decrease in gastric acid secretion and an increase in GBF and mucosal generation of DNA synthesis. Salivectomy, which decreased the luminal content of epidermal growth factor (EGF) (by about 80%), markedly attenuated this adaptation, and this was reversed by the addition of exogenous EGF. Capsaicin-induced ablation of sensory nerves eliminated gastric adaptation to WRS, and this was accompanied by a significant decrease in the GBF, but pretreatment with calcitonin gene-related peptide restored gastric adaptation to stress in capsaicin-denervated rats. Selective vagotomy and adrenalectomy failed to affect gastric adaptation to WRS, whereas gastric acid inhibition by ranitidine enhanced this adaptation.

CONCLUSIONS

The stomach is able to adapt to repeated stress insults by enhancing GBF and DNA synthesis, and this adaptation is mediated, at least in part, by sensory nerves and EGF.

Restraint stress in biomedical research: an update

Since the publication of our initial review of restraint stress in 1986, much work has continued with this technique, either as a tool for the investigation of other pharmacological, physiological, or pathologic phenomena or with restraint stress itself serving as the object of the study. As we noted in 1986, the major use of restraint has been for the induction of stress responses in animals and, more specifically, for the investigation of drug effects, particularly as they affect typical stress-related pathology--gastrointestinal, neuroendocrine, and immunological agents have been extensively studied. In compiling this update on restraint stress and its effects, we noted an increasing emphasis on central nervous system mechanisms in peripheral disease, especially gastrointestinal disease. In particular, many CNS-active agents have been tested for their effects on gastric and duodenal lesion formation and gastric secretion, including antidepressants, antipsychotics, anxiolytics, noradrenergic, serotonergic, dopaminergic, and peptidergic compounds. Some of these agents are especially active in the gastrointestinal tract even when administered centrally, further solidifying the concept of a brain-gut axis. The present update includes studies of: methods and procedures, pre-restraint manipulations, post-restraint/healing effects, and drug effects. In addition, a current bibliography of reports that have employed restraint is included.