Cell proliferation during the development of stress erosions in mouse stomach

Epithelial cell proliferation in the digestive tract induced by space restriction and water-immersion stress

The effects of space restriction and water-immersion stress on epithelial cell proliferation in the digestive tract, with special attention to the esophagus, stomach and duodenum, in 8-week-old SD male rats were examined. Histological assessment revealed spotted hemorrhagic lesions in the fundus of the glandular stomach, accompanied by statistically increased 5-bromo-2'-deoxyuridine (BrdU) labeling index in the fundic and pyloric regions. Furthermore, biochemical analysis demonstrated an increased activity of ornithine decarboxylase (ODC) and spermidine/spermine N1-acetyltransferase (SAT), known as key late-limiting enzymes of the polyamine pathway, in the gastric fundus. The stress may induce a remarkable increase in expression of c-fos, c-jun and c-myc mRNAs in both fundic and pyloric regions of the glandular stomach. There were no remarkable changes in the esophagus. These results indicate that space restriction and water-immersion stress induced cell proliferation in the glandular stomach through overexpression of proto-oncogenes and increased ODC and SAT activities that might be related to the promotion of gastric carcinogenesis.

Expression of epidermal growth factor and transforming growth factor-alpha after exposure of rat gastric mucosa to stress

BACKGROUND

This study was designed to determine whether transforming growth factor-alpha (TGF-alpha), epidermal growth factor (EGF), and their common receptor (EGFR) are involved in the recovery of the gastric mucosa after exposure to water immersion and restraint stress.

METHODS

Wistar rats were exposed to a standard period (3.5 h) of water immersion and restraint stress. Animals were killed immediately or 2 h, 4 h, 6 h, or 12 h after the stress. Tissues were removed, the area of the ulcerations was measured planimetrically, half of the stomach was taken for measurement of DNA synthesis, and the other half was embedded in paraffin. Sections were stained immunohistochemically for proliferating nuclear antigen (an index of cellular proliferation) and TGF-alpha, EGF, and EGFR.

RESULTS

A single stress insult resulted in numerous haemorrhagic erosions in the oxyntic mucosa and a significant drop in DNA synthesis. During the recovery phase a marked increase in the expression of EGF peaked at 4 h, whereas the expression of EGFR peaked 6 h after stress. Thereafter the labelling indices for EGF and EGFR decreased, whereas DNA synthesis showed a gradual increase starting after about 6 h and peaking 12 h after the stress. In contrast, immunohistochemical expression of TGF-alpha showed a constant increase for up to 12 h after stress. Cell proliferation reached a maximum after 6 h and returned to normal values 12 h after the stress.

CONCLUSIONS

EFG and TGF-alpha and their receptors are involved in the mucosal recovery from stress, and this is followed by enhanced DNA synthesis and mucosal cell proliferation.

The effect of the autonomic nervous system on cell proliferation of the gastric mucosa in stress ulcer formation

The role of the autonomic nervous system in cell proliferation of the gastric mucosa during restraint water immersion stress was investigated utilizing the spontaneously hypertensive rat (SHR) and its progenitor, the Wistar-Kyoto rat (WKY). Three hours of water-immersion restraint induced gastric lesions more frequently in WKY than in SHR, although there were few visual lesions in either strain in two hours of stress. The number of 5-bromo-2'-deoxyuridine (BrdU) positive cells in the corpus ventriculi mucosa markedly decreased in the WKY, but did not change in the SHR after two hours of water-immersion restraint stress. The acetylcholine content in the mucosa significantly decreased and the density of acetylcholinesterase (ACh-E) containing fiber of mucosa remarkably increased in only WKY after two hours stress exposure. On the other hand, there was no significant difference in either the responsiveness or the content of norepinephrine and epinephrine, which indicates sympathetic nervous function, after stress exposure in WKY and SHR. Similarly, the response of serum gastrin was not significantly different between the two strains. These results strongly suggest that the parasympathetic nerve plays an essential role in cell proliferation of the gastric mucosa in the pathogenesis of stress ulcer.

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

This study was designed to determine whether repeated exposures to stress lead to the adaptation of the gastric mucosa to stress ulcerogenesis. Wistar rats with intact or resected salivary glands were exposed to a standard period (3.5 h) of water-immersion and restraint stress every other day up to 8 days. The significant reduction in the severity of gastric lesions was first noticed after the second exposure to stress and was maximal after 6-day exposures to stress. This tolerance to stress ulcerogenesis disappeared after a 6-day rest during which animals were not exposed to stress. Histologically, the hemorrhages and edema seen after a single stress were less frequent during adaptation; instead the mucosa regenerated in spite of continuation of exposure to stress. During adaptation, the mucosal blood flow (MBF) and mucosal biosynthesis of PG were markedly increased. Administration of indomethacin (5 mg/kg i.p.) completely abolished gastric adaptation to stress and this was accompanied by about 85% reduction in mucosal generation of PG and significant decrease in the MBF. Salivectomy, which significantly reduced the luminal contents of epidermal growth factor (EGF) in the stomach, delayed and reduced the adaptation. We conclude that the stomach has the ability to adapt to repeated exposures to stress and that this adaptation is mediated, at least in part, by endogenous PG and EGF.

Role of salivary glands and epidermal growth factor (EGF) in gastric secretion and mucosal integrity in rats exposed to stress

EGF, produced mainly by salivary glands, inhibits gastric acid secretion, stimulates the proliferation of gastric mucosal cells and protects the mucosa against various ulcerogens, but its role in the pathogenesis of stress ulcerations is unknown. In this study, rats with intact or resected salivary glands were exposed to water immersion and restraint stress (WRS) without and with pretreatment with exogenous EGF or dimethyl PGE2 (dmPGE2) at doses which were shown previously to protect the mucosa against topical irritants. During 1.5-12 h of WRS, the formation of gastric ulcerations increased progressively with the duration of stress reaching peak after 6 h of stress and being significantly higher in rats with removed salivary glands than in intact animals. Gastric acid secretion and DNA synthesis in oxyntic mucosa declined with the duration of WRS, but after sialoadenectomy a significant increase in gastric acid secretion and a further decline in DNA synthesis were observed after WRS. EGF contents in the gastric lumen and the gastric mucosa were several times higher in rats subjected to stress than in control unstressed animals, indicating that stress causes an extensive release of EGF. Both exogenous EGF (17 nmol/kg/h) and dmPGE2 (143 nmol/kg) prevented, in part, the formation of gastric lesions, while inhibiting gastric acid secretion both in rats with intact or resected salivary glands. We conclude that water immersion and restraint stress is accompanied by an excessive release of EGF, which appears to attenuate gastric secretion, enhances the DNA synthesis and may limit the formation of stress-induced gastric ulcerations.

Role of epidermal growth factor, prostaglandin, and sulfhydryls in stress-induced gastric lesions

Epidermal growth factor promotes the growth of and protects gastric mucosa against various ulcerogens, including stress, but little is known about its role in the pathogenesis of stress ulcerations. In this study, Wistar rats with intact and resected salivary glands were exposed to water-immersion and restraint stress. During 2-14 hours of water-immersion restraint stress, the formation of gastric ulcerations increased progressively and the duration of stress was accompanied by a decrease in DNA synthesis in the gastric mucosa. Following sialoadenectomy, a significant increase in the number of stress ulcerations and further reduction in DNA synthesis were observed. Exogenous epidermal growth factor and dimethyl prostaglandin E2 significantly reduced the ulcerations in the stressed rats with intact salivary glands, but this reduction was significantly less pronounced after sialoadenectomy. Water-immersion restraint stress also resulted in about 50% reduction in mucosal prostaglandin E2 generation, and the pretreatment with indomethacin, which suppressed prostaglandin E2 by about 90%, almost doubled the number of stress ulcerations and abolished the gastro-protective effect of exogenous epidermal growth factor (but not dimethyl prostaglandin E2) against the stress lesions. An inhibition of ornithine decarboxylase activity by difluoromethyl ornithine also augmented stress-induced ulcerogenesis and abolished the protective action of epidermal growth factor while the administration of spermine almost completely prevented stress ulcerations in rats both without and with pretreatment with difluoromethylornithine. Water-immersion restraint stress also significantly reduced mucosal content of glutathione. Cysteamine increased tissue glutathione and reduced stress ulcerations but N-ethylmaleimide, an sulfhydryl blocker, decreased mucosal content of glutathione without affecting the stress ulcerations. This study indicates that the stress ulcers are accompanied by the reduction in mucosal synthesis of DNA, prostaglandin, and glutathione and that the presence of salivary glands attenuates the stress ulcerogenesis probably by releasing epidermal growth factor which acts, in part, by enhancing ornithine decarboxylase activity, mucosal growth, and prostaglandin and glutathione formation.

Chronobiologic factors in experimental stress ulcer

The available literature on chronobiologic factors in experimental stress ulcer is extremely small and thematically limited. It focuses almost exclusively on circadian rhythms and, within that, on rhythms related to light-dark cycles, activity and body temperature. Among these, only differences in ulcer induction related to circadian activity patterns have been adequately demonstrated. Other circadian patterns and other temporal phase relationships might be profitably explored, including those related to postnatal development. It is also likely that the important relationships between biorhythms and stress ulcer are not limited to ulcer induction. Future studies should address chronobiologic factors in predisposition, severity of illness, the probability of recovery and response to various therapeutic interventions.

Restraint stress in biomedical research: a review

The use of restraint or immobilization for investigations of animal physiology, pathology and pharmacology has an extensive history. The major use of this technique has been as a "stressor" for the induction of stress response syndromes in animals. Many such syndromes have been characterized from the behavioral level to the neurochemical concomitants of stress. As a consequence of this particular use of the restraint procedure, much information concerning drug effects on stress response syndromes has been obtained. Indeed, many researchers in the area of gastrointestinal drugs routinely screen their new compounds in a restraint model of gastric stress ulcer. The purpose of this review is to present for researchers, a summary of the methods for, the parameters of, and known drug effects on, restraint-induced pathology. In our experience, this technique has proven to be a very useful one for the examination of both central and peripheral mechanisms of stress-related disorders, as well as for studying drug effects upon these disorders.

Effects of water immersion restraint stress and chronic indomethacin ingestion on gastric antral and fundic epithelial proliferation

We studied the effects on gastric fundic and antral epithelial proliferation of acute water immersion restraint stress in rats and of chronic indomethacin ingestion in rats and humans using autoradiographic methods. Acute stress appeared to inhibit fundic epithelial proliferation but had no effect on antral proliferation in rats. We conjecture that this inhibition of fundic epithelial proliferation may help explain the development of stress-related mucosal lesions, which are more likely to occur in fundic mucosa. Chronic indomethacin ingestion stimulated fundic epithelial proliferation but had no effect on antral proliferation in both rats and humans. From these observations we conjecture that the failure of antral epithelial proliferation to respond to indomethacin may account in part for the ulcerogenic action of this drug.

Duodenal epithelial thymidine uptake in patients with duodenal ulcer or endoscopic duodenitis

To evaluate the relationship between duodenal ulcer disease and duodenitis, duodenal epithelial cell renewal was measured in mucosal biopsies by the incorporation of [3H]thymidine. When 14 patients with duodenal ulcer were compared to 13 control subjects or 7 with endoscopic duodenitis alone, the crypt size was the same in all groups. Similar to other inflammatory processes of the gastrointestinal tract, patients with endoscopic duodenitis showed increased proliferative indices including a greater number of cells incorporating [3H]thymidine. In contrast, the proliferative indices from the duodenal mucosa of patients with duodenal ulcers did not differ from a control group. In a group of 6 patients with both endoscopic duodenitis and duodenal ulcer, the [3H]thymidine incorporation was intermediate between control subjects or patients with duodenal ulcer alone and those with endoscopic duodenitis alone. When subjects were divided according to the histologic appearance of the duodenal mucosa, those having chronic duodenitis demonstrated enhanced [3H]thymidine incorporation in comparison to a control group or patients with chronic active duodenitis (polymorphonuclear leukocytes present). Although there are many possible explanations of these findings, one may speculate that duodenal ulceration does not stimulate duodenal epithelial proliferation.

Prostaglandin prevents alterations in DNA, RNA, and protein in damaged gastric mucosa

Fasted rats were given either 16,16-dimethyl-PGE2 (dmPGE2) (1 microgram/kg) or normal saline subcutaneously followed by the oral administration of 1 ml of 100% ethanol or saline 30 min later. At 1, 3, 6, and 24 hr later, animals were sacrificed, their stomachs examined for necrotic ulcerations, and the incorporation of [3H]thymidine into DNA as well as tissue levels of DNA, RNA, and protein content of glandular mucosa determined. Compared with control animals, severe ulcerations of 70-80% of the glandular mucosa were observed in rats given 100% ethanol at all time periods. Accompanying these ulcerations were marked depressions in tissue levels of DNA and RNA at 1, 3, 6, and 24 hr after exposure to ethanol, and protein at 1, 3, and 6 hr following ethanol. In rats pretreated with dmPGE2 before ethanol administration, these alterations in tissue levels of DNA, RNA, and protein were prevented as were ulcerations of the glandular stomach at each time period. Synthesis of mucosal DNA was not significantly different from control rats in any of the groups studied. It is concluded that (1) gastric mucosal damage by alcohol is associated with a decrease in tissue levels of DNA, RNA, and protein; (2) dmPGE2 maintains normal tissue levels of DNA, RNA, and protein by preventing the shedding of mucosal cells by alcohol; and (3) the ability of dmPGE2 to prevent gastric damage by alcohol is not mediated through stimulation of DNA synthesis.

Early life events and peptic ulcer susceptibility: an experimental model

In the rat premature separation from the mother increases the probability that gastric erosions will occur when the animal is subjected to physical restraint later in life. This increased susceptibility to erosion formation is induced by the early loss of maternal milk and is expressed as a disturbance of body temperature regulation at the time of restraint. One of the gastric consequences of the thermoregulatory disturbance appears to be an increase in acid secretion during restraint. The increased susceptibility to restraint-induced erosion formation in prematurely separated rats may reflect a disruption of the normal developmental organization of functionally related systems.

Measurement of glycoprotein content and cell kinetics in preulcerous gastric mucosa

In an attempt to evaluate the role of gastric mucosal defense factors in ulcerogenesis, we measured the levels of glycoproteins in the mucosa as well as mucosal cell turnover in the preulcerous phase and compared these parameters to the normal mucosa in the same animal. Ovalbumin-presensitized Praomys (Mastomys) natalensis were challenged in the gastric wall with ovalbumin and a gastric ulcer developed at the challenge site 3 days later as a result of a mucosal anaphylactic reaction. This model enabled us to study the events occurring at the site of a future ulceration. Gas-liquid chromatographic determination of mucosal glycoproteins showed that the normal and preulcerous mucosae had similar levels. Cell turnover, determined by [3H]thymidine incorporation, was stimulated as a result of the preulcerous anaphylactic reaction at 24 hours postchallenge whereas at 48 hours the values were not different from those obtained in controls. These results suggest that the pathogenesis of anaphylactic gastric ulcer involves a change in cell turnover but no changes in the production of gastric mucus.

The influence of carbenoxolone on steroid-induced ulcer and mucus secretion in the rat

In rats, gastric mucus was decreased by starvation. The administration of carbenoxolone sodium, prednisolone, or their combination to starved rats brought the level of gastric mucus to that of nonstarved controls. Concomitant treatment with carbenoxolone sodium did not prevent prednisolone-induced ulceration of the glandular stomach in starved rats. The ulcerations of the prostomach (squamous spithelium)induced by starvation were prevented by carbenoxolone sodium, prednisolone, or the combination of the two.