Circadian rhythm of melatonin and prostaglandin in modulation of stress-induced gastric mucosal lesions in rats

Prostaglandin F2α Affects the Cycle of Clock Gene Expression and Mouse Behavior

Prostaglandins are bioactive compounds, and the activation of their receptors affects the expression of clock genes. However, the prostaglandin F receptor (Ptgfr) has no known relationship with biological rhythms. Here, we first measured the locomotor period lengths of Ptgfr-KO (B6.129-Ptgfrtm1Sna) mice and found that they were longer under constant dark conditions (DD) than those of wild-type (C57BL/6J) mice. We then investigated the clock gene patterns within the suprachiasmatic nucleus in Ptgfr-KO mice under DD and observed a decrease in the expression of the clock gene cryptochrome 1 (Cry1), which is related to the circadian cycle. Moreover, the expression of Cry1, Cry2, and Period2 (Per2) mRNA were significantly altered in the mouse liver in Ptgfr-KO mice under DD. In the wild-type mouse, the plasma prostaglandin F2α (PGF2α) levels showed a circadian rhythm under a 12 h cycle of light-dark conditions. In addition, in vitro experiments showed that the addition of PTGFR agonists altered the amplitude of Per2::luc activity, and this alteration differed with the timing of the agonist addition. These results lead us to hypothesize that the plasma rhythm of PGF2α is important for driving clock genes, thus suggesting the involvement of PGF2α- and Ptgfr-targeting drugs in the biological clock cycle.

Impact of Subjective and Objective Sleep Quality on Peptic Ulcer Rebleeding in Older Adults

OBJECTIVE

This study aimed to examine the association of subjective and objective sleep quality with subsequent peptic ulcer rebleeding among older patients.

METHODS

Of 1196 older patients with peptic ulcer bleeding (PUB) recruited from 12 grade A hospitals in the People's Republic of China, 1106 achieved full recovery from PUB, and they were followed up for up to 30 days. Using multiple measures at 1-week intervals, patients who presented PUB symptoms were invited to have an esophagogastroduodenoscopy examination. Subjective sleep quality was measured using the Pittsburgh Sleep Quality Index. Objective sleep quality domains were measured using an accelerometer, including sleep onset latency, sleep efficiency, total sleep time, and the number of awakenings.

RESULTS

This study documented a 30-day cumulative ulcer rebleeding rate of 15.3%. Multivariate analyses showed that longer sleep onset latency (hazard ratio [HR] = 2.136 [1.336-2.558]) and more nighttime awakenings (HR = 1.698 [1.169-2.666]) increased the risk of ulcer rebleeding. However, a longer total sleep time (HR = 0.768 [0.698-0.887]) and better sleep efficiency (HR = 0.795 [0.682-0.975]) protected against ulcer rebleeding. Older patients who perceived poorer sleep quality were also more likely to experience ulcer rebleeding (HR = 2.295 [1.352-3.925]).

CONCLUSIONS

The present results highlight the importance of proper treatment and prevention of sleep problems in older adults after successful PUB treatment. Our results, if replicable in future studies with more rigorous design and representative samples, might shed light on the etiology of ulcer rebleeding and suggest new pathways for preventing this disease.

Effects of Insomnia on Peptic Ulcer Disease Using Mendelian Randomization

OBJECTIVES

Observational studies indicate that insomnia may increase risk of peptic ulcer disease (PUD). Our purpose is to clarify the possible causal relationship between insomnia and PUD by Mendelian randomization analyses.

METHODS

We carried out analyses using summary statistics data for genetic variants reported from a GWAS of insomnia (N = up to 1,331,010 individuals) and from a GWAS of PUD (N = up to 456,327 individuals). Three Mendelian randomization approaches were used to explore whether insomnia might play a causal role in PUD, and pathway and functional enrichment analyses were conducted to anticipate the underlying mechanisms.

RESULTS

Conventional Mendelian randomization analysis showed clear causality between insomnia and PUD; 1 SD increased insomnia incident was related to a 19% higher risk of PUD (P = 6.69 × 10-16; OR, 1.19 (95% CI, 1.14-1.24)). The associations between insomnia and PUD were consistent in the other two analyses performed using the weighted median method (P = 7.75 × 10-7; OR, 1.16 (95% CI, 1.09-1.23)) and MR-Egger regression (P = 5.00 × 10-3; OR, 1.27 (95% CI, 1.07-1.50)). Moreover, no evidence indicated a reverse causality between PUD events and insomnia symptoms. Pathway and functional enrichment analyses indicated that the mechanisms of insomnia effect on PUD may be through various ways, such as the immune system and oxidative stress.

CONCLUSIONS

This Mendelian randomization study suggests insomnia as a causal risk factor for PUD. The potential mechanisms included may be immune and oxidative stress. These findings indicate that improving sleep quality could have substantial health benefits.

Effect of Subjective and Objective Sleep Quality on Subsequent Peptic Ulcer Recurrence in Older Adults

OBJECTIVE

To examine the effect of subjective and objective sleep quality on subsequent recurrence of peptic ulcer disease (PUD) among older patients after Helicobacter pylori eradication.

SETTING

Eight grade A hospitals in China.

PARTICIPANTS

Of 1689 older Chinese with H. pylori-infected PUD recruited between January 2011 and October 2014, H. pylori were eradicated and PUD was cleared in 1538 patients by the end of 2014; 1420 of these patients were followed up for up to 36 months.

MEASUREMENTS

Using multiple measures at 6-month intervals, PUD recurrence was determined with esophagogastroduodenoscopy. Subjective sleep quality was measured using the Pittsburgh Sleep Quality Index. Objective sleep quality domains were measured using an accelerometer, including sleep onset latency, sleep efficiency, total sleep time, and number of awakenings.

RESULTS

This study documented a 36-month cumulative PUD recurrence of 8.3% (annual rate = 2.8%). Multivariate analyses showed that participants who reported poorer sleep quality were more likely to experience PUD recurrence during the 36-month follow-up period (hazard ratio [HR] = 1.895; 95% confidence interval [CI] = 1.008-3.327). Regarding objective sleep quality domains, longer sleep onset latency (HR = 1.558; 95% CI = 1.156-2.278) and more nighttime awakenings (HR = 1.697; 95% CI = 1.168-2.665) increased the risk of PUD recurrence. However, a longer total sleeping time protected against PUD recurrence (HR = 0.768; 95% CI = 0.699-0.885).

CONCLUSIONS

Poor sleep quality predicts a greater risk of PUD recurrence. Accurate diagnosis and effective treatments should, therefore, be provided for older adults afflicted with poor sleep, particularly for those who previously had PUD. It is equally important to include sleep assessment as an integral part while dealing with these patients.

Association between Poor Sleep Quality and Subsequent Peptic Ulcer Recurrence in Older Patients with Mild Cognitive Impairment: Examining the Role of Social Engagement

This study aims to examine whether perceived poor sleep quality predicts subsequent recurrence of peptic ulcer disease (PUD) in older patients with mild cognitive impairment following Helicobacter pylori eradication and to investigate whether social engagement status alters this association. Of 1,689 older patients with H. pylori-infected PUD recruited from eight Grade-A hospitals in the People's Republic of China between 2011 and 2014, H. pylori was eradicated and PUD cleared in 1,538 patients by the end of 2014; 1,420 of these were followed for up to 36 months. The Kaplan-Meier method was used to compare the proportion of PUD recurrence, as confirmed with esophagogastroduodenoscopy, among older patients with different levels of sleep quality and social engagement statuses. Multivariate Cox-proportional hazards models were performed to examine the association between sleep quality and PUD recurrence, and the role of social engagement in altering this relationship. The results showed that PUD recurrence was more prevalent in poor (10.8%) compared with good sleepers (5.5%). However, increased and continued social engagement reduced the proportion to 7.2% and 8.2% among poor sleepers, respectively. Poor sleep quality was associated with subsequent PUD recurrence (hazard ratio [HR] 1.965 (1.002, 3.518)). However, no significant difference was observed between good and poor sleepers who reported increased (HR 1.428 (0.736, 2.380)) and continued (HR 1.273 (0.915, 2.492)) social engagement, suggesting that increased and continued social engagement prevented the effect of poor sleep quality on PUD recurrence. To conclude, poor sleep quality is associated with subsequent PUD recurrence. However, increased and continued social engagement may moderate this association.

Women Who Sleep More Have Reduced Risk of Peptic Ulcer Disease; Korean National Health and Nutrition Examination Survey (2008-2009)

Sleep is integral to life and sleep duration is important in sleep quality, physical, and psychological health. Disturbances in sleep duration have been associated with increased risk of metabolic disorders, hypertension, and overall mortality. Sleep disturbance has also been linked with various gastrointestinal disorders. However, the association between sleep and peptic ulcer disease (PUD) has not been evaluated. We investigated the association between sleep duration and PUD. Subjects were included from the fifth Korean National Health and Nutrition Examination Survey conducted from 2008-2009. Individuals with PUD were defined as those with a physician diagnosis of PUD. Daily sleep duration was established by asking participants the amount of time that they slept per day. Multiple logistic regression models were used to evaluate the association of PUD and sleep duration. This study included 14,290 participants (8,209 women). The prevalence of PUD was 5.7% and was higher in men (6.8%) than in women (4.9%). Women who slept ≥9 hours were significantly less likely to have PUD compared to women who slept 7 hours. In men, longer sleep duration (≥9 hours) had a tendency toward PUD prevention. Our results suggest that longer sleep duration may play a protective role for PUD development.

Tocotrienol Attenuates Stress-Induced Gastric Lesions via Activation of Prostaglandin and Upregulation of COX-1 mRNA

The present study aims to distinguish the effect of tocotrienol on an important gastric protective factor, prostaglandin E2 (PGE2), in stress-induced gastric injury. Twenty-eight Wistar rats were divided into four groups of seven rats each. Two control groups were fed commercial rat diet, and two treatment groups were fed the same diet but with additional dose of omeprazole (20 mg/kg) or tocotrienol (60 mg/kg). After 28 days, rats from one control group and both treated groups were subjected to water-immersion restraint stress for 3.5 hours once. The rats were then sacrificed, their stomach isolated and gastric juice collected, lesions examined, and gastric PGE2 content and cyclooxygenase (COX) mRNA expression were determined. Both the regimes significantly attenuated the total lesion area in the stomach compared to the control. Gastric acidity, which was increased in stress, was significantly reduced in rats supplemented with omeprazole and tocotrienol. The PGE2 content was also significantly higher in the rats given tocotrienol supplementation compared to the control followed by an increase in COX-1 mRNA expression. We conclude that tocotrienol supplementation protected rat gastric mucosa against stress-induced lesions possibly by reducing gastric acidity and preserving gastric PGE2 by increasing COX-1 mRNA.

Day/night differences in stress-induced gastric lesions in rats with an intact pineal gland or after pinealectomy

The formation of acute gastric lesions depends upon the balance between the aggressive factors promoting mucosal damage and the natural defense mechanisms. Previous studies have shown that melatonin inhibits gastric acid secretion, enhances the release of gastrin, augments gastric blood flow (GBF), increases the cyclooxygenase-2 (COX-2)-prostaglandin (PG) system and scavenges free radicals, resulting in the prevention of stress-induced gastric lesions. Besides the pineal gland, melatonin is also generated in large amounts in the gastrointestinal tract and due to its antioxidant and anti-inflammatory properties; this indole might serve as local protective endogen preventing the development of acute gastric damage. The results of the present study indicate that stress-induced gastric lesions show circadian variations with an increase in the day time and a decline at night. These changes are inversely related to plasma melatonin levels. Following pinealectomy, stress-induced gastric mucosal lesions were more pronounced both during the day and at night, and were accompanied by markedly reduced plasma melatonin levels with a pronounced reduction in mucosal generation of prostaglandin E(2) (PGE(2)), GBF and increased free radical formation and by small rise in plasma melatonin during the dark phase. We conclude that stress-induced gastric ulcerations exhibit a circadian variation with an increase in the day and attenuation at night and that these fluctuations of gastric stress ulcerogenesis occur also after pinealectomy, depending upon the interaction of COX-PG and free radicals, probably mediated by the changes in local gastric melatonin.

Melatonin accelerates the process of wound repair in full-thickness incisional wounds

The pineal gland hormone melatonin is known to have both anti-inflammatory and immunomodulatory effects. Given this, we propose that melatonin is an ideal candidate to enhance the process of wound healing. The present study assessed the effects of exogenously administered melatonin (1.2 mg/kg intra-dermal), on scar formation using a full-thickness incisional rat model of dermal wound healing. Melatonin treatment significantly improved the quality of scarring, both in terms of maturity and orientation of collagen fibres. An increase in nitric oxide synthase (NOS) activity and therefore nitric oxide production is detrimental during inflammation but is favourable during granulation tissue formation. Melatonin treatment significantly decreased inducible NOS (iNOS) activity during the acute inflammatory phase but significantly increased iNOS activity during the resolving phase. Cyclooxygenase-2, which has been shown to have anti-inflammatory effects, was elevated in the melatonin-treated rats following wounding. In addition, melatonin treatment also accelerated the angiogenic process, increasing the formation of new blood vessels and elevating the level of vascular endothelial growth factor protein expression during granulation tissue formation. Melatonin treatment increased arginase activity (which generates proline, a building block for collagen synthesis) from earlier time points. The protein profiles of hemoxygenase-1 (HO-1) and HO-2 isoforms, vital participants in the repair process, were also up-regulated upon melatonin treatment. This study has therefore demonstrated, for the first time, that melatonin can significantly improve the quality of wound healing and scar formation.

Protective effect of palm vitamin E and α-tocopherol against gastric lesions induced by water immersion restraint stress in Sprague-Dawley rats

OBJECTIVE

Stress can lead to various changes in the gastrointestinal tract of rats. The present study was designed to compare the effect of palm vitamin E (PVE) and α-tocopherol (α-TF) supplementations on the gastric parameters important in maintaining gastric mucosal integrity in rats exposed to water immersion restraint stress (WRS). These parameters include gastric acidity, plasma gastrin level, gastric prostaglandin E(2) (PGE(2)), and gastric lesions.

MATERIALS AND METHODS

Sixty male Sprague-Dawley rats (200-250 g) were divided into three equal groups: a control group, which received a normal rat diet (RC), and two treatment groups, receiving oral supplementation of either PVE or α-TF at 60 mg/kg body weight for 28 days. Each group was further divided into two groups: the nonstress and stress groups. The stress groups were subjected to 3.5 h of WRS once at the end of the treatment period. Blood samples were then taken to measure the gastrin level, after which the rats were killed. Gastric juice was collected for measurement of gastric acidity and gastric tissue was taken for measurement of gastric mucosal lesions and PGE(2).

RESULTS

Exposure to stress resulted in the production of gastric lesions. PVE and α-TF lowered the lesion indices as compared to the stress control group. Stress reduced gastric acidity but pretreatment with PVE and α-TF prevented this reduction. The gastrin levels in the stress group were lower as compared to that in the nonstress control. However, following treatment with PVE and α-TF, gastrin levels increased and approached the normal level. There was also a significant reduction in the gastric PGE(2) content with stress exposure, but this reduction was blocked with treatment with both PVE and α-TF.

CONCLUSION

In conclusion, WRS leads to a reduction in the gastric acidity, gastrin level, and gastric PGE(2) level and there is increased formation of gastric lesions. Supplementation with either PVE or α-TF reduces the formation of gastric lesions, possibly by blocking the changes in the gastric acidity, gastrin, and gastric PGE(2) induced by stress. No significant difference between PVE and α-TF was observed.

Worsening effect of partial sleep deprivation on indomethacin-induced gastric mucosal damage

The present study was to investigate the roles of cyclooxygenase-1 and -2 (COX-1 and COX-2) and prostaglandin (PG) on gastric mucosal integrity of partially sleep deprived (PSD) rats. A slowly moving drum was used to induce PSD. The PG levels in the gastric mucosa of PSD rats, with or without indomethacin or rofecoxib treatment, were determined. Exogenous prostaglandin E (PGE) analog, misoprostol, was administered to PSD rats to investigate the modulating effect of PG in indomethacin-induced gastric damage. It was observed that COX-1 mRNA and protein were up-regulated in the gastric mucosa of PSD rats. Selective COX-2 inhibition by rofecoxib failed to decrease mucosal PGE2 levels nor to affect mucosal integrity in both PSD and sleep undisturbed rats. However, indomethacin, a COX-1 preferential non-selective COX inhibitor, significantly reduced mucosal PGE2 content and produced more severe mucosal damage in PSD rats than in the controls. The deleterious effect of indomethacin on gastric mucosal integrity of PSD rats was significantly attenuated with the administration of misoprostol. These results suggest that PSD enhances COX-1 biosynthesis of gastroprotective PGE2 as an adaptive response of the stomach to stress. The administration of non-selective COX inhibitors to subjects with chronic sleep deprivation may induce more gastric damages.

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

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 microg/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.

Melatonin as an organoprotector in the stomach and the pancreas

Melatonin was thought to originate primarily from the pineal gland and to be secreted during the night, but recent studies revealed that gastrointestinal (GI) tract presents another, many times larger, source of melatonin that contributes significantly to the circulating concentration of this indole. Melatonin may exert a direct effect on GI tissues but its major influence on GI organs seems to occur indirectly, via the brain-gut axis including peripheral receptors, sensory afferent (vagal or sympathetic) pathways and central nervous system (CNS) acting on these organs via autonomic efferents and neuromediators. This article reviews and updates our experience with the fascinating molecule, as related to GI organs, with special focus on secretory activity of the stomach and pancreas and the maintenance of their tissue integrity. In addition to being released into the circulation, melatonin is also discharged into the gut lumen and this appears to be implicated in the postprandial stimulation of pancreatic enzyme secretion, mediated by melatonin-induced release of cholecystokinin, acting through entero-gastro-pancreatic reflexes. Although exerting certain differences in the mechanism of action on gastric and pancreatic secretory activities, melatonin derived from its precursor L-tryptophan, exhibits similar highly protective actions against the damage of both the stomach and the pancreas and accelerates the healing of chronic gastric ulcerations by stimulating the microcirculation and cooperating with arachidonate metabolites such as prostaglandins, with nitric oxide released from vascular endothelium, and/or sensory nerves and with their neuropeptides such as calcitonin gene related peptide. The beneficial effects of melatonin results in gastro- and pancreato-protection, prevents various forms of gastritis and pancreatitis through the activation of specific MT2-receptors and scavenges reactive oxygen species (ROS). Melatonin counteracts the increase in the ROS-induced lipid peroxidation and preserves, at least in part, the activity of key anti-oxidizing enzymes such as superoxide dismutase. It is proposed that melatonin should be considered as the agent exerting an important role in prevention of gastric and pancreatic damage and in accelerating healing of gastric ulcers.

Exposure to continuous darkness ameliorates gastric and colonic inflammation in the rat: both receptor and non-receptor-mediated processes

BACKGROUND AND AIM

Melatonin is a hormone involved in the transduction of photoperiodic information, and appears to modulate a variety of neural and endocrine functions. The present study was designed to determine the impact of continuous darkness (CD) on acute gastric and colonic inflammation and the involvement of melatonin receptors in the darkness-related alterations in oxidant gut injury.

METHODS

Rats were housed either in CD or in standardized light/dark (12/12 h) cycles for 15 days before the induction of colitis or gastric ulcer. Luzindole (MT(2) receptor antagonist) was given at a dose of 0.25 mg/kg intraperitoneally 30 min before and 6 and 18 h following the induction of colitis with acetic acid or gastric ulcer with ethanol. Rats were decapitated at 24 h, and the colons and stomachs were removed for macroscopic scoring, histologic assessment and for the determination of tissue malondialdehyde and glutathione levels.

RESULTS

All inflammation parameters were increased by acetic acid-induced colitis or ethanol-induced gastric ulcer compared with the control group. Our results indicate that the severity of both gastric and colonic injury is reduced by a 2-week exposure to CD prior to the induction of inflammatory event, while luzindole treatment reversed the protective effect of CD on the colonic and gastric injury. However, darkness-related alterations in malondialdehyde and glutathione levels were not altered by luzindole.

CONCLUSION

Although the CD-induced amelioration of gut injury involves melatonin receptors, the direct antioxidant effects on melatonin appear to be independent of receptor activity.

Seasonal variation in the onset of acute pancreatitis

AIM: A circannual variation in the onset of several acute diseases, mostly dealing with cardiovascular system, has been reported. The present study was to verify the possible existence of a seasonal variability in the onset of acute pancreatitis.

METHODS: All patients consecutively admitted to the Hospital of Ferrara, Italy, between January 1998 to December 2002, whose discharge diagnosis was acute pancreatitis, were considered. According to the time of admission, cases were categorized into twelve 1-mo intervals and in four periods by season. χ² test for goodness of fit and partial Fourier series were used for statistical analysis.

RESULTS: During the study period, 549 cases of acute pancreatitis were observed. A significant peak of higher incidence was found in March-May, both for total population, males and subgroups with and without cholelithiasis or alcoholism. Fourier analysis showed the existence of a circannual rhythmic pattern with its main peak in March (95%C.L.: February-April, P = 0.005), and a secondary one in September. Death occurred more frequently in December-February, compared to the other periods (P = 0.029), and chronobiologic analysis yielded a seasonal peak in November-December (P < 0.001).

CONCLUSION: This study shows the existence of a circannual variation in the onset of acute pancreatitis, with a significantly higher frequency of events in the spring, especially for patients with cholelithiasis or alcoholism. Moreover, events occurring during the colder months seem to be characterized by a higher mortality rate.

Gene expression analysis in the stomachs of water immersion-restraint stress rats using high-density oligonucleotide array

BACKGROUND AND AIM

Research on gastric lesions developing in response to stress is essential to elucidating the pathogenesis of these lesions as well as the interplay with other factors, including Helicobacter pylori infection and non-steroidal anti-inflammatory drug use. Genes expressed individually or in sets, such as heat shock proteins, growth factors, proto-oncogenes and cyclooxygenases, have been investigated in the stomach. However, gene expression in the stomach after stress exposure have not yet been comprehensively examined. We investigated the gastric gene expression profile in response to stress.

METHODS

A high-density oligonucleotide array, representing approximately 850 genes, was used to determine gene expression changes in the stomachs of water immersion-restraint stress (WIRS) rats.

RESULTS

Fifty-eight genes including expressed sequence tag (EST) genes were upregulated more than twofold in the 30 min-WIRS rat stomach as compared with the control. Concomitantly, five genes were downregulated. Numbers of up- or downregulated genes decreased rapidly at 1 and 2 h of WIRS. Altered gene expression of heat shock proteins, cell cycle regulators, proto-oncogenes and metabolic enzymes were recognized. Several of these genes, including p38 mitogen-activated protein kinase, did not reportedly show gastric expression changes in response to stress.

CONCLUSION

These results suggest that, in addition to the previously identified stress-induced genes, expression of a number of other genes in the stomach is also involved in stress response.

The circadian rhythm of melatonin modulates the severity of caerulein-induced pancreatitis in the rat

Melatonin, an antioxidant, protects the pancreas against acute inflammation but, although this indole is released mainly at night, no study has been undertaken to determine circadian changes of plasma melatonin levels and the severity of acute pancreatitis. The aims of this study were: (a) to compare the severity of caerulein-induced pancreatitis (CIP) produced in the rat during the day and at the night, and (b) to assess the changes of plasma melatonin level and the activity of an antioxidative enzyme; superoxide dismutase (SOD), in the pancreas subjected to CIP during the day time and at night without or with administration of exogenous melatonin or its precursor; l-tryptophan. Rats were kept in 12 hr light/dark cycle. CIP was induced by subcutaneous infusion of caerulein (5 microg/kg/hr for 5 hr). Melatonin (5 or 25 mg/kg) or l-tryptophan (50 or 250 mg/kg) was given intraperitoneally 30 min prior to the start of CIP. CIP induced during the day time was confirmed by histological examination and manifested by pancreatic edema, and rises of amylase and lipase plasma activities (by 400 and 500%, respectively), whereas pancreatic SOD, pancreatic blood flow (PBF) and oxygen consumption by pancreatic tissue (VO(2)) were decreased by 70, 40 and 45%, respectively, as compared with the appropriate controls. All morphological and biochemical parameters of CIP induced at night were significantly less severe, compared with those recorded during the light phase. Plasma melatonin immunoreactivity was significantly higher during the night, than during the day, especially following administration of melatonin or its precursor, which reversed all manifestations of CIP. In conclusion, a circadian rhythm modulates the severity of CIP with a decrease of pancreatitis severity during the night compared with that at the day time and this may be due to the increased plasma level of melatonin and higher activity of SOD in the pancreas.