Dynamic functional and ultrastructural changes of gastric parietal cells induced by water immersion-restraint stress in rats

Protective effect of cannabinoids on gastric mucosal lesions induced by water immersion restrain stress in rats

OBJECTIVES

This study aimed to determine the impact of cannabinoid agonists and antagonists on the mucosal lesion progress in the stomach induced by water-immersion restraint stress (WIRS).

MATERIALS AND METHODS

Rats subjected to WIRS for 4 hr were treated with Dimethyl sulfoxide (DMSO), CBR1 agonist (NADA, 1 mg/kg), CBR1 antagonist (Rimonabant, 1 mg/kg), CBR2 agonist (GW405833 1 mg/kg) or CBR2 antagonist (AM630, 1 mg/kg SC) 30 min before WIRS. Microscopic lesions, oxidative stress, inflammatory cytokines biomarkers, and (Myeloperoxidase) MPO in gastric tissues were determined.

RESULTS

Results indicated development of severe gastric lesions with a substantial increase in the contents of (nitric oxide) NO, (malondialdehyde) MDA, (interleukin-1 beta) IL-1β, MPO, (tumor necrosis factor-alpha) TNF-α, and a significant fall in the content of GSH and the activity of PON-1 after WIRS.

CONCLUSION

Treatment with NADA and AM630 protected gastric tissues against ulcers as demonstrated by a decrease in the contents of MDA, TNF-α, MPO, and IL-1β along with an increase in the content of PON-1 activity and GSH in the stomach tissues. On the other hand, treatment with SR141716A or GW405833 showed no protective effects on ulcers development. It seems that cannabinoids exert their antioxidant potential and anti-inflammatory effects against WIRS-induced gastric ulcers by activation of CB1R.

Neurons and Astrocytes in Ventrolateral Periaqueductal Gray Contribute to Restraint Water Immersion Stress-Induced Gastric Mucosal Damage via the ERK1/2 Signaling Pathway

BACKGROUND

The restraint water immersion stress (RWIS) model includes both psychological and physical stimulation, which may lead to gastrointestinal disorders and cause gastric mucosal damage. The ventrolateral periaqueductal gray (VLPAG) contributes to gastrointestinal function, but whether it is involved in RWIS-induced gastric mucosal damage has not yet been reported.

METHODS

The expression of glial fibrillary acidic protein, neuronal c-Fos, and phosphorylated extracellular signal regulated kinase 1/2 in the VLPAG after RWIS was assessed using western blotting and immunocytochemical staining methods. Lateral ventricle injection of astrocytic toxin L-a-aminoadipate and treatment with extracellular signal-regulated kinase (ERK)1/2 signaling pathway inhibitor PD98059 were further used to study protein expression and distribution in the VLPAG after RWIS.

RESULTS

The expression of c-Fos, glial fibrillary acidic protein, and phosphorylated extracellular signal regulated kinase 1/2 in the VLPAG significantly increased following RWIS and peaked at 1 hour after RWIS. Lateral ventricle injection of the astrocytic toxin L-a-aminoadipate significantly alleviated gastric mucosal injury and decreased the activation of neurons and astrocytes. Treatment with the ERK1/2 signaling pathway inhibitor PD98059 obviously suppressed gastric mucosal damage as well as the RWIS-induced activation of neurons and astrocytes in the VLPAG.

CONCLUSIONS

These results suggested that activation of VLPAG neurons and astrocytes induced by RWIS through the ERK1/2 signaling pathway may play a critical role in RWIS-induced gastric mucosa damage.

Nervous mechanisms of restraint water-immersion stress-induced gastric mucosal lesion

Stress-induced gastric mucosal lesion (SGML) is one of the most common visceral complications after trauma. Exploring the nervous mechanisms of SGML has become a research hotspot. Restraint water-immersion stress (RWIS) can induce GML and has been widely used to elucidate the nervous mechanisms of SGML. It is believed that RWIS-induced GML is mainly caused by the enhanced activity of vagal parasympathetic nerves. Many central nuclei, such as the dorsal motor nucleus of the vagus, nucleus of the solitary tract, supraoptic nucleus and paraventricular nucleus of the hypothalamus, mediodorsal nucleus of the thalamus, central nucleus of the amygdala and medial prefrontal cortex, are involved in the formation of SGML in varying degrees. Neurotransmitters/neuromodulators, such as nitric oxide, hydrogen sulfide, vasoactive intestinal peptide, calcitonin gene-related peptide, substance P, enkephalin, 5-hydroxytryptamine, acetylcholine, catecholamine, glutamate, γ-aminobutyric acid, oxytocin and arginine vasopressin, can participate in the regulation of stress. However, inconsistent and even contradictory results have been obtained regarding the actual roles of each nucleus in the nervous mechanism of RWIS-induced GML, such as the involvement of different nuclei with the time of RWIS, the different levels of involvement of the sub-regions of the same nucleus, and the diverse signalling molecules, remain to be further elucidated.

Proteomics of the mediodorsal thalamic nucleus of rats with stress-induced gastric ulcer

BACKGROUND

Stress-induced gastric ulcer (SGU) is one of the most common visceral complications after trauma. Restraint water-immersion stress (RWIS) can cause serious gastrointestinal dysfunction and has been widely used to study the pathogenesis of SGU to identify medications that can cure the disease. The mediodorsal thalamic nucleus (MD) is the centre integrating visceral and physical activity and contributes to SGU induced by RWIS. Hence, the role of the MD during RWIS needs to be studied.

AIM

To screen for differentially expressed proteins in the MD of the RWIS rats to further elucidate molecular mechanisms of SGU.

METHODS

Male Wistar rats were selected randomly and divided into two groups, namely, a control group and an RWIS group. Gastric mucosal lesions of the sacrificed rats were measured using the erosion index and the proteomic profiles of the MD were generated through isobaric tags for relative and absolute quantitation (iTRAQ) coupled with two-dimensional liquid chromatography and tandem mass spectrometry. Additionally, iTRAQ results were verified by Western blot analysis.

RESULTS

A total of 2853 proteins were identified, and these included 65 dysregulated (31 upregulated and 34 downregulated) proteins (fold change ratio ≥ 1.2). Gene Ontology (GO) analysis showed that most of the upregulated proteins are primarily related to cell division, whereas most of the downregulated proteins are related to neuron morphogenesis and neurotransmitter regulation. Ingenuity Pathway Analysis revealed that the dysregulated proteins are mainly involved in the neurological disease signalling pathways. Furthermore, our results indicated that glycogen synthase kinase-3 beta might be related to the central mechanism through which RWIS gives rise to SGU.

CONCLUSION

Quantitative proteomic analysis elucidated the molecular targets associated with the production of SGU and provides insights into the role of the MD. The underlying molecular mechanisms need to be further dissected.

Effects of Restraint Water-Immersion Stress-Induced Gastric Mucosal Damage on Astrocytes and Neurons in the Nucleus Raphe Magnus of Rats via the ERK1/2 Signaling Pathway

Restraint water-immersion stress (RWIS) consists of psychological and physical stimulation, and it has been utilized in the research of gastric mucosal damage. It has been shown by previous studies that the nucleus raphe magnus (NRM) is closely involved in the gastrointestinal function, but its functions on the stress-induced gastric mucosal injury (SGMI) have not been thoroughly elucidated to date. Consequently, in this research, we aim to measure the expression of astrocytic glial fibrillary acidic protein (GFAP), neuronal c-Fos, and phosphorylation extracellular signal regulated kinase 1/2 (p-ERK1/2) in the process of RWIS with immunohistochemistry and western blot methods. What is more, we detect the relation between astrocytes and neurons throughout the stress procedure and explore the regulation of the ERK1/2 signaling pathway on the activity of astrocytes and neurons after RWIS. The results indicated that all three proteins expression multiplied following peaked 3 h substantially. The SMGI, astrocyte and neuron activity were affected after the astrocytotoxin L-A-aminohexanedioic acid (L-AA) and c-fos antisense oligonucleotide (ASO) injections. After the injection of PD98059, the gastric mucosal injury, astrocyte and neuron activity significantly fell off. These results suggested that RWIS-induced activity of astrocytes and neurons in the NRM may play a significant part in gastric mucosa damage via the ERK1/2 signaling pathway.

Aggravated mucosal and immune damage in a mouse model of ulcerative colitis with stress

The aim of the present study was to determine the influence of stress on the colonic mucosa and immune system and to further investigate the association between stress and development and pathogenesis of ulcerative colitis (UC). Mice were treated with 2,4,6-trinitrobenzenesulfonic acid to induce an animal model of UC, and stress was induced by water immersion and restraint. Subsequently, the disease activity index (DAI), secretory immunoglobulin A (sIgA), IgA, interleukin (IL)-6 and -8, tumor necrosis factor-α (TNF-α), complement component (C)3 and C4, and alterations in the colonic mucosa were observed. The DAI scores and the expression levels of IL-6, IL-8 and TNF-α significantly increased in the experimental UC mice compared with the control mice, while the expression levels of IgA and sIgA decreased (all P<0.01). DAI and colonic mucosa damage scores increased in the stress-treated mouse models of UC compared with the untreated mouse models of UC (P<0.05). Expression levels of IgA and sIgA decreased, while IL-6, IL-8 and TNF-α further increased in the stress-treated UC mice (P<0.05). The expression levels of C3 and C4 were not affected by stress or UC (P>0.05). These results indicated that UC may be associated with an immune disorder and that stress can aggravate colonic mucosa injury and alter the immune response. Furthermore, stress and immunity may serve roles in the pathogenesis of UC.

Global transcriptome‑wide analysis of the function of GDDR in acute gastric lesions

Acute gastric lesions induced by stress are frequent occurrences in medical establishments. The gastric dramatic downrelated gene (GDDR) is a secreted protein, which is abundantly expressed in normal gastric epithelia and is significantly decreased in gastric cancer. In our previous study, it was found that GDDR aggravated stress-induced acute gastric lesions. However, the role of GDDR in acute gastric lesions remains to be fully elucidated. In the present study, RNA sequencing was performed in order to examine the gene expression profile regulated by GDDR in acute gastric lesions. The dataset comprised four stomach samples from wild-type (WT) mice and four stomach samples from GDDR-knockout mice. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed to analyze the differentially-expressed genes (DEGs). Weighted correlation network analysis was used to identify clusters of highly correlated genes. Cytoscape was used to construct a protein-protein interaction network (PPI) of the DEGs. Based on the GO analysis, the upregulated DEGs were distinctly enriched in muscle contraction and response to wounding; and the downregulated DEGs were significantly enriched in the regulation of nitrogen compound metabolic process and regulation of RNA metabolic process. The results of the KEGG pathway analysis showed that the upregulated DEGs were enriched in ECM-receptor interaction and the signaling pathway of cGMP-PKG, and the downregulated DEGs were enriched in the renin-angiotensin system and glycerolipid metabolism. The co-expression network revealed a group of genes, which were associated with increased wound healing in the WT mice. Significant pathways were identified through the PPI network, including negative regulation of the signaling pathway of glucocorticoid receptor, regulation of cellular stress response, and regulation of hormone secretion. In conclusion, the present study improves current understanding of the molecular mechanism underlying acute gastric lesions and may assist in the treatment of gastric lesions.

Comparative proteomic analysis of rats subjected to water immersion and restraint stress as an insight into gastric ulcers

In the present study, comparative proteomic analysis was performed in rats subjected to water immersion-restraint stress (WRS). A total of 26 proteins were differentially expressed and identified using matrix-assisted laser desorption/ionization time of flight mass spectrometry. Among the 26 differentially expressed protein spots identified, 13 proteins were significantly upregulated under WRS, including pyruvate kinase and calreticulin, which may be closely associated with energy metabolism. In addition, 12 proteins were downregulated under WRS, including hemoglobin subunit β-2 and keratin type II cytoskeletal 8, which may be important in protein metabolism and cell death. Gene Ontology analysis revealed the cellular distribution, molecular function and biological processes of the identified proteins. The mRNA levels of certain differentially expressed proteins were analyzed using fluorescence quantitative polymerase chain reaction analysis. The results of the present study aimed to offer insights into proteins, which are differentially expressed in gastric ulcers in stress, and provide theoretical evidence of a radical cure for gastric ulcers in humans.

Interactions between astrocytes and neurons in the brainstem involved in restraint water immersion stress-induced gastric mucosal damage

Restraint water-immersion stress (RWIS) is considered a compound stress model as it includes both psychological and physical stimulation. Studies have shown that neurons are involved in RWIS, but the role of astrocytes in RWIS has not been reported as yet. Here, we tested our hypothesis that astrocytes are involved in RWIS and interact with neurons in the brainstem to regulate gastric mucosal damage induced by RWIS. RWIS of different durations (0.5, 1, 2, 3, and 5 h) induced significant gastric mucosal damage and activated astrocytes by increasing the expression of glial fibrillary acidic protein and neurons, as indicated by the Fos expression in the nucleus of solitary tract and the dorsal motor nucleus of the vagus. Intracerebroventricular administration of both astroglial toxin L-α-aminoadipate and c-fos antisense oligodeoxy nucleotides reduced RWIS-induced gastric mucosal damage. Immunohistochemistry results showed that L-α-aminoadipate decreased the activation of both astrocytes and neurons by RWIS. Similarly, antisense oligodeoxy nucleotides significantly suppressed activation of both neurons and astrocytes induced by RWIS. Our data showed that astrocytic and neuronal activations may be closely related to the gastric mucosal damage induced by RWIS through reciprocal 'crosstalk'. This study suggests that an intervention targeting this interaction may offer some novel therapeutic strategies for gastric ulcers.

Serotonin and histamine mediate gastroprotective effect of fluoxetine against experimentally-induced ulcers in rats

Research in the treatment of gastric ulcer has involved the investigation of new alternatives, such as anti-depressant drugs. The present study was designed to investigate the gastroprotective effects of fluoxetine against indomethacin and alcohol induced gastric ulcers in rats and the potential mechanisms of that effect. Fluoxetine (20 mg/kg) was administered IP for 14 days. For comparative purposes, other rats were treated with ranitidine (30 mg/kg). Thereafter, after 24 h of fasting, INDO (100 mg/kg) or absolute alcohol (5 ml/kg) was administered to all rats (saline was administered to naïve controls) and rats in each group were sacrificed 5 h (for INDO rats) or 1 h (for alcohol rats) later. Macroscopic examination revealed that both fluoxetine and ranitidine decreased ulcer scores in variable ratios, which was supported by microscopic histopathological examination. Biochemical analysis of fluoxetine- or ranitidine-pre-treated host tissues demonstrated reductions in tumor necrosis factor (TNF)-α and myeloperoxidase (MPO) levels and concomitant increases in gastric pH, nitric oxide (NO) and reduced glutathione (GSH) contents. Fluoxetine, more than ranitidine, also resulted in serotonin and histamine levels nearest to control values. Moreover, immuno-histochemical analysis showed that fluoxetine markedly enhanced expression of cyclo-oxygenases COX-1 and COX-2 in both models; in comparison, ranitidine did not affect COX-1 expression in either ulcer model but caused moderate increases in COX-2 expression in INDO-induced hosts and high expression in alcohol-induced hosts. The results here indicated fluoxetine exhibited better gastroprotective effects than ranitidine and this could be due to anti-secretory, anti-oxidant, anti-inflammatory and anti-histaminic effects of the drug, as well as a stabilization of gastric serotonin levels.

An enhanced cAMP pathway is responsible for the colonic hyper-secretory response to 5-HT in acute stress rats

5-hydroxytryptamine (5-HT) is involved in the stress-induced alteration of colonic functions, specifically motility and secretion, but its precise mechanisms of regulation remain unclear. In the present study, we have investigated the effects of 5-HT on rat colonic mucosal secretion after acute water immersion restraint stress, as well as the underlying mechanism of this phenomenon, using short circuit current recording (I(SC)), real-time polymerase chain reaction, Western blot analysis, and enzyme-linked immunosorbance assays. After 2 h of water immersion restraint stress, the baseline I(SC) and 5-HT-induced I(SC) responses of the colonic mucosa were significantly increased. Pretreatment with selective 5-HT(4) receptor antagonist, SB204070, inhibited the 5-HT-induced colonic I(SC) response by 96 % in normal rats and 91.2 % in acute-stress rats. However, pretreatment with the selective antagonist of 5-HT(3) receptor, MDL72222 or Y-25130, had no obvious effect on 5-HT-induced I(SC) responses under either set of conditions. Total protein expression of both the mucosal 5-HT(3) receptors and the 5-HT(4) receptors underwent no significant changes following acute stress. Both colonic basal cAMP levels and foskolin-induced I(SC) responses were significantly enhanced in acute stress rats. 5-HT significantly enhanced the intracellular cAMP level via 5-HT(4) receptors in the colonic mucosa from both control and stressed animals, and 5-HT-induced cAMP increase in stressed rats was not more than that in control rats. Taken together, the present results indicate that acute water immersion restraint stress enhances colonic secretory responses to 5-HT in rats, a process in which increased cellular cAMP accumulation is involved.

Gastric mucosal damage in water immersion stress: Mechanism and prevention with GHRP-6

AIM: To investigate the mechanism of gastric mucosal demage induced by water immersion restraint stress (WRS) and its prevention by growth hormone releasing peptide-6 (GHRP-6).

METHODS: Male Wistar rats were subjected to conscious or unconscious (anesthetized) WRS, simple restraint (SR), free swimming (FS), non-water fluid immersion, immersion without water contact, or rats were placed in a cage surrounded by sand. To explore the sensitivity structures that influence the stress reaction besides skin stimuli, a group the rats had their eyes occluded. Cervical bilateral trunk vagotomy or atropine injection was performed in some rats to assess the parasympathetic role in mucosal damage. Gastric mucosal lesions, acid output and heart rate variability were measured. Plasma renin, endothelin-1 and thromboxane B2 and gastric heat shock protein 70 were also assayed. GHRP-6 was injected [intraperitoneal (IP) or intracerebroventricular (ICV)] 2 h before the onset of stress to observe its potential prevention of the mucosal lesion.

RESULTS: WRS for 6 h induced serious gastric mucosal lesion [lesion area, WRS 81.8 ± 6.4 mm²vs normal control 0.0 ± 0.0 mm², P < 0.01], decreased the heart rate, and increased the heart rate variability and gastric acid secretion, suggesting an increase in vagal nerve-carrying stimuli. The mucosal injury was inversely correlated with water temperature (lesion area, WRS at 35 °C 56.4 ± 5.2 mm²vs WRS at 23 °C 81.8 ± 6.4 mm², P < 0.01) and was consciousness-dependent. The injury could not be prevented by eye occlusion, but could be prevented by avoiding contact of the rat body with the water by dressing it in an impermeable plastic suit. When water was replaced by vegetable oil or liquid paraffin, there were gastric lesions in the same grade of water immersion. When rat were placed in a cage surrounded by sand, there were no gastric lesions. All these data point to a remarkable importance of cutenuous information transmitted to the high neural center that by vagal nerves reaching the gastric mucosa. FS alone also induced serious gastric injury, but SR could not induce gastric injury. Bilateral vagotomy or atropine prevented the WRS-induced mucosal lesion, indicating that increased outflow from the vagal center is a decisive factor in WRS-induced gastric injury. The mucosal lesions were prevented by prior injection of GHRP-6 via IP did, but not via ICV, suggesting that the protection is peripheral, although a sudden injection is not equivalent to a physiological release and uptake, which eventually may affect the vagal center.

CONCLUSION: From the central nervous system, vagal nerves carry the cutaneous stimuli brought about by the immersion restraint, an experimental model for inducing acute gastric erosions. GHRP-6 prevents the occurrence of these lesions.

Effect of the IGF-1/PTEN/Akt/FoxO signaling pathway on the development and healing of water immersion and restraint stress-induced gastric ulcers in rats

Insulin-like growth factor 1 (IGF-1) and Akt [also known as protein kinase B (PKB)] proteins have been reported to exhibit gastroprotective effects by reducing water immersion and restraint stress (WRS)-induced gastric mucosal cellular apoptosis. To confirm whether the IGF-1/PTEN/Akt/FoxO signaling pathway is effective in protecting against gastric ulcers, our current study was conducted to examine the expression and localization of IGF-1, phosphatase and tensin homologue deleted on chromosome 10 (PTEN), Akt and O subfamily of forkhead box (FoxO) proteins, caspase-3 activity and the number of apoptotic cells in gastric mucosa of rats subjected to WRS. Our results demonstrated that WRS induced gastric ulcers by enhancing cell apoptosis in rat gastric mucosa. In addition, in normal rat gastric mucosa, PTEN, total Akt and FoxO1 were found mainly in the cell cytoplasm of fundic glands in the lamina propria close to the muscularis mucosa. In addition, strong staining of IGF-1, FoxO3a and FoxO4 in the gastric mucosa was primarily concentrated in the cell cytoplasm of the fundic glands in whole lamina propria. However, in rat gastric ulcers, IGF-1, total Akt, FoxO3a and FoxO4 were localized in proximity to the base of the ulcer margin and were also present in the granulation tissues of the gastric ulcers. Moreover, in the rat gastric ulcers, the mRNA transcript levels of IGF-1, PTEN, Akt-1, Akt-2, FoxO3 and FoxO4 were upregulated in the gastric ulcer margin, with a peak between Days 4 and 8 following 7 h of WRS. In conclusion, our results imply that the IGF-1/PTEN/Akt/FoxO signaling pathway plays a certain role(s) in the protection against ulceration through the regulation of cellular apoptosis as observed in the development and healing of rat gastric ulcers.

Altered physiology of acid secretion in depression-prone Flinders rats results in exacerbated NSAID and stress-induced gastric damage

BACKGROUND

Flinders Sensitive Line (FSL) rats are characterized by hypersensitivity to cholinergic stimuli and have been extensively used for studying depressive disorders. A link between depression and peptic ulcers has long been established; however, there is a lack of data from animal models.

METHODS

We studied the physiology of acid secretion in FSL and Flinders Resistant Line (FRL) rats in vivo and in vitro. We also examined the susceptibility of Flinders rats to water immersion restraint stress (WIRS) or NSAID-induced gastric damage and explored the effect of an anticholinergic agent, atropine, in reversing this effect.

KEY RESULTS

Basal acid output was more than twofold greater in FSL compared with FRL rats in vivo, 213.5 and 92.8 μEq/3 h/100 g (P = 0.02), respectively. Carbachol was a more potent secretagog in vitro, and somatostatin was a less potent inhibitory agent, while paradoxically stimulating acid secretion over and above the carbachol response in gastric glands from FSL rats. The FSL rats were more susceptible to indomethacin and WIRS-induced gastric mucosal damage compared with FRL rats. Atropine reduced acid output, which resulted in a reduction in indomethacin and stress-induced gastric damage in FSL rats.

CONCLUSIONS & INFERENCES

Our study, for the first time, demonstrates that the altered vagally mediated physiology of acid secretion in depression-prone FSL rats contributes to gastric hypersecretion and, consequently, results in exacerbated stress and NSAID-induced gastric damage. Flinders rats may be a useful animal model for studying acid-related and also gastrointestinal functional disorders in depression.

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.

Contribution of sensory neurons to sex difference in the development of stress-induced gastric mucosal injury in mice

BACKGROUND & AIMS

Sensory neurons play a critical role in reducing stress-induced gastric mucosal injury by releasing calcitonin gene-related peptide (CGRP) through an increase in gastric mucosal levels of prostacyclin (PGI(2)). Because estrogen enhances nerve growth factor-mediated CGRP production in sensory neurons, we hypothesized that stress-induced gastric mucosal injury occurs less in females than in males.

METHODS

Gastric ulcer index, gastric myeloperoxidase activity, and gastric tissue levels of CGRP and 6-keto-PGF(1alpha), a stable metabolite of PGI(2), were determined in male and female wild-type (CGRP(+/+)) mice and CGRP knockout (CGRP(-/-)) mice subjected to water-immersion restraint stress.

RESULTS

In CGRP(+/+) mice, ulcer index and myeloperoxidase activities were lower and gastric tissue levels of CGRP and 6-keto-PGF(1alpha) were higher in female mice than in male mice, but there were no such sex differences in CGRP(-/-)mice. Sex differences in CGRP(+/+) mice were eliminated by pretreatment with SB366791 (500 microg/kg intraperitoneally), a vanilloid receptor antagonist, and by ovariectomy. Reversal of sex differences by ovariectomy was not observed in female CGRP(+/+) mice with estradiol replacement (1 mg . kg(-1). wk(-1) for 3 weeks). Levels of CGRP messenger RNA in dorsal root ganglion neurons isolated from female CGRP(+/+) mice were decreased by ovariectomy, and these decreases were reversed by estradiol replacement.

CONCLUSIONS

Estrogen-mediated increases in CGRP levels in sensory neurons might contribute to reduce stress-induced gastric mucosal injury by attenuating inflammatory responses. This might at least partly explain the sex difference observed in the development of stress-induced gastric mucosal injury in mice.