Remote ischemic preconditioning (RIPC) is one of the most effective approaches to attenuate tissue injury caused by severe ischemia-reperfusion (I/R). Experimental studies have demonstrated that RIPC is capable of producing a protective effect not only on heart, but also on brain, lungs, kidneys, liver, intestine, and stomach. We previously demonstrated that glucocorticoids participate in protective effect of local gastric ischemic preconditioning against I/R-induced gastric injury. In the present study we investigated whether RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids. Anesthetized fasted Sprague Dawley male rats were exposed to prolonged gastric I/R (30 min occlusion of celiac artery followed by 3 h of reperfusion) alone or with preliminary brief RIPC (10 min non-invasive occlusion of right hind limb blood flow followed by reperfusion for 30 min). First, we investigated the effect of RIPC on I/R-induced injury by itself. Then to study the role of glucocorticoids similar experiments were carried out: 1) in rats pretreated with the inhibitor of glucocorticoid synthesis, metyrapone (30 mg/kg, i.p), and in control animals; 2) in adrenalectomized rats without or with corticosterone replacement (4 mg/kg, s.c.) and in sham-operated animals; 3) in rats pretreated with glucocorticoid receptor antagonist RU-38486 (20 mg/kg, s.c.) and in control animals. I/R induced corticosterone rise and resulted in the gastric erosion formation. RIPC significantly reduced the erosion area in control animals. Metyrapone injected shortly before RIPC caused a decrease in plasma corticosterone levels and prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. Adrenalectomy performed 1 week before experiment created long-lasting corticosterone deficiency and had no effect on the gastroprotective effect of RIPC. Nevertheless, corticosterone replacement which mimics the corticosterone rise, similar to RIPS, significantly reduced erosion areas of gastric mucosa in adrenalectomized rats supporting the role of glucocorticoids in gastroprotection. RU-38486, which occupied glucocorticoid receptors, similar to metyrapone prevented the gastroprotective effect of RIPC and, moreover, further aggravated the deleterious effect of I/R. The results of the present study demonstrate for the first time that RIPC may protect the gastric mucosa against I/R-induced injury through involvement of glucocorticoids.

Glucocorticoids may have dual action on the stomach: gastroprotective and proulcerogenic one. Our previous study was designed to investigate how physiological gastroprotective action of glucocorticoids can be transformed to pathological ulcerogenic effect. The results obtained demonstrate that single injection of dexamethasone at the dose of 1 mg/kg may attenuate or aggravate indomethacin‐induced gastric erosions depending on the time of its injection before indomethacin (prolongation of dexamethasone action). At the present study to elucidate the mechanisms of transformation of gastroprotective action of dexamethasone into ulcerogenic one we tested the hypothesis that disbalance between the glucocorticoid and mineralocorticoid receptors (GR and MR) may contribute to this transformation. To test the hypothesis, effect ща dexamethasone at the dose of 1 mg /kg, (i.p.) on the expression of GR and MR in the gastric mucosa was studied 1 h (a short‐term action when the gastroprotective action was observed) and 24 h (long‐term action when the proulcerogenic effect was observed) after its administration. The expression of GR and MR was detected by a immunohistochemical staining technique using α‐glucocorticoid (ab3580; 1:500. Abcam) and mineralоcorticoid (ab41912; 1:500. Abcam) receptor antibodies. The results of the staining were assessed by a morphometric study of microscopic images in five fields of view using the ImajeJ software. A distribution of cytoplasmic staining was estimated with relative stained area (%) in gastric glands and smooth muscle cells of muscularis mucosae. We found that GR are presented in the parietal cells, whereas MR are ubiquitous. Dexamethasone provoked translocation of both GR and MR into nuclei. The short‐term effect of dexamethasone resulted in a decrease of cytoplasmic GR and their translocation into the cell nuclei. The long‐term dexamethasone exposure increased cytoplasmic GR expression not accompanied by nuclear translocation. The short‐term dexamethasone action caused an increase of cytoplasmic MR level, but did not lead to nuclear translocation of these receptors. The long‐term action of dexamethasone induced nuclear translocation of MR, without significant changes of MR expression in cytoplasm. The results suggest that disbalance between GR and MR may contribute to transformation of gastroprotective action of dexamethasone to proulcerogenic effect and support the hypothesis.Support or Funding InformationThe study was supported by grant of Russian Science Foundation (RSF) N 14‐15‐00790.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Introduction Gastrointestinal ulceration is associated with high mortality despite advanced management, therefore, understanding of the mucosal protective mechanisms is important. Somatostatin is present in the endocrine cells and sensory nerves, and its analogues were shown to reduce mucosal blood flow, pepsin and gastric acid secretion. Our group discovered that its anti‐inflammatory and analgesic actions are exerted via the somatostatin receptor subtype 4 (sst4). Therefore, we investigated its expression and role in gastrointestinal injury. Methods Sst4 gene‐deleted (sst4−/−) and wildtype mice were treated s.c. with indomethacine (IDM; 35 mg/kg) or vehicle. RNA scope in situ hybridization was performed to localize, qPCR to quantify sst4 and somatostatin mRNA. Macroscopic and microscopic lesions in the stomach and small intestine were evaluated after 4 and 48 h. Plasma protein extravasation was measured by fluorescent, neutrophil myeloperoxidase (MPO) activity bioluminescent ex vivo imaging, TNFα, IL‐1 and COX2 mRNA by qPCR. Results Somatostatin mRNA is present in the neuroendocrine D‐cells and significantly upregulated 48 h after IDM. Sst4 mRNA in located in the myenteric plexus neurons, it’s expression did not change in response to mucosal injury. IDM‐induced gastric and small intestinal macroscopic lesions (4, 24 h), gastric MPO activity (24, 48 h) and plasma extravasation (30 min) were significantly greater in sst4−/− mice. TNFα, IL‐1, COX2 expressions significantly increased after 4 h in the stomach of sst4−/− mice, but in wild‐types the same pattern was observed only later, at the 48 h time‐point. IDM‐evoked histopathological alterations and small intestinal length reduction were not altered by the sst4 deletion. Conclusion This is the first evidence for sst4 expression in myenteric plexus neurons and its protective roles against chemically‐induced gastrointestinal mucosal damage and inflammation. This suggests the safety of sst4 agonist drug candidates in the gastrointestinal tract, and even their potential use for gastroprotective indication. Support or Funding Information Supported by: GINOP‐2.3.2‐15‐2016‐00050 – PEPSYS, GINOP‐2.3.2 STAY ALIVE, EFOP‐3.6.2‐16‐2017‐00008, ÚNKP‐19‐3‐III‐PTE‐211

Despite recent advancements in the pharmacologic and endoscopic management of gastrointestinal ulceration, it is still associated with high mortality. Therefore, it is important to understand mucosal protective mechanisms. Somatostatin, present in the endocrine cells & sensory nerves, and its analogues reduce mucosal blood flow, pepsin and gastric acid secretion. Its receptor subtype 4 (sst4) mediates anti-inflammatory & analgesic actions, as discovered by our group. Therefore, our aim was to investigate its role in gastrointestinal injury. We treated sst4 gene-deleted (sst4−/−) and wildtype mice with indomethacine (IDM; 35 mg/kg) or vehicle s.c.. Gastric & small intestine lesions were evaluated after 4 & 48 h macroscopically & microscopically. Plasma protein extravasation & myeloperoxidase (MPO) activity were assessed by ex vivo imaging, TNFα, IL-1, COX2, sst4 & somatostatin mRNA levels by qPCR. Gastric (4h) and small intestinal macroscopic (24 h) lesions, MPO activity (24, 48 h), and plasma extravasation (30 min) were significantly greater in IDM-treated sst4−/− mice, while histopathological scores & small intestinal length did not show strain difference. TNFα, IL-1, COX2 significantly upregulated after 4h in the stomach of sst4−/− mice, and the same pattern was observable in wildtype mice at later timepoint (48 h). These results provide evidence for the protective role of the sst4 receptor against IDM-induced gastrointestinal mucosal injury. This suggests the safety of sst4 agonist drug candidates in the gastrointestinal tract, and even their potential use for gastroprotective indication. Supported by: GINOP-2.3.2-15-2016-00050 – PEPSYS, GINOP-2.3.2 STAY ALIVE, EFOP-3.6.2-16-2017-00008, ÚNKP-19-3-III-PTE-211