Mehmet Bülbül

Effect of orexin-a on ischemia-reperfusion-induced gastric damage in rats.

BackgroundOrexins are involved in the regulation of sleeping behavior and energy homeostasis, and they are also implicated in the regulation of gastrointestinal functions. Previous reports have demonstrated the expression of orexin receptors in the gastrointestinal system. The aim of this study was to investigate the gastroprotective effect of orexin-A in ischemia-reperfusion-induced gastric mucosal injury.MethodsThe gastric ischemia-reperfusion model was established by clamping the celiac artery for 30 min and reperfusing for 60 min. Orexin-A was administered in doses of 500 pmol·kg−1·min−1 by infusion throughout the ischemia-reperfusion period. The mean lesion area, gastric prostaglandin E2 and mucus content, myeloperoxidase activity, and production of thiobarbituric acid reactive substances were measured.ResultsOrexin-A significantly attenuated the ischemia-reperfusion-induced gastric lesions and also decreased myeloperoxidase activity and the thiobarbituric acid reactive substances content in gastric mucosa of rats exposed to ischemia-reperfusion. However, the decline in gastric prostaglandin E2 and mucus content was not restored by orexin-A treatment.ConclusionsOrexin-A exhibited a gastroprotective effect against ischemia-reperfusion-induced lesions by decreasing neutrophil activation and lipid peroxidation.

Effect of stress-induced lipid peroxidation on functions of rat peritoneal macrophages.

The aim of the present study was to investigate the effects of stress‐induced lipid peroxidation on macrophages functions. Animals were subjected to 4 h immobilization at 4 °C in restraining devices. The peritoneal macrophages obtained from rats exposed to cold and restraint stress exhibited an increase in lipid peroxidation and a decline of chemotaxis and phagocytosis compared with control rats. After supplementation with vitamin E, the increment in thiobarbituric acid reactive substances (TBARS) content as the oxidative stress marker and the decline of chemotaxis and phagocytosis in peritoneal macrophages observed during cold‐restraint stress was significantly removed. No significant change in catalase activity of peritoneal macrophages was observed in groups exposed to cold‐restraint stress and treated with vitamin E. These findings indicate that phagocytic and chemotactic capacities of peritoneal macrophages are decreased by cold‐restraint stress and this effect of stress may be related to lipid peroxidation.

Endogenous orexin-A modulates gastric motility by peripheral mechanisms in rats

Orexin-A (OXA) and orexin receptor type 1 (OX1R) are found in enteric nervous system and smooth muscle cells in the digestive tract. Fasting is a stimulant for OXA synthesis. The aim of the present study was to investigate central and peripheral effects of endogenous OXA on gastric motility. Endogenous OXA synthesis was induced by 36h fasting. Vagotomy was used to evaluate N.vagus-mediated effects of OXA. Gastric emptying and interdigestive gastric motility were measured by spectrophotometric and manometric methods, respectively. Rats were pretreated with OX1R antagonist SB-334867 prior to measurements. Plasma OXA concentration was assayed with radioimmunoassay while preproorexin (PPO) expression was determined with Western blotting in gastric and hypothalamic tissues. OXA immunoreactivity in antrum was determined with immunohistochemistry. Plasma OXA level, PPO protein expression and OXA immunoreactivity were significantly increased in response to 36h fasting. Endogenous OXA facilitated gastric emptying and inhibited gastric interdigestive motility. As these effects were abolished with SB-334867, it is likely that gastrokinetic effects of OXA are mediated via OX1R. Vagotomy did not alter OXA-mediated effects. According to current data, OXA is up-regulated both centrally and peripherally upon fasting. Endogenous OXA accelerates gastric emptying while it inhibits interdigestive motility.

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

1 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. 2 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. 3 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. 4 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.

Opposite effects of central oxytocin and arginine vasopressin on changes in gastric motor function induced by chronic stress

HIGHLIGHTSHypothalamic OXT was increased following AS and CHS.AVP was increased following AS and CHeS.OXT antagonist prevented CHS‐induced recovery of GE.AVP antagonist restored CHeS‐induced delayed GE.OXT and AVP mediate chronic stress‐induced gastric motor changes independently. ABSTRACT Hypothalamic oxytocin (OXT) and arginine vasopressin (AVP) are known to act oppositely on hypothalamic‐pituitary‐adrenal (HPA) axis, stress response and gastrointestinal (GI) motility. In rodents, exposure to restraint stress (RS) delays gastric emptying (GE), however, repeated exposure to the same stressor (chronic homotypic stress (CHS)), the delayed GE is restored to basal level, while hypothalamic OXT is upregulated. In contrast, when rats are exposed to chronic heterotypic stress (CHeS), these adaptive changes are not observed. Although the involvement of central OXT in gastric motor adaptation is partly investigated, the role of hypothalamic AVP in CHeS‐induced maladaptive paradigm is poorly understood. Using in‐vivo brain microdialysis in rats, the changes OXT and AVP release from hypothalamus were monitored under basal non‐stressed (NS) conditions and in rats exposed to acute stress (AS), CHS and CHeS. To investigate the involvement of central endogenous OXT or AVP in CHS‐induced habituation and CHeS‐induced maladaptation, chronic central administration of selective OXT receptor antagonist L‐371257 and selective AVP V1b receptor antagonist SSR‐149415 was performed daily. OXT was measured higher in AS and CHS group, but not in CHeS‐loaded rats, whereas AVP significantly increased in rats exposed to AS and CHeS. Additionally, the response of the hypothalamic OXT‐ and AVP‐producing cells was amplified following CHS and CHeS, respectively. In rats exposed to AS for 90 min solid GE significantly delayed. The delayed‐GE was completely restored to the basal level following CHS, however, it remained delayed in CHeS‐loaded rats. The CHS‐induced restoration was prevented by L‐371257, whereas SSR‐149415 abolished the CHeS‐induced impaired GE. A significant correlation was observed between GE and (i) OXT in CHS‐loaded rats (rho = 0.61, p < 0.05, positively), (ii) AVP in CHeS‐loaded rats (rho = 0.69, p < 0.05, negatively). Under long term stressed conditions, the release of AVP and OXT from hypothalamus may vary depending on the content of the stressors. Central AVP appears to act oppositely to OXT by mediating CHeS‐induced gastric motor maladaptation. Long term central AVP antagonism might be a pharmacological approach for the treatment of stress‐related gastric motility disorders.

Central apelin mediates stress-induced gastrointestinal motor dysfunction in rats.

Apelin, an endogenous ligand for APJ receptor, has been reported to be upregulated in paraventricular nucleus (PVN) following stress. Central apelin is known to stimulate release of corticotropin-releasing factor (CRF) via APJ receptor. We tested the hypothesis that stress-induced gastrointestinal (GI) dysfunction is mediated by central apelin. We also assessed the effect of exogenous apelin on GI motility under nonstressed (NS) conditions in conscious rats. Prior to solid gastric emptying (GE) and colon transit (CT) measurements, APJ receptor antagonist F13A was centrally administered under NS conditions and following acute stress (AS), chronic homotypic stress (CHS), and chronic heterotypic stress (CHeS). Plasma corticosterone was assayed. Strain gage transducers were implanted on serosal surfaces of antrum and distal colon to record postprandial motility. Stress exposure induced coexpression of c-Fos and apelin in hypothalamic PVN. Enhanced hypothalamic apelin and CRF levels in microdialysates were detected following AS and CHeS, which were negatively and positively correlated with GE and CT, respectively. Central F13A administration abolished delayed GE and accelerated CT induced by AS and CHeS. Central apelin-13 administration increased the plasma corticosterone and inhibited GE and CT by attenuating antral and colonic contractions. The inhibitory effect elicited by apelin-13 was abolished by central pretreatment of CRF antagonist CRF9-41 in antrum, but not in distal colon. Central endogenous apelin mediates stress-induced changes in gastric and colonic motor functions through APJ receptor. The inhibitory effects of central exogenous apelin-13 on GI motility appear to be partly CRF dependent. Apelin-13 inhibits colon motor functions through a CRF-independent pathway.

Peripheral apelin-13 administration inhibits gastrointestinal motor functions in rats: The role of cholecystokinin through CCK1 receptor-mediated pathway.

Apelin is the endogenous ligand of the G protein-coupled receptor APJ. The APJ receptor is widely expressed in gastrointestinal (GI) tissues including stomach and small intestine. Apelin administration was shown to induce the release of cholecystokinin (CCK) which is a well-known alimentary hormone with its inhibitory actions on GI motor functions through CCK1 receptors on vagal afferent fibers. We investigated whether; (i) peripherally injected apelin-13 alters GI motor functions, (ii) apelin-induced changes are mediated by APJ receptor or CCK1 receptor and (iii) vagal afferents are involved in inhibitory effects of apelin. Solid gastric emptying (GE) and colon transit (CT) were measured, whereas duodenal phase III-like contractions were recorded in rats administered with apelin-13 (300μg/kg, ip). CCK1 receptor antagonist lorglumide (10mg/kg, ip) or APJ receptor antagonist F13A (300μg/kg, ip) was administered 30min prior to the apelin-13 injections. Vagal afferent denervation was achieved by systemic administration of vanilloid receptor agonist capsaicin (125mg/kg, sc). Apelin-13 administration significantly (p<0.01) increased the CCK level in portal venous plasma samples. Compared with vehicle-treated rats, apelin-13 significantly delayed both GE (p<0.001) and CT (p<0.01). Pretreatment of lorglumide or F13A completely abolished the apelin-13-induced inhibitory effects on GE and CT, moreover, apelin-13 was found ineffective in rats underwent afferent denervation. F13A administration alone significantly accelerated the basal CT. Apelin-13 noticeably disturbed the duodenal fasting motor pattern by impairing phase III-like contractions while increasing the amplitudes of phase II contractions which were prevented by pretreatment of lorglumide and capsaicin. Compared with vehicle-treated rats, lorglumide and capsaicin significantly (p<0.05) reduced the apelin-13-induced increases in phase II motility index. Peripherally administered apelin-13 inhibits GI motor functions through CCK-dependent pathway which appears to be mediated by CCK1 receptors on vagal afferents. Peripheral apelin might contribute to the motility changes occurred in postprandial period.

Dietary Silica Modifies the Characteristics of Endothelial Dilation in Rat Aorta

Considering the importance of nitric oxide generation in the regulation of vessel tone, reduced endothelial nitric oxide synthase (eNOS) expression in alveolar macrophages exposed to short-term silica (Si) suggests the possibility of Si-induced changes in endothelial functions. In this experimental study, the functional changes of the endothelial cells were investigated in the aortic rings of rats subjected to 50 mg Si/kg body weight in their drinking water for 8 days. Norepinephrine elicited contractility and dilation response to acetylcholine (ACh) was significantly high in the aortic rings of Si-treated group. Alteration in receptor-independent endothelial response to A23187 in the aortic rings of Si-exposed rats was less obvious, but sodium nitroprusside (SNP)-elicited dilation was reduced significantly. A23187-induced relaxation was fully eliminated with N-nitro-L-arginine methyl ester (L-NAME) pretreatment, whereas 19.24 +/- 4.36% of ACh response was L-NAME resistant and eliminated with 10-5 M tetraethylammonium (TEA). Despite a significant reduction in the share of NO, the contribution of indomethacine (IND)-sensitive relaxation to ACh response remained unchanged in Si group. As a result, our findings demonstrated that Si both modifies the characteristics of endothelial relaxants and attenuates smooth muscle cell responsiveness to NO. Si-induced reduced NO association with elevated endothelium-derived hyperpolarizing factor (EDHF) in response to ACh, together with reduced NO sensitization, might have clinical importance in cardiovascular pathology.

Central apelin administration and restraint stress induce hypothalamic cholecystokinin release via the APJ receptor

Exposure to an acute stressor induces up‐regulation of apelin and cholecystokinin (CCK) in the hypothalamic paraventricular nucleus (PVN), which is the key brain centre integrating the stress‐induced alterations in neuroendocrine, autonomic and behavioural functions. We tested the hypothesis that the release of CCK from the PVN is increased by centrally administered or stress‐induced up‐regulated endogenous apelin via the APJ receptor. Additionally, the effect of hypothalamic CCK on autonomic outflow was investigated under basal and stressed conditions. In vivo brain microdialysis was performed in rats that received (i) intra‐PVN administration of apelin‐13 or (ii) acute restraint stress (ARS). For chemical stimulation of the neurones in the PVN, a high concentration of KCl was applied by reverse microdialysis. CCK‐8 levels in microdialysates were quantified by an enzyme immunoassay. The immunoreactivity of the APJ receptor and CCK was detected by immunofluorescence in hypothalamic sections. Heart rate variability was assessed in rats that received PVN stimulation or ARS following pre‐administration of vehicle or CCK1 receptor antagonist lorglumide. Both intra‐PVN exogenous apelin‐13 and ARS increased the CCK‐8 levels in dialysates significantly. The ARS‐induced elevations in CCK levels were reversed by intra‐PVN pre‐administration of the APJ receptor antagonist F13A. Within the PVN, robust APJ receptor expression was detected on the CCK‐producing mediocellular cells, in addition to the parvocellular neurones in the periventricular region. Dual immunoreactivity of APJ/CCK was observed in magnocellular cells to a lesser degree. Both exogenous apelin and ARS increased the CCK immunoreactivity markedly within the PVN, which was diminished significantly by F13A. Sympathetic tonus was increased markedly both by PVN stimulation and ARS, which was attenuated by lorglumide. These results revealed the interaction between apelin and CCK in the brain, suggesting that hypothalamic CCK may contribute to the apelin‐induced alterations in autonomic outflow under stressed conditions.

Peripheral apelin mediates stress‐induced alterations in gastrointestinal motor functions depending on the nutritional status

Exposure to stress induces gastrointestinal (GI) dysmotility. In rodents, acute restraint stress (ARS) inhibits gastric emptying (GE) and intestinal transit (IT) via central and peripheral corticotropin‐releasing factor (CRF)‐mediated pathways. Peripherally administered apelin‐13 was shown to inhibit GI motor functions; moreover, stress‐induced upregulation of gastric apelin content was demonstrated in rats suggesting that peripheral apelin may mediate stress‐induced alterations in GI motility. We investigated the role of endogenous peripheral apelin in stress‐induced GI dysfunction. GE, IT and gastro‐duodenal fasting motility were measured in non‐stressed (NS), CRF‐injected and ARS‐loaded rats. CRF and apelin receptor antagonists astressin or F13A was administered before ARS or peripheral CRF injection. Apelin and APJ receptor expressions were determined using immunohistochemistry and quantified by qRT‐PCR. Double immunofluorescence was performed for enteric neuronal apelin. GE and IT were delayed by CRF and ARS. ARS‐induced changes were attenuated by F13A, whereas astressin was ineffective. CRF‐induced alterations in GE and IT were restored completely by astressin, while they were diminished by F13A. Antral phase III‐like contractions were disturbed following ARS which were preserved by preadministration of astressin, but not F13A. CRF impaired gastric and duodenal fasting contractions, while these changes were not altered by F13A. ARS increased apelin expression in stomach and duodenum. Apelin immunoreactivity was detected in mucosa, smooth muscles and myenteric plexi, whereas dense APJ receptor expression was observed within tunica muscularis. APJ receptor was downregulated in rats fasted overnight. These results suggest that enteric apelin acts as an inhibitor stress mediator in the postprandial state.