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Glucagon-like peptide-1 inhibits gastric emptying via vagal afferent-mediated central mechanisms

Exogenous administration of glucagon-like peptide-1-(7-36) amide (GLP-1), an insulinotropic hormone, inhibits gastric emptying and acid secretion in humans. The role of GLP-1 as a regulator of gastric function is elusive. In gastric fistula rats, vagal afferent denervation and peripheral administration of the GLP-1 receptor antagonist exendin(9-39) amide enhanced emptying of a glucose meal, whereas intracerebroventricular exendin was ineffective. The rate of saline emptying was attenuated by peripheral as well as by central administration of GLP-1, and pretreatment with exendin by the respective routes reversed the inhibition by GLP-1. Vagal afferent denervation abolished the central and peripheral action of GLP-1 on gastric emptying. Neither peripheral cholinergic nor adrenergic blockade altered the delay of methyl cellulose meal emptying by intracisternal GLP-1 injection. Acid secretion in conscious pylorus-ligated rats was inhibited by intracisternal GLP-1 administration, whereas systemic GLP-1 was ineffective. These results support the notion that GLP-1 receptors participate in the central and peripheral regulation of gastric function. Furthermore, vagal afferent nerves mediate the inhibitory action of GLP-1 on gastric motor function. GLP-1 may be a candidate brain-gut peptide that acts as a physiological modulator of gastric function.Exogenous administration of glucagon-like peptide-1-(7-36) amide (GLP-1), an insulinotropic hormone, inhibits gastric emptying and acid secretion in humans. The role of GLP-1 as a regulator of gastric function is elusive. In gastric fistula rats, vagal afferent denervation and peripheral administration of the GLP-1 receptor antagonist exendin-(9-39) amide enhanced emptying of a glucose meal, whereas intracerebroventricular exendin was ineffective. The rate of saline emptying was attenuated by peripheral as well as by central administration of GLP-1, and pretreatment with exendin by the respective routes reversed the inhibition by GLP-1. Vagal afferent denervation abolished the central and peripheral action of GLP-1 on gastric emptying. Neither peripheral cholinergic nor adrenergic blockade altered the delay of methyl cellulose meal emptying by intracisternal GLP-1 injection. Acid secretion in conscious pylorus-ligated rats was inhibited by intracisternal GLP-1 administration, whereas systemic GLP-1 was ineffective. These results support the notion that GLP-1 receptors participate in the central and peripheral regulation of gastric function. Furthermore, vagal afferent nerves mediate the inhibitory action of GLP-1 on gastric motor function. GLP-1 may be a candidate brain-gut peptide that acts as a physiological modulator of gastric function.

Melatonin prevents methotrexate‐induced hepatorenal oxidative injury in rats

Abstract:  Regarding the mechanisms of methotrexate (MTX) hepatotoxicity and nephrotoxicity, several hypotheses have been put forward, among which oxidative stress (including depletion of glutathione) is likely. This investigation elucidates the role of free radicals in MTX‐induced toxicity and the protection by melatonin. Wistar albino rats were injected with MTX intraperitoneally. Following a single dose of MTX (20 mg/kg), either saline (MTX group) or melatonin (10 mg/kg, MTX + Mel group) was administered for 5 days. In other rats, physiologic saline (control group) or melatonin (10 mg/kg, Mel group) was injected for 5  days, following a single injection of saline. On the sixth day, rats were killed to obtain blood, liver, and kidney tissue samples. Malondialdehyde (MDA), an end product of lipid peroxidation, and glutathione (GSH), a key antioxidant, levels were evaluated in blood and tissue homogenates. Reactive oxygen metabolite‐induced inflammatory changes in kidney and liver tissues were evaluated by measuring myeloperoxidase (MPO) activity, an index of neutrophil infiltration. MTX administration resulted in increased MDA levels and MPO activity and decreased GSH levels in the blood, liver, and kidney whereas melatonin reversed these effects. When melatonin was administered alone, no significant changes in biochemical parameters were noted. In conclusion, the present study suggests that melatonin may be of therapeutic benefit when used with MTX.

Oxytocin ameliorates oxidative colonic inflammation by a neutrophil-dependent mechanism.

UNLABELLED Oxytocin (OT), a nonapeptide produced in the paraventricular and the supraoptical nuclei in the hypothalamus has a wide range of effects in the body. However, the role of OT on the gastrointestinal (GI) tract has to be settled. OT may participate in the regulation of motility, secretion, blood flow, cell turnover and release of neurotransmitters and/or peptides in the GI tract, possesses antisecretory and antiulcer effects, facilitates wound healing and is involved in the modulation of immune and inflammatory processes. The present work was conducted to assess the possible therapeutic effects of OT against the acetic acid-induced colonic injury in the rat. METHODS Colitis was induced by intracolonic administration of acetic acid (5%) in Sprague-Dawley rats (200-250 g). Either saline or OT (0.5 mg/kg) was injected subcutaneously, immediately after the induction of colitis and repeated two times a day for 4 days. On the 4th day, rats were decapitated and distal 8 cm of the colon were removed for the macroscopic and microscopic damage scoring, determination of tissue wet weight index (WI), malondialdehyde (MDA) levels, an end product of lipid peroxidation; glutathione (GSH) levels, a key antioxidant; and myeloperoxidase (MPO) activity, as an indirect index of neutrophil infiltration. Colonic collagen content, as a fibrosis marker was also determined. Lactate dehydrogenase (LDH) and tumor necrosis factor-alpha (TNF-alpha) levels were assayed in serum samples. In the acetic acid-induced colitis, macroscopic and microscopic damage scores, WI, MDA and MPO levels were significantly increased, while GSH levels were decreased when compared to control group (p <0.05-<0.001). Treatment with OT abolished the colitis-induced elevations in damage scores, WI, MDA and MPO levels and restored the GSH levels (p <0.05-0.001). Similarly, acetic acid increased the collagen content of colonic tissues and OT-treatment reduced this value to the level of the control group. Serum LDH and TNF-alpha levels were also elevated in the acetic acid-induced colitis group as compared to control group, while this increase was significantly decreased by OT treatment. The results suggest that OT, which improves the antioxidative state of the colonic tissue and ameliorates oxidative colonic injury via a neutrophil-dependent mechanism, requires further investigation as a potential therapeutic agent in colonic inflammation.

Melatonin Protects Against Oxidative Organ Injury in a Rat Model of Sepsis

PurposeBased on the potent antioxidant effects of melatonin, we investigated the putative protective role of melatonin against sepsis-induced oxidative organ damage in rats.MethodsSepsis was induced by cecal ligation and puncture (CLP) in Wistar albino rats. Animals subjected to CLP and sham-operated control rats were given saline or melatonin 10 mg/kg intraperitoneally 30 min before and 6 h after the operation. The rats were killed 16 h after the operation and the biochemical changes were investigated in the liver, kidney, heart, lung, diaphragm, and brain tissues by examining malondialdehyde (MDA) and glutathione (GSH) levels, and myeloperoxidase (MPO) activity. We also examined the tissues microscopically.ResultsSepsis resulted in a significant decrease in GSH levels and a significant increase in MDA levels and MPO activity (P < 0.05–P < 0.001) showing oxidative damage, which was confirmed by histological examination. Melatonin clearly reversed these oxidant responses and the microscopic damage, demonstrating its protective effects against sepsis-induced oxidative organ injury.ConclusionThe increase in MDA levels and MPO activity and the concomitant decrease in GSH levels demonstrate the role of oxidative mechanisms in sepsis-induced tissue damage. Melatonin, by its free radical scavenging and antioxidant properties, ameliorated oxidative organ injury. Thus, supplementing antiseptic shock treatment with melatonin may be beneficial in the clinical setting.

The protective effect of melatonin on renal ischemia–reperfusion injury in the rat

Oxygen free radicals are considered to be important components involved in the pathophysiological tissue alterations observed during ischemia–reperfusion (I/R). In this study, we investigated the putative protective effects of melatonin treatment on renal I/R injury. Wistar albino rats were unilaterally nephrectomized and subjected to 45 min of renal pedicle occlusion followed by 1, 3, 6, 24, 48 hr or 1 wk of reperfusion. Melatonin (10 mg/kg, s.c.) or vehicle was administered twice, 15 min prior to ischemia and immediately before the reperfusion period. At the end of the reperfusion periods, rats were decapitated. Kidney samples were taken for histological examination or the determination of renal malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity and protein oxidation (PO). Serum creatinine and blood urea nitrogen (BUN) concentrations were measured for the evaluation of renal function. The results revealed that I/R induced nephrotoxicity, as evidenced by increases in BUN and creatinine levels at each time point, was reversed by melatonin treatment. The decrease in GSH and increases in MDA, MPO and PO induced by I/R indicated that renal injury involves free radical formation. As melatonin administration reversed these oxidant responses, improved renal function and microscopic damage, it seems likely that melatonin protects kidney tissue against oxidative damage.

Resveratrol treatment protects against doxorubicin-induced cardiotoxicity by alleviating oxidative damage.

The possible protective effects of resveratrol (RVT) against cardiotoxicity were investigated in Wistar albino rats treated with saline, saline+doxorubicin (DOX; 20 mg/kg) or RVT (10 mg/kg)+DOX. Blood pressure and heart rate were recorded on the 1st week and on the 7th week, while cardiomyopathy was assessed using transthoracic echocardiography before the rats were decapitated. DOX-induced cardiotoxicity resulted in decreased blood pressure and heart rate, but lactate dehydrogenase, creatine phosphokinase, total cholesterol, triglyceride, aspartate aminotransferase and 8-OHdG levels were increased in plasma. Moreover, DOX caused a significant decrease in plasma total antioxidant capacity along with a reduction in cardiac superoxide dismutase, catalase and Na+,K+-ATPase activities and glutathione contents, while malondialdehyde, myelopreoxidase activity and the generation of reactive oxygen species were increased in the cardiac tissue. On the other hand, RVT markedly ameliorated the severity of cardiac dysfunction, while all oxidant responses were prevented; implicating that RVT may be of therapeutic use in preventing oxidative stress due to DOX toxicity.

The protective effect of oxytocin on renal ischemia/reperfusion injury in rats

AIM Oxytocin was previously shown to have anti-inflammatory effects in different inflammation models. The major objective of the present study was to evaluate the protective role of oxytocin (OT) in protecting the kidney against ischemia/reperfusion (I/R) injury. MATERIALS AND METHODS Male Wistar albino rats (250-300 g) were unilaterally nephrectomized, and subjected to 45 min of renal pedicle occlusion followed by 6 h of reperfusion. OT (1 mg/kg, ip) or vehicle was administered 15 min prior to ischemia and was repeated immediately before the reperfusion period. At the end of the reperfusion period, rats were decapitated and kidney samples were taken for histological examination or determination of malondialdehyde (MDA), an end product of lipid peroxidation; glutathione (GSH), a key antioxidant; and myeloperoxidase (MPO) activity, an index of tissue neutrophil infiltration. Creatinine and urea concentrations in blood were measured for the evaluation of renal function, while TNF-alpha and lactate dehydrogenase (LDH) levels were determined to evaluate generalized tissue damage. Formation of reactive oxygen species in renal tissue samples was monitored by chemiluminescence technique using luminol and lucigenin probes. RESULTS The results revealed that I/R injury increased (p<0.01-0.001) serum urea, creatinine, TNF-alpha and LDH levels, as well as MDA, MPO and reactive oxygen radical levels in the renal tissue, while decreasing renal GSH content. However, alterations in these biochemical and histopathological indices due to I/R injury were attenuated by OT treatment (p<0.05-0.001). CONCLUSIONS Since OT administration improved renal function and microscopic damage, along with the alleviation of oxidant tissue responses, it appears that oxytocin protects renal tissue against I/R-induced oxidative damage.

L-Carnitine ameliorates methotrexate-induced oxidative organ injury and inhibits leukocyte death

Methotrexate (MTX), a folic acid antagonist widely used for the treatment of a variety of tumors and inflammatory diseases, affects normal tissues that have a high rate of proliferation, including the hematopoietic cells of the bone marrow and the gastrointestinal mucosal cells. To elucidate the role of free radicals and leukocytes in MTX-induced oxidative organ damage and the putative protective effect of L-carnitine (L-Car), Wistar albino rats were administered a single dose of MTX (20 mg/kg) followed by either saline or L-Car (500 mg/kg) for 5 days. After decapitation of the rats, trunk blood was obtained, and the ileum, liver, and kidney were removed for histological examination and for the measurement of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity, and collagen content. Our results showed that MTX administration increased the MDA and MPO activities and collagen content and decreased GSH levels in all tissues, while these alterations were reversed in L-Car-treated group. The elevated serum TNF-α level observed following MTX treatment was depressed with L-Car. The oxidative burst of neutrophils stimulated by Annexin V was reduced in the saline-treated MTX group, while L-Car abolished this inhibition. Similarly, flow cytometric measurements revealed that leukocyte apoptosis was increased in MTX-treated animals, while L-Car reversed these effects. Severe degeneration of the intestinal mucosa, liver parenchyma, and glomerular and tubular epithelium observed in the saline-treated MTX group was improved by L-Car treatment. These results suggest that L-Car, possibly via its free radical scavenging and antioxidant properties, ameliorates MTX-induced oxidative organ injury and inhibits leukocyte apoptosis. Thus, supplementation with L-Carnitine as an adjuvant therapy may be promising in alleviating the systemic side-effects of chemotherapeutics.

Melatonin improves oxidative organ damage in a rat model of thermal injury

Animal models of burn injury indicate oxygen radicals as causative agents in the local wound response, as well as in the development of burn shock and distant organ injury. This study was designed to determine the possible protective effect of melatonin treatment against oxidative damage in the liver, lung and intestine induced by burn injury. Under ether anaesthesia, the shaved dorsum of rats was exposed to a 90 degrees C bath for 10s to induce burn injury. Rats were decapitated either 3 or 24h after burn injury. Melatonin was administered i.p. immediately after burn injury. In the 24h burn group, melatonin injections were repeated for two more occasions. In the sham group the same protocol was applied except that the dorsum was dipped in a 25 degrees C water bath for 10s. Liver, lung and intestine tissues were taken for the determination of malondialdehyde (MDA) and glutathione (GSH) levels, myeloperoxidase (MPO) activity and protein oxidation (PO). Severe skin scald injury (30% of total body surface area) caused a significant decrease in GSH level, significant increases in MDA and PO levels, and MPO activity at postburn 3 and 24h. Treatment of rats with melatonin (10mg/kg) significantly elevated the reduced GSH levels while it decreased MDA and PO levels as well as MPO activity.

The Anti-Inflammatory and Neuroprotective Effects of Ghrelin in Subarachnoid Hemorrhage-Induced Oxidative Brain Damage in Rats

To elucidate the putative neuroprotective effects of ghrelin in subarachnoid hemorrhage (SAH)-induced brain injury, Wistar albino rats (n = 54) were divided into sham-operated control, saline-treated SAH, and ghrelin-treated (10 microg/kg/d IP) SAH groups. The rats were injected with blood (0.3 mL) into the cisterna magna to induce SAH, and were sacrificed 48 h after the neurological examination scores were recorded. In plasma samples, neuron-specific enolase (NSE), S-100beta protein, TNF-alpha, and IL-1beta levels were evaluated, while forebrain tissue samples were taken for the measurement of malondialdehyde (MDA), glutathione (GSH), reactive oxygen species levels, myeloperoxidase (MPO), Na(+)-K(+)-ATPase activity, and DNA fragmentation ratio. Brain tissue samples containing the basilar arteries were obtained for histological examination, while cerebrum and cerebellum were removed for the measurement of blood-brain barrier (BBB) permeability and brain water content. The neurological scores were impaired at 48 h after SAH induction, and SAH caused significant decreases in brain GSH content and Na(+)-K(+)-ATPase activity, and increases in chemiluminescence, MDA levels, and MPO activity. Compared with the control group, the protein levels of NSE, S-100beta, TNF-alpha, and IL-1beta in plasma were also increased, while ghrelin treatment prevented all SAH-induced alterations observed both biochemically and histopathologically. The results demonstrate that ghrelin alleviates SAH-induced oxidative brain damage, and exerts neuroprotection by maintaining a balance in oxidant-antioxidant status, by inhibiting proinflammatory mediators, and preventing the depletion of endogenous antioxidants evoked by SAH.