Gastroprotective activity of melatonin and its precursor, L-tryptophan, against stress-induced and ischaemia-induced lesions is mediated by scavenge of oxygen radicals

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Identification of a Novel Streptomyces sp. Strain HU2014 Showing Growth Promotion and Biocontrol Effect Against Rhizoctonia spp. in Wheat

Wheat sharp eyespot is a serious disease caused by the phytopathogens Rhizoctonia cerealis and R. solani. Some species in the genus Streptomyces have been identified as potential biocontrol agents against phytopathogens. In this investigation, the physiological, biochemical, phylogenetic, and genomic characteristics of strain HU2014 indicate that it is a novel Streptomyces sp. most closely related to Streptomyces albireticuli. Strain HU2014 exhibited strong antifungal activity against R. cerealis G11 and R. solani YL-3. Ultraperformance liquid chromatography-mass spectrometry on the four extracts from the extracellular filtrate of strain HU2014 identified 10 chemical constituents in the Natural Products Atlas with high match levels (more than 90%). In an antifungal efficiency test on wheat sharp eyespot, two extracts significantly reduced the lesion areas on bean leaves infected by R. solani YL-3. The drenching of wheat in pots with spore suspension of strain HU2014 demonstrated a control efficiency of 65.1% against R. cerealis G11 (compared with 66.9% when treated by a 30% hymexazol aqueous solution). Additionally, in vitro and pot experiments demonstrated that strain HU2014 can produce indoleacetic acid, siderophores, extracellular enzymes, and solubilized phosphate, and it can promote plant growth. We conclude that strain HU2014 could be a valuable microbial resource for growth promotion of wheat and biological control of wheat sharp eyespot.

Gut melatonin: A potent candidate in the diversified journey of melatonin research

After being discovered from the bovine pineal gland by Aaron Lerner and co-workers in the year 1958, various distinguished researchers have reported melatonin (5-methoxy-N-acetyl-tryptamine) from several extra-pineal sources, including the gastrointestinal tract (GIT). In the year 1974, Raikhlin and Kvetnoy first detected this molecule in the gastrointestinal tissue. Later, within the last 45 years, many renowned investigators found that the GIT is a rich source of melatonin, in addition to the pineal gland. In the carp gut, the estimation of Arylalkylamine-N-acetyltransferase (AANAT) mRNA/protein levels, which is the rate-determining enzyme for melatonin biosynthesis in the pineal gland, confirmed the endogenous synthesis of melatonin. The remarkable feature of the pineal gland melatonin is its rhythmic synthesis with a peak at dark-phase and lowest at light-phase in synchronization with seasonal environmental light-dark (LD) cycle. Recent studies on carp demonstrated that the melatonin concentrations and the AANAT protein intensities in different gut segments underwent significant daily fluctuations. However, compared to the melatonin rhythm in the pineal gland, the melatonin profiles in gut tissue displayed daily rhythm in parallel with the feeding cycle of the carp, irrespective of LD conditions of the environment. Notably, in carp, the temporal pattern of the gut melatoninergic system found to vary with the environmental non-photic signal(s), such as food entrainment factors (viz. availability of food, timing of food supply, number(s) of feed per day, quality of food) those act as the most dependable synchronizer(s) in daily rhythm characteristics of gut melatonin and AANAT. Thereby in this review, it appears meaningful to highlight the existing data on the mode of synthesis of melatonin in cells of the digestive tract, and most importantly, the regulation of its synthesis. Finally, in comparison with the dynamic actions of melatonin derived from the pineal gland, this review will lead to underline the role of gut-derived melatonin in a variety of physiological functions.

Cytoprotective, antioxidant and anti-inflammatory mechanism related to antiulcer activity of Cissampelos sympodialis Eichl. in animal models

ETHNOPHARMACOLOGICAL RELEVANCE

The leaves and roots of Cissampelos sympodialis (Menispermaceae) are used by indian tribes and in folk medicine to treat genitourinary infections, inflammation, asthma and gastrointestinal disorders.

MATERIAL AND METHODS

The standardized ethanolic extract (Cs-EtOHE) and alkaloids total fraction (Cs-TAF) obtained from aerial parts of C. sympodialis were evaluated in several models of acute gastric ulcers. The antisecretory and/or neutralizing mechanisms of the gastric acid secretion, cytoprotective, antioxidant and immunoregulatory mechanisms were also evaluated.

RESULTS

Cs-EtOHE and Cs-TAF presented a reduction in gastric mucosa lesions against ethanol, NSAIDs, hypothermic restraint-stress and gastric juice containment induced ulcer models. This activity is related to alkaloids present in the extract, and involves the participation of sulfhydryl compounds, nitric oxide, K_ATP channels, prostaglandins, decreased levels of IL-1β and TNF-α and increased levels of GSH and IL-10.

CONCLUSION

The data indicate gastroprotective activity, due to the participation of the cytoprotective, antioxidant and immunoregulatory mechanisms.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Remote ischemic postconditioning protects against gastric mucosal lesions in rats

AIM: To investigate the protective effects of remote ischemic postconditioning (RIP) against limb ischemia-reperfusion (IR)-induced gastric mucosal injury.

METHODS: Gastric IR was established in male Wistar rats by placing an elastic rubber band under a pressure of 290-310 mmHg on the proximal part of both lower limbs for 3 h followed by reperfusion for 0, 1, 3, 6, 12 or 24 h. RIP was performed using three cycles of 30 s of reperfusion and 30 s of reocclusion of the femoral aortic immediately after IR and before reperfusion for up to 24 h. Rats were randomly assigned to receive IR (n = 36), IR followed by RIP (n = 36), or sham treatment (n = 36). Gastric tissue samples were collected from six animals in each group at each timepoint and processed to determine levels of malondialdehyde (MDA), superoxide dismutase (SOD), xanthine oxidase (XOD) and myeloperoxidase (MPO). Additional samples were processed for histologic analysis by hematoxylin and eosin staining. Blood samples were similarly collected to determine serum levels of lactate dehydrogenase (LDH), creatine kinase (CK), tumor necrosis factor (TNF)-α and interleukin (IL)-10.

RESULTS: The pathologic changes in gastric tissue induced by IR were observed by light microscopy. Administration of RIP dramatically reduced the gastric damage score after 6 h of reperfusion (5.85 ± 0.22 vs 7.72 ± 0.43; P < 0.01). In addition, RIP treatment decreased the serum activities of LDH (3.31 ± 0.32 vs 6.46 ± 0.03; P < 0.01), CK (1.94 ± 0.20 vs 4.54 ± 0.19; P < 0.01) and the concentration of TNF-α (53.82 ± 0.85 vs 88.50 ± 3.08; P < 0.01), and elevated the concentration of IL-10 (101.46 ± 5.08 vs 99.77 ± 4.32; P < 0.01) induced by IR at 6 h. Furthermore, RIP treatment prevented the marked elevation in MDA (3.79 ± 0.29 vs 6.39 ± 0.81) content, XOD (7.81 ± 0.75 vs 10.37 ± 2.47) and MPO (0.47 ± 0.05 vs 0.82 ± 0.03) activities, and decrease in SOD (4.95 ± 0.32 vs 3.41 ± 0.38; P < 0.01) activity in the gastric tissue as measured at 6 h.

CONCLUSION: RIP provides effective functional protection and prevents cell injury to gastric tissue induced by limb IR via anti-inflammatory and antioxidant actions.

Expression of melatonin synthesizing enzymes in Helicobacter pylori infected gastric mucosa

Helicobacter pylori colonization of gastric mucosa causes pain of unknown etiology in about 15-20% of infected subjects. The aim of the present work was to determine the level of expression of enzymes involved in the synthesis of melatonin in gastric mucosa of asymptomatic and symptomatic H. pylori infected patients. To diagnose H. pylori infection, histological analysis and the urea breath test (UBT C13) were performed. The levels of mRNA expression of arylalkylamine-N-acetyltransferase (AA-NAT) and acetylserotonin methyltransferase (ASMT) were estimated in gastric mucosa with RT-PCR. The level of AA-NAT expression and AMST was decreased in H. pylori infected patients and was increased after H. pylori eradication. We conclude that decreased expression of melatonin synthesizing enzymes, AA-NAT and ASMT, in patients with symptomatic H. pylori infection returns to normal level after H. pylori eradication.

Preclinical efficacy of melatonin to reduce methotrexate-induced oxidative stress and small intestinal damage in rats

BACKGROUND

Methotrexate is widely used as a chemotherapeutic agent for leukemia and other malignancies. The efficacy of this drug is often limited by mucositis and intestinal injury, which are the major causes of morbidity in children and adults.

AIM

The present study investigates whether melatonin, a powerful antioxidant, could have a protective effect.

METHOD

Rats were pretreated with melatonin (20 and 40 mg/kg body weight) daily 1 h before methotrexate (7 mg/kg body weight) administration for three consecutive days. After the final dose of methotrexate, the rats were sacrificed and the small intestine was used for light microscopy and biochemical assays. Intestinal homogenates were used for assay of oxidative stress parameters malondialdehyde and protein carbonyl content, and myeloperoxidase activity, a marker of neutrophil infiltration as well as for the activities of the antioxidant enzymes.

RESULT

Pretreatment with melatonin had a dose-dependent protective effect on methotrexate (MTX)-induced alterations in small intestinal morphology. Morphology was saved to some extent with 20 mg melatonin pretreatment and near normal morphology was achieved with 40 mg melatonin pretreatment. Biochemically, pretreatment with melatonin significantly attenuated MTX-induced oxidative stress (P < 0.01 for MDA, P < 0.001 for protein carbonyl content) and restored the activities of the antioxidant enzymes (glutathione reductase P < 0.05, superoxide dismutase P < 0.01).

CONCLUSION

The results of the present study demonstrate that supplementation by exogenous melatonin significantly reduces MTX-induced small intestinal damage, indicating that it may be beneficial in ameliorating MTX-induced enteritis in humans.

Distribution, function and physiological role of melatonin in the lower gut

Melatonin is a hormone with endocrine, paracrine and autocrine actions. It is involved in the regulation of multiple functions, including the control of the gastrointestinal (GI) system under physiological and pathophysiological conditions. Since the gut contains at least 400 times more melatonin than the pineal gland, a review of the functional importance of melatonin in the gut seems useful, especially in the context of recent clinical trials. Melatonin exerts its physiological effects through specific membrane receptors, named melatonin-1 receptor (MT1), MT2 and MT3. These receptors can be found in the gut and their involvement in the regulation of GI motility, inflammation and pain has been reported in numerous basic and clinical studies. Stable levels of melatonin in the lower gut that are unchanged following a pinealectomy suggest local synthesis and, furthermore, implicate physiological importance of endogenous melatonin in the GI tract. Presently, only a small number of human studies report possible beneficial and also possible harmful effects of melatonin in case reports and clinical trials. These human studies include patients with lower GI diseases, especially patients with irritable bowel syndrome, inflammatory bowel disease and colorectal cancer. In this review, we summarize the presently available information on melatonin effects in the lower gut and discuss available in vitro and in vivo data. We furthermore aim to evaluate whether melatonin may be useful in future treatment of symptoms or diseases involving the lower gut.

Melatonin as a natural ally against oxidative stress: a physicochemical examination

Oxidative stress has been proven to be related to the onset of a large number of health disorders. This chemical stress is triggered by an excess of free radicals, which are generated in cells because of a wide variety of exogenous and endogenous processes. Therefore, finding strategies for efficiently detoxifying free radicals has become a subject of a great interest, from both an academic and practical points of view. Melatonin is a ubiquitous and versatile molecule that exhibits most of the desirable characteristics of a good antioxidant. The amount of data gathered so far regarding the protective action of melatonin against oxidative stress is overwhelming. However, rather little is known concerning the chemical mechanisms involved in this activity. This review summarizes the current progress in understanding the physicochemical insights related to the free radical-scavenging activity of melatonin. Thus far, there is a general agreement that electron transfer and hydrogen transfer are the main mechanisms involved in the reactions of melatonin with free radicals. However, the relative importance of other mechanisms is also analyzed. The chemical nature of the reacting free radical also has an influence on the relative importance of the different mechanisms of these reactions. Therefore, this point has also been discussed in detail in the current review. Based on the available data, it is concluded that melatonin efficiently protects against oxidative stress by a variety of mechanisms. Moreover, it is proposed that even though it has been referred to as the chemical expression of darkness, perhaps it could also be referred to as the chemical light of health.

Oxidative stress and ischemia-reperfusion injury in gastrointestinal tract and antioxidant, protective agents

Exacerbation of hypoxic injury after reoxygenation is a crucial mechanism mediating organ injury in transplantation, and in myocardial, hepatic, gastrointestinal, cerebral, renal, and other ischemic syndromes. The occlusion and reperfusion of the splanchnic artery is a useful animal model to elucidate the mechanism of gastrointestinal injury induced by ischemia-reperfusion (I/R). Although xanthine oxidase is a major source of reactive oxygen species (ROS), which plays an important role in the I/R-induced intestinal injury, there are many other sources of intracellular ROS. Various treatment modalities have been successfully applied to attenuate the I/R injury in animal models. This review focuses on the role of oxidant stress in the mechanism of I/R injury and the use of antioxidant agents for its treatment.

Secretion of melatonin and 6-sulfatoxymelatonin urinary excretion in functional dyspepsia

AIM: To evaluate blood concentration of melatonin and urinary excretion of its metabolite, 6-sulfatoxymelatonin (6-OHMS), in functional dyspepsia (FD).

METHODS: Ninety individuals were enrolled in the study: 30 in each study group: patients with postprandial distress syndrome (PDS), epigastric pain syndrome (EPS), and controls. Blood samples were drawn at 02:00 and 09:00 h and 24-h urine collection was performed. Serum melatonin and urinary 6-OHMS concentrations were measured by enzyme-linked immunosorbent assay.

RESULTS: Serum melatonin concentration at night and in the morning was significantly (P < 0.001) higher in PDS patients [at 02:00 h-93.3 pg/mL, quartile range (QR): 79.8-116.2; at 09.00 h-14.3 pg/mL, QR: 7.06-19.0] than in EPS (57.2 pg/mL, QR: 42.6-73.1; 8.1 pg/mL, QR: 4.1-9.3) and control patients (57.7 pg/mL, QR: 51.2-62.5; 8.1 pg/mL, QR: 5.4-10.3). A similar relationship was observed for urinary 6-OHMS excretion. Patients with severe PDS symptoms had a higher melatonin concentration than these with moderate syndromes, whereas patients with severe EPS had a lower urinary 6-OHMS excretion than patients with moderate symptoms.

CONCLUSION: Evaluation of melatonin serum concentrations and 24-h urinary 6-OHMS excretion are useful methods for differential diagnosis of various clinical forms of FD.

Gastric healing effect of melatonin against different gastroinvasive agents in cholestatic rats

BACKGROUND AND OBJECTIVE

The frequency of gastrointestinal ulceration is higher in jaundiced patients than in healthy population. The aim of this study was to assess the effect of pretreatment with melatonin, a potent scavenger of reactive oxygen species, on stress-induced gastric ulcers of cholestatic rats.

MATERIALS AND METHODS

Cholestasis was induced by surgical ligation of bile-duct and sham-operated rats served as sham animals. The animals received saline or melatonin (1, 3 or 10mg/kg) before stress induction. Three different types of gastroinvasive agents including ethanol, indomethacin or water immersion were used as stress agents to induce gastric ulceration.

RESULTS

Gastric mucosal damage induced by different gastroinvasive agents was significantly greater in bile-duct-ligated rats than in sham ones. Melatonin was protective against ethanol-, indomethacin- and water immersion-induced gastric damage in bile-duct-ligated and sham rats, dose-dependently, but the protective effect of melatonin was greater in cholestatic rats than sham rats in all three different series of experiments.

CONCLUSIONS

In conclusion, pretreatment of rats with melatonin protected gastric mucosa of cholestatic rats more effectively than the sham ones possibly by a mechanism involving the scavenging of free radicals.

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.

Therapeutic effect of melatonin in patients with functional dyspepsia

BACKGROUND AND GOAL

Melatonin may inhibit reactive oxygen species-related pathogenesis in the alimentary tract by neutralizing free radicals. In the present study we assessed the potential protective action of melatonin in ulcerlike dyspepsia.

STUDY

Sixty patients aged 19 to 39 years with the diagnosis of functional dyspepsia according to the Rome Criteria II and no Helicobacter pylori infection were involved in the study. Melatonin, at a dose of 5 mg (n=30), or placebo (n=30) were taken in the evening for a period of 12 weeks. At this time, patients were on an equivalent diet and were only to take an alkaline drug in case of the abdominal pain.

RESULTS

After 12 weeks, the dyspeptic symptoms completely subsided in 17 patients in the melatonin-treatment group (56.6%). In other 9 individuals (30.0%) a partial improvement in health was achieved, especially in the frequency and intensity of nocturnal pain. After placebo, the majority of patients (93.3%) did not experience any improvement in symptoms. Multivariate analysis indicated that melatonin (odds ratio 95.86, 95% confidence interval 3.72-2469.37, P<0.01) correlated independently with significantly improved patients health. H. pylori past infection decreased positive effect of melatonin in ulcerlike dyspepsia.

CONCLUSIONS

Melatonin can be considered as an auxiliary drug in the treatment of ulcerlike dyspepsia.

Effects of L-carnitine on neutrophil-mediated ischemia-reperfusion injury in rat stomach

Reactive oxygen metabolites play an important role in ischemia-reperfusion related gastric injury. Primary sources of reactive oxygen metabolites seem to be the xanthine/xanthine oxidase system and neutrophils accumulating within the reperfused tissue. Tissue myeloperoxidase activity is an important index of neutrophil accumulation. The purpose of the present study was to clarify the effect of L-carnitine on the accumulation of neutrophils and neutrophil-induced gastric mucosal damage in rats exposed to ischemia-reperfusion. Rats were randomly divided into three groups: sham-operated, ischemia-reperfusion and ischemia-reperfusion plus L-carnitine groups. Ischemia was induced by clamping the celiac artery for 30 min and then reperfusion was established for 60 min. Gastric injury was assessed by measuring myeloperoxidase activity in gastric tissue. The neutrophil accumulation and hemorrhagic lesions due to ischemia-reperfusion in gastric mucosa were ascertained in a histological study. L-Carnitine (100 mg kg(-1)) administrated intravenously 5 min before ischemia significantly reduced both the gastric injury and myeloperoxidase activity compared with the ischemia-reperfusion group. The results suggest that L-carnitine provides marked protection against ischemia-reperfusion-related gastric injury which could be due to its ability to reduce neutrophil accumulation in ischemic tissue.

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.

The effect of L-tryptophan on hemorrhagic shock induced bacterial translocation1

Hemorrhagic shock causes mucosal damage in intestine and it results in translocation of bacteria to distant organs. In this study, effects of various doses of L-Tryptophan on the prevention of bacterial translocation in hemorrhagic shock induced rabbits were investigated. This study was carried out on six groups, each was consisting of 10 rabbits. While any procedure was conducted on the rabbits in group 1 (as a control group), 1 x 10(10)Escherichia coli isolate were administered rabbits in the other groups by gavage. In groups 3, 4, 5, and 6, hemorrhagic shock was induced. After induction of hemorrhagic shock, 10, 50, and 200 mg/kg L-Tryptophan were intragastrically administered to animals in groups 4, 5, and 6, respectively. Blood and terminal ileum samples were taken to detect bacterial translocation by polymerase chain reaction and mucosal damage by histopathological examination at 24 h after hemorrhagic shock. The occurrence of bacterial translocation increased as well when intestinal bacterial intensity was increased (P < 0.05). The most intensive bacterial translocation was formed in group 3 as a result of the additive effect of hemorrhagic shock to bacterial augmentation. It was observed that bacterial translocation was significantly reduced in groups 5 and 6 that are 50 and 200 mg/kg L-Tryptophan were administered (P < 0.01). Histopathological changes on mucosa and submucosa support these results. As a result, we concluded that augmentation of intestinal bacterial intensity induces bacterial translocation, the addition of hemorrhagic shock to bacterial augmentation makes more excessive translocation and mucosal changes have effective roles in these events. L-Tryptophan decreased the intestinal mucosal damage and bacterial translocation induced by hemorrhagic shock, in a dose-dependent manner.

The protective effect of vitamin C, vitamin E and selenium combination therapy on ethanol-induced duodenal mucosal injury

In this study, the effect of a combination of vitamin C, vitamin E and selenium on ethanol-induced duodenal mucosal damage in rats was investigated morphologically and biochemically. The duodenal mucosal injury was produced by oral administration of 1 mL of absolute ethanol to each rat. Animals received vitamin C (250 mg/ kg), vitamin E (250 mg/kg) and selenium (0.5 mg/kg) for 3 days and absolute ethanol 1 hour after last antioxidant administration and were sacrificed 1 hour after absolute ethanol. Extreme degeneration in intestinal mucosa of rats given ethanol was observed morphologically. In addition, an increase in neuronal nitric oxide synthase immunoreactive areas was observed in the rats of the group given ethanol. On the other hand, a normal morphological appearance and a decrease in neuronal nitric oxide synthase immunoreactive areas were detected in the rats given ethanol+vitamin C+vitamin E+ selenium. In the group to which ethanol was administered, an increase in serum cholesterol and a decrease in serum albumin levels were determined. On the other hand, in the group to which ethanol+vitamin C+vitamin E+selenium were administered, serum cholesterol value decreased, and the serum albumin level increased. As a result, we can say that the combination of vitamin C, vitamin E and selenium has a protective effect on ethanol-induced duodenal mucosal injury.

Gastroprotective activity of Nigella sativa oil and its constituent, thymoquinone, against gastric mucosal injury induced by ischaemia/reperfusion in rats

Ischaemia/reperfusion (I/R) induced gastric lesion, is known to be linked with free radical (FR) formation. Therefore, this model was used to assess the antioxidant effects of Nigella sativa oil (N.O) and thymoquinone (TQ) on gastric mucosal redox state and gastric lesions, 1 and 24 h after reperfusion. Male Wistar rats were subjected to I/R and were injected with either N.O (2.5 and 5 ml/kg, p.o) or TQ (5, 20, 50 and 100 mg/kg, p.o). The results showed that I/R elevated the levels of lipid peroxide (LPX) and lactate dehydrogenase (LDH), while decreased those of reduced glutathione (GSH) and superoxide dismutase (SOD). These biochemical changes were accompanied by an increase in the formation of gastric lesions, which was reduced by either treatment. N.O tended to normalize the level of LDH, GSH and SOD. However, its effect to restore LPX was only seen 24 h after reperfusion. Moreover, the aforementioned parameters were nearly reinstated by TQ. On the other hand, high doses of TQ (50 and 100 mg/kg) severely reduced the GSH content, 1 h after reperfusion. These results indicate that both N.O and TQ possess gastroprotective effect against gastric lesions which may be related to the conservation of the gastric mucosal redox state.

Melatonin protects against gastric ulceration and increases the efficacy of ranitidine and omeprazole in reducing gastric damage

The antiulcer effect of melatonin on gastric lesions caused by restraint-cold stress was studied with the intent of determining the mechanism of action of this agent. Melatonin dose-dependently prevented restraint-cold stress-induced gastric damage with around 90% inhibition at a dose of 60 mg/kg BW. When compared with already marketed antiulcer drugs such as ranitidine and omeprazole, melatonin was found to be more effective than ranitidine but less effective than omeprazole in preventing stress ulcer. As stress-induced gastric lesions are mainly caused by oxidative damage because of hydroxyl radicals (*OH), the effect of melatonin in scavenging the.OH generated during stress conditions in vivo as well as in an in vitro model system were studied. The results indicate that melatonin caused an 88% reduction of endogenous *OH during stress in vivo, an observation confirmed in an established in vitro system. Furthermore, a decrease in the activity of gastric peroxidase (GPO) and an increase in the gastric mitochondrial superoxide dismutase (Mn-SOD) activity because of restraint-cold stress was attenuated by melatonin pretreatment indicating that the indole possibly exerts its gastroprotective effects through its direct as well as indirect antioxidant activities. Moreover, in separate experiments, cotreatment of rats with melatonin and ranitidine or omeprazole was found to protect against stress ulceration in doses at which either of these alone could not protect the stomach. The findings raise the possibility of melatonin being considered as an effective gastroprotective agent individually or as a cotreatment with either ranitidine and omeprazole.

Role of prostaglandins, nitric oxide, sensory nerves and gastrin in acceleration of ulcer healing by melatonin and its precursor, L-tryptophan

Melatonin, a major hormone of pineal gland, was recently shown to attenuate acute gastric lesions induced by strong irritants because of the scavenging of free radicals but its role in ulcer healing has been little investigated. In this study we compared the effects of intragastric (i.g.) administration of melatonin and its precursor, L-tryptophan, with or without concurrent treatment with luzindole, a selective antagonist of melatonin MT2 receptors, on healing of chronic gastric ulcers induced by serosal application of acetic acid (ulcer area 28 mm2). The involvement of endogenous prostaglandins (PG), nitric oxide (NO) and sensory nerves in ulcer healing action of melatonin and L-tryptophan was studied in rats treated with indomethacin and NG-nitro-L-arginine (L-NNA) to suppress, respectively, cyclo-oxygenases (COX) and NO synthases or in those with functionally deactivated sensory nerves with capsaicin. The influence of melatonin on gastric secretion during ulcer healing was tested in separate group of rats with gastric ulcer equipped with gastric fistulas (GF). At day 8 and 15 upon the ulcer induction, the area of gastric ulcers was measured by planimetry, the mucosal blood flow (GBF) was determined by H2-gas clearance technique and gastric luminal NO2-/NO3- levels was assessed by Griess reaction. Plasma melatonin and gastrin levels were measured by specific radioimmunoassay (RIA). Biopsy mucosal samples were taken for expression of constitutive NO-synthase (cNOS) and inducible NOS (iNOS) by reverse transcriptase-polymerase chain reaction (RT-PCR). Melatonin (2.5-20 mg/kg-d i.g.) and L-tryptophan (25-100 mg/kg-d i.g.) dose-dependently accelerated ulcer healing, the dose inhibiting by 50% (ED50) of ulcer area being 10 and 115 mg/kg, respectively. This inhibitory effect of melatonin (10 mg/kg-d i.g.) and L-tryptophan (100 mg/kg-d i.g.) on ulcer healing was accompanied by a significant rise in the GBF at ulcer margin and an increase of plasma melatonin. luminal NO2-/NO3- and plasma gastrin levels. Gastric acid and pepsin outputs were significantly inhibited during the ulcer healing in melatonin-treated gastric mucosa as compared with those in vehicle-treated animals. Luzindole abolished completely the healing effects of melatonin and L-tryptophan and attenuated significantly the rise in plasma gastrin evoked by the hormone and its precursor. Indomethacin (5 mg/kg-d i.p). that blocked PG biosynthesis by 90% or L-NAME (20 mg/kg i.v), inhibitor of NOS. that suppressed luminal NO release, attenuated significantly melatonin and L-tryptophan-induced acceleration of ulcer healing and accompanying rise in GBF at ulcer margin and luminal NO release. The melatonin-induced acceleration of ulcer healing, hyperemia at ulcer margin and increase in the release of NO were enhanced when L-arginine but not D-arginine was added to L-NAME. The ulcer healing and the GBF effects of melatonin and L-tryptophan were significantly impaired in rats with capsaicin-induced denervation of sensory nerves and both, ulcer healing and the hyperemia at ulcer margin were restored in these rats by addition of exogenous CGRP to melatonin and L-tryptophan. Expression of cNOS mRNA was detected by RT-PCR in the intact gastric mucosa as well as at the edge of gastric ulcers treated with both, vehicle and melatonin, while iNOS mRNA that was undetectable in the intact gastric mucosa, appeared during ulcer healing and especially this was strongly up-regulated in the melatonin-treated gastric mucosa. We conclude that (1) exogenous melatonin and that derived from its precursor, L-tryptophan, accelerate ulcer healing probably via interaction with MT2 receptors; (2) this ulcer healing action is caused by an enhancement by melatonin of the microcirculation at the ulcer margin possibly mediated by COX-derived PG and NO because of overexpression of iNOS and (3) gastrin, which exhibits trophic activity in the gastric mucosa and calcitonin gene related peptide (CGRP), released from sensory nerves, may also contribute to the ulcer healing action of melatonin.

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

BACKGROUND

We previously demonstrated the circadian variation of water-immersion restraint stress (WRS)-induced gastric mucosal lesions in rats.

AIM

To investigate the roles of melatonin and prostaglandin in the gastric mucosa in circadian modulation of WRS.

METHODS

Fasted rats were subjected to 4-h WRS during both the diurnal and nocturnal phases of a light/dark cycle. Mucosal lesions, serum melatonin concentrations, mucosal generation of prostaglandin E2 (PGE2) and mucosal gene expressions of cyclooxygenase (COX)-1 and -2 were evaluated.

RESULTS

Lesion area after 4-h stress during the dark phase was significantly smaller than that in light-phase controls. Serum melatonin concentration in control rats during the light phase was significantly increased 4 h after WRS, but PGE2 generation was decreased by 48% as compared to that in intact mucosa before stress. In the dark phase, melatonin concentration after 4-h WRS was significantly depressed as compared with the control level at the corresponding time. PGE2 concentrations after 4-h WRS in the dark phase were not decreased compared with the control level at the corresponding time, although PGE2 level was significantly lower than that in light-phase controls. Expression of COX-1 and COX-2 mRNA was detected after exposure to stress in both the light and dark phases.

CONCLUSION

These results suggest that circadian rhythm has an important role in the formation of stress-induced gastric mucosal lesions in rats. The circadian rhythm of melatonin responses and PGE2 generation may contribute to nocturnal/diurnal rhythmicity of gastric mucosal defences between day and night.

Food intake inhibition by melatonin in goldfish (Carassius auratus)

Feeding regulation by monoamines, neuropeptides and certain hormones has been studied in fish, but a possible role of melatonin is unknown. The purpose of the present study was to investigate the effects of melatonin on food intake in goldfish. Fishes were housed in 12L:12D and injected with different doses of either melatonin or 2-iodomelatonin. Two routes of administration, intracerebroventricular and intraperitoneal injections, and two times of the daily photocycle, midday and midnight, were tested. Food intake was measured at 2, 5 and 8 h postinjection. Melatonin and its analog, 2-iodomelatonin intracerebroventricularly injected had no effect on food intake at any time. However, intraperitoneal injections of both indoleamines significantly reduced food intake at different postinjection times. The inhibitory effect of melatonin was blocked by intraperitoneal administration of its antagonist, luzindole. These results demonstrate the in vivo efficiency of luzindole as melatonin antagonist, and thus provide a useful experimental tool to investigate melatonin functions. In conclusion, both melatonin and its agonist 2-iodomelatonin administered peripherally, inhibit food intake in goldfish, and this inhibitory effect appears to be mediated via luzindole-sensitive melatonin receptors. Our results strongly suggest that melatonin is involved in the peripheral satiety mechanisms in goldfish.

Melatonin attenuates acute renal failure and oxidative stress induced by mercuric chloride in rats

We evaluated the effect of melatonin (Mel), a potent scavenger of reactive oxygen species, in the course of HgCl(2)-induced acute renal failure. Rats received by gastric gavage 1 mg/kg of Mel (n = 21) or vehicle (n = 21), 30 min before the subcutaneous injection of HgCl(2) (2.5 mg/kg). Rats were killed at 24, 48, and 72 h, and plasma creatinine (S(cr)), renal histology, proliferative activity, apoptosis, and superoxide-producing cells were studied. We also determined the renal content of malondialdehyde (MDA) and glutathione (GSH) and the activities of glutathione peroxidase and catalase. Mel pretreatment (Mel plasma levels of 3.40 +/- 3.15 microgram/ml at the time of HgCl(2) injection) prevented the increment in S(cr) and reduced tubular necrosis from 41.0 +/- 10.5 to 4.2 +/- 5.1% of proximal tubules (P < 0.01). Apoptosis and postnecrotic proliferative activity were twice more intense in the group untreated with Mel. Increment in renal content of MDA and decrease in GSH resulting from HgCl(2) toxicity were prevented by Mel. Mel also induced an important reduction in superoxide-positive cells. In contrast to the beneficial effects of pretreatment with Mel, the administration of Mel in conjunction with HgCl(2) had no effect on the oxidative damage and did not prevent nephrotoxicity. We conclude that the beneficial effects of pharmacological doses of Mel are due to its antioxidant properties.

Role of gastric acid secretion in progression of acute gastric erosions induced by ischemia-reperfusion into gastric ulcers

Ischemia followed by reperfusion is known to produce gastric lesions due to oxidative stress, but the role of gastric H(+) secretion in the formation of this mucosal injury remains unknown. We studied alterations in gastric acid secretion and gastric histamine content, as well as the expression of histidine-decarboxylase and interleukin-1beta during the mucosal recovery from ischemia-reperfusion erosions. Gastric secretion was studied in rats (series A) with gastric fistula before, during and after the ischemia induced by clamping of celiac artery for 0.5 h followed by reperfusion in animals pretreated with vehicle (saline), omeprazole, a proton pump inhibitor, or ranitidine, a histamine (H(2)) receptor antagonist. In series B, the animals were submitted to 0.5 h of ischemia followed by 1 h of reperfusion and then anesthetized at 0, 3, 12 and 24 h or 3, 5, 10 or 15 days after the end of ischemia-reperfusion to determine gastric blood flow by H(2)-gas clearance technique, area of gastric lesions, plasma gastrin and interleukin-1beta levels, histamine content by radioimmunoassay (RIA) and expression of histidine-decarboxylase and interleukin-1beta mRNA by reverse transcription polymerase chain reaction. Clamping of celiac artery caused cessation of gastric blood flow and almost complete suppression of basal gastric acid secretion (series A) that returned gradually to the control value at day 3 after ischemia-reperfusion, accompanied by the rise in plasma gastrin levels, pronounced expression of histidine-decarboxylase mRNA and increased mucosal histamine content. Ischemia, followed by 1 h of reperfusion, produced gastric erosions (series B) that reached maximum at 12 h, but then declined at 24 h. These erosions progressed at day 3 into deeper ulcers whose area declined progressively within the next 5-15 days. The gastric blood ceased to flow (series B) during 30 min of clamping and was reduced throughout the period of healing of acute erosions, being accompanied by a gradual rise in mucosal interleukin-1beta mRNA content and in plasma interleukin-1beta levels. Treatment with omeprazole or ranitidine, which completely suppressed gastric acid secretion and significantly raised plasma gastrin level, greatly reduced the formation of erosive lesions preventing the progression of these lesions to chronic gastric ulcers, and this was accompanied by the rise in gastric blood flow and plasma gastrin levels and the significant attenuation of plasma interleukin-1beta levels. The ranitidine and omeprazole-induced suppression of ischemia-reperfusion erosions were abolished by the instillation of exogenous 0.2 N HCl into the stomach of these rats. The histidine-decarboxylase was faintly expressed in the intact gastric mucosa, but strongly upregulated during mucosal recovery from the damage induced by ischemia-reperfusion. We conclude that following ischemia-reperfusion: (1) gastric acid secretion, gastric microcirculation and histamine production markedly decline, while interleukin-1beta release significantly increases, probably playing an important role in the progression of acute lesions into chronic gastric ulcerations; (2) the suppression of gastric acid secretion by omeprazole and ranitidine, that induces hypergastrinemia, prevents the progression of gastric erosions into ulcers; and (3) the addition of exogenous acid restores the progression of the acute lesions into gastric ulcers, indicating that gastric acid plays a key role in ulcerogenesis induced by ischemia-reperfusion.

Reduction of gastrointestinal toxicity of NSAIDs via molecular modifications leading to antioxidant anti-inflammatory drugs

Reactive oxygen species and free radical reactions are related to several pathologic conditions including inflammation and gastric ulceration. The latter is the major undesired side-effect of almost all NSAIDs. Since this effect of NSAIDs is greatly influenced not only by the type of cyclooxygenase which is inhibited but also by the acidic nature of the molecule, we considered it interesting to modify their structure in such a way that it would lead to an antioxidant, neutral molecule or a molecule with greatly reduced acidic character. Thus, we synthesized amide derivatives of four well-known NSAIDs, i.e. diclofenac acid, tolfenamic acid, ibuprofen and indomethacin, with cysteamine, a well-known antioxidant. The synthesized derivatives, with demonstrated good anti-inflammatory and antioxidant activities, showed very significant reduction of ulcerogenicity in the investigation of gastrointestinal (GI) toxicity. As indices of ulcerogenic toxicity in rats, we used the mortality (%), the incidence of GI ulcers (%), body weight reduction (g/100 g BW) and the incidence of melena. All amide derivatives of the NSAIDs with cysteamine were almost non-toxic in the GI tract, under our experimental conditions, in contrast to their parent NSAIDs. These results are attributed to the acquired antioxidant activity as well as to the reduction of acidic character compared with the parent compounds. Therefore, it can be concluded that the combination of these two properties, anti-inflammatory and antioxidant activity, with a simultaneous drastic reduction of acidic character, may lead to the development of novel, useful anti-inflammatory and cytoprotective pharmacomolecules, with potentially important therapeutic applications.

Circadian variation of portal, arterial and venous blood levels of melatonin in pigs and its relationship to food intake and sleep

Circadian levels of melatonin were determined in the hepatic portal vein, cranial vena cava, and the lower aorta of ten juvenile pigs. Blood was sampled every hour for a total of 24 hr via temporary cannulas introduced into blood vessels under anesthesia. No peak levels of melatonin were found in the mid-scotophase, but hepatic portal concentrations peaked at 06.00 hr. Overall levels of melatonin were highest in the hepatic portal vein (range 35-65 pg/mL), followed by an artery (range 30-55 pg/mL) and the vena cava (range 25-35 pg/mL). Levels of melatonin exhibit strong variation between individual pigs, but generally the average levels from all three sources follow each other's time course. However, on occasion, melatonin levels in the hepatic portal vein varied independently from the levels in the vena cava. Large portal peaks were usually preceded by a feeding period and were associated with a subsequent period of sleep. The data indicate that: 1) there is no clear circadian rhythm of melatonin in the peripheral blood of pigs, 2) relatively little melatonin is metabolized during the first liver passage, 3) food intake may elevate melatonin levels in the hepatic portal vein, and 4) increased levels of melatonin originated in the gastrointestinal tract may induce sleep.

Melatonin concentrations in the luminal fluid, mucosa, and muscularis of the bovine and porcine gastrointestinal tract

Melatonin concentrations were measured in serum, luminal fluid, and tissues of the mucosa and muscularis of the entire bovine and porcine gastrointestinal tract (GIT). In both species, GIT levels profoundly exceeded serum levels. In pigs, melatonin was lowest in the luminal fluid and highest in the mucosa. No difference was found in various layers of bovine GIT. Compared to pigs, cows had higher melatonin levels in the stomach and ileum, but lower in the cecum and colon. There was no difference in melatonin levels between anterior and posterior segments of bovine GIT, whereas pigs exhibited several fold higher concentration of melatonin in the posterior segment (cecum and colon). Conversely, melatonin values in the anterior segment were significantly higher in cows, but in the posterior segments porcine values were higher. In cows, concentrations in the mucosa correlated with levels in the muscularis. Melatonin levels in the mucosa and muscularis were higher in the rumen and reticulum than in the omasum and abomasum. The species-specific levels and a distinct distribution of melatonin in the layers of the digestive tube indicates that this indole may be involved in the modulation of gastrointestinal function of monogastric as well as polygastric ungulates, albeit in a different capacity.

Protective role of melatonin and the pineal gland in modulating water immersion restraint stress ulcer in rats

We investigated the protective effect of melatonin on stress-induced gastric lesions in rats. Fasted rats were subjected to water immersion restraint stress for 4 h and the percentage of corpus mucosa containing hemorrhagic lesions was determined. Thirty minutes before restraint stress, melatonin or vehicle was administered i.p. In another experiment, pinealectomy was performed 1 week before water immersion restraint stress. Administration of melatonin at 1 and 5 mg/kg significantly decreased gastric lesions by 46 and 74%, respectively. In contrast, pinealectomy significantly enlarged the lesion area, although this effect was counteracted by melatonin at a dose of 1 mg/kg i.p. However, this protective effect of melatonin was abolished by i.p. pretreatment with indomethacin at 5 mg/kg. These results suggest that melatonin has gastroprotective properties against stress-induced gastric injury in rats and that the pineal gland contributes to gastric protection via prostaglandin-dependent mechanisms.

Alcoholism abolishes the effects of melatonin on growth hormone secretion in humans

Chronic alcohol consumption profoundly affects hypothalamic-pituitary function. The present study was performed in order to establish whether alcoholism modifies the effects of melatonin (MEL) on the neuroendocrine control of growth hormone (GH) secretion. For this purpose, the effects of oral administration of 12 mg MEL or placebo on basal and hypoglycemia-stimulated GH secretion were tested in nine (40-52-year-old) alcoholic men after 10-31 days of abstinence and in nine age- and weight-matched normal controls. Hypoglycemia was induced with an intravenous bolus injection of 0.15 IU/kg body weight of insulin. MEL but not placebo administration induced a small, but significant increase in basal GH secretion in the normal controls. In contrast, neither MEL nor placebo treatment significantly changed the basal serum GH levels in alcoholic men. Both groups showed a similar hypoglycemic pattern after insulin administration. The GH response to insulin-induced hypoglycemia was significantly lower in alcoholic than in normal subjects. MEL administration significantly reduced hypoglycemia-induced GH rise in the normal controls, but not in alcoholic patients. These data show that alcoholism not only reduces the GH response to insulin-induced hypoglycemia, but also abolishes MEL actions on basal and hypoglycemia-stimulated GH secretion.

Relationship between melatonin levels in plasma and gastrointestinal tissues and the incidence and severity of gastric ulcers in pigs

Four weeks of administration of melatonin mixed in the diet (5 mg/kg of food) significantly reduced the incidence of gastric ulcers in young pigs. In control and melatonin supplemented animals, significantly higher levels of melatonin were found in the stomach tissues as compared to jejunum, ileum, or colon. Pigs with the most severe ulcers exhibited significantly lower concentrations of melatonin in their stomach tissue and the blood plasma. Pigs fed coarsely ground diet exhibited higher tissue levels of melatonin in the stomach than animals fed a finely ground diet. Coarse diet was also associated with a lower score of gastric ulcers. No relationship between tissue levels of melatonin and the severity of gastric ulcers was found in other segments of the gastrointestinal tract. In the second experiment we determined that there was no significant difference between the gastro-protective effects of 2.5, 5.0, and 10.0 mg of melatonin mixed per 1 kg of food. A coarsely ground diet is hypothesized to have a gastro-protective effect by stimulating the production of melatonin in the stomach tissues. Dietary supplementation of food with melatonin, at threshold levels perhaps lower than 2.5 mg/kg/feed, may significantly reduce the incidence of gastric ulcers in pigs.