Chronic Melatonin Administration Research Articles

Chronic melatonin treatment reduces the age‐dependent inflammatory process in senescence‐accelerated mice

It is hypothesized that, besides increased free radical production, aging is a process also related to inflammation. Thus, female and male senescence-accelerated (SAMP8) and senescence-resistant (SAMR1) mice of 5 and 10 months of age were studied to assess this hypothesis. Plasma from these mice was processed to determine nitric oxide (NO), and pro-inflammatory [interleukin (IL)-1beta, IL-2, interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and granulocyte-macrophage colony-stimulating factor] and anti-inflammatory (IL-4, IL-5 and IL-10) cytokines. The results show the presence of an age-dependent increase in IFN-gamma and TNF-alpha and a reduction in IL-2 levels, with minor changes in the remaining cytokines. Moreover, age was associated with a significant increase in NO levels. Chronic melatonin administration between 1 and 10 months of age counteracted the age-dependent production of pro-inflammatory cytokines and NO, reducing them to the levels found at 5 months of age. Melatonin also reduced the levels of the anti-inflammatory cytokines. The results of this study suggest the existence of an inflammatory process during aging and further support that melatonin behaves as an essential molecule against aging, for its anti-inflammatory properties together with its antioxidative role reported elsewhere.

Chronic melatonin treatment prevents age-dependent cardiac mitochondrial dysfunction in senescence-accelerated mice

Heart mitochondria from female senescence-accelerated (SAMP8) and senescence-resistant (SAMR1) mice of 5 or 10 months of age, were studied. Mitochondrial oxidative stress was determined by measuring the levels of lipid peroxidation, glutathione and glutathione disulfide and glutathione peroxidase and reductase activities. Mitochondrial function was assessed by measuring the activity of the respiratory chain complexes and ATP content. The results show that the age-dependent mitochondrial oxidative damage in the heart of SAMP8 mice was accompanied by a reduction in the electron transport chain complex activities and in ATP levels. Chronic melatonin administration between 1 and 10 months of age normalized the redox and the bioenergetic status of the mitochondria and increased ATP levels. The results support the presence of significant mitochondrial oxidative stress in SAM mice at 10 months of age, and they suggest a beneficial effect of chronic pharmacological intervention with melatonin, which reduces the deteriorative and functional oxidative changes in cardiac mitochondria with age.

The influence of long-term melatonin administration on basic physiological and metabolic variables of young Wistar:Han rats

The question of effects of long-term melatonin (MEL) administration have not yet been explained sufficiently, especially its metabolic consequences in young persons and animals. The aim of the present study was to analyze the effects of MEL given during prolonged time (for 3 months) and chronically (for 6 months) at the dose of 4 µg/mL of tap water, on the selected metabolic and hormonal parameters in young female and male Wistar:Han (WH) rats. The weights of selected organs, tissues, body weight gains and food and water intake were registered. Six weeks aged rats were adapted to standard housing conditions and light regimen L:D=12:12 h, fed standard laboratory diet and drank tap water (controls) or MEL solution ad libitum; finally they were sacrificed after overnight fasting. Prolonged MEL administration decreased serum glucose concentration and increased triacylglycerol and malondialdehyde concentration/content in the liver in females. In males MEL increased concentrations of serum phospholipids, corticosterone and liver malondialdehyde. MEL treatment reduced the body weight in both sexes and weight of epididymal fat in males, without any alterations of food and water intake. Chronic MEL administration reduced serum glucose concentration and increased concentration/content of glycogen, triacylglycerol and cholesterol in the liver and glycogen concentration/content in heart muscle in males. In females, the significant rise of serum corticosterone concentration and liver malondialdehyde content was recorded. MEL significantly increased liver weight and decreased thymus weight in males. MEL administration increased temporarily water intake in males, body and epididymal fat weights were similar to that in controls. Body weight of MEL drinking females was reduced in the 1st half of experiment only; the food and water intake did not differ from control group. The response in WH rats on MEL was more prominent as in the Sprague-Dawley strain (our previous studies). Male rats were generally more affected, probably due to higher daily and total consumption of melatonin.

Reversal of Diazepam Tolerance and Withdrawal-induced Hyper Locomotor Activity and Anxiety by Melatonin in Mice

Background & Objectives: Earlier studies from our laboratory have confirmed the role of melatonin in the reversal of morphine tolerance and dependence in mice. The present study was performed to explore the possible involvement of melatonin in the reversal of diazepam tolerance and dependence in mice. Methods: Diazepam (20 mg/kg/day, i.p.) was administered chronically on days 1–21. Mirrored-chamber was used to evaluate the anxiogenic reaction in mice due to withdrawal. Melatonin (2.5 or 5mg/kg; i.p.) was administered daily prior to diazepam administration for 21 days. Results: Chronic administration of diazepam (20 mg/kg/day, i.p.) on days 1–21 and its withdrawal produced anxiogenic reaction in mice as assessed in the mirrored-chamber test. Daily administration of melatonin (2.5 or 5 mg/kg, i.p.) prior to diazepam for 21 days prevented withdrawal-induced anxiety in mice. However, acute administration of a single dose of melatonin (2.5 or 5 mg/kg), to animals withdrawn from diazepam, i.e. on the 22nd day, did not prevent withdrawal-induced anxiety. Diazepam withdrawal also induced a significant increase in the locomotor activity of mice indicating an anxiogenic response. Daily administration of melatonin (2.5 or 5 mg/kg) prior to diazepam for 21 days also prevented withdrawal- induced increased locomotor activity. Both acute and chronic administration of melatonin (2.5 and 5 mg/kg) exhibited a significant protection against diazepam withdrawal-induced anxiety and hyper locomotor activity in mice. Conclusions: The result suggests the protective effect of this safe drug, melatonin, in the management of diazepam withdrawal reactions. doi: 10.5214/ans.0972.7531.2006.130202

ACTH cells of pituitary pars distalis of viscacha ( Lagostomus maximus maximus): Immunohistochemical study in relation to season, sex, and growth

Corticotrope or ACTH cells were immunohistochemically identified in the pituitary pars distalis (PD) of viscacha by using the polyclonal antiserum against ACTH (1–24). The localization, distribution, shape, percentage immunopositive area, and major cellular and nuclear diameters of these cells were analyzed by image analysis in adult male viscachas captured in their natural habitat during the year and after the chronic administration of melatonin. The same parameters were analyzed in immature male and adult female viscachas. ACTH cells in adult males were mainly localized in the dorsal and cephalic regions of PD. They were isolated, forming small groups and in contact with follicular structures and blood vessels. They were pleomorphic, with some of them being polygonal, oval, round, and others, stellate with cytoplasmic extensions. The percentage immunopositive area and the major cellular diameter showed seasonal variations with lower values during June and July (early winter). A decrease in the percentage immunopositive area was observed after the administration of melatonin in adult male animals. ACTH cells of immature animals differed from the adults’ cells in their distribution, shape, pattern of immunolabeling, and percentage immunopositive area. These parameters in adult females did not vary in relation to adult males at the same time of the year although. However, the cells in females were smaller in size during April–May. In pregnant viscachas (June–July), these parameters did not show significant differences with the results of non-pregnant females (April–May). This suggests that the environmental stressors do not exert the same influence on the hypothalamo–pituitary–adrenal axis in adult male and female viscachas, probably due to the physiological changes caused by pregnancy. Our results in adult male viscacha demonstrate that the morphology of the ACTH cells varies according to the different seasonal conditions, thus participating in the adaptation process of this rodent to the environment. The elevated levels of melatonin during winter months might inhibit the synthesis of ACTH, probably when affecting some secretagogue of this pituitary hormone. Moreover, the morphological variations observed between adult and immature male viscachas and between both sexes suggest that the steroid gonadal hormones might act on the development and activity of ACTH cells.

Sex-Dependent Effect of Melatonin on Systemic Erythematosus Lupus Developed in Mrl/Mpj-Faslpr Mice: It Ameliorates the Disease Course in Females, whereas It Exacerbates It in Males

In this study, the effect of chronic administration of melatonin on MRL/MpJ-Fas(lpr) mice has been studied. These mice spontaneously develop an autoimmune disease that has many features resembling human systemic lupus erythematosus. In fact, histological studies showed that all female mice and most male mice exhibited glomerular abnormalities, arteritic lesions, and cellular interstitial inflammatory infiltrate ranging from mild to severe patterns. Treatment with melatonin improved the histological pattern in females and worsened it in males. Moreover, female mice treated with melatonin showed a diminution of titers of total serum IgG, IgM, and anti-double-stranded DNA and anti-CII autoantibodies; a decrease in proinflammatory cytokines (IL-2, IL-6, interferon-gamma, TNF-alpha, and IL-1beta), an increase in antiinflammatory cytokines (IL-10), and a decrease in nitrite/nitrate. In male mice, treatment with melatonin exhibited the opposite effect, worsening all the immunological parameters with an elevation of titers of autoantibodies and a prevalence of proinflammatory vs. antiinflammatory cytokines. Similar results were obtained when lymphocytes from spleen and lymph nodes were cultured. Again, melatonin treatment in females decreased proinflammatory cytokines and increased antiinflammatory cytokines produced by lymphocytes; in males, the effect was the opposite. These findings suggest that melatonin action in MRL/MpJ-Fas(lpr) mice is gender dependent, probably through modulation and inhibition of sex hormones.

Effect of light/dark cycle alteration on morphine-induced conditioned place preference

The influence of acute and chronic light/dark cycle alteration on morphine-induced conditioned place preference was evaluated in mice. In chronic experiments, morphine (1-10 and 2.5-10 mg/kg) induced conditioned place preference in animals maintained on 12/12 and 6/18 light/dark cycles, respectively. In mice maintained on 18/6 light/dark cycle, however, morphine produced conditioned place preference only by the dose of 10 mg/kg. This latter effect was abolished by chronic daily administration of melatonin (10, 20 mg/kg). Moreover, our data showed that both abrupt increase and decrease in photoperiod on the day before testing reduced the ability of morphine to produce place conditioning. A single melatonin (10 mg/kg) injection reversed the attenuating effect of a 6-h delay in the dark cycle on morphine conditioned place preference.

Melatonin improves learning and memory performances impaired by hyperhomocysteinemia in rats

Oxidative stress has been proposed as a possible mechanism underlying many neurodegenerative diseases associated with hyperhomocysteinemia. In the present study, we investigated the possible link between oxidative stress, expression of neural cell adhesion molecules and spatial learning deficits induced by chronic hyperhomocysteinemia. Furthermore, the effectiveness of antioxidant melatonin against homocysteine neurotoxicity was also examined. Male Wistar rats were treated with either saline or methionine to induce hyperhomocysteinemia and half of methionine-treated rats administered daily melatonin in a dose of 10 mg/kg. We observed that chronic administration of melatonin significantly reduced the lipid peroxidation and restored the decreased glutathione levels induced by chronic hyperhomocysteinemia. Chronic hyperhomocysteinemia significantly impaired learning and memory performance in the passive avoidance test and Morris water maze task. We also found that these cognitive deficits were reversed by chronic treatment with antioxidant melatonin. Furthermore, melatonin administration was able to modulate the expression pattern of neural cell adhesion molecules in hippocampus. The results provide evidence that homocysteine induces long-lasting behavioral deficits, which are possibly caused by oxygen reactive species generation, and by changing in synaptic plasticity and also suggest that melatonin treatment has the ability to prevent nervous system against homocysteine toxicity.

Study on pre-treatment of melatonin against radiation-induced oxidative stress in mice

Antioxidants are part of the primary cellular defense against radiation-generated free radicals. Reports on low-level chronic administration of melatonin with its antiradiation influence are scanty. Although compelling logic suggests that melatonin may be effective for a variety of disorders, the mode and optimal dose of melatonin are still not clear. Most studies have used doses of supraphysiological blood levels. Present investigation reported that pre-treatment with the lower concentration of melatonin (0.1 mg/kg b.w./day) for 15 consecutive days affords potential protective effect against radiation-induced oxidative stress and mortality in mice. Radiation-induced augmentation in the levels of lipid peroxidation, glutathione disulphide (GSSG) and acid phosphatase was significantly ameliorated by melatonin pre-treatment. Radiation-induced depletion in the level of reduced glutathione (GSH), as well as glutathione peroxidase (GSH-Px) and alkaline phosphatase activities, was inhibited significantly by melatonin administration. Regression analysis of survival data yielded LD 50/30 as 7.16 and 11Gy for control (irradiation alone) and experimental (melatonin-treated irradiated) mice, respectively, and produced a dose reduction factor (DRF), 1.53. Radiation-induced deficit in the body and organ weight also got inhibited significantly in the melatonin pre-treated mice. The findings support property of melatonin as a free radical scavenger and singlet oxygen quencher and indicate the antioxidative properties of melatonin against the gamma radiation.

Effect of Low-dose Chronic Melatonin Administration on Metabolic and Hormonal Variables of Young Laboratory Rats

Markova M., E. Adamekova, B. Bojkova, P. Kubatka, M. Kassayova, E. Ahlersova, I. Ahlers: Effect of Low-dose Chronic Melatonin Administration on Metabolic and Hormonal Variables in Young Laboratory Rats. Acta Vet. Brno 2004, 73: 445-453. The introduction of melatonin (MEL) as a drug remains open due to insufficient data about the effects of its long-term administration on metabolism. We explored effects of MEL given for 26 weeks at low doses, 4 µg/ml of tap water, on selected metabolic and hormonal indices in young female and male Sprague-Dawley rats. Male and female rats aged 5 weeks were adapted to standard housing conditions and artificial light regimen L:D = 12:12 h. The animals were fed standard laboratory diet and drank tap water (controls) or MEL solution ad libitum. Body weight gain, food and water intake was regularly recorded. Oral glucose tolerance tests (OGTTs) were carried out before and 24 weeks after MEL administration. At the end of the experiment following an overnight fast the animals were sacrificed, selected organs and tissues were weighed, selected metabolic indices and hormone concentrations were determined in the serum, liver, heart muscle and bone marrow (femur). Chronic MEL administration increased in females serum corticosterone concentration, decreased glycogen concentration in the liver and heart muscle, increased triacylglycerol concentration in the bone marrow. An increased absolute weight of periovarial fat and body weight gain were found in last 5 weeks of the experiment. In males, MEL decreased insulin concentration in the serum and body weight gain from week 2 to week 17 of its administration; it decreased relative liver weight in males and females. MEL did not alter food or water intake in both sexes. MEL treatment decreased glucose tolerance (i.e. reduced area under curve values in OGTTs) in males and prolonged the return of afterload glycemia values to initial level in females. Alterations of carbohydrate metabolism regulation and of body weigth gain were found in both sexes of young rats after long term melatonin administration.

Prophylactic action of melatonin against cyclophosphamide-induced oxidative stress in mice.

The present study investigated the prophylactic influence of melatonin against cyclophosphamide-induced oxidative stress in mouse tissues. Lipid peroxidation, reduced glutathione (GSH), glutathione disulphide (GSSG), glutathione peroxidase (GSH-Px) and serum phosphatase levels were analyzed in brain, spleen liver, lungs, kidney and testes. Fifteen days oral administration with melatonin (0.1 mg/kg bw per day) before treatment checked the augmentation of the level of lipid peroxidation, blood GSSG and acid phosphatase caused by an acute treatment with a radiomimetic drug, cyclophosphamide (75 mg/kg bw). Cyclophosphamide-induced depletion in the level of GSH, GSH-Px and alkaline phosphatase was made up statistically significant by chronic melatonin administration given orally. The results indicate the antioxidative properties of melatonin resulting into its prophylactic property against the cyclophosphamide-induced biochemical alterations. The finding support the idea that melatonin is a potent free-radical scavenger and antioxidant.

Melatonin-induced reduction in age-related accumulation of oxidative damage in mice.

The ever-increasing understanding of oxygen radical-linked diseases, including the biological process of aging, has stimulated general interest in modulating these biological events. Melatonin has been reported to have antioxidant properties in addition to its known hormonal activities. However, reports on low-level chronic administration with its anti-aging influence are scanty. Hence, the present study was aimed to investigate the influence of low-dose chronic administration (0.10 mg/kg body weight/day for 3 months) of melatonin against age-induced oxidative stress in mice tissues, namely brain, liver, spleen and kidney. Sixteen-month-old mice were supplemented with melatonin (0.10 mg/kg body weight/day) for three months and then autopsied (at the age of 19 months) for the biochemical estimation of lipid peroxidation, reduced glutathione (GSH), glutathione disulphide (GSSG), glutathione peroxidase (GSH-Px) and serum phosphatase activity. Results indicate that age-induced augmentation (compared to 6-8-week-old mice) in the level of lipid peroxidation, GSSG and acid phosphatase is significantly (P < 0.001) ameliorated in melatonin-treated mice. Age-induced decline in the level of GSH, GSH-Px and alkaline phosphatase activity is inhibited significantly by the long-term administration of melatonin. The findings indicate that low-dose chronic administration of melatonin acts as a free radical scavenger and anti-aging agent.

Melatonin induces tyrosine hydroxylase mRNA expression in the ventral mesencephalon but not in the hypothalamus.

We have evaluated the effect of chronic administration of melatonin in terms of mRNA expression for tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, and in the terms of dopamine (DA) transporter (DAT) by means of in situ hybridization. Experimental rats received daily late afternoon injections of 1.5 mg/kg melatonin for 30 days and analysis were performed in the ventral mesencephalon including the substantia nigra (SN) and ventral tegmental area (VTA), and hypothalamus. In the ventral mesencephalon, melatonin treatment significantly induced TH mRNA levels in individual dopaminergic neurons in SN and VTA. In contrast, DAT mRNA levels remained at control levels. Striatal synaptosomal DA uptake was not modified by melatonin treatment as compared with controls. Analysis of glutamic acid decarboxylase (GAD) mRNA in SN, the biosynthetic enzyme for GABAergic neurons, revealed no effect of melatonin treatment on mRNA levels for this marker. In the hypothalamus, we performed mRNA quantitation for TH in arcuate nucleus (Arc) and supraoptic nucleus (SO). Melatonin treatment failed to alter mRNA levels in either area. We detected weak but significant mRNA levels for DAT in Arc, SO, zona incerta (ZI) and periventricular hypothalamic nucleus (Pe). However, because of the low levels of mRNA in hypothalamic areas we were unable to perform a reliable measurement of DAT mRNA levels in response to melatonin treatment. We conclude that melatonin administration, that combines antioxidant capacity and a tissue-specific TH inducing effect, may be useful as a pharmacological agent to protect dopaminergic neurons from degeneration.

Possible antioxidant mechanism in melatonin reversal of aging and chronic ethanol-induced amnesia in plus-maze and passive avoidance memory tasks

Cognitive dysfunction is one of the most striking age-related impairments seen in human beings and animals. This impairment probably is due to the vulnerability of the brain cells to increased oxidative stress during aging process. Pineal hormone melatonin is reported to be an endogenous antioxidant, whose peak plasma level declines during aging and in Alzheimer’s disease (AD). Present experiments were performed to study the possible effect of exogenously administered melatonin on cognitive performance of young, aged, or ethanol-intoxicated mice (an animal model for AD) using one trial step-down type of passive avoidance and elevated plus-maze task. Aged or chronic ethanol-treated mice showed poor retention of memory in step-down passive avoidance and in elevated plus-maze task. Chronic administration of melatonin (0.1–10 mg/kg, sc) for 30 d or its coadministration with ethanol (15% W/V, 2 g/kg perorally) for 24 d significantly reversed the age-induced or chronic ethanol-induced retention deficits in both the test paradigms. However, in both the memory paradigms chronic administration of melatonin failed to modulate the retention performance of young mice. Chronic administration of melatonin (0.1–10 mg/kg) for 30 d also reversed age-associated decline in forebrain total glutathione (tGSH) level. Chronic ethanol administration to young mice produced decline in forebrain tGSH level and enhanced brain lipid peroxidation, which was significantly reversed by coadministration of melatonin (10 mg/kg). The results of this study showed chronic melatonin treatment reverses cognitive deficits in aged and ethanol-intoxicated mice, which is associated with its antioxidant property.

Melatonin enhances Th2 cell mediated immune responses: lack of sensitivity to reversal by naltrexone or benzodiazepine receptor antagonists.

Chronic administration of melatonin for 5 days to antigen-primed mice increased the production of pro-inflammatory cytokine IL-10 but decreased the secretion of anti-inflammatory cytokine TNF-alpha. These results further confirm that melatonin activates Th2-like immune response. Whether melatonin-mediated Th2 response is dependent on opioid or central and peripheral benzodiazepine receptors was also examined. Hence, melatonin was administered to antigen-sensitised mice with either naltrexone (a mu opioid receptor antagonist) or flumazenil (a central benzodiazepine receptor antagonist) or PK11195 (a peripheral benzoidiazepine receptor antagonist). No significant difference in melatonin-induced Th2 cell response was observed by naltrexone, flumazenil or PK11195 treatment. These findings suggest that the Th2 cell response induced by melatonin in antigen sensitised mice neither dependent on endogenous opioid system nor is modulated through the central or peripheral benzodiazepine receptors.

Melatonin stimulates thyroid-stimulating hormone accumulation in the thyrotropes of the rat pars tuberalis.

We have reported that the unique thyroid-stimulating hormone-immunoreactive cells (TSH cells) in the intact adult and fetal rat pars tuberalis (PT) show an intense spot-like TSH immunoreaction in the perinuclear region. The present study was designed to investigate the relationship between melatonin and these unique TSH cells. We classified TSH cells in the PT (PT-TSH cells), on the basis of immunoreactivity, into spot-like stained cells (SC) and whole cytoplasm stained cells (WC), and estimated the proportion of each TSH cell type to total cells in the experimental rats by morphometry. Chronic administration of melatonin to control rats leads to an increase of WC in number but a decrease of SC. On the other hand, the intensity of TSH immunoreactivity and the number of rat PT-TSH cells significantly decreased after pinealectomy and recovered by melatonin administration. Radioimmunoassay showed that melatonin treatment increased the TSH content in the PT. Moreover, electron microscopy showed that the number of TSH secretory granules in the PT-TSH cells increased in the melatonin-replaced rats. These results demonstrated that melatonin stimulates the accumulation of TSH in the rat PT-TSH cells via secretory granule formation and suggest that melatonin regulates TSH release from PT-TSH cells.

Sex differences in forced-swim and open-field test behaviours after chronic administration of melatonin

The effects of melatonin administered chronically on forced-swim test and open-field test behaviours were examined in male and female rats. The forced-swim test has been shown to be sensitive to all major classes of antidepressants and evidence indicates that melatonin possesses putative antidepressive properties. Male and female Long-Evans rats received either a regimen of chronic administration of melatonin or the control condition for 14 days via the drinking water. On day 15, each animal was individually introduced into a swim chamber, and was scored for 15 min on the duration of swimming, struggling, and immobility. After 24 h, each animal was again tested in the forced-swim test for 10 min. On day 18, all animals were tested in the open-field test apparatus for 5 min. Results revealed that females consistently showed higher activity levels than males in the forced-swim and open-field tests. Melatonin significantly increased struggling in males on day 15, but failed to do so in females. Also, whereas melatonin-treated females showed higher levels of behavioural immobility during their first exposure to the forced-swim test, this effect was prevented upon a second exposure. In both males and females, melatonin decreased swimming in the forced-swim test while increasing open-field ambulatory behaviour. Therefore, it is unlikely that melatonin's mechanism of action is a general inhibitory effect on motor activity. Taken together, the results suggest that the effects of melatonin treatment on forced-swim test behaviours are sex- and test-dependent.

Serum cholesterol and lipid peroxidation are decreased by melatonin in diet-induced hypercholesterolemic rats.

The purpose of this study was to investigate the effect of melatonin, at pharmacological doses, on serum lipids of rats fed with a hypercholesterolemic diet. Therefore, different groups of animals were fed with either the regular Sanders Chow diet or a diet enriched in cholesterol. Moreover, animals were treated with or without melatonin in the drinking water for 3 months. We show that melatonin treatment did not affect the levels of cholesterol or triglycerides in rats fed with a regular diet. However, the increase in total cholesterol and low-density lipoprotein (LDL)-cholesterol induced by a cholesterol-enriched diet was reduced significantly by melatonin administration. On the other hand, melatonin administration prevented the decrease in high-density lipoprotein (HDL)-cholesterol induced by the same diet. No differences in the levels of very low-density lipoprotein (VLDL)-cholesterol and triglycerides were found. We also found that melatonin administration slightly decreased serum uric, bilirubin and increased serum glucose levels. Other biochemical parameters, including total proteins, creatinine, urea, phosphorus, calcium, glutamic oxalacetic transaminase (GOT), glutamic pyruvic transaminase (GPT), gamma-glutamyltranspeptidase (gamma-GT), acetyl cholinesterase (AcCho), and alkaline phosphatase (ALP) were not modified by melatonin treatment. Finally, lipid peroxidation (LPO) was studied in membranes of liver, brain, spleen, and heart as an index of membrane oxidative damage. Results show that hypercholesterolemic diet did not modify the LPO status in any of the tissues studied. However, chronic melatonin administration significantly decreased LPO. Results confirm that melatonin participates in the regulation of cholesterol metabolism and in the prevention of oxidative damage to membranes.

Ascorbic acid and alpha-tocopherol attenuate methylmalonic acid-induced convulsions.

The effects of chronic administration of alpha-tocopherol or melatonin, or acute ascorbic acid administration on the convulsant action of methylmalonic acid (MMA) were investigated in adult male rats. Animals were chronically injected with alpha-tocopherol (40 mg kg(-1), i.p.), melatonin (5 mg kg(-1), i.p.) or vehicle for 7 days. Buffered MMA (6 micromol/2 microl) or NaCl (9 micromol/2 microl) was injected intrastriatally and the animals were observed for the appearance of clonic or tonic-clonic convulsions and rotational behavior. Ascorbic acid (100 mg kg(-1), s.c.) was administered 30 min before MMA injection. Alpha-tocopherol and ascorbic acid pretreatment decreased the duration of the convulsive episodes and the rotational behavior elicited by MMA. This study provides evidence that free radical generation may participate in the convulsant effects of methylmalonic acid.

Melatonin and taurine reduce early glomerulopathy in diabetic rats

Oxidative stress occurs in diabetic patients and experimental models of diabetes. We examined whether two antioxidants, melatonin and taurine, can ameliorate diabetic nephropathy. Enhanced expression of glomerular TGF-β1 and fibronectin mRNAs and proteinuria were employed as indices of diabetic nephropathy. Experimental diabetes was induced by intravenous injection of streptozotocin 50 mg/kg. Two days after streptozotocin, diabetic rats were assigned to one of the following groups: i) untreated; ii) melatonin supplement by 0.02% in drinking water; or iii) taurine supplement by 1% in drinking water. Four weeks after streptozotocin, diabetic rats ( n = 6: plasma glucose 516 ± 12 mg/dl) exhibited 6.1 fold increase in urinary protein excretion, 1.4 fold increase in glomerular TGF-β1 mRNA, 1.7 fold increase in glomerular fibronectin mRNA, 2.2 fold increase in plasma lipid peroxides (LPO), and 44 fold increase in urinary LPO excretion above the values in control rats ( n = 6: plasma glucose 188 ± 14 mg/dl). Chronic administration of melatonin ( n = 6) and taurine ( n = 6) prevented increases in glomerular TGF-β1 and fibronectin mRNAs and proteinuria without having effect on blood glucose. Both treatments reduced lipid peroxidation by nearly 50%. The present data demonstrate beneficial effects of melatonin and taurine on early changes in diabetic kidney and suggest that diabetic nephropathy associated with hyperglycemia is largely mediated by oxidative stress. Science