摘要:

Abstract:Carbon tetrachloride (CC14) exerts its toxic effects by the generation of free radicals. In this study we investigated whether melatonin, a potent free radical scavenger, could prevent the deleterious effects of CC14. Liver homogenates and liver microsomes were incubated with CCI4 in the presence of melatonin and lipid peroxidation and glucose‐6 phosphatase (G6Pase) activity were determined. All doses of CC14(1, 0.5, 0.1 raM) produced significantly high levels of lipid peroxidation, as reflected by increased levels of malonaldehyde and 4‐hydroxyalkenals, in both liver homogenates and liver microsomes. These doses of CC14concommitantly reduced the activity of microsomal G6Pase. Co‐incubation with melatonin dose‐dependently (2, 1, 0.5 raM) inhibited the production of lipid peroxidation, but it was unable to restore the activity of G6Pase. In in vivo studies, rats were also treated with melatonin (10 mg/kg, i.p.), given 30 min before and 60 min after the administration of CC14(5 ml/kg, i.p.). Significantly elevated levels of lipid peroxidation were measured in the liver and kidney. Melatonin prevented the CCl4‐induced lipid peroxidation in the kidney, but not in the liver. These data suggest that melatonin may provide protection against some of the damaging effects of CCI4, possibly due to its ability to scavenge toxic free

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00164.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:Plasma melatonin was measured at the winter and summer solstices and the autumn and spring equinoxes in four mares held under natural conditions at 35°S. At all seasons the onset of the nightly elevated melatonin was coincident with or after the time of sunset and the melatonin offset after the time of sunrise. The duration of elevated melatonin was not different from the duration of natural scotophase for each season, with the duration of elevated melatonin longer in winter than the other seasons. Immediately following each 24 hr sampling two mares were resampled in acutely extended darkness to determine the melatonin profile of the endogenous rhythm of the circadian pacemaker, originating from the suprachiasmatic nuclei (SCN). At each season melatonin secretion commenced earlier and decreased later than that measured under the natural photoperiodic condition, suggesting that the expression of the melatonin rhythm is normally gated by natural environmental light both at dusk and dawn. The interval from the onset of melatonin measured under acutely extended darkness to the time of sunset was greater in the spring/ summer than the autumn/winter suggesting a possible alternating signal throughout the year. Thus the mare appears to exhibit a similar interaction between endogenous circadian rhythmic activity and the natural photoperiod as the ewe which may underlie the mechanism for timing reproductive activity through the year

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00165.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:Differences and similarities in the temporal organization of hormone secretion in plasma reflect the activity of CNS pacemakers. One aspect of this activity, the temporal synchronization of the secretion of different hormones is still poorly understood. We report the analysis of melatonin and testosterone plasma concentrations during two nights in 6 normal healthy young men. Blood was collected every 20 min between 2040 and 0640. Plasma testosterone concentrations increased by 1.5‐ to 2‐fold during the second part of the night, and melatonin by 2.5‐ to 4‐fold. In each subject, the individual temporal pattern of melatonin was quite stable over the two nights of sampling, while testosterone profiles showed fluctuations. There was a high degree of parallelism in these two hormones nocturnal secretion. These results, together with previous studies, suggest that melatonin might entrain the nocturnal secretion of testo

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00166.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:Photic regulation of the pineal melatonin synthesis was studied in 3‐ to 21‐day‐old rat pups by exposing the animals to light at night (30–40 min) or to darkness during the day (30–240 min). The pineal melatonin contents were measured by radioimmunoassay. A significant day/night difference in the melatonin content and the nocturnal light‐induced decrease were not found until second postnatal week. A novel finding was that at the age of 13–17 days a daytime dark exposure elevated the pineal melatonin content; it was twofold as compared with the normal daytime level and about half of the nocturnal peak level. In 21‐day‐old rats the response had disappeared, while the nocturnal suppression by light persisted. The dark‐induced increase of the melatonin synthesis was independent of the opening of the eyelids which occurs in pups at the age of two weeks, but it was greater in maternally isolated than non‐isolated pups. The results suggest that one component of the circadian regulatory system matures at the end of the third postnatal week. This mechanism inhibits the elevation of the melatonin synthesis by darkne

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00167.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:Melatonin administration reduces the severity of dextran sodium sulphate (DSS)‐induced colitis in mice. After 7 weeks of daily intraperitoneal melatonin administration (150 μg/kg), rectal bleeding and occult blood was eliminated in all mice in which colitis was induced by DSS. In addition the frequency and severity of focal lesions in the mucosa was dramatically reduced. Furthermore, weight loss and higher food consumption observed in DSS‐treated mice was reversed in DSS‐treated mice injected with melatonin. All treated groups exhibited significant alterations in goblet cell distribution as a result of DSS or melatonin administration. Surprisingly, serum melatonin levels were more than 10 times higher in mice that received DSS as compared to controls. The significant improvement in the conditions of melatonin‐treated mice might be due to its effect on the smooth muscles of the colon, the blood supply in the mucosa, its capability as an antioxidant and scavenger of free radicals, or its effect on the immune system of the gut. The higher plasma levels of melatonin in DSS‐treated mice might be due to a stress‐induced increase in the production of gastrointestinal (GI

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00168.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:The pineal gland (PG) is a source of several trophic factors. In this study, PG and superior cervical ganglia (SCG) from Sprague‐Dawley neonates (1‐day‐old) were co‐cultured to test the hypothesis that endogenous release of PG NGF (or an NGF‐like cytokine) is sufficient to promote survival of SCG neurons. Neuronal density of SCG neurons was significantly enhanced when co‐cultured with PG for 7 days compared to SCG cultured alone. SCG survival and neurite formation in PG co‐cultures was less than in SCG treated with exogenous NGF (100 ng/ml). The neurotrophic effect of PG co‐cultures was abolished when 1% anti‐NGF was added to the medium. Co‐cultures of SCG neurons with established 7‐day PG cultures induced extensive SCG neurite formation within 24 hr compared to SCG co‐cultured with 1‐day PG cultures. This suggests that PG neurotrophic effects are due to PG non‐neuronal cells (nnc) that proliferate to confluency by 7 days in culture. S‐antigen‐positive pinealocytes did not proliferate in culture. There was decreased SCG survival when neurons were seeded onto PG cultures that had been previously killed by drying, which suggests that the neurotrophic effects of nnc are not substrate‐dependent. Immunocytochemical characterization of PG nnc revealed a heterogenous mixture of astrocytes, macrophage/ microglia, and fibroblasts. These findings support the hypothesis that NGF is actively secreted by PG and that nnc are the pri

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00169.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:The ability of melatonin to modify H2O2‐induced lipid peroxidation in brain homogenates was determined. The concentrations of brain malonaldehyde (MDA) and 4‐hydroxyalkenals (4‐HDA) were assayed as an index of induced membrane oxidative damage. Homogenates from five different regions of the brain (cerebral cortex, cerebellum, hippocampus, hypothalamus, and corpus striatum) derived from two different strains of rats, Sprague‐Dawley and Wistar, were incubated with either H2O2(5 mM) alone or H2O2together with melatonin at increasing concentrations ranging from 0.1 to 4 mM. The basal level of lipid peroxidation was strain‐dependent and about 100% higher in homogenates from the brain of Wistar rats than those measured in Sprague‐Dawley rats. MDA + 4‐HDA levels increased after H2O2treatment in homogenates obtained from each region of the brain in both rat strains but the sensitivity of the homogenates from Sprague‐Dawley rats was greater than that for the homogenates from Wistar rats (increases after H2O2from 45 to 165% compared 20 to 40% for Sprague‐Dawley and Wistar rats, respectively). Melatonin co‐treatment reduced H202‐induced lipid peroxidation in brain homogenates in a concentration‐dependent manner; the degree of protection against lipid peroxidation was simil

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1995.tb00170.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY