The production of the pineal hormone melatonin is synchronized with day-night cycle via multisynaptic pathway including suprachiasmatic nucleus linking several physiological functions to diurnal cycle. The recent data indicate that impaired melatonin production is involved in several cardiovascular pathologies including hypertension and ischemic heart disease. However, the mechanisms of melatonin effect on cardiovascular system are still not completely understood. The activation of melatonin receptors on endothelial and vascular smooth muscle cells and antioxidant properties of melatonin could be responsible for the melatonin effects on vascular tone. However, the data from in vitro studies are controversial making the explanation of the melatonin effect on blood pressure in vivo difficult. In vivo, melatonin also attenuates sympathetic tone by direct activation of melatonin receptors, scavenging free radicals or increasing NO availability in the central nervous system. The central and peripheral antiadrenergic action of chronic melatonin treatment might eliminate the mechanisms counter-regulating decreased blood pressure, providing thus additional cardioprotective mechanism. The extraordinary antioxidant activity and antilipidemic effects of melatonin may enhance the modulation of blood pressure by melatonin and probably play the most important role in the amelioration of target organ damage by chronic melatonin treatment. Further investigation of these mechanisms should provide novel knowledge about pathophysiological mechanisms of cardiovascular diseases, additional explanation for their circadian and seasonal variability and potentially generate new impulses for the development of therapeutic arsenal., Ľ. Paulis, F. Šimko., and Obsahuje bibliografii a bibliografické odkazy
Melatonin has been shown to play a role in antioxidative defence. We therefore studied its effect on oxidative damage to the rat cerebral cortex evoked by painful stimulation and immobilization-induced stress. Moreover, the effect of melatonin on chronic pain perception was examined. Rats were injected with either a high dose of melatonin (100 mg/kg i.p.) or a vehicle for five days and were subjected to painful stimulation or immobilization stress 30 min after the treatment. To determine the degree of oxidative stress, the levels of free radicals, thiobarbituric acid reactive substances (TBARS) as indicators of lipid peroxidation and glutathione peroxidase (GSHPx) were estimated in somatosensory cortex. Pain perception was measured by the tail-flick and plantar test. Melatonin reduced the level of TBARS previously increased by painful stimulation. Melatonin also exhibited a slight analgesic effect in those animals exposed to painful stimulation but its role in free radical scavenging did not contribute to this effect., I. Pekárková, S. Parara, V. Holeček, P. Stopka, L. Trefil, J. Racek, R. Rokyta., and Obsahuje bibliografii
Chronic continuous light exposure leads to melatonin deficiency along with complex neurohumoral activation resulting in hypertension development in rats. The aim of this study was to show, whether continuous light in duces fibrotic rebuilding of the aorta and whether the treatment with melatonin or angiotensin converting enzyme inhibitor captopril can prevent these potential alterations. In a six-week experiment, 3-month-old Wistar rats were divided into 4 groups (t en per group): controls, rats exposed to continuous light, exposed to continuous light plus treated with captopril (100 mg/kg/24 h) and exposed to continuous light plus treated with melatonin (10 mg/kg/24 h). Systolic blood pressure (SBP) and collagen type I and III in the media of thoracic aorta were me asured. Continuous light induced hypertension and fibrotic rebuilding of the aorta in terms of enhancement of collagen I and III concentration in the aortic media. Both captopril and melatonin prevented SBP rise and reduced collagen III concentration in the aorta. However, only melatonin reduced collagen I and the sum of collagen I and III in the aortic tissue. We conclude that in continuous light-induced hypertension, administration of melatonin, along with SBP reduction, decreases collagen I and III concentration in the aorta. It is suggested that antifibrotic effect of melatonin may reduce the stiffness of the aorta and small arteries and beneficially influence the nature of the pulse wave and peripheral vascular resistance., K. Repová-Bednárová ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
The occurrence of melatonin is known in nearly all organisms, but nothing is known exactly about its function outside of vertebrates. Long-term perifusions as well as short-term batch incubations of brains and moulting glands of the cockroach Periplaneta americana were used to identify the effect of melatonin on the release of prothoracicotropic hormone, a glandotropic neuropeptide in the brain, which stimulates the production of the moulting hormone ecdysone in the moulting gland. This is the first experimental evidence of a neurohormonal releasing effect of melatonin in the insect nervous system., Klaus Richter, Elmar Peschke, Dorothee Peschke, and Lit
Melatonin mediates many physiological processes in animals and plants. To examine the potential roles of melatonin in salinity tolerance, we investigated the effects of exogenous melatonin on growth and antioxidant system in cucumber under 200 mM NaCl stress conditions. The results showed that the melatonin-treated plants significantly increased growth mass and antioxidant protection. Under salinity stress, the addition of melatonin effectively alleviated the decrease in the net photosynthetic rate, the maximum quantum efficiency of PSII, and the total chlorophyll content. Our data also suggested that melatonin and the resistance of plants exhibited a concentration effect. The application of 50-150 μM melatonin significantly improved the photosynthetic capacity. Additionally, the pretreatment with melatonin reduced the oxidative damage under salinity stress by scavenging directly H2O2 or enhancing activity of antioxidant enzymes (including superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and concentrations of antioxidants (ascorbic acid and glutathione). Therefore, the melatonin-treated plants could effectively enhance their salinity tolerance., L. Y. Wang, J. L. Liu, W. X. Wang, Y. Sun., and Obsahuje seznam literatury
Here we analyzed associations between muscles mass, total bone mineral content (BMC), lumbar spine bone density (BMD L1-L4) and serum or urine hormones in healthy peripubertal girls. Total BMC and areal BMD L1-L4, muscle mass and fat were measured by dual-energy X-ray absorptiometry (DXA). Muscle force (N) was estimated by a dynamometer. Circulating estradiol, folliclestimulating hormone (FSH), luteinizing hormone (LH), 25-hydroxy vitamin D, parathyroid hormone (PTH), insulin-like growth factor 1 (IGF-1), leptin, osteocalcin, bone isoenzyme of alkaline phosphatase (bALP) and total calcium and phosphorus were quantified as the nocturnal melatonin and serotonin urinary excretion. Partial correlations adjusted for height, Tanner score and physical activity confirmed positive relationships between BMC or BMD L1-L4 (Z-score) and lean mass or fat. Furthermore, positive relationship was observed between BMC or BMD L1-L4 (Z-score) and serum leptin. After adjustment for Tanner score and physical activity, positive associations were observed between lean mass and IGF-1, leptin levels or muscle force. We proved positive relationships between bone mass and serum leptin in peripubertal girls., V. Cirmanova, I. Zofkova, P. Kasalicky, V. Lanska, M. Bayer, L. Starka, R. Kanceva., and Obsahuje bibliografii
In hemodialyzed patients hormonal disturbances are known to occur. However, melatonin levels have not been completely studied. The aim of the study was to find whether changes in calcaemia affect melatonin secretion. For this reason we followed the nocturnal serum concentrations of melatonin and parathyroid hormone (PTH) in 9 hemodialyzed patients (6 women and 3 men, aged 37-65 years) both before and 1-3 months after parathyroidectomy at 6 p.m., 9 p.m., 11 p.m., 2 a.m., 5 a.m. and 7 a.m. At 6 p.m. blood samples to evaluate the levels of calcium and phosphate were also collected. Parathyroidectomy resulted in an increase in nocturnal melatonin levels. As expected, the parathyroidectomy was followed by considerable PTH decrease. PTH showed no nocturnal variation before or after parathyroidectomy. Calcium levels significantly decreased after the operation while phosphate levels increased. In summary, in hemodialyzed patients with hyperparathyroidism, parathyroidectomy significantly increases the nocturnal secretion of melatonin. Relationships between the pineal gland and parathyroid glands have yet to be elucidated., R. Kancheva, S. Sulková, F. Švára, M. Hill, L. Kanchev, I. Žofková., and Obsahuje bibliografii a bibliografické odkazy
Photothrombotic model of ischemia (PT) is based on free radical-mediated endothelial dysfunction followed by thrombosis. Free radicals are also involved in hypoxic preconditioning. We tested the sensitivity of PT to preconditioning with hypobaric hypoxia and to pretreatment with melatonin. In adult Wistar rats, after intravenous application of Rose Bengal, a stereo-tactically defined spot on the denuded skull was irradiated by a laser for 9 min. The first experimental group underwent hypobaric hypoxia three days before irradiation. In the second experimental group, melatonin was applied intraperitoneally one hour before irradiation. Three days after irradiation, animals were sacrificed, the brains perfused, and stained with TTC. Ischemic lesions were divided into grades (I, II, III). In the control group (where no manipulation preceded photothrombosis), most animals displayed deep damage involving the striatum (grade III). The group pre-exposed to hypoxia showed similar results. Only 28.57 % of the melatonin pretreated animals exhibited grade III lesions, and in 57.14 % no signs of lesions were detected. Pre-exposure to hypoxia was not protective in our model. Pretreatment with melatonin lead to a significant reduction of the number of large ischemic lesions. This result is probably caused by protection of endothelial cells by melatonin., I. Matějovská, K. Bernášková, D. Krýsl, J. Mareš., and Obsahuje bibliografii a bibliografické odkazy
Melatonin plays a key role in the circadian timing system. At present, many other functions of melatonin are known. Question remains whether changes in endogenous melatonin may be associated with food intake. Hence, the levels of melatonin, C-peptide and glucose were followed during a daily regimen (16 hours) including standardized food intake using commercial kits. The diurnal profiles of the hormones and serum glucose were evaluated using ANOVA with Period and Subject as independent factors. Pearson’s correlations and using a multiple stepwise backward regression model consisting of the time factor as a polynomial, and serum C-peptide and glucose assessed the correlations between melatonin and the remaining parameters. Our results showed a significant negative correlation between melatonin and C-peptide. The profile of melatonin was physiological, decreasing after wake-up, showing minor changes during the daytime and increasing in the evening. As documented, lesser alterations were indicated in the course of the melatonin daytime profile, which may reflect periodic food intake. Food intake is not the primary factor influencing the melatonin course. While previous studies have mostly considered the protective effect of melatonin in diabetic subjects, our study brought the results suggesting food intake as a factor contributing to daytime melatonin variation in humans. However, the physiological role of melatonin association with food intake in daytime remains in question and should be further investigated., L. Stárka, M. Dušková, B. Rácz, K. Šimůnková, M. Hill, R. Kancheva., and Obsahuje bibliografii a bibliografické odkazy
We aimed to explore the effects of melatonin and n-3 polyunsaturated fatty acids (PUFA) supplementation on plasma and aortic nitric oxide (NO) levels in isoproterenol (Iso) affected spontaneously hypertensive (SHR) and Wistar rats. Untreated control rats were compared with Iso injected (118 mg/kg, s.c.) rats, and Iso injected plus supplemented with melatonin (10 mg/kg, p.o.) or PUFA (1.68 g/kg, p.o.) for two months. Plasma and aortic basal, L-NAME inhibited, adrenaline and acetylcholine stimulated NO were determined using Griess method. Plasma NO levels were lower in SHR versus Wistar rats. Iso decreased NO in Wistar while not in SHR. PUFA but not melatonin intake of Iso treated SHR increased plasma NO along with a decrease in systolic blood pressure. Basal aortic NO level was higher in SHR than Wistar rats and not altered by Iso. Intake of melatonin increased but PUFA decreased basal NO levels in Wistar+Iso and did not affect in SHR+Iso rats. Acetylcholine and adrenaline induced aortic NO release was significantly increased in Wistar+Iso but not SHR+Iso group. Melatonin intake increased Ach induced aortic NO in Wistar+Iso and SHR+Iso groups, whereas there was no effect of PUFA intake. Findings suggest that PUFA modulates plasma and melatonin aortic NO levels of isoproterenol affected rats in a strain-dependent manner., K. K. Chaudagar, C. Viczenczova, B. Szeiffova Bacova, T. Egan Benova, M. Barancik, N. Tribulova., and Obsahuje bibliografii