In recent years researchers attracted much attention pineal hormone melatonin. He is involved in cell proliferation and differentiation, has sedative, anti-tumor, anti-stress properties, improves performance. Conclusions publications on the issue of the impact of melatonin on liver parenchyma mixed state. This may be due to experiments at different times of day or season, the introduction of various doses of exogenous melatonin, the use of animals in experiments different ages, line and etc. The aim of this study was to investigate the effect of exogenous melatonin on morphological and biochemical indicators of liver parenchyma Wistar and SHR rats. Studies were performed in 48 rats of Wistar and SHR (spontaneously hypertensive rats) aged 3 months in spring (April). Rats in all groups were unified under a standard diet and natural lighting. Rats from the experimental groups received exogenous melatonin (Unipharm Inc., USA) orally at a dose of 5 mg / kg body weight every day at 10 am. The duration of the experiment was 28 days. All manipulations with laboratory animals were carried out in accordance with international principles of the European Convention for the Protection of Vertebrate Animals. State of the liver parenchyma was assessed by morphological, morphometric and biochemical methods. Samples of liver tissue were taken for morphological and morphometric studies. Histological preparations were made by the standard method. Sections were stained by the method of Van Ghisoni, Mason, hematoxylin and eosin. Morphometry was performed on digital images micropreparations using computer programs «Image J». Mitochondria were isolated from rat liver by differential centrifugation. Biochemical methods were used for determine the activity of succinate dehydrogenase, cytochrome oxidase and protein concentration in hepatocyte mitochondrial suspension. Analysis of the histological preparations showed that the liver parenchyma in animal of experimental groups saved a physiological structure. Hepatic plates were placed radially. The central vein and branches of portal vein and sinusoids had moderate blood filling. Interlobular connective tissue was poorly expressed. Hepatocytes were medium and large sizes and had a well-defined membrane. Hepatocytes nuclei were round, with a central location in the cell. Nuclear membrane was preserved and had sharp contours. Nucleoli are clearly visible, mostly medium-sized and had a rounded shape and clear boundaries. There are some differences in the obtained morphometric and biochemical indicator of the liver parenchymal elements between the lines of Wistar and SHR rats were administered melatonin. The increase in cross-sectional area of the nucleus of hepatocytes (line Wistar), the number of nucleoli and binuclear hepatocytes, nuclear-cytoplasmic and nucleolar-nuclear ratio, reducing the distance between adjacent nuclei of hepatocytes was detected after 28-daily melatonin administration to rats of Wistar and SHR line in the spring. This may indicate an increase functional and synthetic activity of liver parenchyma, increase its physiological regeneration Significant decreasing of succinate dehydrogenase and cytochrome oxidase activity and increasing of protein concentration in the suspension of hepatocytes mitochondria was found in Wistar and SHR rats that received melatonin. This may indicate a decrease in activity on aerobic oxidation and increased of hepatocytes protein synthetic activity. Investigated morphometric and biochemical indicators of liver tissue of rats SHR, after the effects of melatonin, significantly more varied than that of animals line Wistar. In the future it is necessary to conduct experiments on animals of different age groups, to determine the dose-dependent effect of exogenous melatonin and explore the mechanisms of hormone action in rat liver parenchyma different lines.
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