The purpose of the article is evaluation of the combined application of exogenous melatonin and the nuclear factor κB (NF-κB) inhibitor on free radical processes in the body of rats (blood, liver, skeletal muscle) during the carbohydrate-lipid modeling of insulin resistance (IR) syndrome under hypopinealism induced by round-the-clock lighting. 35 Wistar white male rats weighing 215-255 g in 5 series of experiments were examined. The first series was designed to identify the necessary parameters in intact animals (control series), the second series was to obtain the parameters in the rats after the development of modeled IR syndrome; in the third and fourth series of the experiment, tested animals with modeled IR syndrome were administered exogenous melatonin and NF-κB inhibitor ammonium pyrrolidinedithiocarbamate (PDTC) respectively; and in the fifth series, these compounds were co-administered. To simulate the IR syndrome, rats were kept on a carbohydrate-lipid diet for two months. In addition, from the 30th day of the experiment the animals were exposed to round-the-clock lighting with intensity of 1500 lx for the following 30 days. Melatonin ("Sigma-Aldrich, Inc.", USA) was administered as an aqueous solution intragastrally in a dose of 0.3 mg/kg body weight per day for the following 30 days of the experiment. PDTC ("Sigma-Aldrich, Inc.", USA) was administered in a dose of 76 mg/kg 3 times per week, starting on the 30th day of the experiment. The concentration of melatonin in serum was determined by the immune enzyme method (Rat Melatonin ELISA Kit, Wuhan EIAab Sci CO., China). Spectrophotometry was used to assess the formation of by-products of lipid peroxidation (TBA-reactants), the superoxide anion radical (SAR) production with inductors as NADH, NADPH, and bacterial lipopolysaccharide, the activity of antioxidant enzymes, superoxide dismutase (SOD) and catalase, activity of NO-synthase (NOS) and peroxynitrite concentration. It was found out that combined application of melatonin and PDTC to the rats kept under the round-the-clock lighting and kept on the carbohydrate-lipid diet highly reduces the concentration of TBA-active compounds, secondary products of lipid peroxide oxidation, compared with the separate application. The combined application of melatonin and PDTC in the experimental conditions limits the production of superoxide anion radical by NADPH-dependent (microsomal and NOS) and NADH-dependent (mitochondrial) electron transport chains in liver tissues and the respiratory chain of mitochondria in the femur muscle more than under the separate administration of the agents mentioned. It is under these conditions that liver tissues suppress the formation of superoxide anion radical with leukocyte NADPH oxidase. The co-administration of melatonin and NF-κB PDTC to rats under the round-the-clock illumination and carbohydrate-lipid diet considerably lowers the formation of reactive nitrogen species in the liver tissues (total activity of NO synthase and peroxynitrite concentration), lipid peroxidation, and increases the antioxidant potential more than it is observed during separate application of the compounds.
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