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The relevance of this study stems from the growing interest in the impact of acute desynchronosis (AD) on oxidative disorders and the insufficiently studied effect of flavonoids on these processes in kidney tissue. This study investigates the effect of quercetin on oxidative and nitrosative stress in rat kidney homogenate under AD and 3 lipopolysaccharide (LPS)-induced systemic inflammatory response (SIR). The animals were randomly divided into five groups: group 1 served as the control, group 2 underwent LPS-induced SIR modeling for 8 weeks, group 3 experienced AD reproduction by shifting the light-dark cycle 6 hours earlier for 7 days, group 4 underwent AD modeling during the last week of LPS-induced SIR, and rats in group 5 were administered a water-soluble form of quercetin (corvitin) intragastrically was administered at a dose of 200 mg/kg (20 mg/kg in terms of quercetin) daily during the AD modeling against LPS-induced SIR. It was found that the modeling of LPS-induced oxidative stress and AD significantly increased the rate of superoxide anion radical production in kidney homogenate by microsomal monooxygenases and NO synthase (NOS), mitochondrial respiratory chain, leukocyte NADPH oxidase, inducible NOS activity, and decreased the activity of the constitutive NOS isoform and its coupling index. Under AD modeling, the rate of superoxide anion radical production by leukocyte NADPH oxidase, total and inducible NOS activity was significantly lower compared with LPS-induced SIR. When modeling AD against the background of LPS-induced SIR, the production of superoxide anion radical by microsomes, mitochondria and leukocyte NADPH oxidase exceeded the respective results of group 2 by 15.9%, 16.0% and 38.5%, and group 3 by 24.4%, 17.5% and 74.6%. The inducible NOS activity was 22.9% higher compared to the value of group 2 and 93.4% higher in group 3, the concentration of peroxynitrites of alkali and alkaline earth metals was 35.5% higher than the respective parameters of group 2 and 57.9% higher than in group 3. Administration of quercetin during AD modeling and LPS-induced oxidative stress significantly reduced the rate of superoxide anion radical production by microsomal monooxygenases by 17.1%, mitochondrial respiratory chain by 31.2%, leukocyte NADPH oxidase by 19.4%, total and inducible NOS activity by 50.4% and 55.5%, respectively; the concentration of peroxynitrites of alkali and alkaline earth metals diminished by 41.4% compared to the value of group 4. It has been concluded that the administration of quercetin significantly reduces the signs of oxidative-nitrosative stress in the kidney homogenate of rats. [ABSTRACT FROM AUTHOR]