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Photoperiod-induced alterations in biomarkers of oxidative stress in rats of different ages and individual physiological reactivity

This study was undertaken to investigate the photoperiod- and age-related variability between the activity of oxidative stress biomarkers in rats with different physiological reactivity estimated by different resistance to hypoxia. The study was carried out on 96 male Wistar rats divided into 16 groups based on resistance to hypoxia (LR, low resistance, HR, high resistance) and age, i.e. 6 and 21 months. The studies were conducted at four photoperiod points: winter (January), spring (March), summer (July), and autumn (October). Lower levels of oxidative stress biomarkers (P<0.05) were observed in the younger rats when compared to older rats, as well as in HR rats compared to LR rats. The levels of lipid peroxidation end product, 2-thiobarbituric acid reactive substances (TBARS) as the major indicator of oxidative stress, were found to increase with age, and summer resulted in further elevation compared to other seasons. Also, oxidative stress biomarkers were lower (P<0.05) in winter than in other seasons, especially in the HR rats. TAC level in the hepatic tissue of the 6 months aged rats was significantly higher (P<0.05) elevated when compared to older rats. A similar higher TAC level was in the hepatic tissue of HR rats compared to the LR rats. The adult rats with HR maintained TAC with minimal fluctuations throughout the year. It should be noted that the difference in TAC was higher for the groups of the adult animals with HR in winter, spring, and summer, which may indicate effective mechanisms preventing the formation of reactive oxygen species and systems of elimination thereof.