OBJECTIVES: Melatonin is a hormone with strong antioxidant activity. It is biosynthesized in the pineal gland and serves in the biological signaling and control of the circadian rhythm. Though there is evidence of beneficial effects of melatonin, the substance was not investigated in greater details associated with specific regulation of oxidative stress in organs and tissues. DESIGN: The experiment is based on exposure of BALB/c mice to doses from 10 µg to 1mg of melatonin. Mice were euthanized after one and 24 hours, respectively. Biochemical markers in plasma, ferric reducing antioxidant power (FRAP), thiobarbituric acid reactive substances (TBARS) and activity of caspase-3 were examined in selected organs. RESULTS: We confirmed significant alteration in high-density lipoprotein and total cholesterols and glucose. After one day, levels of glucose and high-density lipoprotein cholesterol were decreased, while total cholesterol increased in a dose dependent manner. FRAP values increased in spleen, liver, kidney, heart, and brain indicating a growing potential of low molecular weight antioxidants 24 hours after exposure. However, TBARS values indicating oxidative stress were elevated in heart, kidney, and liver. CONCLUSIONS: Despite the antioxidant properties of melatonin, its effect on the organism is more complicated. It influences not only the oxidative homeostasis but also the basal metabolism, as represented by, e.g., cholesterol and glucose. This substance could thus be used for therapeutical purposes such as amelioration of pathologies associated with generation of reactive species or some metabolic dysfunctions.

Faculty of Military Health Sciences University of Defence Hradec Kralove Czech Republic