Circadian and circaannual oscillations of tissue lipid peroxides (LPO) were studied in young male Wistar rats. The concentration of malondialdehyde, one of LPO degradation products, was measured at 3-h intervals during 24 hours in rats, adapted to lightrdark 12:12 h regimen in the course of the year. LPO in the liver, thymus and bone marrow oscillated rhythmically in the course of the day and year. Circadian oscillations in all tissues were two-peaked, with zeniths at various times of the light and dark parts of the day. In the liver and thymus, the highest mesors were found during the winter, in the bone marrow during the spring. The same holds for amplitude values, with the exception of the bone marrow which exhibited the highest values during the summer. The reason for the LPO oscillations is probably resulting from the changing ratio of pro- and anti-oxidative capacities in various tissues during the day and the year.
We studied the circadian oscillation of lipid peroxides (TBARS) in the pineal gland of rats adapted to light:dark 12:12 h regimen. The concentration of TBARS was determined at 3-h intervals during 24 hours. TBARS of pineal gland oscillated rhytmically during the 24 h period. The maximal concentration of lipoperoxidative products was found at 20.00 h and 02.00 h and the lowest values at 08.00 h and 23.00 h. The determination of antioxidant capacity is needed for explaining the mechanism of TBARS oscillations in the pineal gland.