[Role of photoperiodicity and circadian rhythm of glucocorticoids in synchronizing the fluctuations in free-radical oxidation of lipids in rats].

A biphasic circadian rhythm in the content of liver lipid peroxidation products has been demonstrated in male Wistar rats housed under the conditions of 12L: 12D, with 3 hours of morning and evening twilight. Maxima of the concentration of the products were observed in the morning and early at night. The rhythm of lipid anti-oxidative activity was found in an anti-phase. Inversion of both the L: D cycle and glucocorticoid circadian rhythms (cortisol injections) led after 14-16 days to the same shifts in the rhythm of anti-oxidative activity. The data indicate that glucocorticoids modulate the diurnal rhythms of lipid anti-oxidative activity and may be responsible for the shifts in the rhythms of free radical oxidation, induced by inversion of the L: D cycle.