Endogenous rhythms of melatonin, total antioxidant status and superoxide dismutase activity in several tissues of chick and their inhibition by light

Melatonin was recently shown to be a component of the antioxidative defense system of organisms due to its free radical scavenging ability and to its capacity to stimulate several antioxidant enzymes. In this report, we studi ed the endogenous rhythm of the antioxidant enzyme superoxide dismutase (SO D) in three different tissues (cerebral cortex, liver and lung) of chick (G allus domesticus) (three weeks, at age and sacrificed every 2 hr). During t he study the chicks were under a light:dark cycle of 12:12. Total antioxida nt status of the plasma was correlated with physiological blood melatonin c oncentrations. Superoxide dismutase activity exhibited a marked 24 hr rhyth m in cerebral cortex. lung and liver, with peak activity coincident with th e melatonin and total antioxidant status peaks. The exposure of chicks to c onstant light for 7 days eliminated the melatonin rhythm as well as the pea ks in superoxide dismutase activity and the total antioxidant status. These findings suggest that the melatonin rhythm may be related to the nighttime increase in the superoxide dismutase activity and to total antioxidant cap acity of the blood.