RHYTHMS OF GLUTATHIONE-PEROXIDASE AND GLUTATHIONE-REDUCTASE IN BRAIN OF CHICK AND THEIR INHIBITION BY LIGHT

Melatonin was recently shown to be a component of the antioxidative de fense system of organisms due to its free radical scavenging and antio xidant activities. Pharmacologically, melatonin stimulates the activit y of the peroxide detoxifying enzyme glutathione peroxidase in rat bra in and in several tissues of chicks. In this report, we studied the en dogenous rhythm of two antioxidant enzymes, glutathione peroxidase and glutathione reductase, in five regions (hippocampus, hypothalamus, st riatum, cortex and cerebellum) of chick brain and correlated them with physiological blood melatonin concentrations. Glutathione peroxidase exhibited a marked 24 h rhythm with peak activity in each brain region which had acrophases about 8 h after lights off and about 4 h after t he serum melatonin peak was detected. Glutathione reductase activity e xhibited similar robust rhythms with the peaks occurring roughly 2 h a fter those of glutathione peroxidase. We suggest that neural glutathio ne peroxidase increases due to the rise of nocturnal melatonin levels while glutathione reductase activity rises slightly later possibly due to an increase of its substrate, oxidized glutathione. The exposure o f chicks to constant light for 6 days eliminated the melatonin rhythm as well as the peaks in both glutathione peroxidase and glutathione re ductase activities. These findings suggest that the melatonin rhythm m ay be related to the nighttime increases in the enzyme activities, alt hough other explanations cannot be excluded. (C) 1998 Elsevier Science Ltd. All rights reserved.