Resultsand Discussion

Glutathione peroxidase exhibited a marked circadian rhythm with a peak activity which had an acrophase of 0781 ± 0073 h. after lights off (mesor: 33.8 ± 1.2 m units./mg prot; amplitude: 9.4 ± 0.6 m units/mg prot.) and about 4 h after serum melatonin peak. Glutathione reductase and Catalase exhibited similar robust rhythms with the peak occurring respectively 1540 ± 0142 h (mesor: 11.67 ± 0.58 m units/mg prot.;

Figure 1. Population cosinor. Comparison between: Cerebral cortex GSH-Px, GRRG-Rd, Catalase activities and serum Melatonin acrophases.

amplitude: 2.42 ± 1.03 m units/mg prot.) and 1526 ± 0041 h (mesor: 4.42 ± 0.25 U.I/mg prot; amplitude: 1.28 ± 0.39/mg prot.) after lights off about 8 h after glutathione per-oxidase peak and after 11 h after melatonin peak (Figure 1).

In the Figure 1 we show the comparison between: Cerebral cortex GSH-Px, GRRG-Rd, Catalase activities and serum melatonin acrophases. We suggest that neural glutathione peroxidase activity increase due to the rise of nocturnal melatonin levels while glutathione reductase and catalase activities rise slightly later, possibly due to an increase of their substrates.

Exposure of chicks to constant light for 6 days eliminated the melatonin rhythm as well as the peaks in glutathione peroxidase, glutathione reductase and catalase. Exposure of chicks to constant light for 6 days eliminated the melatonin rhythm as well as the peaks in glutathione peroxidase, glutathione reductase and catalase (Figure 2).

Figure 2. Inhibition of GSH-Px and GSSG-Rd activities and variation of catalase activity, in cortex cerebral of chicks exposed to constant light and killed at 0600 h, control chicks were kept in 12L: 12D and killed in darkness at 0600 h. Data are mean ± SEM.

In this paper we demonstrate that three major antioxidant enzymes, GSH-Px, GSSG-Rd and Catalase, exhibit a circadian rhythm in chick cerebral cortex. Glutathione peroxidase exhibited a marked circadian rhythm with a peak activity which had an acrophase of 0781 ± 0073 h after lights off (mesor: 33.8 ± 1.2U.I./mg prot; amplitude: 9.4 ± 0.6U.I./mg prot.) and about 4h after serum melatonin peak. Glutathione reductase and Catalase exhibited similar robust rhythms with the peak occurring respectively 1540 ± 0142h (mesor: 11.67 ± 0.58U.I./mg prot.; amplitude: 2.42 ± 1.03U.I./mg prot.) and 1526 ± 0041 h (mesor: 4.42 ± 0.25 U.I./mg prot; amplitude: 1.28 ± 0.39U.I./mg prot.) after lights off about 8 h after glutathione peroxidase peak and after 11 h after melatonin peak. Exposure of chicks to constant light for 6 days eliminated the melatonin and Catalase rhythms as well as the peaks in Glutathione perox-idase and Glutathione reductase activities.

This work was supported by Junta de Castilla y Leon reference project VA45/98. (B.O.C. y L. January 29th 1998).

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