We examined the influences of dietary restriction (DR) on the circadian profile of liver catalase (CAT), glutathione peroxidase (GPx), and interacting systems required for removal of H2O2 (support systems), in 18-week old female Fischer 344 rats fed 60% of their ad libitum (AL) diet for six weeks. Food was presented to the DR animals during the early light-span. Regardless of diet, enzyme levels were generally consistent with circadian patterns. In CR animals, maximum activities often occurred at the time of food presentation. CAT and GPx activities generally were significantly higher in DR animals than in AL animals at the time of feeding. When assessing glucose-6-phosphate dehydrogenase (G6PDH) activity using saturating substrate (NADP(+)) concentrations, higher activities were seen at all times of day in the AL animals; however, when activity was measured in the presence of lower (i.e., physiologic) NADP(+) concentrations, the reverse was true. In contrast, glutathione reductase (GR) activity was not influenced by DR. Cytosolic levels of NADPH peaked and were higher in DR than in AL rodents prior to feeding. NADH levels were not influenced by diet, but did manifest a significant circadian pattern with a maximum occurring toward the middle of the dark span. These data suggest that even at a young age and following only a relatively brief duration of DR, there exists an enhanced enzymatic capability in rats subjected to DR to remove free radicals generated as a consequence of normal oxidative metabolism. Further, these data support emerging trends suggesting metabolic regulation of antioxidant defense systems in response to free radical generation.
