A CIRCADIAN STUDY OF LIVER ANTIOXIDANT ENZYME-SYSTEMS OF FEMALE FISCHER-344 RATS SUBJECTED TO DIETARY RESTRICTION FOR 6 WEEKS

We examined the influences of dietary restriction (DR) on the circadia n profile of liver catalase (CAT), glutathione peroxidase (GPx), and i nteracting systems required for removal of H2O2 (support systems), in 18-week old female Fischer 344 rats fed 60% of their ad libitum (AL) d iet for six weeks. Food was presented to the DR animals during the ear ly light-span. Regardless of diet, enzyme levels were generally consis tent with circadian patterns. In CR animals, maximum activities often occurred at the time of food presentation. CAT and GPx activities gene rally were significantly higher in DR animals than in AL animals at th e time of feeding. When assessing glucose-6-phosphate dehydrogenase (G 6PDH) activity using saturating substrate (NADP(+)) concentrations, hi gher activities were seen at all times of day in the AL animals; howev er, when activity was measured in the presence of lower (i.e., physiol ogic) NADP(+) concentrations, the reverse was true. In contrast, gluta thione reductase (GR) activity was not influenced by DR. Cytosolic lev els 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 s ignificant circadian pattern with a maximum occurring toward the middl e of the dark span. These data suggest that even at a young age and fo llowing only a relatively brief duration of DR, there exists an enhanc ed enzymatic capability in rats subjected to DR to remove free radical s generated as a consequence of normal oxidative metabolism Further, t hese data support emerging trends suggesting metabolic regulation of a ntioxidant defense systems in response to free radical generation.