Effects of age and dietary restriction on liver endogenous antioxidant defenses in male Lobund-Wistar rats

Dietary restriction (DR) of 30% in caloric intake extends both median and maximum life span by about 30%. DR retards the aging process, but the mechanism of action is not clearly understood. The effects of DR on major endogenous antioxidant defenses were studied in 80 male Lobund-Wistar (LW) rats at various ages throughout the life span. Two groups of rats were fed ad libitum (AL) or restricted diet (DR) from 6 weeks of age. Adult DR rats received 30% less diet with regard to calories per day when compared to adult AL rats. Eight rats in each diet group were killed at 6, 12, 18, 24 and 30 months of age. The livers were excised and prepared for the determinations of major endogenous antioxidant defense parameters. Hepatic reduced glutathione (GSH) levels were decreased at old age in the AL group, however, DR eliminated this decrease. Activities of glutathione reductase (GR) and Se-dependent glutathione peroxidase (GPx) were not affected by age nor by DR. Superoxide dismutase (SOD) activity decreased from 6 to 12 months of age and catalase activity decreased with aging in the AL group, while DR maintained the enzyme activities at similar levels for all ages. Quinone reductase (QR) activity increased with increasing age in the AL group, and DR further increased the enzyme activity at all ages. The results suggest that 30% DR may contribute to the delaying of the aging process by improving endogenous antioxidant defense capability which decreases by 20 to 30% during aging.