[Circadian rhythm and aging].

The circadian variation of several lipogenic enzymes of rat liver and of serum triglyceride and insulin levels was measured in dependence on age. In female rats of the Wistar strain subjected to a 12 hr light--12 hr darkness schedule malic enzyme and isocitrate dehydrogenase show a circadian cycle with maximum activities in the dark period, alpha-glycerophosphate dehydrogenase has a maximum at 14,00 hr. The circadian rhythm of these enzymes is synchronous in young and old animals, but the activities of malic enzyme and alpha-glycerophosphate dehydrogenase are lower in the liver of 18 months old rats in contrast to 3 months old animals at all time points. The activity of glucose-6-phosphate dehydrogenase of the liver of young rats increases during the light period and reaches a maximum at night. The enzyme in old animals does not show this circadian rhythm. There is no age-dependence of the circadian variation of serum triglyceride and insulin levels.