The Effect of Age on the Orcadian Rhythms of 23 Liver or Brain Enzymes from C57BL/6J Mice

Abstract

Mice were standardized to 12 h of light exposure alternating with 12 h of darkness and were fed ad libitum. The mice in the first group were 8 weeks old and in the other 104–116 weeks old. Subgroups of 7 animals from each age group were killed at 6 circadian stages. Enzyme activities of 23 enzymes from liver or brain were measured by an analysis of variance for each age group. All but 1 enzyme from young mice, and all but 9 from older mice showed significant changes over time (p < 0.01). The data from the 22 enzymes from young mice and the 14 enzymes from old mice were fit to the cosinor regression model to further characterize the rhythm. 15 enzymes from the young and 8 from the aged mice showed a significant regression to a 24-hour cosine curve (p < 0.01); of the 8, 7 were the same enzymes in both groups. Amplitude changes, where they could be compared from the cosinor data (7 enzymes), were not statistically different. When total variance was compared, 12 enzymes showed unequal variance. Of these, old mice had the larger variance in 9 enzymes. Another difference between the young and the old was changes in mean enzyme activities. 12 enzymes from aged mice had decreased mesors, 2 had increased mesors, and 9 were unchanged. In general, our data suggest that some enzyme activity rhythms were lost, others were altered and a few were not affected by aging. In the case of many enzymes, older mice have a diminished ability to synchronize to the light signals.

Increased effective activity of rat liver catalase by dietary restriction

“…Additionally, maintenance of enzyme activity and regulation of these rhythms often deteriorate with aging (24). We observed that while food consumption in AL (BN x F344)F 1 rats peaked during the dark span, considerable feeding also occurred during the light span.…”