A preliminary report of circadian effects of interleukin-2 (IL-2) on the activity of enzymes of intermediary metabolism of mice.

Since it previously has been reported that IL-2 has profound circadian dependent effects upon DNA synthesis in the liver of mice (Scheving et al., 1988; Tsai et al., 1988) the effects of IL-2 on enzyme activities were studied. The objective was to determine the effect of IL-2 when administered at different times to mice who were fed ad libitum, and standardized to 12 h of light alternating with 12 h of dark. Three groups were injected intraperitoneally with either 1 or 4 mg/kg of IL-2, one group was given the vehicle only. The treatment time for each dose and the vehicle was a 2 h into the light for one group and the other was at 2 h into the dark span. Subgroups of 5 mice were killed 4, 8, 12, 16, 20, 24, and 30 h after each treatment, livers were taken and frozen to await preparation and analysis of enzyme activities by our standard procedures. When treatment was in the light span IL-2 had no statistically significant effect on enzymes of lipid, carbohydrate or amino acid metabolism. On the contrary when treatment was given in the dark span IL-2 produced statistically significant increases in enzymes of glycolysis, and lipid synthesis beginning 8 h after treatment (changes ranged from 20 to 43%) with both the higher and lower doses (higher doses always yielded higher activities), and these activities continued to increase through the 24 h post-treatment span (changes ranged from 42 to 64%). At 30 h, activities were returning to normal levels. Amino acid metabolism, on the other hand, was decreased during these post-treatment times (the range of decrease was from 18 to 44%). Thus, we report for the first time that the duration of time, pathway affected, as well as the magnitude of the effect seen and the dosage of IL-2 were all circadian-stage dependent even with two time point samplings. We believe, however, that these two time points represent different critical extremes in liver metabolism, but studies with denser sampling are planned. Interleukin-2 was generously supplied by Cetus Corp. of Emeryville, CA.

Effect of chronic caloric restriction on hepatic enzymes of intermediary metabolism in aged B6C3F1 female mice.

Caloric restriction (CR) extends maximum life span and significantly retards the rate of occurrence of most age-associated degenerative diseases. The effect of CR in female mice on several hepatic enzymes was examined after 33 month old mice were killed at either the onset of dark, the onset of light or the mid-dark span. Animals had been singly caged with 12 hr of light followed by 12 hr of dark. All feeding was in the early dark span. CR mice were given 60% of the caloric intake of ad libitum fed mice throughout their lives (CR was initiated at 14 weeks of age). Livers were frozen to await preparation and then analysis for 14 enzymes of intermediary metabolism by our standard procedures. Enzymes of gluconeogenesis and amino acid metabolism were increased at all times due to CR. Enzymes of glycolysis and lipid metabolism were decreased at all times. However, maximum differences between ad libitum and CR mice occurred during the mid-dark span (this is the time of normal acrophase in younger mice). Circadian variation was lost and mesors changed for nearly all enzymes measured from mice that had been fed ad libitum. CR mice were found to maintain circadian variation of activities and activity profiles were similar to those seen in younger ad libitum fed mice. These observations suggest that the mechanism through which CR elicits its effects may involve a circadian component.