This study examines the effect of age on the induction of the rate- limiting enzyme in gluconeogenesis, phosphoenolpyruvate carboxykinase (PEPCK), in response to fasting and refeeding in male Fischer 344 rats aged 3-18 mo. The rats were fasted for 30 h to increase the activity of PEPCK and subsequently were refed for 24 h to lower activity toward basal levels. PEPCK activity increased 2.2-fold in the 3-mo-old rats and 2.3-fold in the 18-mo- old rats during the 30-h fast. Therefore PEPCK induction during the 30-h fast was not altered with age. Similarly, refeeding resulted in a significant decrease in PEPCK activity at all ages. After the 24-h refeeding period, the rats were fasted a second time, and the time course of induction from the basal refed level was measured. In the young rats (6 mo), the activity of PEPCK increased rapidly from 18.12 ± 1.61 to 42.66 ± 5.94 U/g protein, (P < 0.01) within 8 h of fasting. However, in the 18-mo-old rats, the initiation of the induction of PEPCK activity was delayed, and, after 12 h, PEPCK activity had increased from 17.34 ± 1.34 to only 32.50 ± 3.21 U/g protein (P < 0.01). Furthermore, the rate of induction appears to be decreased in the older animals. The activity after 24 h of fasting was equivalent in all four age groups (ranging from 44.72 ± 5.38 at 3 mo to 40.18 ± 5.42 U/g protein at 18 mo). Therefore, the time course of the adaptation of PEPCK activity in response to fasting is altered with age in these animals, although the magnitude of the induction is not compromised, at least until after 18 mo of age.
|Original language||English (US)|
|Journal||American Journal of Physiology - Gastrointestinal and Liver Physiology|
|Issue number||2 30-2|
|State||Published - 1994|
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