Effect of age on the activity of phosphoenolpyruvate carboxykinase in the kidney following fasting and refeeding.
The activity of renal phosphoenolpyruvate carboxykinase (PEPCK) was measured in 3-18 month old male Fischer 344 rats after alternate periods of fasting and refeeding. To compare the induction of renal PEPCK activity in response to fasting in young and old rats, 3, 6, 12 and 18 month old animals were fasted for 30 h followed by a 24 h ad libitum refeeding period to reduce PEPCK activity toward basal levels. The refeeding period was followed by a second 24 h fasting period during which the time course of PEPCK induction was monitored in the young and old animals. The first fast resulted in over a 20% increase in renal PEPCK activity in the 3 month old and slightly over a 70% increase in the 6 month old animals. In contrast, the activity did not increase significantly in the 12 or 18 month old animals during this fasting period. Therefore the induction of PEPCK in the kidney in response to fasting appears to be altered in the older animals. Refeeding for 24 h resulted in a decrease in PEPCK activity in all four age groups; therefore there was no indication of an age-related impairment in the response of renal PEPCK to refeeding. After the refeeding period, the food was removed again and the activity was measured at short intervals over the next 24 h to determine the time course of the induction in PEPCK activity. Interestingly, during the second fast, the activity of renal PEPCK was not significantly induced in either the young or the older animals. However, the activity measured in the older 18 month rats was consistently lower during the first 12 h of the second fast as compared to the activity in the 6 month old rats. In summary, the induction of PEPCK activity in the kidney is altered with age during an initial fast; in addition, PEPCK activity is not induced in either young or old rats during a second fasting period.
Van Remmen
H
H
Department of Physiology, University of Texas Health Science Center, San Antonio 78284, USA.
Ward
W F
WF
D000367:Age Factors; D000375:Aging / Q000378:metabolism*; D000818:Animals; D004435:Eating / Q000502:physiology*; D005215:Fasting / Q000502:physiology*; D007668:Kidney / Q000201:enzymology*; D008297:Male; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344
D010729:Phosphoenolpyruvate Carboxykinase (GTP)