title: Effect of age on induction of hepatic phosphoenolpyruvate carboxykinase by fasting.
abstract: 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).(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Physiology, University of Texas Health Science Center at San Antonio 78284.
authors.forename: H
authors.initials: H
authors.lastname: Van Remmen
authors.forename: W F
authors.initials: WF
authors.lastname: Ward
mesh_terms: D000375:Aging / Q000502:physiology*; D000818:Animals; D001835:Body Weight; D004790:Enzyme Induction; D005215:Fasting; D005502:Food; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D013997:Time Factors
chemical_list: D010729:Phosphoenolpyruvate Carboxykinase (GTP)