INFLUENCE OF ENDURANCE TRAINING ON THE AGE-RELATED DECLINE IN HEPATICGLYCONEOGENESIS

Hepatic gluconeogenic and glyconeogenic capabilities were investigated in Fischer 344 rat livers (ages 7, 15 and 25 months; n = 66) to deter mine if endurance training affected age related decrements in these he patic functions. Animals were trained 1 h/day, 5 days/week for 10 week s at treadmill speeds of 75% of age-specific maximal capacity. After t raining, rats were injected (300 mg/kg) with a known gluconeogenic inh ibitor, 3-mercaptopicolinic acid (MPA). Two endurance tests were perfo rmed to help assess the contribution of gluconeogenesis to exercise pe rformance, an initial test 4 days prior to injection and a final test immediately postinjection. MPA significantly (P < 0.05) reduced runnin g times in all trained groups compared to their control test: 89%, 81% , and 51% in the young, middle-aged, and old, respectively. MPA reduce d running times in the untrained animals 19%, 11%, and 8%, respectivel y. Three days after the last exercise bout, the animals were anestheti zed and liver sections were sliced and incubated in [C-14]lactic acid or [C-14]fructose. An age-related decline was found in [C-14]lactate i ncorporation (middle-aged down arrow 66%, old down arrow 54%) and in [ C-14]fructose incorporation (middle-aged down arrow 51%, old down arro w 48%) into glycogen. Differences existed in lactate incorporation in trained compared to untrained animals for the young, middle-aged, and old groups: 150.1 +/- 11.3 vs. 102.1 +/- 10.0; 75.3 +/- 6.2 vs. 34.9 /- 6.4; and 69.3 +/- 14.9 vs. 47.0 +/- 4.7 nmol/g/h, respectively. No differences were found with training in any of the age groups for fruc tose; Phosphoenolpyruvate carboxykinase (PEPCK) activity and messenger RNA (mRNA) were significantly reduced in the old compared to the youn g rats (down arrow 64% and down arrow 58%, respectively).