AJP - Regulatory, Integrative and Comparative Physiology, Vol 270, Issue 2 365-R372, Copyright © 1996 by American Physiological Society

ARTICLES

Hormonal regulation of hepatic gluconeogenesis: influence of age and training

D. A. Podolin, T. T. Gleeson and R. S. Mazzeo
Department of Kinesiology, University of Colorado, Boulder 80309, USA.

The contributions of three major gluconeogenic regulators, glucagon (10(-7) M), alpha-adrenergic agonist phenylephrine (10(-5) M), and beta-agonist isoproterenol (10(-5) M) to hepatic glucose synthesis in liver slices from Fischer 344 rats were examined in relation to age and endurance training. Young (4 mo), middle-aged (12 mo), and old (22 mo) male Fischer 344 rats (n = 66) were divided into trained or sedentary groups. Trained animals were run 10 wk on a treadmill at 75% of maximal capacity, 1 h/day, 5 days/wk. Animals were killed at rest, and sections of liver were removed and sliced in a tissue microtome. Slices were incubated in L-[U-14C]lactic acid, Ringer solution, and one of the aforementioned gluconeogenic regulators. Rates of lactate incorporation into glucose and glycogen were significantly greater in young compared with old animals for all three regulators in both trained and untrained animals. Training elicited a 35, 52, and 63% improvement in lactate incorporation into glucose compared with untrained when the livers of young (16.9 +/- 1.2 vs. 10.9 +/- 1.1 mumol.g protein-1.min-1), middle-aged (12.8 +/- 1.3 vs. 6.1 +/- 1.2 mumol.g protein-1.min-1), and old (11.2 +/- 1.1 vs. 4.1 +/- 0.6 mumol.g protein-1.min-1) animals, respectively, were incubated in glucagon. Rates with phenylephrine followed a similar pattern to that with glucagon across age and training, but absolute rates were significantly lower. No training effect in gluconeogenic rate was found when liver was incubated in the presence of isoproterenol. It is concluded that the gluconeogenic capacity of liver declines with age regardless of the gluconeogenic regulator and that training was able to partially offset age-related declines in glucagon-stimulated and alpha-receptor-mediated gluconeogenesis.

This article has been cited by other articles:

				C. O. Mattern, M. J. Gutilla, D. L. Bright, T. E. Kirby, K. W. Hinchcliff, and S. T. Devor Maximal lactate steady state declines during the aging process J Appl Physiol, December 1, 2003; 95(6): 2576 - 2582. [Abstract] [Full Text]

				K. D. Sumida, S. M. Arimoto, M. J. Catanzaro, and F. Frisch Effect of age and endurance training on the capacity for epinephrine-stimulated gluconeogenesis in rat hepatocytes J Appl Physiol, August 1, 2003; 95(2): 712 - 719. [Abstract] [Full Text] [PDF]

				D. A. Podolin, B. K. Wills, I. O. Wood, M. Lopez, R. S. Mazzeo, and D. A. Roth Attenuation of age-related declines in glucagon-mediated signal transduction in rat liver by exercise training Am J Physiol Endocrinol Metab, September 1, 2001; 281(3): E516 - E523. [Abstract] [Full Text] [PDF]

				B. C. Bergman, M. A. Horning, G. A. Casazza, E. E. Wolfel, G. E. Butterfield, and G. A. Brooks Endurance training increases gluconeogenesis during rest and exercise in men Am J Physiol Endocrinol Metab, February 1, 2000; 278(2): E244 - E251. [Abstract] [Full Text] [PDF]