Hormonal regulation of hepatic gluconeogenesis: influence of age
and training.
Podolin, Deborah A., Todd T. Gleeson, and Robert S. Mazzeo.
Departments of Kinesiology, and Environmental, Population,
Organismic Biology, University of Colorado, Boulder, Colorado,
80309
APStracts 2:0253R, 1995.
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 hr/day, 5 days/wk. Animals were sacrificed
at rest, sections of liver removed and sliced in a tissue microtome.
Slices were incubated in L-[14C(U)]-lactic acid, Ringer's solution
and one of the aforementioned gluconeogenic regulators. Rates of tate
incorporation into glucose and glycogen were significantly greater in
young compared to 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 to
untrained when the livers of young (16.9+/-1.2 vs 10.9+/-1.1),
middle-aged (12.8+/-1.3 vs 6.1+/-1.2) and old (11.2+/-1.1 vs 4.1+/
-0.6 [mu]mol/g protein/min) 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.
Received 10 April 1995; accepted in final form 22 August 1995.
APS Manuscript Number R232-5.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.