AJP - Regulatory, Integrative and Comparative Physiology, Vol 240, Issue 5 330-R334, Copyright © 1981 by American Physiological Society
Effect of endurance training on liver cAMP response to prolonged submaximal exercise
W. W. Winder, R. T. Holman and S. J. Garhart
Endurance-trained rats utilize liver glycogen at a reduced rate during
exercise compared to nontrained rats. We have compared liver cAMP responses
to exercise in trained and nontrained rats in an attempt to elucidate the
mechanism of this adaptation. Rats were trained on a motor-driven rodent
treadmill 5 days/wk for 12 wk. On the day of the test, trained and
nontrained rats were quickly anesthetized after running at 21 m/min up a
15% grade for periods up to 90 min. After 45 min of running, liver cAMP had
increased from 0.60 +/- 0.01 to 0.90 +/- 0.03 pmol/mg in nontrained rats
whereas no significant increase had occurred in livers of trained rats.
Plasma glucagon and norepinephrine levels were significantly lower in
trained rats at this point. At the end of 90 min hepatic cAMP was 1.28 +/-
0.12 in nontrained compared to 0.83 +/- 0.06 pmol/mg in trained rats.
Plasma glucagon was markedly elevated in nontrained but not in trained rats
at this time. The lower rate of liver glycogen utilization in trained rats
is consistent with the lower cAMP levels maintained early in exercise.
