Postexercise muscle glycogen resynthesis in obese insulin-resistant Zucker rats.
Bruce, Clinton R., Jong Sam Lee, and John A. Hawley.
Exercise Metabolism Group, School of Medical Sciences, Faculty of Life Sciences,
RMIT University, Bundoora, Victoria, 3083, Australia
APStracts 8:0299A, 2001.
We determined the effect of an acute bout of swimming (8 × 30 min) followed by either
carbohydrate administration (0.5 mg/g glucose ip and ad libitum access to chow; CHO)
or fasting (Fast) on postexercise glycogen resynthesis in soleus muscle and liver from
female lean (ZL) and obese insulin-resistant (ZO) Zucker rats. Resting soleus muscle
glycogen concentration ([glycogen]) was similar between genotypes and was reduced by
73 (ZL) and 63% (ZO) after exercise (P < 0.05). Liver [glycogen] at rest was greater in
ZO than ZL (334 ± 31 vs. 247 ± 16 mumol/g wet wt; P < 0.01) and fell by 44 and 94%
after exercise (P < 0.05). The fractional activity of glycogen synthase (active/total)
increased immediately after exercise (from 0.22 ± 0.05 and 0.32 ± 0.04 to 0.63 ± 0.08 vs.
0.57 ± 0.05; P < 0.01 for ZL and ZO rats, respectively) and remained elevated above
resting values after 30 min of recovery. During this time, muscle [glycogen] in ZO
increased 68% with CHO (P < 0.05) but did not change in Fast. Muscle [glycogen] was
unchanged in ZL from postexercise values after both treatments. After 6 h recovery,
GLUT-4 protein concentration was increased above resting levels by a similar extent for
both genotypes in both fasted (~45%) and CHO-supplemented (~115%) rats.
Accordingly, during this time CHO refeeding resulted in supercompensation in both
genotypes (68% vs. 44% for ZL and ZO). With CHO, liver [glycogen] was restored to
resting levels in ZL but remained at postexercise values for ZO after both treatments. We
conclude that the increased glucose availability with carbohydrate refeeding after
glycogen-depleting exercise resulted in glycogen supercompensation, even in the face of
muscle insulin-resistance.
Received 2 February 2001; accepted in final form 10 May 2001
APS Manuscript Number A0106-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 18 June 2001