Fiber type specific effects of clenbuterol and exercise training on
insulin resistant muscle.
Torgan, C. E., G. J. Etgen, Jr, H. Y. Kang, and J. L. Ivy.
Exercise Physiology and Metabolism Laboratory, Department of
Kinesiology, The University of Texas, Austin, TX 78712
APStracts 2:0119A, 1995.
The interrelationships among glucose uptake, GLUT4 protein, and
citrate synthase activity in insulin resistant skeletal muscle were
investigated. Female obese (fa/fa) Zucker rats were randomly assigned
to treadmill training, ingestion of the selective [beta]2-adrenergic
agonist, clenbuterol, or sedentary control groups. After 7-8 wk of
treatment, hindlimbs were perfused to determine maximal insulin
-stimulated (10 mU/ml) 2-deoxyglucose (2-DG) uptake. Exercise training
significantly enhanced 2-DG uptake and GLUT4 protein in red
gastrocnemius and plantaris. Alternatively, 2-DG uptake was not
altered in soleus following exercise training despite a 52% increase
in GLUT4 protein. The increases in GLUT4 protein in red
gastrocnemius, plantaris and soleus of the trained rats were
accompanied by increases in citrate synthase activity. In contrast to
exercise training, clenbuterol administration decreased citrate
synthase activity in red and white gastrocnemius, yet had no effect
on GLUT4 protein levels or maximal insulin-stimulated 2-DG uptake.
Clenbuterol treatment did, however, increase citrate synthase
activity and GLUT4 protein in soleus. These findings indicate that
total GLUT4 protein largely determines the maximal rate of insulin
-stimulated glucose uptake in fast-twitch muscle, whereas in slow
-twitch muscle, it does not. In addition, the results demonstrate that
coordination of proteins governing glucose uptake and disposal may be
disrupted in a fiber type specific manner. Overall, the findings
raise important questions as to whether regulation of proteins
governing glucose uptake and disposal differs significantly among
fiber types.
Received 29 September 1994; accepted in final form 9 March 1995.
APS Manuscript Number A1010-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 28 March 1995.