Interaction of exercise training and clenbuterol on glut4 protein
in muscle of obese zucker rats.
Kuo, Chia-Hua, Zhenping Ding, and John L. Ivy.
Exercise Physiology and Metabolism Laboratory, Department of
Kinesiology, The University of Texas at Austin, Austin, Texas
APStracts 3:0159E, 1996.
Chronic administration of clenbuterol, a [beta]2-adrenergic agonist,
attenuates the exercise training-induced improvement in muscle
insulin resistance of the obese Zucker rat. The present study was
conducted to determine if clenbuterol also attenuates the increase in
muscle GLUT4 protein which occurs with exercise training, and to
determine if the action of clenbuterol is related to its ability to
down regulate the [beta]-adrenergic receptors. Female, obese Zucker
rats were randomly assigned to one of the following four groups:
control (CON, n=7), clenbuterol (CL, n=8), exercise training (TR,
n=8) and clenbuterol with exercise training (CL+TR, n=8). Rats
assigned to the training groups were run on a rodent, motor-driven
treadmill for 6-7 wk. Rats receiving clenbuterol were intubated with
0.8 mg/kg body weight 30 min before running each day. Red quadriceps
(RQ) and white quadriceps (WQ) GLUT4 protein concentrations of TR
rats were significantly greater than CON, and CL+TR rats. The RQ
GLUT4 protein concentration of the CL+TR rats was significantly
greater than CON, but this difference did not occur in the WQ. GLUT4
protein concentrations were not difference between the CON and CL
rats. The patterns of RQ and WQ GLUT4 mRNA were similar to that of
their GLUT4 proteins, respectively. Rats receiving daily injections
of propranolol (30 mg/kg body wt), a [beta]-adrenergic receptor
antagonist, demonstrated no increase in GLUT4 protein in RQ or WQ
after 6 wk of exercise training. These results indicate that, 1)
clenbuterol can attenuate the increase in muscle GLUT4 protein
associated with exercise training, and 2) that this effect is likely
mediated by a down regulation of the [beta]-adrenergic receptors.
Received 16 January 1996; accepted in final form 26 June 1996.
APS Manuscript Number E16-6.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996