AJP - Endocrinology and Metabolism, Vol 264, Issue 3 E373-E379, Copyright © 1993 by American Physiological Society

ARTICLES

Exercise training and clenbuterol reduce insulin resistance of obese Zucker rats

C. E. Torgan, J. T. Brozinick Jr, E. A. Banks, M. Y. Cortez, R. E. Wilcox and J. L. Ivy
Department of Kinesiology, University of Texas, Austin 78712.

This study compared the effects of aerobic exercise training and chronic administration of the selective beta 2-adrenergic agonist clenbuterol on whole body and skeletal muscle insulin resistance in obese (fa/fa) Zucker rats. Obese rats were randomly assigned to training, clenbuterol, or sedentary control groups. Lean littermates served as a second control group. After 4-5 wk of treatment, an oral glucose tolerance test was performed, followed 1 wk later by hindlimb perfusion, during which time the rates of glucose uptake and 3-O-methyl-D-glucose (3-MG) transport were assessed in the presence of a submaximal (500 microU/ml) insulin concentration. Training resulted in a significant increase in citrate synthase and cytochrome oxidase activity in the recruited muscles. Clenbuterol induced a large increase in muscle mass but provoked a significant decrease in oxidative enzyme activity and beta-adrenergic receptor density. Both treatments increased glucose tolerance and reduced the postglucose insulin response, with the improvements being more pronounced in the clenbuterol group. However, only exercise training improved insulin-stimulated hindlimb muscle glucose uptake (11.37 +/- 0.65, 8.73 +/- 0.77, and 8.27 +/- 0.41 mumol.g-1.h-1 for trained, clenbuterol, and sedentary control groups, respectively) and 3-MG transport. These results suggest that aerobic exercise training attenuated the insulin-resistant condition in the obese Zucker rat by a mechanism other than or in addition to beta 2-adrenergic receptor activation.

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