The effects of clenbuterol and interval training on exercise performance and myosin light chain isoform expression in mouse skeletal muscle

Abstract

Although the quantitative effects of p2-adrenergic agonists on protein accretion have been well established, less is known about the qualitative effects of these drugs on protein isoform expression and functional capacity of the animal. Therefore, the purpose of this study was to determine the separate and combined effects of clenbuterol (CB) and interval training on running performance and myosin light chain (LC) isoform expression in mouse skeletal muscle. Mice were randomly assigned to one of four treatm ent groups: 1) control (CON), 2) exercise (EX), 3) drug (CB), or 4) exercise+drug (EX+CB). CB and EX+CB mice were given CB (1.6 mg/kg) orally 4 days/week. EX and EX +C B mice were trained 4 days/week on a motorized treadmill (3 sets of 3 min, 36-40 m/min, 6-10° grade, 30 s recovery). Exercise performance was determined before and after 8 weeks o f treatment with a run-to-exhaustion test. Following 8 weeks of treatment, exercise conditioning increased total work (58%), while clenbuterol decreased total work (25%) on the treadmill. The simultaneous application of both treatments did not cause significant changes in work after eight weeks of treatment. Comparisons between treatments at the post-study exercise test indicated that the CON, CB, and EX +CB were not significantly different from each other, whereas, the EX group exhibited markedly greater exercise performance than the other groups. Gel electrophoresis indicated that neither the separate nor combined treatments promoted any changes (p>.05) in fast and slow myosin LC isoforms. Although not different from each other after 8 weeks, CB and EX+CB treatments produced greater values than CON for the following variables: muscle mass (25-34%), total protein (17- 50%), and myofibrillar protein (26-81%). There were no differences between EX and CON animals for any of these morphological variables. It was concluded: 1. Interval training enhances exercise performance without quantitatively altering total or myofibrillar protein contents. 2. Clenbuterol may decrease work indirectly by promoting muscle hypertrophy. 3. The adaptations in exercise performance are not a consequence of qualitative changes in the expression of myosin LC isoforms. 4. The combination of the two treatments have antagonistic effects on total work, while the two treatments do not interact to diminish the muscle-specific anabolic effects.