ASGSB 1998 Annual Meeting Abstracts

[71]
MUSCLE-SPECIFIC EFFECTS OF CLENBUTEROL ON PROTEIN DENSITY AND WET WEIGHT IN SOLEUS AND PLANTARIS MUSCLES OF MATURE, HINDLIMB-SUSPENDED RATS.   L.E. Wineski, D.A. von Deutsch, W-D Chen, S.A. Pitts, B.J. Klement, E. Joseph, D.E. Potter, C. Nokkaew, B. George, M. Cray, T. Nguyen, and D.F. Paulsen. Musculoskeletal Research Group, Space Medicine and Life Sciences Research Center, Morehouse School of Medicine, Atlanta, GA

The Я-adrenergic agonist, clenbuterol (Cb), produces skeletal muscle hypertrophy and diminishes muscle atrophy caused by a variety of conditions. Most studies in rats have been carried out in subadult animals. In this study, we further characterize the effects of this potential countermeasure to microgravity-induced muscle atrophy on the muscles of mature rats, in which fiber type and myosin heavy chain (MHC) expression are stable. Mature, male, Sprague Dawley rats (6 months old; > 400 g) were subjected to standard hindlimb suspension for two weeks and treated in a 2-days-on-2-days-off regimen of subcutaneous Cb injections (1 mg Cb/kg body weight). Pair-fed controls included vehicle treated suspended rats, vehicle and Cb treated non-suspended rats, and vehicle and Cb treated "tethered" rats which were fitted with the hindlimb-suspension apparatus but not suspended. The predominantly slow-twitch soleus, and the predominantly fast-twitch plantaris muscles, from each group of animals, were analyzed for both muscle wet weight and protein density (µg protein/mg muscle wet weight). Cb induced a significant increase in the wet weight of both muscles in the nonsuspended and tehtered animals. In the suspended animals there was a significant Cb-induced increase in wet weight in the plantaris, but not in the soleus. Conversely, Cb treatment significantly increased muscle protein density in the soleus, but not the plantaris. These findings suggest that Cb increases muscle wet weight, but not protein density, in predominantly fast muscles and increases protein density, but not wet weight, in predominantly slow muscles. This suggests that mechanisms for regulating Я-agonist-induced muscle growth and atrophy differ in slow and fast fiber types. Analyses of MHC expression and protein content in these and several other hindlimb muscles are underway to test this conclusion. (Supported by NASA 1NA4A438 & NAG9-971 and by NIH GM08248 & RR03034).

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