ASGSB 2001 Abstracts - THE CORRELATION BETWEEN MUSCLE MASS, PROTEIN CONTENT AND POLYAMINE LEVELS UNDER UNLOADING CONDITIONS. D.A. von Deutsch, I.K. Abukhalaf, S.W. Sahlu, S.A. Abera, N.A. Silvestrov, L.E. Wineski, S.A. Pitts, D.E. Potter, R.R.Roper

ASGSB 2001 Annual Meeting Abstracts

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THE CORRELATION BETWEEN MUSCLE MASS, PROTEIN CONTENT AND POLYAMINE LEVELS UNDER UNLOADING CONDITIONS. D.A. von Deutsch^1,2, I.K. Abukhalaf^1,2,3, S.W. Sahlu^1,2, S.A. Abera^1,2, N.A. Silvestrov^2,3, L.E. Wineski⁴, S.A. Pitts⁴, D.E. Potter^1,2, R.R.Roper^1,2. ¹Space Medicine and Life Sciences Research Center, ²Department of Pharmacology & Toxicology, and the ³Clinical Research Center, ⁴Department of Anatomy and Neurobiology, Morehouse School of Medicine, Atlanta, GA 30310

Anabolic agents such as Я2-adrenoceptor agonists are useful tools for probing the mechanisms by which muscles respond to disuse. One such agent, clenbuterol (Cb), was examined under different loading conditions with respect to its effects on skeletal muscle mass, protein (total and myofibrillar) content, and polyamines in mature male rats. The hindlimb muscles used in these studies were the predominately slow-twitch (type I) adductor longus [ADL] and fast-twitch (type II) extensor digitorum longus [EDL]. Pair-fed rats were divided into four experimental groups: vehicle- and Cb-treated non-suspended, vehicle- and Cb-treated (1 mg/kg) hindlimb suspended. Unloading caused significant decreases in ADL mass, myofibrillar and cytosolic protein content of such magnitude that treatment with Cb could not fully overcome the loss. On the other hand, Cb did significantly increase unloaded ADL spermidine levels. In the EDL, unloading had little effect on muscle mass or total protein content. However, a significant decrease in EDL’s myofibrillar protein content was observed along with significant increases in cytosolic proteins and spermidine. Treatment with Cb significantly increased all parameters in the EDL. Conclusion: Unloading results in a general decrease in both myofibrillar and cytosolic protein content in the ADL as well as a significant decrease in spermidine content. In contrast, the EDL presents a more complex response to unloading. Understanding why EDL’s cytosolic protein content increased under unloading conditions may help provide greater insight into the nature of this muscle’s resistance to unloading. This work was supported, in part, by NASA grant NCC9-112 (I.K.A.) and NIH grant RCRII 2P20 RR11104-07 (I.K.A.).

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