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Reduction-Oxidation State and Protein Degradation in Skeletal Muscle of Fasted and Refed Rats¹

Department of Biochemistry, University of Arizona, Tucson, AZ 85724

Redox state and protein degradation were measured in isolated muscles of fasted (up to 10 d) and refed (up to 4 d) 7- to 14-wk-old rats. Protein degradation in the extensor digitorum longus muscle, but not in the soleus muscle, was greater in the fasted rats than in weight-matched muscle from fed rats. The NAD couple was more oxidized in incubated and fresh extensor digitorum longus muscles and in some incubated soleus muscles of fasted rats than in weight-matched muscle from fed rats. In the extensor digitorum longus muscle of refed or prolonged fasted rats, protein degradation was slower and the NAD couple was more reduced than in the fed state. Therefore, oxidation of the NAD couple was associated with increased muscle breakdown during fasting, whereas reduction of the NAD couple was associated with muscle conservation and deposition.

KEY WORDS: • skeletal muscle • protein breakdown

¹ This work was supported by an Established Investigatorship from the American Heart Association and in part by Grant AM-28647 from the U.S. Public Health Service and Grant NAGW-227 from the National Aeronautics and Space Administration. Some results were presented at the Fifth International Symposium on Intracellular Protein Catabolism, Airlie, VA, May 31, 1984.

² Present address: Department of Physiology and Biophysics, Harvard Medical School, Boston, MA 02115.

³ Established Investigator of the American Heart Association. To whom reprint requests should be addressed.

Manuscript received 7 February 1986. Revision accepted 7 May 1986.