The effects of dietary protein levels and anabolic steroid ad- ministration (stanozolol, 10 mg/kg body weight per day) on alterations in some properties of rat soleus and plantaris muscle by hindlimb suspension (3 weeks) were studied. Female rats were assigned to six groups control (CONT), suspension (SUS), suspension with ababolic steroid treatment (SUS+AS) for 20% -casein and 30% - casein diet respectively. Wet weight and maximum tetanic tension (Pmax) in both muscles decreased considerably by SUS. In only soleus, specific tension (Pmax/muscle cross sectional area) decreased. This result indicates lower myofibrillar protein cocentration and higher interstitial fluid volume in SUS than in CONT.
　The decrease in twitch duration and fatigability in soleus were induced by SUS, but not in plantaris. Inhibitory effects of AS on the loss of weight and Pmax were found, particularly in fast-twitch plantaris. This observation supports the evidence that AS may have fiber-type specific effects. In suspended soleus fibers, however, central corelike lesion and disruption of intermyofibrillar networks were observed. The percent change of these aberrant fibers was significantly higher in 20% -casein SUS than in 20% -casein SUS+AS, 30%-casein SUS and SUS+AS. These results suggest that the higher protein diet and AS diminished the pathological changes. No effects of AS were observed on twitch duration and fatigability. We provided some evidence to suggest that anabolic steroids during unweighting ameliorate the loss of weight and force-generating capacity in skeletal muscle, regardless of the amount of dietary protein which is required for growth and maintenance of muscle in the present study.

DESCENTE SPORTS SCIENCE Vol.16/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE