CONTRACTILE RESPONSES OF RAT FAST-TWITCH AND SLOW-TWITCH MUSCLES TO GLUCOCORTICOID TREATMENT

In an attempt to determine whether chronic glucocorticoid treatment affects speed‐ and strength‐related properties of fast‐twitch muscle and slow‐twitch muscle, in‐situ contractile properties of soleus and gastrocnemius muscles were measured in rats after 14 days on a regimen of triamcinolone acetonide injected at a dosage of 2 mg/kg/day. No effects on contractile speed or strength were noted for either muscle. The time to peak tension in soleus muscle was significantly longer in the treated group (43.0 ± 1.0 msec) than in the control group (38.7 ± 0.7 msec); however, this was attributed to a prolongation of “active state” duration, as suggested by the fact that treated muscles also showed significantly elevated twitch‐tetanus ratios. The treatment‐induced enhancement of the specific twitch tension was more pronounced in the gastrocnemius muscles (198% ± 19% of control) than in the soleus muscles (153% ± 9% of control). The difference in response to steroid treatment may reflect structural and functional difference in fast‐ and slow‐muscle membrane systems. Copyright © 1979 Houghton Mifflin Professional Publishers