Effects of glucocorticoid treatment and food restriction on rat hindlimb muscles.

Various metabolic, histochemical, and contractile measurements were made on soleus and gastrocnemius muscles of adult rats treated with triamcinolone acetonide (1 mg . kg-1 . day-1 for 6 wk), and compared to similar measurements in pair-fed and control animals. Contractile measurements were performed in situ under pentobarbital anesthesia. Gastrocnemius muscles from steroid-treated rats showed higher twitch and tetanic tensions when expressed in grams/gram of muscle, compared to control rats. Similar, although less marked, trends occurred in the less atrophied gastrocnemius muscles from pair-fed rats. Soleus muscles from steroid-treated rats exhibited significantly higher (139% of control) twitch tension (grams/gram of muscle), and elevated twitch/tetanus ratios, compared to control and pair-fed groups. No alterations occurred in muscle contractile speed in either muscle. The greater atrophy of fast compared to slow fiber types in gastrocnemius muscles under both experimental conditions did not occur in the soleus, a predominantly slow-twitch muscle. The atrophic and contractile responses of fast and slow muscles to these two conditions were quantitatively as well as qualitatively different.