Effect of immobilization on collagen synthesis in rat skeletal muscles

The activities of prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyltransferase (GGT), both enzymes of collagen biosynthesis, and the concentration of hydroxyproline (Hyp) were measured in the soleus, gastrocnemius, and tibialis anterior muscles of rats after cast immobilization in the middle position for 1 or 3 wk. The specific activity of PH decreased by 54 and 70-75% (P less than 0.001) in the soleus muscle after 1 and 3 wk, respectively, the corresponding decreases in GGT activity were 43 and 47% (P less than 0.001). A less pronounced decrease in the activities of these enzymes was observed in gastrocnemius and tibialis anterior muscles. The Hyp concentration in the soleus increased during the first week of immobilization but began to decrease thereafter, and the total muscular Hyp content was reduced after immobilization for 3 wk. The results suggest a marked inhibition of muscular collagen synthesis during immobilization. Electrical stimulation of the sciatic nerve partially prevented this disuse atrophy and the decreases in PH, GGT, and Hyp in the tibialis anterior muscle but not in the gastrocnemius or soleus muscles.