Collagen synthesis in rat skeletal muscle during immobilization and remobilization

The activities of prolyl 4-hydroxylase (PH) and galactosylhydroxylysine glucosyltransferase (GGT), which are both enzymes of collagen biosynthesis, and the concentration of hydroxyproline (Hyp) were measured in the soleus muscle (S) of rats after 3 and 42 days of cast immobilization. PH, GGT, and Hyp were also observed in S and tibialis anterior muscle (TA) at 0, 3, 7, and 14 days of remobilization after 7 days of cast immobilization. The activities of PH and GGT decreased significantly in shortened S after an immobilization of 3 days and were low thereafter. Immobilization for 7 days caused a decrease in the content of the soluble collagen in shortened S. Remobilization resulted in a rapid increase in the activities of collagen marker enzymes and the soluble collagen in S. In stretched TA, the specific activities of PH and GGT were increased significantly after 1 wk of immobilization and returned to the control levels during the remobilization period. The content of soluble collagen was above the control level after immobilization and returned to control level during the remobilization period in stretched TA. There were, at most, slight changes in the total content of insoluble collagen in S and TA. The results suggest rapid changes in the fractional synthesis rate of procollagen but, at most, slow changes in the stable content of muscular collagen during cast immobilization and remobilization. Muscle contractile activity and tension seem to be positive regulators of PH and GGT activities.