The effects of remobilization and exercise on collagen biosynthesis in rat tendon

The activities of prolyl 4-hydroxylase (PH) and galactosylhydroxylysyl glucosyl-transferase (GGT), and the concentration of hydroxyproline (Hyp) were measured in the Achilles and tibialis anterior tendons of rats after periods of 0, 3, 7 and 14 days remobilization following a 7-day cast immobilization. PH, GGT and Hyp were also observed in the soleus and tibialis anterior muscles and the Achilles tendon 2, 5 and 10 days after a single bout of exhaustive exercise. During immobilization, the specific activity of PH decreased by 23% (P less than 0.05) and 54% (P less than 0.01) in the Achilles and tibialis anterior tendons. A less pronounced decrease was observed in GGT activity. During the remobilization experiment the specific activity of PH increased gradually, whereas GGT activity increased rapidly. The GGT activity was 61-66% (P less than 0.01) above the control value in the Achilles and tibialis anterior tendons after 3 days, decreasing to the control level after 14 days. Hyp concentration did not change significantly. In the exercise experiment, the specific activity of PH in the soleus muscle increased by 64% (P less than 0.05) 2 days after the prolonged exercise and then decreased gradually to the control level. There were no significant changes in PH or GGT activity in the tibialis anterior muscle. The specific activity of PH and GGT and Hyp concentration remained unchanged in the Achilles tendon. The results suggest that, in the tendon, restoring normal cage activity after immobilization results in acceleration of collagen synthesis. The results suggest also that collagen synthesis of the tendon is insensitive, but that of the soleus muscle is sensitive, to an acute increase in physical activity.