Physical activity and inactivity influences on 14C-leucine incorporation in reinnervated rat gastrocnemius.

The influence of activity and inactivity in reinnervated gastrocnemius muscles of adult rats was evaluated by measuring muscle mass, sarcoplasmic proteins (SP), myofibrillar proteins (MP), and 14C-leucine incorporation. Both sciatic nerves were crushed in 18 adult female Wistar rats, 6 of which were exercised daily on a 35% grade treadmill at a running speed of 27 m/min, 6 others underwent bilateral cast-immobilization of the ankle, knee, and hip joints at 90 degrees, and 6 were kept as sedentary controls between 2 and 6 weeks after denervation. During this period, all animals received daily an injection of 0.2 ml of 14C-leucine (sp. activity 51.4 muCi/mM). The exercised rats had similar muscle mass, but significantly increased in both MP and 14C-leucine incorporation, when compared to the sedentary rats. In contrast, the cast-immobilization group showed significant decreases in muscle weight and 14C-leucine incorporation in SP. These results suggest that activity enhances the apparent synthesis of MP in reinnervating muscles, but does not indicate that inactivity interferes with or limits the process of reinnervation by impeding the synthesis of SP or MP.