Enzymatic adaptations to suspension hypokinesia in skeletal muscle of young and old rats.

Hindlimb hypokinesia was induced in young and old rats. After 3 weeks, the activities of five enzymes have been measured in soleus and medial gastrocnemius muscles. Soleus showed increased activity of hexokinase and decreased activity of phosphofructokinase, lactate dehydrogenase and malate dehydrogenase in both groups. The activity of 3-hydroxyacyl-CoA-dehydrogenase was decreased in the old muscle. Medial gastrocnemius showed decreased activity of phosphofructokinase and lactate dehydrogenase in both groups. The activity of 3-hydroxyacyl-CoA-dehydrogenase was decreased in the old muscle whereas hexokinase increased its activity in the young one. It is concluded that suspension hypokinesia results in changes at the enzymatic level. These changes appear to be related to the age of the muscle and to its fibre composition.