Age-related Changes in Rat Muscle Glycogen Synthase Activity

Dall'aglio, Elisabetta; Chang, Helen; Reaven, Gerald M.; Azhar, Salman

This study was designed to evaluate effects of aging on glycogen synthase activity in rat skeletal muscle. Total enzyme activity was shown to be significantly, (p < .001) lower in tensor fascia latae, biceps femoris, and soleus muscle obtained from 24-month-old compared with 2-month-old rats. Similarly, values for the active form of enzyme were significantly lower, (p < .001) in all three muscle types of 24-month-old compared with 2-month-old rats. This age-related decline in glycogen synthase activity was not due to a reduction in the affinity of the enzyme for its activator (glucose-6-phosphate) and was independent of the concentration of substrate (UDP-glucose) in the assay system. Because similar age-related changes were seen when enzyme activity was expressed per milligram of muscle protein or per gram of muscle tissue, the fall in enzyme activity was not a simple function of an age-related decline in muscle mass. Glycogen levels also were reduced significantly in tensor fascia latae, biceps femoris, and soleus of 24-monthold rats compared with 2-month-old rats, p < .001. These results document an age-related change in a key enzyme regulating glycogen metabolism in muscle.