ADRENERGIC STIMULATED SKELETAL-MUSCLE GLYCOGENOLYSIS IN PERFUSED HINDLIMBS OF YOUNG AND OLD MALE FISCHER-344 RATS

Epinephrine (Epi)- and forskolin (FSK)-stimulated glycogenolysis of sk eletal muscle was evaluated in perfused hindlimb isolated from male Fi scher 344 (F344) rats, ages 6, 12, and 26 mo. Muscle glycogen stores w ere reduced by sciatic nerve stimulation and replenished by infusing 1 0 mM glucose, 500 mu U insulin, and 5 mu Ci [C-14]glucose via a left c arotid artery cannula. Then the hindlimb was perfused with a modified Krebs-Henseleit buffer (pH 7.4). At minute 20 of the perfusion, Epi [0 .0 (perfusate), 0.25, 0.50, or 0.75 mu M] or 40 mu M FSK were infused for 10 min. Radioactivity (C-14) in the effluent perfusate was collect ed every 60 s during a 20-min preinfusion, a 10-min Epi infusion, and a 20-min postinfusion period and was used to determine the rate of mus cle glycogen utilization. Total C-14 release increased with Epi and 40 mu M FSK. However, the pattern of release did not differ significantl y with age. In general, the fraction of the perfusate released as (CO2 )-C-14 increased in the presence of FSK and Epi but did not significan tly differ with age. [C-14]lactate released in response to Epi increas ed in the 6-mo-old group, remained unchanged in the 12-mo-old group, a nd decreased in the 26-mo-old group compared with 0.0 Epi (perfusate) values. It appears that stimulation of skeletal muscle glycogenolysis via adrenergic receptor or postreceptor/adenosine 3',5'-cyclic monopho sphate-mediated mechanisms is unaffected by age. However, the utilizat ion of carbohydrate by isolated hindlimb muscle is altered in the agin g rat, resulting in a more oxidative metabolism.