Inhibition of glycogenesis in rat muscles partially depleted of glycogen

This study aimed to examine the extent to which repletion of glycogen in muscles partially depleted of glycogen may be inhibited by contractions and epinephrine. Four experiments were carried out on untrained male Wistar rats. 1) Animals ran 150 min (1,200 m/h) on a treadmill set at +10 degrees incline. After 60, 90, and 120 min of running, they were given glucose (40% solution, 1 ml/100 g) by a stomach tube. 2) Rats ran on a treadmill set as above for 20 min at 3,200 m/h and then 2 h at 800 m/h. 3) In anesthetized rats, gastrocnemius-plantaris muscle group was made to contract isometrically by means of stimulation of the sciatic nerve. The nerve was stimulated with tetanic pulses (7 V, 0.05-ms duration, delivered in 100-ms trains at 100 Hz): first 15 min, 2 pulses/s, then 2 h, 1 pulse/2 s. 4) Epinephrine (0.5 mg/kg) was administered subcutaneously 10 min before onset of stimulation of the sciatic nerve. The nerve was stimulated 15 min with tetanic pulses (as above), 2 pulses/s. Next, rats were rested for 2 h. Level of glycogen was determined in samples of white and red gastrocnemius, plantaris, and soleus. Initial running or stimulation resulted in pronounced glycogen depletion in each muscle. Thereafter, either considerable or full repletion of glycogen occurred in the muscles despite continued contractile activity or the presence of epinephrine. The degree of repletion depended both on the type of muscle and the type of activation of glycogenolysis (running, stimulation of the nerve, epinephrine).(ABSTRACT TRUNCATED AT 250 WORDS)