Preferential resynthesis of muscle glycogen in fasting rats after exhausting exercise.

Despite carbohydrate starvation (fasting or fat feeding) considerable glycogen accumulation, ranging from 20 to 30 mumol glucose/g, occurred in hindlimb muscles of rats following exhausting exercise that caused severe muscle and liver glycogen depletion and hypoglycemia. The largest increase in muscle glycogen occurred during the first 3 h after exercise when plasma levels of glucagon and epinephrine were very high and insulin concentration was low. The concentrations of glycogen attained in different hindlimb muscles in the fasting and fat-fed animals were between 50 and 100% of the values found in rats fed carbohydrate after the exhausting exercise. In rats fed carbohydrate following exercise, liver glycogen accumulation greatly exceeds muscle glycogen accumulation. A remarkable difference in the response of liver glycogen was seen in the carbohydrate starved rats. In contrast to the rapid increase in muscle glycogen, liver glycogen was still essentially completely depleted in the fasting and fat-fed rats 24 h after exercise. This indicates that the glucose made available via gluconeogenesis was preferentialy channeled away from liver glycogen synthesis into muscle glycogen.