Muscle glycogen synthesis after a glucose infusion during post-excercise recovery in diabetic and non-diabetic subjects

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Abstract
Post-exercise muscle glycogen repletion after a glucose infusion was studied in diabetic (D) and non-diabetic (ND) subjects in two series of experiments; one in which muscle biopsies were examined and another in which arterial-femoral vein (a-fv) glucose differences were investigated. The results were compared with a control experiment where the subjects rested before the infusion. All experiments were performed after 12-14 h fast. The diabetics had not taken their morning insulin. The subjects bicycled till exhaustion. 15 min after cessation of exercise 0.5 g glucose per kg body weight was infused. Blood samples were drawn before exercise, in the last minute of exercise and repetetively during recovery. Biopsies were obtained before exercise, immediately after exercise and 65 min after the infusion. During exercise muscle glycogen content decreased from 68.7 ± 5.0 (D) and 81.4 ± 8.6 (ND) to 33.9 ± 5.1 (D) and 21.6 ± 3.3 (ND) mmol glucosyl units/kg w.w. After the glucose infusion muscle glycogen increased to 44.2 ± 3.8 (D) (P < 0.005) and 35.8 ± 5.7 (ND) (P < 0.005) mmol glucosyl units/kg w.w. Glycogen synthesis rates during recovery were 9.6 ± 1.5 (D) and 13.6 ± 2.6 (ND) mmol glucosyl units/kg w.w. per hr. No significant differences were observed in glycogen content or glycogen synthesis rate between the two groups. In the control experiments, no increase in muscle glycogen content was observed. The post-infusion a-fv-glucose differences were similar in diabetic and non-diabetic subjects during recovery, and in both groups larger than in the control experiments. It is concluded that during recovery after exercise a major portion of glucose infused as a single injection 15 min after exercise in diabetic and non-diabetic subjects, is utilized by muscle; mainly for glycogen synthesis. The rate of glycogen synthesis is similar in both groups. When glucose is infused without previous exercise, no changes in muscle glycogen content is observed.

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