Key result
Treadmill exercise to exhaustion in normal and diabetic rats demonstrated an inverse relationship between cardiac glycogen content and glycogen synthase %I activity during recovery.
Why the study?
Does a treadmill run to exhaustion affect cardiac glycogen repletion, glycogen synthase activity, and glucose 6-phosphate levels in normal and diabetic rats?
Does a treadmill run to exhaustion affect cardiac glycogen repletion, glycogen synthase activity, and glucose 6-phosphate levels in normal and diabetic rats?
Cardiac glycogen repletion after exercise is driven by combined increases in glycogen synthase activity and glucose 6-phosphate levels, with an inverse relationship between glycogen content and synthase activity in both normal and diabetic hearts.
Answers are grounded in this paper and cite their sources.
Findings in diabetic rat models warrant caution before clinical extrapolation; extends mechanistic insights on glycogen recovery but leaves human relevance open.
Previous studies have shown that cardiac glycogen content is replenished to supranormal levels after exercise. To better understand this phenomenon glycogen synthase (GS) %I activity as well as glucose 6-phosphate (G-6-P) and glycogen (G) concentrations were measured in hearts from normal and alloxan diabetic rats killed at various time intervals before or after a treadmill run to exhaustion. In normal animals at exhaustion G was reduced but GS %I and G-6-P were elevated. During 2-8 h of recovery G was elevated, %I depressed, and G-6-P unchanged when compared to their preexercise values. By contrast, diabetic hearts that had elevated G and low %I were characterized by abnormally high G-6-P concentrations. At exhaustion in these hearts %I increased significantly in response to a decrease in G. These findings suggest that glycogen repletion occurs in normal heart as a result of the combined increases in GS %I and G-6-P levels present at the cessation of work. In both normal and diabetic hearts there exists an inverse relationship between G content and GS %I activity.
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Conlee et al. (1977) studied Normal and alloxan diabetic rats. Treadmill run to exhaustion vs. Preexercise values was evaluated on Glycogen synthase %I activity, glucose 6-phosphate, and glycogen concentrations. Treadmill exercise to exhaustion in normal and diabetic rats demonstrated an inverse relationship between cardiac glycogen content and glycogen synthase %I activity during recovery.
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