Glucose feeding during exercise : the mechanism for muscle and liver glycogen sparing in untrained rats

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Porter, David A.
Costill, David L.
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Thesis (M.S.)--Ball State University, 1985.
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The purpose of this study was to examine the effect of glucose ingestion on glycogen use andresynthesis during moderate exercise in untrained rats. Female Wistar rats (avg. wt.= 262 g) were assigned to either a control (C), control exercise (CE) or experimental exercise (EE) group. To examine glycogen resynthesis during exercise from a carbohydrate feeding, the EE animals were given 1 ml of a 10% glucose solution enriched with U-14C-glucose via stomach tube and run for 1h at 20.6 m/min. To distinguish between glycogen synthesis from endogenous versus exogenous sources, the CE animals were given a 0.1 ml tail-vein injection of U-14C-glucose tracer and run for 1h at 20.6 m/min. The C animals served as resting controls. Immediately after sacrifice, samples of the liver, soleus m., plantaris m., gastrocnemius m. and w. vastus m. were removed and analyzed for glycogen concentration and 14C activity in a glycogen pellet. Muscle and liver glycogen was 4.72 umol/g and 5.16 umol/g, respectively, higher (p<0.05) in the EE animals than in the CE animals. The average 14C activity of the muscle glycogen (mean ± SE) (182.85+ 31.79 cpm/g) was greater (p<0.05) than that of the liver (47.44 + 8.10 cpm/g), indicating a greater exogenous glucose incorporation into muscle glycogen than liver glycogen during exercise. However, this activity represented less than 2% of the remaining glycogen found in each tissue. Thus, it appears that the glycogen sparing observed with the glucose feeding in untrained rats was the result of an increased contribution of blood glucose to muscle metabolism.Ball State UniversityMuncie, IN 47306