EFFECT OF HIGH AND LOW CARBOHYDRATE DIET ON THE SYNTHESIS OF PROGLYCOGEN AND MACROGLYCOGEN IN HUMAN SKELETAL MUSCLE

Abstract

1471 The present study examined the role of carbohydrate(CHO) on the resynthesis of the two pools of glycogen, proglycogen(PG) and macroglycogen(MG), in human skeletal muscle. Ten subjects completed an exhaustive glycogen depletion exercise bout at 70% VO2 max on two occasions separated by 2 weeks. The diet was controlled by providing weighed, pre-packaged food such that either 75%(HC) or 32%(LC) of the energy was CHO. Muscle biopsies were taken at exhaustion(EXH), 4, 24 and 48 hours. The total muscle glycogen(TotG) at EXH was 79±15.6 and 113±20.1mmol glucosyl units/kg dw for HC and LC respectively. At exhaustion the MG concentration represented about 12% in each group. From EXH-4h there was an increase in the PG only for HC, and no change in MG in either diet(p<0.05). From 4-24h the concentration of PG increased in both conditions(p<0.05). Between 24-48h in HC all of the increase in TotG was due to the MG fraction(p<0.05). The MG and PG concentrations for HC were significantly greater than in LC at 24 and 48h (p<0.05). At 48h the MG represented 40% of the TotG for the HC diet and only 21% for LC. There was no change in the net rates of synthesis of PG or MG over 48h in LC(p<0.05). The net rate of PG synthesis from 0-4h in the HC was 16±1.68mmol glucosyl units/kg dw/h which is 3-fold greater than in the LC(p<0.05). The rate of PG synthesis decreased significantly 4-24h while the rate of MG synthesis was not significantly different over 48h but was significantly greater than LC(p<0.05). It appears that the two pools are dynamic and sensitive to CHO, especially the PG pool. The glycogen supercompensation is first generated in PG and the final increase in TotG occurs exclusively in MG. These data suggest that the MG pool is an important reservoir for glycogen synthesis at later time points if the CHO availability is high.