DIRECT MEASUREMENT OF CHANGE IN MUSCLE GLYCOGEN CONCENTRATION AFTER AMIXED MEAL IN NORMAL SUBJECTS

Postprandial storage of carbohydrate as glycogen in muscle was quantit ated in normal subjects (n = 8) by natural abundance C-13-nuclear magn etic resonance spectroscopy with proton decoupling in a 4.7-tesla magn et. After an overnight fast three basal measurements of gastrocnemius muscle glycogen were made and a mixed meal was given. Muscle glycogen concentration rose from 83.3 +/- 5.2 to a maximum of 100.2 +/- 6.7 mmo l/l muscle at 4.9 h (P < 0.01) and fell thereafter to 90.6 +/- 5.9 mmo l/l muscle at 7 h postprandially (P < 0.006). The meal brought about a n increase in plasma glucose from 5.4 +/- 0.2 to 7.3 +/- 0.4 mmol/I at 30 min but this was followed by a rapid fall to 6.2 +/- 0.4 mmol/I at 75 min. Plasma insulin rose from 62.4 +/- 11.4 to 900 +/- 216 pmol/l at 30 min and declined steadily thereafter. It was calculated from tot al muscle mass measurements and estimation of carbohydrate absorption rates that at peak muscle glycogen concentrations between 26 and 35% o f the absorbed carbohydrate was stored as muscle glycogen. These data quantitate the role of skeletal muscle glycogen synthesis in postprand ial carbohydrate storage and demonstrate that this tissue acts as a dy namic buffer to maintain glucose homeostasis during postprandial subst rate storage.