Level of glycogen stores and amount of ingested glucose regulate net carbohydrate storage by different mechanisms.

摘要

The respective effects of the level of glycogen stores and the size of the glucose load on the pathways of carbohydrate (CHO) metabolism were compared over the 5-hour period following glucose ingestion in normal human subjects. For this purpose, labeling of the oral glucose load with [3-(3)H]- and [U(14)C] glucose was combined with indirect calorimetry. In group I, 75 g glucose was given to subjects who had either been "fed" with intravenous (IV) glucose or fasted for 13, 24, or 36 hours, or 4 days. In fed versus 4-day-fasted subjects, net CHO storage averaged approximately 15 versus 63 g/5 h (P <.001). About 83% of the increase in fasted subjects was due to suppression of glycogen breakdown, with only minimal stimulation of glycogen synthesis from oral glucose. Over the whole range of nutritional conditions tested, a strong positive correlation existed between basal CHO oxidation and glycogen breakdown occurring during the oral glucose tolerance test (OGTT), suggesting that the initial degree of repletion of hepatic glycogen stores is a major determinant of postprandial glycogen turnover. In group II, OGTTs with 33 and 100 g glucose were compared in 13-hour-fasted subjects. Net storage rose from approximately -6 to approximately 37 g/5 h (P <.001) solely because of an increase in glycogen synthesis with no inhibition of glycogen turnover. Overall, these results show that the initial dietary state and the size of the glucose load modulate postprandial net CHO accumulation by different mechanisms.