Abstract
Although muscle is considered to be the most important site for postprandial glucose disposal, the metabolic fate of oral glucose taken up by muscle remains unclear. We, therefore, employed the dual isotope technique (intravenous, [6-3H]-glucose; oral, [1-14C]glucose), indirect calorimetry, and forearm balance measurements of glucose, lactate, alanine, pyruvate, O2, and CO2 in nine normal volunteers to determine the relative importance of muscle glycogenic, glycolytic, and oxidative pathways in disposal of an oral glucose load. During the 5 h after glucose ingestion (1 g/kg), 37 +/- 3% (24.9 +/- 2.3 g) of the load was oxidized and 63 +/- 3% (42.8 +/- 2.7 g) was stored. At least 29% (19.4 +/- 1.3 g) was taken up by splanchnic tissues. Muscle took up 26% (17.9 +/- 2.9 g) of the oral glucose coincident with a 50% reduction in its oxidation of fat. 15% of the oral glucose taken up by muscle (2.5 +/- 0.9 g) was released as lactate, alanine, or pyruvate; 50% (8.9 +/- 1.4 g) was oxidized, and 35% (6.4 +/- 2.3 g) was available for storage. We conclude that muscle and splanchnic tissues take up a comparable percentage of an oral glucose load and that oxidation is the predominant fate of glucose taken up by muscle, with storage in muscle accounting for less than 10% of the oral load. Thus, contrary to the prevailing view, muscle is neither the major site of storage nor the predominant site of disposal of an oral glucose load.