Muscle glycogen synthesis and disposition of infused glucose in humans with reduced rates of insulin-mediated carbohydrate storage.

Six men with a low rate of insulin-stimulated, non-oxidative carbohydrate disposal (storage) and six with a high storage rate were recruited for study of the fate of insulin-stimulated glucose uptake. [3-3H]glucose was infused before and during a 4-h hyperinsulinemic euglycemic clamp procedure in a dosage regimen designed to maintain a constant specific activity. From the disposition of label, the rate of insulin-mediated glucose incorporation into glycogen in the low-storage subjects was one-fourth that of the high-storage subjects (P less than .02). The insulin-mediated increase in muscle glycogen synthase activity in the low-storage subjects was one-fourth that of the high-storage subjects (P less than .05), suggesting the possibility of a causal relationship. In the high-storage but not the low-storage subjects, the rate of glycolysis inferred from the appearance of metabolized tritium in body water exceeded the carbohydrate oxidation rate (P less than .002). This suggests that in these subjects there is a significant fraction of glycolysis that is not oxidized and that this component of carbohydrate metabolism therefore contributes to storage.