Muscle Glycogen Synthesis and Disposition of Infused Glucose in Humans With Reduced Rates of Insulin-Mediated Carbohydrate Storage

Abstract

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 < .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 < .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 < .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.