Hindlimb suspension increases insulin binding and glucose metabolism

After 28 days of hindlimb-suspension, insulin binding, 2-deoxy-D-glucose (2-DG) uptake, and glucose metabolism (glycolysis and glycogenesis) were determined at various insulin concentrations (0.2-30 nM) in soleus muscle of young (18-day-old) and adult (150-day-old) rats. Compared with age-matched controls the young (YS) and adult suspended (AS) rats had lower soleus and body weights and insulin levels (P less than 0.05). Per milligram of protein, insulin binding, 2-DG uptake, and the rate of glycolysis were increased by approximately 200%, and the rate of glycogenesis was increased approximately 100% in the YS group (P less than 0.05). Except for a reduction in glycogenesis (P less than 0.05) all other parameters also increased in the AS rats (P less than 0.05). On the basis of the whole muscle the rate of glucose metabolism (glycogenesis + glycolysis) was reduced in the YS rats (P less than 0.05), but in the AS rats glucose metabolism was similar to the controls. Thus the increased glucose metabolism (i.e., per milligram of protein) in the YS and AS groups may represent a compensatory response by atrophied muscle to attempt to sustain glucose removal from the circulation. Because greater insulin binding occurred in YS muscle [35% slow-twitch (ST)] than in the control group (70% ST), and greater insulin binding occurred in the AS (81% ST) than in the control group (90% ST), higher insulin binding capacities are not always related to a high proportion of ST muscle fibers. In conclusion, after hindlimb suspension, marked increments in insulin binding and glucose metabolism occur in the soleus muscle.