GCG and Hyperglycemia: Finally, D’Alessio et al. [256], by using the intravenous glucose tolerance test and the minimal model of glucose kinetics to derive indices of insulin sensitivity and glucose effectiveness, suggested that GLP-1 may have direct effects on tissues involved in postprandial glucose handling by potentiating insulin-independent glucose disposal (i.e., induced by hyperglycemia per se) in the liver and/or skeletal muscle.