Figure 1.

Compartmental representation of the four single-compartment model. All models are composed by a single compartment representing plasma insulin I(t). Plasma glucose G acts as input for all models through the k_GL parameter for Model 1 and 4 and k_GL1 for Model 2 and 3; similarly, amino acids act as input for all models through k_AA parameter for Model 1, 2 and 3 and through the time-varying parameter k_AA(t) for Model 4. In all models, k_I represents the insulin elimination rate from plasma and BR_I is the basal insulin appearance rate due to factors other than glucose and amino acids. In Model 2, a further dependence on glucose rise is included through the k_GL2 parameter; in Model 2 this rise is accounted for by glucose derivative G˙ hereas in Model 3 by glucose exponentiation G(t)k^GL2 .