Kinetics of human and porcine insulins in normal and type I diabetic subjects.

Human and porcine insulin were infused intravenously at various rates into 4 normal and 6 Type I diabetic subjects, using a double-blind cross-over design and a euglycaemic glucose clamp, to study the relationship between the steady state plasma free insulin concentration and its plasma disappearance rate. By mathematical model validation procedures both human and porcine insulin were found to obey saturation kinetics in normal subjects and first order kinetics in diabetic subjects in the insulin concentration range studied (0-2 nmol/l). No differences in parameters were observed between the two types of insulin in the study groups. The median clearance rate of insulin in normal subjects was 31 ml.kg-1.min-1 at infinitesinal plasma insulin concentrations versus 21 ml.kg-1.min-1 in the diabetic subjects. Thus, at physiological plasma concentrations both human and porcine insulin disappear faster via the saturable mechanism(s) found in normal subjects than via the apparently linear mechanism(s) found in diabetic subjects.