Relationship between plasma leucine concentration and clearance in normal and type 1 diabetic subjects

In a series of studies in normal and type 1 diabetic subjects, we analysed the relationship between isotope-calculated leucine clearance and plasma leucine concentration. All studies were performed under euglycaemic conditions. Plasma leucine concentrations were either experimentally decreased by means of insulin infusion, or increased by means of exogenous amino acid infusion in the presence of hyperinsulinaemia. Leucine clearance rates were compared in normal and diabetic subjects at similar plasma insulin levels. The effect of hyperinsulinaemia was examined by measuring clearance rates in normal subjects at comparable leucine levels but different insulin concentrations. Our data show that leucine clearance is inversely related to leucine concentration, and that it is not independently stimulated by hyperinsulinaemia. Type 1 diabetes is not associated with decreased leucine clearance. A general equation relating leucine concentration and clearance is proposed. These data support the view that peripheral leucine utilization is not decreased in type 1 diabetes mellitus.