Glomerular clearance and tubular reabsorption of transferrin in microtransferrinuric patients with non-insulin-dependent diabetes.

Our objective was to determine the role of increased glomerular clearance (GC) or reduced tubular reabsorption (TR) of transferrin in producing microtransferrinuria. An infusion of L-arginine was used to inhibit TR of transferrin, permitting the determination of both GC and TR of transferrin in 64 patients with non-insulin-dependent diabetes mellitus (NIDDM), with or without microtransferrinuria. Thirty-one healthy volunteers served as control subjects. The GC of transferrin in NIDDM patients with microtransferrinuria did not differ significantly from that in healthy controls or in NIDDM patients with normal transferrin excretion rates (TfER). No correlation was found between TfER and GC of transferrin in any group of the subjects. However, the TR of transferrin was inversely correlated with TfER in healthy controls and in the NIDDM patients, with or without microtransferrinuria. When transferrin absorption was plotted against the filtered load of transferrin, the regression lines for the three subject groups were parallel. The regression line for NIDDM patients with microtransferrinuria was shifted to the right of those for healthy controls and NIDDM patients with a normal TfER. These findings suggest that microtransferrinuria in patients with NIDDM is caused by the impaired tubular reabsorption of transferrin.