Renal transport of lysine and arginine in lysinuric protein intolerance

In a patient with lysinuric protein intolerance, renal handling of lysine and arginine was examined to study the renal transport mechanism of this disease. The tubular reabsorption of lysine or arginine of the patient, when the filtered load of amino acid was increased by intravenous infusion, was not raised as much as that of control subjects at low filtered loads, but the ability for amino acid reabsorption seemed to exist under these conditions. However, when the filtered load was greatly increased, instead of a net reabsorption, a net secretion of amino acid was obtained. This seems to mean that at low filtered loads the amino acid in the tubular lumen is accumulated by the tubular cell across the intact luminal membrane, leading to a small amino acid excretion in the urine. With a great increase of the filtered load the saturated intracellular amino acid, which is not transported to the capillary because of a transport defect of the basolateral membrane, is assumed to leak back into the lumen. This causes a marked urinary amino acid loss exceeding filtered load at high tubular loads. The intravenous load of lysine depressed the percentage of arginine reabsorption and arginine load depressed lysine reabsorption. The percentage of the depressed amino acid reabsorption of the patient decreased almost linearly with increases of the inhibitor load.