Interactions of amino acids in renal tubular transport

Abstract

The effects of intravenous infusions of l-lysine, l-arginine, l-histidine, l-ornithine and l-cysteine at three rates on the plasma levels and excretions of naturally occurring amino acids were studied in dogs. Conventional clearance techniques were used, and the amino acid concentrations in both plasma and urine were determined by column chromatography. A number of changes were observed in plasma amino acid concentrations, the most striking of which was a 20-fold increase in ornithine following arginine infusion. This increase is probably the result of conversion of arginine to ornithine via the Krebs-Henseleit cycle. Lysine, ornithine, arginine and cystine or cysteine showed marked mutual inhibition of tubular reabsorption. Histidine modestly inhibited reabsorption of these amino acids, and in turn its reabsorption was modestly depressed by them. The basic amino acid infusions also caused modest depression of the reabsorption of glycine and slight depression of that of several other amino acids. The reabsorptive mechanisms for lysine, arginine, ornithine and cystine are closely related and may be identical. There is, however, minor reabsorptive competition between these amino acids and certain others, suggesting that the mechanisms are not completely specific.