THE RENAL TUBULAR RESPONSE TO AMINO ACID LOADING 1

Abstract

Merck''s 10% solution of free amino acids was given to 3 normal human subjects at faster rates than previously employed in order to determine the effect of additional increase in total filtered load of amino acids. As the total filtered load of amino acids was raised to 2200 [mu]M/minute, greater quantities were both reabsorbed and excreted. The amounts of alanine, arginine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, tryptophan, and valine reabsorbed continued to increase as their filtered loads were elevated. On the other hand, the amounts of glycine, serine, and threonine reabsorbed were no greater in the high load than in the load periods, and in the case of histidine significantly less reabsorption occurred. A suggested explanation for this latter finding is the simultaneous operation of 2 factors, competition among individual amino acids for reabsorption and a "fatiguing" of specific transport systems. Although during the infusion of the amino acid mixture the filtered load of cystine was not changed, its clearance increased to a maximum of 32.6 ml/minute, a value approaching that which we have observed in some patients with cystinuria. Glycine, when infused alone, was more completely reabsorbed than when incorporated into an amino acid mixture and comparable filtered loads achieved. The infusion of glycine was accompanied by an increase in the excretion of serine and threonine and in one instance by an elevation in plasma concentration of serine and threonine. The infusion of glycine proved to be toxic and separate data were collected indicating that this may have been due to ammonia intoxication.