Jejunal and ileal absorption of dibasic amino acids and an arginine-containing dipeptide in cystinuria.

Ileal transport of dibasic amino acids has not previously been studied in the intestine of healthy volunteers or cystinuric patients. Experiments have therefore been designed to compare ileal and jejunal absorption of lysine and arginine both in normal subjects and cystinuric patients. In addition, jejunal perfusion experiments have been carried out to investigate absorption of the dipeptide L-arginyl-L-leucine. The results indicate that, at the concentrations studied (4.2 mM lysine, 1 mM arginine), severe transport defects exist throughout the whole small intestine for both amino acids in cystinuria. Despite the transport defect for free arginine, cystinuric patients absorbed the dipeptide L-arginyl-L-leucine normally. Because of the transport defect for free arginine, it has been possible to show that during absorption of L-arginyl-L-leucine in cystinuria approximately 30% of dipeptide-bound arginine can be recovered from the gut lumen in the free form. These findings indicate that the prime function of specific amino acid transport systems during the absorption of protein digestion products may be as a "recapture mechanism" for amino acids liberated as a result of mucosal cell peptide hydrolysis.