Utilization of calcium L-phenyllactate as a substitute for phenylalanine by uremic patients

The efficacy of calcium L-phenyllactate as a substitute for phenylalanine was examined in eight uremic patients who were also receiving calcium salts of the α-keto analogues of the branched-chain amino acids and the D,L-α-hydroxy analogue of methionine in addition to the remaining four essential amino acids themselves. Nitrogen balance, corrected for urea accumulation but not for cutaneous losses, was measured while the patients ate a virtually protein-free diet supplemented with the above mixture and glycine as a source of nonessential nitrogen. Two men were in negative nitrogen balance whether receiving this regimen (?2.58 ± 0.43 g N/day) or 21.5 g/day of essential amino acids, including 2 g of phenylalanine (?2.76 ± 0.46 g N/day). There was no apparent reason for their excessive catabolism. In contrast, six women had an average measured nitrogen balance of +0.73 ± 0.23 g N/day on this regimen. If an estimate for unmeasured nitrogen losses is included in their measured nitrogen balances, one patient was in positive balance (+0.90 g N/day), three in neutral balance (+0.43, +0.42, +0.11 g N/day) and two in negative balance, (?0.26, ?0.56 g N/day), yielding an average balance of +0.23 ± 0.23 g N/day. These data contrast with reported negative balances of ?1.8 to ?3.8 g N/day of subjects eating a phenylalanine-free diet. We conclude that in this group of six uremic patients, calcium L-phenyllactate was converted to phenylalanine and utilized to maintain nitrogen balance.