The effects of age and sex on the plasma free amino acid pattern of healthy men and women aged from 80 to 100 years were compared with those in younger adults (20 to 45 years old). Plasma amino acid concentrations were determined by ion-exchange chromatography on a 6300 Beckman analyzer. The plasma concentrations of valine, leucine, isoleucine, proline, glutamine + glutamic acid and phenylalanine were higher in males than in females. Citrulline, half-cystine, histidine, glutamine+glutamic acid, lysine, ornithine and phenylalanine plasma concentrations and the total plasma amino acids were higher in elderly than in younger subjects.
