ALTERED CEREBROSPINAL-FLUID AMINO-ACID PATTERN IN THE ANOREXIA OF AGING - RELATIONSHIP WITH BIOGENIC-AMINE METABOLISM

To study the possible role of several amino acids on feeding in the an orexia of aging, we have measured plasma and cerebrospinal fluid (CSF) concentrations of 22 amino acids in 14 elderly persons with idiopathi c anorexia and 10 healthy subjects with normal weight in a similar age range. Plasma and CSF amino acid concentrations and CSF homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) levels were all mea sured by HPLC methods. Elderly anorectic subjects had significantly lo wer levels of glutamic acid but increased concentrations of glutamine in both plasma and CSF compared to controls. Likewise, a significant i ncrease of histidine, threonine, alanine, arginine, valine, methionine , isoleucine, leucine, phenylalanine, tryptophan, ornithine and lysine was found in CSF, but not in plasma, from patients with anorexia. Bes ides, the CSF histidine/LNAA (large neutral amino acids) and tryptopha n/LNAA ratios were elevated in anorectic patients as compared with con trols of similar age. In addition, we found higher CSF concentrations of HVA and 5-HIAA, as well as a positive correlation between CSF LNAA and either HVA (r=0.74, p=0.002) or 5-HIAA (r=0.61, p=0.020) concentra tions in elderly anorectics. CSF tryptophan correlated positively with 5-HIAA levels (r=0.59, p=0.026) and CSF tyrosine with HVA levels (r=0 .77, p=0.002). Our results suggest that changes in the CSF concentrati on of amino acids could contribute to an increased biogenic amine meta bolism in the central nervous system of elderly anorectic subjects, po ssibly increasing the synaptic liberation of biogenic amines involved in the appetite regulation.