[Imbalances of neutral plasma amino acids as a pathogenetic factor in anorexia]

Studies in anorectic tumor-bearing rats indicate that anorexia is correlated to imbalances of neutral amino acids in blood and CNS. Consequently plasma amino acids of patients with neoplastic and non-neoplastic internal diseases were studied during phases of anorexia; special regard was given to the precursors of dopamine and serotonin. Anorectic patients were compared to non-anorectic patients with neoplasia. During anorexia, plasma levels of valine and leucine and hence the ratio of the molar concentrations of Val + Leu + Ile/Phe + Tyr were significantly decreased in each anorectic patient as compared to non-anorectic patients whose ratios were always within the normal ranges. As aromatic and branched-chain amino acids compete for penetration of the blood brain barrier, the decrease of the amino acid ratio may induce a raised flux of phenylalanine and tyrosine into the CNS which results in an increased activation of dopaminergic neurons--known to cause anorexia.