title: L-dopa competes with tyrosine and tryptophan for human brain uptake.
abstract: Tyrosine and tryptophan have been assayed spectrofluorometrically in postmortem human brain areas of patients with Parkinson's disease treated orally with or without 3,4-dihydroxyphenylalanine (L-dopa) plus the peripherally acting decarboxylase inhibitor benserazide. Tyrosine as well as tryptophan decrease significantly after treatment with L-dopa, thus showing a competitive action of L-dopa to other aromatic amino acids on human brain uptake. It is suggested that some of the side effects of L-dopa treatment in Parkinson's disease are due to a disturbance in the brain and neural uptake of other, specially aromatic and branched-chain amino acids. An influence of L-dopa administration on protein synthesis also cannot be excluded.
mesh_terms: D000368:Aged; D001545:Benserazide / Q000627:therapeutic use; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism*; D005260:Female; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use*; D008297:Male; D010300:Parkinson Disease / Q000188:drug therapy / Q000378:metabolism*; D014364:Tryptophan / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism*
chemical_list: D014443:Tyrosine; D007980:Levodopa; D001545:Benserazide; D014364:Tryptophan