title: Effect of chronic protein ingestion on tyrosine and tryptophan levels and catecholamine and serotonin synthesis in rat brain.
abstract: OBJECTIVE
  Previous studies have shown that brain tyrosine (TYR) levels and catecholamine synthesis rate increase in rats as chronic dietary protein content increases from 2 to 10% (% weight). A single protein, casein, was examined. The present study explores how TYR levels and catecholamine synthesis (and tryptophan (TRP) levels and serotonin synthesis) change when different proteins are ingested chronically over the same range of dietary protein contents.
  
  
  METHODS
  Male rats ingested for 8 days diets contain 2 or 10% protein (zein, gluten, casein, soy protein, or alpha-lactalbumin). On the last day, they were killed 2.5 hours into the dark period, 30 minutes after receiving an injection of m-hydroxybenzylhydrazine, an inhibitor of aromatic l-amino acid decarboxylase. Brain samples were analyzed for amino acids, including 5-hydroxytryptophan (index of serotonin synthesis rate) and dihydroxyphenylalanine (index of catecholamine synthesis rate), by HPLC-electrochemical detection.
  
  
  RESULTS
  TYR levels and catecholamine synthesis rate in brain were unaffected by the particular protein ingested. However, TRP levels and serotonin synthesis rate varied markedly, depending on the protein ingested, with effects being most prominent in the 10% protein groups. The effect of dietary protein on brain TRP correlated very highly with its effect on serotonin synthesis.
  
  
  CONCLUSIONS
  The results indicate that the protein ingested can chronically modify TRP levels and serotonin synthesis in brain, but not TYR levels or catecholamine synthesis, with effects most distinct at an adequate level of protein intake (10%).
authors: Department of Biomedical Sciences, Marquette University, Milwaukee, WI 53201, USA.
authors: SuJean
authors: S
authors: Choi
authors: Briana
authors: B
authors: DiSilvio
authors: Madelyn H
authors: MH
authors: Fernstrom
authors: John D
authors: JD
authors: Fernstrom
mesh_terms: D006916:5-Hydroxytryptophan / Q000378:metabolism; D000818:Animals; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002364:Caseins / Q000008:administration & dosage; D002395:Catecholamines / Q000378:metabolism*; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D018753:Diet, Protein-Restricted / Q000009:adverse effects; D004044:Dietary Proteins / Q000008:administration & dosage*; D004295:Dihydroxyphenylalanine / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006834:Hydrazines / Q000494:pharmacology; D007031:Hypothalamus / Q000187:drug effects / Q000378:metabolism; D008297:Male; D011488:Protein Deficiency / Q000097:blood / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000097:blood / Q000378:metabolism*; D014443:Tyrosine / Q000097:blood / Q000378:metabolism*
chemical_list: D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D002364:Caseins; D002395:Catecholamines; D004044:Dietary Proteins; D004791:Enzyme Inhibitors; D006834:Hydrazines; D012701:Serotonin; D014443:Tyrosine; D004295:Dihydroxyphenylalanine; D014364:Tryptophan; C004297:3-hydroxybenzylhydrazine; D006916:5-Hydroxytryptophan