Control of brain tryptophan concentration in rats on a high fat diet

Abstract

SYNTHESIS in the brain of the neurotransmitter 5-hydroxytryptamine (5-HT) is influenced by the concentration of its precursor tryptophan^1,2. Much attention has therefore been paid to the determinants of brain tryptophan concentration. Evidence suggests that plasma free tryptophan is an important influence on brain tryptophan^3,4 and that both concentrations increase when plasma unesterified fatty acids (UFA) rise^3,5,6 and release plasma tryptophan from albumin^7,8. Other results, however, disagree. Thus feeding rats for 2 h with high fat diets apparently led to large increases in serum UFA and free tryptophan but not brain tryptophan^9,10,11. We now present evidence suggesting that the latter findings may have been due to in vitro lipolysis during either the preparation of serum or its dialysis at 37 °C for 3.5 h to separate free tryptophan⁹. Here we describe work in which precautions were taken to avoid in vitro changes and which is consistent with a relationship between plasma free tryptophan and brain tryptophan concentrations.