Abstract
CHANGES in the tryptophan content of the brain influence the rate of synthesis of brain 5-hydroxytryptamine (5-HT). Therefore, factors that affect the delivery of tryptophan to the brain may affect its 5-HT content. Tryptophan in plasma can be displaced from its binding site on albumin by non-esterified fatty acids (NEFA)1 and by certain drugs2. Although in some circumstances changes in non-albumin bound (NAB) plasma tryptophan, brought about by drugs and changes in plasma NEFA, parallel those of brain tryptophan2,3, this relationship does not apply in all conditions. For example, after administration of glucose plasma NEFA decline, as does NAB tryptophan, but the brain tryptophan content increases4. Thus, it is uncertain whether binding of tryptophan to albumin is important in controlling brain tryptophan and hence brain 5-HT. To resolve this controversy we looked at the influence of albumin on the uptake of tryptophan by brain in vivo. We found that albumin inhibits tryptophan uptake, and that diffusion, a process that will depend only on the NAB plasma tryptophan concentration, has a small but significant role in the uptake of tryptophan by brain.
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ETIENNE, P., YOUNG, S. & SOURKES, T. Inhibition by albumin of tryptophan uptake by rat brain. Nature 262, 144–145 (1976). https://doi.org/10.1038/262144a0
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DOI: https://doi.org/10.1038/262144a0
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