It is probably not due to a tryptophan-specific mechanism, because amphetamine increases the ratio of brain/plasma concentrations not only of tryptophan but also of tryrosine and phenylalanine. Thus, the effect is not associated with changes in the plasma concentrations of NEFA or free tryptophan. Certain well recognised influences upon brain trytophan have been excluded as responsible. This investigation examined the mechanism of the increase in brain tryptophan concentration of rats treated with d-amphetamine.
