The results of this preliminary study suggest that in depressions, the probenecid test is of predictive value with regard to efficacy of treatment with 5-hydroxytryptamine (5-HT) precursors. Although the number of patients investigated is small, the results do suggest that 5-hydroxytryptophan (5-HTP) benefits depressed patients showing a subnormal cercbrospinal fluid 5-hydroxyindoleacetic acid response to probenecid. The relevant implications of these data are that: a) 5-HT deficiency is etiopathogenic in some depressions; b) the probenecid test can be of diagnostic value in such patients; and c) 5-HT precursors, specifically 5-HTP, may be an effective treatment modality in such individuals.
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