The Effects of Tryptophan Enhancement and Depletion on Plasma Catecholamine Levels in Healthy Individuals.

Journal Article (Journal Article)

OBJECTIVE: Central nervous system (CNS) serotonin (5-HT) exerts both excitatory and inhibitory effects on the sympathetic nervous system (SNS) in animals. In this study, we examine the effects of tryptophan enhancement and depletion on plasma catecholamine levels in humans. METHODS: The total sample consisted of 164 healthy men and women who were tested for 2 days. Seventy-nine participants were randomized to a tryptophan enhancement condition and 85 to a tryptophan depletion condition. Both protocols consisted of a "sham day," followed by an "active day." Blood samples for assessment of plasma norepinephrine and epinephrine levels were collected before and after tryptophan enhancement/depletion. Data were analyzed using general linear models. Separate analyses were conducted for each study arm and for each measure. RESULTS: In the depletion condition, both epinephrine (F(5,330) = 2.69, p = .021) and norepinephrine (F(5,335) = 2.79, p = .018) showed small increases on active versus "sham" depletion days. There were also significant day by time interactions for epinephrine (F(3,171) = 39.32, p < .0001) and norepinephrine (F(3,195) = 31.09, p < .0001) levels in the enhancement arm. Tryptophan infusion resulted in a marked increase in epinephrine (Premean = 23.92 (12.23) versus Postmean = 81.57 (62.36)) and decrease in norepinephrine (Premean = 257.2 (106.11) versus Postmean = 177.04 (87.15)), whereas levels of both catecholamines were stable on the "sham day." CONCLUSIONS: CNS 5-HT exerts both inhibitory and excitatory effects on SNS activity in humans, potentially due to stimulation of CNS 5-HT receptors that have shown to have inhibitory (5-HT1A) and excitatory (5-HT1A and/or 5-HT2) SNS effects in animal models.

Full Text

Duke Authors

Cited Authors

  • Boyle, SH; Brummett, BH; Kuhn, CM; Barefoot, JC; Siegler, IC; Williams, RB; Georgiades, A

Published Date

  • January 2019

Published In

Volume / Issue

  • 81 / 1

Start / End Page

  • 34 - 40

PubMed ID

  • 30188382

Pubmed Central ID

  • PMC6825325

Electronic International Standard Serial Number (EISSN)

  • 1534-7796

Digital Object Identifier (DOI)

  • 10.1097/PSY.0000000000000637


  • eng

Conference Location

  • United States