Table 2: Plasma tryptophan disposition.


Parameter Change Mechanism Examples of effectors

Free Trp Decrease TDO/IDO induction Glucocorticoids/interferon- γ
Inhibition of lipolysis Insulin, nicotinic acid, antilipolytic agents
Increase TDO inhibition glucose, nicotinamide, antidepressants
Displacement from albumin NEFA, catecholamines, ethanol, salicylate
Decreased albumin Pregnancy, liver and kidney diseases
Total Trp Decrease TDO/IDO induction Glucocorticoids/interferon- γ
Increase TDO inhibition glucose, nicotinamide, antidepressants
% Free Trp Unaltered TDO/IDO induction, TDO inhibition
Decrease Increased albumin binding
Increase Decreased albumin binding

Reproduced here from Table 2 in ref [ 12 ] A. A.-B. Badawy. Tryptophan metabolism, disposition and utilisation in pregnancy. Biosci Rep. 35, art: be00261 / doi 10.1042/BSR20150197, 2015.
Abbreviations used: IDO (indoleamine 2,3-dioxygenase), NEFA (non-esterified fatty acids), TDO (tryptophan 2,3-dioxygenase, formerly tryptophan pyrrolase)), Trp (tryptophan). The % free Trp is an expression of Trp binding to albumin and is = 100 X [free Trp]/[total Trp].