Possible Interaction: Triiodothyronine and Tryptophan

“ Liothyronine appeared to diminish the side effects of both imipramine and L-tryptophan in both men and women.”

“Inhibition … T3 uptake by tryptophan was dose dependent, with an inhibition constant (Ki) of 2.9 +/- 0.5 mM. Similarly, tryptophan uptake was inhibited by T3 and phenylalanine in a dose dependent way with Ki values of 4.9 +/- 0.5 microM and 15.6 +/- 4.8 microM respectively.”

“ Tryptophan inhibited saturable T3 uptake by about 57% without any significant effect on the non-saturable uptake.”

“Uptake of T3 was inhibited by tryptophan but not phenylalanine, but tryptophan uptake was inhibited both by T3 and phenylalanine.”

“We conclude that there is mutual competitive inhibition between uptake systems for T3 and tryptophan in JAR cells, but the kinetic parameters of cross-inhibition of uptake by the substrates suggest that the carriers are distinct.”

“The aromatic amino acids phenylalanine and tryptophan were found to inhibit the uptake of T3 , but these two amino acids were transported into the cells predominantly via system L. The amino acid transport system T, which is specific for aromatic amino acids, was not detectable in these cells.”

“In fact, the inhibitory effect of tryptophan on T3 transport was greater and significantly different (P=0.0046) from that obtained by sodium depletion alone.”

“In vivo administration (1 hour) of tryptophan alone stimulated hepatic protein synthesis, but addition of T3 negated such stimulation.”

“Our study indicates that T3 competes with tryptophan for hepatic nuclear tryptophan binding, and it also appears to negate tryptophan's stimulatory effect on hepatic protein synthesis.”

“This study evaluated whether selected hormones, 3,5,3'-triiodothyronine T3 ), hydrocortisone (HC), or insulin, would influence the binding of L-tryptophan to rat hepatic nuclei or nuclear envelopes.”

“Thus, T3 competes with tryptophan for hepatic nuclear tryptophan binding and also negates tryptophan's stimulatory effect on hepatic protein synthesis.”

“We evaluated whether selected hormones, 3,5,3'-triiodothyronine (T3), hydrocortisone (HC) or insulin, would influence the binding (saturable, stereospecific, and of high affinity) of L-tryptophan to rat hepatic nuclei or nuclear envelopes.”

“Preloading erythrocytes with tryptophan resulted in trans-acceleration of T3 uptake and a transient 5-fold accumulation of free T3 into erythrocytes.”

“ T3 on the trans side of the membrane inhibited both influx and efflux of tryptophan , with Ki values similar to the Km values of the T3 transport system.”

“Repeated dose loading of tryptophan or 5-hydroxytryptophan increased blood serotonin and plasma T3 and decreased plasma TSH.”

“Uptake of leucine, tyrosine, and tryptophan (10 M) was inhibited by the different iodothyronines (10 M), in particular T3.”

“Vice versa, uptake of 0.1 M T3 was almost completely blocked by coincubation with 100 M leucine, tryptophan , tyrosine, or phenylalanine.”