Possible Interaction: 5-Hydroxytryptophan and Dihydroxyphenylalanine

“1 The present work was designed to examine the interference of L‐3,4‐dihydroxyphenylalanine (L‐DOPA ) on the cell inward transport of L‐5‐hydroxytryptophan (L‐5‐HTP ) and on its decarboxylation by aromatic L‐amino acid decarboxylase (AAAD) in rat isolated renal tubules.”

“6 The results presented suggest that L‐5‐HTP and L‐DOPA are using the same transporter (… probably, the organic cation transporter) in order to be taken up into renal tubular cells; L‐DOPA exerts a competitive type of inhibition … the tubular uptake and decarboxylation of L‐5‐HTP.”

“When the saturation curve … in the presence of L‐DOPA (… L‐5‐HTP in renal tubules was found to be markedly (P < 0.01) reduced (Vmax = 10.5 ± 1.7 nmol … was accompanied by a significant (P < 0.05) increase in Km values (325 [199, 531] μm, n = 4).”

“Daily injection of L-dihydroxyphenylalanine (L-DOPA, a dopamine precursor) given 12 hr after 5-hydroxytryptophan (5-HTP, a serotonin precursor) stimulated testicular growth and body weight increase in the spotted munia Lonchura punctulata.”

“Daily injections of dihydroxyphenylalanine (DOPA), a precursor for dopamine synthesis, given 12 hr after daily injections of 5-hydroxytryptophan (5-HTP), a serotonin precursor, induced uterine growth and increased serum thyroxine and luteinizing hormone (LH) concentrations in scotosensitive female hamsters maintained on short daylengths.”

“A combined administration of 5-hydroxytryptophan (30 mg/kg) and alpha-methyl-dihydroxyphenylalanine (100 mg/kg) resulted in the occurrence on the visual cortex of the effects similar to those produced by ketamine.”

“However, the infusion of dopa , after 5-hydroxytryptophan , decreased its antinatriuretic and antidiuretic effects.”

“ a-Methyldihydroxyphenylalanine inhibited … 5-hydroxytryptophane (5-HTP) but not of histidine2 or of either amine.3 It seemed appropriate to study the effects of other subtances on … uptake of these amines and amino acids in order to see how useful these cells may be for the study of transport.”

“Less dopamine and serotonin are synthesized when L‐DOPA and 5‐HTP are administered as a cocktail.”

“Daily injections of L-dihydroxyphenylalanine (L-DOPA, dopamine precursor) given 4 h after 5-hydroxytryptophan (5-HTP, serotonin precursor) induced inhibitory responses in recrudescing gonad (in the first week of December) of Indian palm squirrel, a seasonally breeding subtropical animal.”

“Using an enzyme preparation from rabbit kidney cortex, the amino acids 3,4-dihydroxyphenylalanine and 5-hydroxytryptophan were found to inhibit each other's enzymatic decarboxylation competitively.”