Possible Interaction: 5-Hydroxytryptophan and Levodopa

“Studies performed in isolated proximal convoluted tubules (PCT) have shown that L-5-HTP and L-DOPA use the same transporter in order to be taken up into the cell and both L-DOPA and L-5-HTP exert a competitive type of inhibition upon their cellular uptake.”

“Supplementation of l-dopa therapy with 5-hydroxytryptophan , a serotonin precursor, resulted in clinical improvements in both twins.”

“This finding suggested to the authors that supplementing the twin’s current l-dopa treatment with a serotonin precursor, 5-hydroxytryptophan , might provide further improvement in their symptoms.”

“Activity against L-DOPA is partially inhibited by 5-hydroxytryptophan (5-HTP).”

“Exposure to dopamine (10 microM) or L-DOPA (100 microM) markedly diminished the forskolin-stimulated release of melatonin, as well as the production of 5-hydroxytryptophan and serotonin.”

“It is obvious that seasonal testicular regression of Indian Palm Squirrel can be eliminated by 12hr relation of 5-HTP and L-DOPA , which is not a pharmacological effect but actually is an alteration of seasonality in this annually breeding subtropical mammal.”

“IC50 values for L-5-HTP (RBE 4, 1026 microM; RBE 4B, 831 microM) obtained in the presence of a nearly saturating (250 microM) concentration of L-DOPA were almost 5-fold those obtained when non-saturating (25 microM) concentrations of L-DOPA were used.”

“In RBE 4 cells, Vmax values for L-DOPA uptake were identical in the absence and the presence of … L-5-HTP or 150 microM BHC, but Km values (microM) were significantly greater (P<0.05) when L-DOPA uptake was studied … the presence of L-5-HTP or ….”

“IC50 values for L-5-HTP (1569 microM) obtained in the presence of a nearly saturating (250 microM) concentration of L-DOPA were 6-fold those obtained when using non-saturating (0.25 and 25 microM) concentrations of L-DOPA (251 and 266).”

“IC50 values for L-DOPA (679 microM) obtained in the presence of a near saturating (250 microM) concentration of L-5-HTP were almost 3-fold those obtained when non-saturating (0.25 and 25 microM) concentrations of L-5-HTP were used (254 and 220).”

“Vmax values (in nmol mg protein-1 6 min-1) for L-5-HTP uptake are identical in the absence (… presence of 250 microM L-DOPA (11.7), but K(m) values (microM) are significantly greater (P < 0.05) when L-5-HTP uptake was … presence of L-DOPA (…).”

“Vmax values (in nmol mg protein-1 6 min-1) for L-DOPA uptake are identical in the absence (13.… of 250 microM L-5-HTP (13.3), but K(m) values (microM) are significantly greater (P < 0.05) when L-DOPA uptake was … of L-5-HTP (90 …).”

“Nonlinear analysis of the saturation curves revealed …-1.6 min-1, respectively, L-5-HTP … L-dopa with a half-maximal inhibitory constant of 29.1 microM. The accumulation of L-dopa and … was found to be saturable only when the substrates were applied from the basolateral cell border.”

“It is concluded that L-5-HTP exerts a competitive type of inhibition of L-DOPA uptake in cultured OK cells, whereas both cyanine 863, an organic cation transport inhibitor and 3,3'-DOC behave as non-competitive inhibitors.”

“Non-linear analysis of the saturation curves revealed for L-DOPA a Km (in … nmol/mg protein per 6 min) of 30.0 +/- 0.4 IC50 values for L-5-HTP (1454 microM) obtained … microM) concentration of L-DOPA were almost 4-fold those … L-DOPA were used (330).”

“Vmax values (in nmol/mg protein per 6 min) for L-DOPA uptake were identical in the absence (36.4 +/- … of L-5-HTP (39.2 +/- 1.3), but Km values (microM) were significantly greater (P < 0.05) when L-DOPA uptake … of L-5-HTP (121 (100, …, 399)).”

“This locomotion-triggering effect of L-DOPA or clonidine was also observed when given after DL-5-HTP or apomorphine.”