Plasma accumulation of metabolism of orally administered single dose L-5-hydroxytryptophan in man.
Single oral doses of L-5-hydroxytryptophan (5-HTP) were administered in combination with L-aromatic amino acid decarboxylase inhibitors. The time courses of plasma concentrations of 5-HTP, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) and the concentrations of 5-HT in blood platelets were measured. Carbidopa enhanced the rise in plasma concentrations of 5-HTP 5-15 fold and counteracted the increase in plasma 5-HIAA levels induced by 5-HTP alone. A single dose of the decarboxylase inhibitor was equipotent to 14 days' pretreatment. Plasma or platelet concentrations of 5-HT failed to reflect the metabolism of 5-HTP. The ratio of 5-HTP to carbidopa influenced the systemic bioavailability of single dose administered 5-HTP indicating dose dependent absorption kinetics. Co-administration of L-dopa with 5-HTP and decarboxylase inhibitors had no effect on gastrointestinal absorption of 5-HTP in six parkinsonian patients.
D006916:5-Hydroxytryptophan / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism*; D000284:Administration, Oral; D000293:Adolescent; D000328:Adult; D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D002230:Carbidopa / Q000494:pharmacology; D006801:Humans; D006897:Hydroxyindoleacetic Acid / Q000097:blood; D007408:Intestinal Absorption; D012701:Serotonin / Q000097:blood
D065105:Aromatic Amino Acid Decarboxylase Inhibitors; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D006916:5-Hydroxytryptophan; D002230:Carbidopa