Differential effect of carbidopa on the concentration of rat pineal and hypothalamic indoleamines.

Carbidopa, an aromatic acid decarboxylase inhibitor, has been shown to significantly decrease the pineal concentration of melatonin, N-acetyl serotonin (NAS), serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) but not the hypothalamic concentrations of these indoles. Increased levels of 5-hydroxytryptophan (5-HTP) indicate that carbidopa directly inhibits 5-HTP decarboxylation, thus limiting 5-HT production. Possible practical implications of selective inhibition of pineal indoleamines by carbidopa are discussed.