Effects of 3-OM-dopa on monoamine metabolism in rat brain.

We studied the effects of 3-methoxy, 4-hydroxy-phenylalanine (3-OM-dopa) on monoamine turnover, L-3-4-dihydroxy-phenylalanine (L-dopa) reversal of catecholamine depletion induced by alpha-methyl-paratyrosine (alpha-MT), and the passage of L-dopa across the blood-brain barrier of the rat brain. 3-OM-dopa did not affect monoamine turnover but interfered with restoration of dopamine levels by L-dopa. In addition, systemic 3-OM-dopa decreased brain uptake of 14C-L-dopa. High 3-OM-dopa blood levels may interfere with the therapeutic response to L-dopa in parkinsonism.