Effects of monoamine oxidase and catechol-O-methyltransferase inhibition on dopamine turnover: a PET study with 6-[18F]L-DOPA

Eur J Pharmacol. 1997 Sep 3;334(1):31-8. doi: 10.1016/s0014-2999(97)01157-6.


The consequences of monoamine oxidase and catechol-O-methyltransferase inhibition on the effective turnover of dopamine were investigated using 6-[18F]L-3-4-dihydroxyphenylalanine (6-[18F]L-DOPA) and positron emission tomography. The effective dopamine turnover was expressed as the ratio between the rate of reversibility of 6-[18F]L-DOPA trapping (k[loss]) and the rate of uptake of 6-[81F]L-DOPA (Ki) in the striatum of normal cynomolgus monkeys. The monkeys received 6-[18F]L-DOPA scans, untreated or after pretreatment with either the peripheral catechol-O-methyltransferase inhibitor nitecapone; the peripheral and central catechol-O-methyltransferase inhibitor tolcapone; the monoamine oxidase inhibitors deprenyl or pargyline; a combination of tolcapone and the monoamine oxidase inhibitors. Tolcapone alone or combined with the monoamine oxidase inhibitors produced a significant decrease in the dopamine turnover (55 to 65%). Neither nitecapone nor monoamine oxidase inhibition alone produced significant changes. These results may have implications for the use of central catechol-O-methyltransferase inhibitors added to routine levodopa therapy in parkinsonian patients.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antiparkinson Agents / metabolism*
  • Benzophenones / pharmacology*
  • Catechol O-Methyltransferase Inhibitors*
  • Catechols / pharmacology*
  • Dopamine / metabolism*
  • Enzyme Inhibitors / pharmacology*
  • Fluorine Radioisotopes
  • Levodopa / metabolism*
  • Macaca fascicularis / metabolism
  • Monoamine Oxidase Inhibitors / pharmacology*
  • Nitrophenols
  • Pentanones / pharmacology*
  • Pilot Projects
  • Tolcapone
  • Tomography, Emission-Computed / methods
  • Visual Cortex / drug effects


  • Antiparkinson Agents
  • Benzophenones
  • Catechol O-Methyltransferase Inhibitors
  • Catechols
  • Enzyme Inhibitors
  • Fluorine Radioisotopes
  • Monoamine Oxidase Inhibitors
  • Nitrophenols
  • Pentanones
  • Levodopa
  • nitecapone
  • Tolcapone
  • Dopamine