An active transport system in the blood-brain barrier may reduce levodopa availability

Exp Neurol. 2005 Sep;195(1):267-71. doi: 10.1016/j.expneurol.2005.04.008.


Levodopa, the primary drug used to treat patients with Parkinson's disease, is transported into the brain by the facilitative amino acid transporter (L1). We present here an unanticipated discovery: levodopa may be pumped out of the brain by a Na(+)-dependent transport system that couples the naturally occurring Na(+) gradient existing between the brain's extracellular fluid and the cytoplasm of capillary endothelial cells. The activity of this system reduces the net availability of levodopa.

Publication types

  • Comparative Study
  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Biological Transport, Active / physiology*
  • Blood-Brain Barrier / metabolism*
  • Capillary Permeability / drug effects
  • Capillary Permeability / physiology
  • Cattle
  • Dopamine Agents / pharmacokinetics*
  • Dose-Response Relationship, Drug
  • Endothelial Cells / drug effects
  • Extracellular Fluid / drug effects
  • Isoleucine / metabolism
  • Levodopa / pharmacokinetics*
  • Models, Biological
  • Sodium / metabolism
  • Time Factors
  • Tritium / pharmacokinetics


  • Dopamine Agents
  • Isoleucine
  • Tritium
  • Levodopa
  • Sodium