title: Norepinephrine precursor therapy in neurogenic orthostatic hypotension.
abstract: BACKGROUND
  In patients with neurogenic orthostatic hypotension (NOH), the availability of the sympathetic neurotransmitter norepinephrine (NE) in the synaptic cleft is insufficient to maintain blood pressure while in the standing posture.
  
  
  RESULTS
  We determined the effect of oral administration of the synthetic amino acid L-threo-3,4-dihydroxyphenylserine (L-DOPS), which is decarboxylated to NE by the enzyme L-aromatic amino acid decarboxylase (L-AADC) in neural and nonneural tissue, on blood pressure and orthostatic tolerance in 19 patients with severe NOH (8 with pure autonomic failure and 11 with multiple-system atrophy). A single-blind dose-titration study determined the most appropriate dose for each patient. Patients were then enrolled in a double-blind, placebo-controlled, crossover trial. L-DOPS significantly raised mean blood pressure both supine (from 101+/-4 to 141+/-5 mm Hg) and standing (from 60+/-4 to 100+/-6 mm Hg) for several hours and improved orthostatic tolerance in all patients. After L-DOPS, blood pressure increases were closely associated with increases in plasma NE levels. Oral administration of carbidopa, which inhibits L-AADC outside the blood-brain barrier, blunted both the increase in plasma NE and the pressor response to L-DOPS in all patients
  
  
  CONCLUSIONS
  Acute administration of L-DOPS increases blood pressure and improves orthostatic tolerance in patients with NOH. The pressor effect results from conversion of L-DOPS to NE outside the central nervous system.
authors.affiliation: Mount Sinai School of Medicine, Box 1052, New York, NY 10029, USA. Horacio.Kaufmann@mssm.edu
authors.forename: Horacio
authors.initials: H
authors.lastname: Kaufmann
authors.forename: Daniela
authors.initials: D
authors.lastname: Saadia
authors.forename: Andrei
authors.initials: A
authors.lastname: Voustianiouk
authors.forename: David S
authors.initials: DS
authors.lastname: Goldstein
authors.forename: Courtney
authors.initials: C
authors.lastname: Holmes
authors.forename: Melvin D
authors.initials: MD
authors.lastname: Yahr
authors.forename: Rachel
authors.initials: R
authors.lastname: Nardin
authors.forename: Roy
authors.initials: R
authors.lastname: Freeman
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000978:Antiparkinson Agents / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use; D001142:Aromatic-L-Amino-Acid Decarboxylases / Q000187:drug effects / Q000378:metabolism; D001794:Blood Pressure / Q000187:drug effects; D002230:Carbidopa / Q000494:pharmacology; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015103:Droxidopa / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use*; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D007024:Hypotension, Orthostatic / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D019636:Neurodegenerative Diseases / Q000150:complications; D009638:Norepinephrine / Q000096:biosynthesis / Q000097:blood / Q000502:physiology*; D011187:Posture; D016037:Single-Blind Method; D016896:Treatment Outcome
chemical_list: D000978:Antiparkinson Agents; D001142:Aromatic-L-Amino-Acid Decarboxylases; D015103:Droxidopa; D002230:Carbidopa; D009638:Norepinephrine