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(Circulation. 2003;108:724.)
© 2003 American Heart Association, Inc.
Clinical Investigation and Reports |
From Mount Sinai School of Medicine (H.K., D.S., A.V., M.D.Y.), New York, NY; Clinical Neurocardiology Section (D.S.G., C.H.), National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Md; and Beth Israel Deaconess Medical Center (R.N., R.F.), Boston, Mass.
Correspondence to Horacio Kaufmann, MD, Mount Sinai School of Medicine, Box 1052, New York, NY 10029. E-mail Horacio.Kaufmann{at}mssm.edu
Received February 12, 2003; revision received May 20, 2003; accepted May 21, 2003.
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.
Methods and 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 Laromatic 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.
Key Words: nervous system, autonomic blood pressure vasoconstriction norepinephrine receptors, adrenergic, alpha
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