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Systemic administration of \u03b2\u2010adrenergic agonists increase brain concentrations of <jats:sc>L<\/jats:sc>\u2010dopa and other large neutral amino acids (LNAA) in rats and monkeys and may improve symptoms and reduce daily <jats:sc>L<\/jats:sc>\u2010dopa requirement in patients with Parkinson's disease. Cerebral blood flow (CBF) using [<jats:sup>3<\/jats:sup>H]nicotine and the extraction fraction of <jats:sup>14<\/jats:sup>C\u2010labeled <jats:sc>L<\/jats:sc>\u2010dopa or <jats:sc>L<\/jats:sc>\u2010leucine were measured simultaneously in various brain regions of conscious rats using the dual\u2010isotope indicator fractionation technique after intraperitoneal administration of isoproterenol (a peripheral nonselective \u03b2\u2010adrenergic agonist), or clenbuterol (a \u03b2<jats:sub>2<\/jats:sub>\u2010adrenergic agonist that crosses the blood\u2013brain barrier), or \u03b2\u2010adrenergic agonist preceded by nadolol (a peripheral nonselective \u03b2\u2010adrenergic antagonist), or saline vehicle. Both \u03b2\u2010adrenergic agonists increased regional brain extraction fraction of <jats:sc>L<\/jats:sc>\u2010dopa and <jats:sc>L<\/jats:sc>\u2010leucine tracers by 35\u201345%, without altering regional CBF. These changes were accompanied by about a 30% decrease in plasma branched chain LNAA concentrations. Nadolol blocked all these effects. \u03b2\u2010Adrenergic agonists increase the brain extraction of <jats:sc>L<\/jats:sc>\u2010dopa and leucine, mainly by peripheral mechanisms that reduce the levels of other competing plasma LNAAs for transport. Thus, \u03b2\u2010adrenergic agonists might be useful in the treatment of patients with Parkinson's disease by enhancing delivery of <jats:sc>L<\/jats:sc>\u2010dopa to the brain. \u00a9 2001 Movement Disorder Society.<\/jats:p>","DOI":"10.1002\/mds.10002","type":"journal-article","created":{"date-parts":[[2004,10,27]],"date-time":"2004-10-27T14:33:09Z","timestamp":1098887589000},"page":"54-59","source":"Crossref","is-referenced-by-count":11,"title":["\u03b2\u2010Adrenergics enhance brain extraction of levodopa"],"prefix":"10.1002","volume":"17","author":[{"given":"Ergun Y.","family":"Uc","sequence":"first","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Gerald A.","family":"Dienel","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nancy F.","family":"Cruz","sequence":"additional","affiliation":[],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Sami 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