<n0:ComplexDefinition xmlns:n0="http://ncicb.nci.nih.gov/xml/owl/EVS/ComplexProperties.xsd#"><n0:def-definition>The bitartrate salt form of levarterenol, the levorotatory isomer of norepinephrine with a vasoconstrictor effect. Levarterenol binds to alpha and beta-1 receptor sites of sympathetic effector cells, thereby causing vasoconstriction of the radial smooth muscle of the arteries, arterioles, and veins and increasing myocardial contractility, heart rate, automaticity, and artrioventricular (AV) conduction, respectively. Stimulation of the beta-2 adrenergic receptors causes bronchiolar and vascular smooth muscle dilatation.</n0:def-definition><n0:def-source>NCI</n0:def-source></n0:ComplexDefinition>