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The receptors are broadly grouped into α and β receptors. There are two subclasses of α-receptor, α 1 and α 2 which are further subdivided into α 1A , α 1B , α 1D , α 2A , α 2B and α 2C . The α 2C receptor has been reclassed from α 1C , due to its greater homology with the α 2 class, giving rise to the somewhat confusing nomenclature. The β receptors are divided into β 1 , β 2 and β 3 . The receptors are classed physiologically, though pharmacological selectivity for receptor subtypes exists and is important in the clinical application of adrenergic agonists (and, indeed, antagonists).
Dobutamine is predominantly a β 1 -adrenergic agonist , with weak β 2 activity, and α 1 selective activity, although it is used clinically in cases of cardiogenic shock for its β 1 inotropic effect in increasing heart contractility and cardiac output. Dobutamine is administered as a racemic mixture consisting of both (+) and (−) isomers ; the (+) isomer is a potent β 1 agonist and α 1 antagonist, while the (−) isomer is an α 1 agonist.  The administration of the racemate results in the overall β 1 agonism responsible for its activity. (+)-Dobutamine also has mild β 2 agonist activity, which makes it useful as a vasodilator.