The a1-adrenergic receptor (AR) family consists of three closely related gene products (a1A, a1B, and a1D). They mediate the actions of norepinephrine (NE) and epinephrine in sympathetically innervated tissues and brain. ?1-ARs belong to the G protein-coupled receptor family and consist of single polypeptide chains that are predicted to form seven transmembrane spanning domains. With similar pharmacological and signaling properties, a1-AR subtypes act through Gq/11 proteins to activate phospholipase C, increase inositol 1,4,5-trisphosphate production, and increase intracellular Ca2+. ADRA1B functions in diverse settings include vasoconstriction and myocardial contractility, neuronal dopaminergic responses, dendritic cell migration and inflammatory responses, as well as neuroendocrine regulation of fertility.