Adrenoceptors are 7-transmembrane receptors which mediate the central and peripheral actions of the neurotransmitter, noradrenaline (norepinephrine), and the hormone and neurotransmitter, adrenaline (epinephrine). Based on both pharmacological and molecular evidence, they are divided into three major types - a1, a2, and ß. The a2 adrenoceptors include 3 subtypes - a2A, a2B, and a2C - each of which couples to Gi/o protein primarily.
The a2B adrenoceptors (ADRA2B) is expressed in the kidney, liver, brain, lung, heart, and skeletal muscle. The development of a2B and a2C knock-out mice has shown that these two subtypes are not involved in the central hypotensive response to a2 agonists.