In general, the pharmacological properties of each subtype are quite homogenous across different species. However, this is not the case for the α2A subtype which was first isolated from human platelets. This subtype shows different pharmacological properties from that of mouse and rat. For this reason, until molecular techniques significantly advanced, it was believed that human α2A and that of mouse and rat (termed α2D) were two different subtypes. Today, it is accepted that these two subtypes are in fact one gene product and is generally termed α2A. One of the main differences between this subtype from the different organisms is its affinity for yohimbine and rauwolscine; rat and mouse α2A displays less affinity compared to human.
