the alpha-1a adrenergic receptor (α adrenoreceptor), also known as adra1a, formerly known also as the alpha-1c adrenergic receptor, is an alpha-1 adrenergic receptor, and also denotes the human gene encoding it. there is no longer a subtype α receptor. at one time, there was a subtype known as α, but it was found to be identical to the previously discovered α receptor subtype. to avoid confusion, the naming convention was continued with the letter d.