adrenergic receptor

…norepinephrine and epinephrine are called adrenergic receptors. They are divided into two types, α and β. These are further classified into subtypes α₁, α₂, β₁, and β₂.

…there are five types of adrenergic receptors (receptors binding epinephrine): α₁, α₂, β₁, β₂, and β₃. These adrenoceptors are found in different combinations in various cells throughout the body. Activation of α₁- adrenoceptors in arterioles causes blood-vessel constriction, whereas stimulation of α₂ autoreceptors (receptors located in sympathetic presynaptic nerve endings)…

…is said to be an adrenoceptor. Ahlquist called the two kinds of adrenoceptor alpha (α) and beta (β). This theory was confirmed when Sir James Black developed a new type of drug that was selective for the β-adrenoceptor.