There are two main types of adrenergic receptors, alpha (α) and beta (β), both linked to G-proteins and each with subtypes (Fig 1).

Noradrenaline has a greater affinity for α receptors, adrenaline for β receptors.

α₁, β₁ and β₂ receptors are all post-synaptic.

α₂ receptors may be presynaptic and post-synaptic.

The receptors may be differentiated by their second messengers and effects in the tissues.