Adrenergic receptors: are a class of G protein-coupled receptors which receive neuronal impulses from postganglionic adrenergic fibres of the sympathetic nervous system. These receptors can be activated by epinephrine and by different adrenergic drugs. Adrenergic receptors are divided into two receptors: alpha-adrenergic, which act in response to sympathomimetic stimuli, and beta-adrenergic.