- Adrenergic Agonists are drugs that lead to stimulation of the adrenergic receptors. In doing so, adrenergic agonists generally simulate activation of certain aspects of the sympathetic nervous system and are thus also known as "sympathomimetics".
- A diverse variety of sympathomimetics exist which operate using distinct mechanisms. In general, these compounds are divided into direct-acting, indirect-acting, or mixed-acting agonists depending on whether they directly activate adrenergic receptors or do so by indirect mechanisms
- Direct-acting Agonists
- Direct agonists physically bind the adrenergic receptor and simulate binding of an endogenous ligand. These compounds can be highly specific, activating only certain subtypes of receptors, or can be rather promiscuous.
- Indirect-acting Agonists
- Indirect agonists do not physically bind adrenergic receptors. Instead, these compounds indirectly lead to receptor activation through a variety of possible mechanisms which include promoting release of endogenously-stored norepinephrine from presynaptic terminals as well as inhibition of norepinephrine re-uptake and degradation from the synapse.
- Mixed-acting Agonists
- Mixed agonists simply refer to those compounds which display both direct and indirect mechanisms of actions. As such, these compounds directly bind adrenergic receptors but also promote the indirect mechanisms described above.