Alpha-2 adrenergic agonists: Nursing pharmacology

Alpha-2 adrenergic agonists are medications that oppose the effects of the sympathetic nervous system, ultimately decreasing smooth muscle contraction.

These medications include clonidine, guanfacine, and methyldopa, which can be administered orally, and clonidine also transdermally, to treat hypertension.

In addition, clonidine can also be used orally to treat attention deficit hyperactivity disorder, or ADHD for short, and less frequently, through epidural infusion for pain management in cancer.

Finally, methyldopa can also be administered intravenously to treat hypertensive crises. Once administered, alpha-2 adrenergic agonists act in the brainstem.

Normally, neurons in the brainstem carry signals to the spinal cord nuclei, where they synapse and release norepinephrine to stimulate the sympathetic nervous system.

This triggers the fight or flight response, which results in smooth muscle contraction, in turn leading to an increase in the heart rate and blood pressure, as well as decreasing gastrointestinal motility and urination by contracting the sphincters.

Now if we zoom into this synapse, we can see that some of the norepinephrine turns around and binds to alpha-2 adrenergic receptors.

This inhibits further release of norepinephrine and serves as a mechanism of negative feedback control.