Learning Objective
By the end of this note, the learner should be able to explain the mechanism, effects, and clinical uses of α₂-adrenergic agonists and identify their role in reducing sympathetic outflow.
Mechanism of Action
- α₂ agonists stimulate presynaptic Gi-coupled α₂ receptors in the CNS.
- This inhibits sympathetic outflow → ↓ NE release.
- Results in reduced heart rate, cardiac output, and peripheral vascular resistance.
Physiologic Effects
- ↓ Sympathetic tone
- ↓ BP (effective for mild–moderate hypertension)
- Possible adverse effects: sedation, dry mouth, rebound hypertension (if abruptly stopped)
Drugs & Uses
Clonidine
- Mild–moderate hypertension
- ADHD
- Hypertensive urgency (oral)
- Withdrawal states (opioids, alcohol)
Methyldopa
- Preferred antihypertensive in pregnancy-associated hypertension (gestational HTN, pre-eclampsia)
