A 60-year-old man on clonidine for hypertension abruptly stops the drug. He presents with severe rebound hypertension and sweating. The mechanism of clonidine's antihypertensive action and the rebound involves which receptor?
- A Imidazoline I1 receptors in the rostral ventrolateral medulla; rebound is due to up-regulation of peripheral alpha-1 receptors
- B Central alpha-2 receptors in the nucleus tractus solitarius and locus coeruleus; rebound is due to down-regulation of these receptors with sudden removal of agonist ✓
- C Peripheral alpha-1 receptors; rebound is due to supersensitivity
- D Beta-1 adrenoceptors in the heart; rebound is due to receptor up-regulation
Correct answer: B. Central alpha-2 receptors in the nucleus tractus solitarius and locus coeruleus; rebound is due to down-regulation of these receptors with sudden removal of agonist
Explanation
Clonidine stimulates central alpha-2 adrenoceptors in the NTS and locus coeruleus, reducing sympathetic outflow. With chronic use, these receptors down-regulate; abrupt discontinuation removes agonist drive, sympathetic outflow surges, and blood pressure rebounds above pre-treatment levels. Imidazoline receptors contribute to some of clonidine's action but are not the primary mechanism for rebound.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.