Clonidine lowers blood pressure primarily by acting on which receptor population?
- A Central alpha-2 adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla ✓
- B Peripheral alpha-1 adrenoceptors on blood vessels
- C Presynaptic alpha-2 autoreceptors in peripheral vessels
- D Imidazoline I2 receptors in the adrenal medulla
Correct answer: A. Central alpha-2 adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla
Explanation
Clonidine is a centrally acting alpha-2 agonist. It activates alpha-2 adrenoceptors in the nucleus tractus solitarius and rostral ventrolateral medulla, reducing sympathetic outflow and lowering blood pressure. It also activates imidazoline I1 receptors in the rostral ventrolateral medulla (contributing to its hypotensive effect). Peripheral alpha-1 stimulation would raise BP; presynaptic alpha-2 activation reduces norepinephrine release peripherally but this is a minor component.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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