Methyldopa is used in hypertension in pregnancy. Its active antihypertensive metabolite and primary site of action are:
- A α-methyldopamine acting on peripheral α1-adrenoceptors as a false neurotransmitter
- B α-methyladrenaline stimulating central β2-adrenoceptors in the ventrolateral medulla
- C α-methylnoradrenaline acting on central presynaptic α2-adrenoceptors in the nucleus tractus solitarius to reduce sympathetic outflow ✓
- D Methyldopa itself directly inhibiting DOPA decarboxylase in the adrenal medulla
Correct answer: C. α-methylnoradrenaline acting on central presynaptic α2-adrenoceptors in the nucleus tractus solitarius to reduce sympathetic outflow
Explanation
Methyldopa is decarboxylated to α-methyldopamine and then β-hydroxylated to α-methylnoradrenaline, which replaces noradrenaline in central adrenergic neurons. α-Methylnoradrenaline stimulates presynaptic α2-adrenoceptors in the nucleus tractus solitarius (NTS) of the brainstem, reducing sympathetic outflow and blood pressure. Its safety profile in pregnancy (no teratogenicity in established cohort data) makes it a preferred antihypertensive in this setting.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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