Hydralazine is an arterial vasodilator used in hypertensive emergencies in pregnancy. Its mechanism of vasodilation is:
- A Direct interference with intracellular Ca2+ release from IP3-sensitive stores via an unknown mechanism, with reduced myosin light-chain phosphorylation ✓
- B Activation of K+ channels (KATP) causing hyperpolarisation of vascular smooth muscle
- C Blockade of voltage-gated L-type Ca2+ channels in vascular smooth muscle
- D Nitric oxide donation, activating soluble guanylate cyclase and increasing cGMP
Correct answer: A. Direct interference with intracellular Ca2+ release from IP3-sensitive stores via an unknown mechanism, with reduced myosin light-chain phosphorylation
Explanation
Hydralazine's exact mechanism is incompletely understood but it primarily reduces intracellular Ca2+ in vascular smooth muscle by interfering with IP3-induced Ca2+ release from the sarcoplasmic reticulum, leading to less myosin light-chain kinase activation and vasodilation. It acts selectively on arterioles (not veins), causing reflex tachycardia and increased cardiac output. KATP channel opening is the mechanism of diazoxide and minoxidil; L-type Ca2+ channel blockade is that of dihydropyridines; NO donation is that of sodium nitroprusside and nitrates.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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