Indomethacin given to a preterm neonate closes a haemodynamically significant patent ductus arteriosus. The mechanism responsible for ductal constriction is:
- A Inhibition of prostaglandin synthesis, removing the vasodilatory effect of PGE1 on ductal smooth muscle ✓
- B Stimulation of thromboxane A2 release, producing ductal vasoconstriction
- C Direct alpha-adrenergic agonist activity on ductal tissue
- D Inhibition of nitric oxide synthase within the ductus wall
Correct answer: A. Inhibition of prostaglandin synthesis, removing the vasodilatory effect of PGE1 on ductal smooth muscle
Explanation
The fetal ductus arteriosus is kept patent by circulating prostaglandins, chiefly PGE1 acting through EP receptors on ductal smooth muscle. Indomethacin inhibits cyclooxygenase, lowers prostaglandin levels, and allows the duct to constrict. This same physiology explains why maintaining a patent ductus in certain cyanotic congenital heart diseases requires intravenous PGE1 infusion. Thromboxane stimulation and alpha-agonism are not involved in ductal patency.
Reference: Katzung Basic and Clinical Pharmacology, 15th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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