Which molecule produced by the endothelium promotes vasodilation and inhibits platelet aggregation?

• A. Endothelin
• B. Thromboxane A2
• C. Nitric oxide
• D. Prostacyclin

Answer: (D)

Endothelium-derived prostacyclin is the molecule that fits this description. It’s produced by the endothelial cells lining blood vessels and acts to keep vessels open while preventing clot formation. Prostacyclin binds to its receptors on smooth muscle and platelets, triggering an increase in cyclic AMP. In vascular smooth muscle, this rise causes relaxation, leading to vasodilation. In platelets, the same signal raises cyclic AMP and inhibits platelet activation and aggregation, making clot formation less likely. This dual action helps maintain proper blood flow and reduces thrombosis, which is why prostacyclin is classically described as promoting vasodilation and inhibiting platelet aggregation. Endothelin is a vasoconstrictor, thromboxane A2 promotes vasoconstriction and aggregation, and while nitric oxide also causes vasodilation and inhibits platelets, the option most specifically associated with the described combination in this context is prostacyclin.