What is the function of endothelin in vascular regulation?

• A. A potent endothelium-derived vasoconstrictor increasing vascular resistance.
• B. A vasodilator reducing vascular resistance.
• C. A hormone that lowers heart rate.
• D. A molecule that reduces endothelial permeability.

Answer: (A)

Endothelin primarily acts to regulate vascular tone by promoting constriction of blood vessels. Endothelin-1 is released by endothelial cells and binds to receptors on vascular smooth muscle, triggering calcium-driven contraction that narrows the vessel lumen and raises vascular resistance. It is one of the body's most potent vasoconstrictors, helping to increase blood pressure when needed. While some receptor subtypes on the endothelium can stimulate nitric oxide release and counteract constriction, the overall and most direct effect in basic vascular regulation is vasoconstriction with increased resistance.