Correct option is A
The correct answer is option (a): Prostacyclin. Prostacyclin (also known as PGI₂) is not a vasoconstrictor; instead, it is a vasodilator and an inhibitor of platelet aggregation. It is synthesized mainly by endothelial cells and plays a crucial role in maintaining vascular homeostasis by counteracting the effects of vasoconstrictors such as thromboxane A2 and angiotensin-II.
Now let’s understand the function of each listed compound:
Thromboxane A2 (TXA2) is a potent vasoconstrictor and promoter of platelet aggregation, primarily produced by activated platelets. It plays a major role in hemostasis and the development of thrombosis.
Angiotensin-II is a well-known vasoconstrictor involved in the renin-angiotensin system. It increases blood pressure by causing constriction of blood vessels and stimulating aldosterone release from the adrenal cortex.
Endothelin-1 is one of the most potent vasoconstrictors known. It is secreted by endothelial cells and contributes significantly to the regulation of vascular tone and blood pressure.
Therefore, Prostacyclin is unique among these choices because it dilates blood vessels and inhibits platelet aggregation, making it not a vasoconstrictor.
