Biochem/physiol Actions Prostacyclin is a short-lived product of the cyclooxygenase pathway in vascular endothelial cells. It is a potent inhibitor of platelet aggregation by antagonizing thromboxane A2 and stimulating platelet adenylyl cyclase.1 Nitric oxide is also produced in vascular endothelium where it inhibits platelet aggregation, regulates inducible cyclooxygenase production, and may work synergistically with prostacyclin to attenuate the thrombotic process. Prostacyclin is vasoprotective, protecting arterial walls from injury-induced lesions and cytoprotective in the liver and gastrointestinal tract. Prostacyclin therapy improves hemodynamics in pulmonary arterial hypertension.