Prostacyclin
Prostacyclin is a member of the family of lipid molecules known as eicosanoids. It is produced in endothelial cells from prostaglandin H2 (PGH2) by the action of the enzyme prostacyclin synthase. Although prostacyclin is considered an independent mediator, it is called PGI2 (prostaglandin I2) in eicosanoid nomenclature, and is a member of the prostanoids (together with the prostaglandins and thromboxane).
Mode of action
Prostacyclin acts chiefly to prevent platelet formation and clumping involved in blood clotting. It is also an effective vasodilator. Prostacyclin's interactions in contrast to thromboxane, another eicosanoid, strongly suggest a mechanism of cardiovascular homeostasis between the two hormones in relation to vascular damage.
Pharmacology
Synthetic prostacyclin analogues (iloprost, cisaprost) are used:
- as a vasodilator in severe Raynaud's phenomenon or ischemia of a limb;
- in pulmonary hypertension.
Its production is inhibited indirectly by aspirin which inactivates the cyclooxygenase enzymes COX1 and COX2, which convert arachidonic acid to PGH2, the immediate precursor of prostacyclin.