Prostacyclin is a member of the family of lipid molecules known as eicosanoids. When given as a drug it is known as epoprostenol. (Dorlands) 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 thromboxanes).
The series-3 prostaglandin PGH3 also follows the prostacyclin synthase pathway, yeilding another prostacyclin, PGI3.(Fischer, 1985) The unqualified term 'prostacyclin' usually refers to PGI2. PGI2 is derived from the ω-6 arachidonic acid. PGI3 is derived from the ω-3 EPA.
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.
Synthetic prostacyclin analogues (iloprost, cisaprost) are used intravenously, subcutaneously or by inhalation:
- as a vasodilator in severe Raynaud's phenomenon or ischemia of a limb;
- in pulmonary hypertension.
Its production is inhibited indirectly by NSAIDs, which inhibit the cyclooxygenase enzymes COX1 and COX2. These convert arachidonic acid to PGH2, the immediate precursor of prostacyclin.