Prostacyclin

Prostacyclin (or PGI₂) is a member of the family of lipid molecules known as eicosanoids.

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Production

 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).

The series-3 prostaglandin PGH₃ also follows the prostacyclin synthase pathway, yielding 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 by activating prostacyclin receptors.

Function

Prostacyclin chiefly prevents 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 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.

References

• Dorlands Medical Dictionary. epoprostenol. Retrieved on February 10, 2006.

• Fischer S, Weber PC (1985). "Thromboxane (TX)A3 and prostaglandin (PG)I3 are formed in man after dietary eicosapentaenoic acid: identification and quantification by capillary gas chromatography-electron impact mass spectrometry". Biomed. Mass Spectrom. 12 (9): 470-6. PMID 2996649.

See also

Essential fatty acid