Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasoconstriction), and the prostacyclins (active in the resolution phase of inflammation.)
Cyclooxygenase). All other prostanoids originate from PGH (as PGH1, PGH2, or PGH3).
Figure 1 shows how PGH2 (derived from Arachidonic acid) is converted:
- By PGE synthetase into PGE (which in turn is converted into PGF)
- By PGD synthetase into PGD
- By Prostacyclin synthase into prostacyclin (PGI2)
- By Thromboxane synthase into thromboxanes
The three classes of prostanoids have distinctive rings in the center of the molecule. They differ in their structures. The PGH compounds (parents to all the rest) have a 5-carbon ring, bridged by two oxygens (a peroxide.) The derived prostaglandins contain a single, unsaturated 5-carbon ring. In prostacyclins, this ring is conjoined to another oxygen-containing ring. In thromboxanes the ring becomes a 6-member ring with one oxygen.
Production of PGE2 in bacterial and viral infections appear to be stimulated by certain cytokines, e.g., interleukin-1.
- University of Kansas Medical Center (2004). "Eicosanoids and Inflammation" (PDF). Retrieved 2007-01-05.