Prostanoid


Prostanoids are a subclass of eicosanoids consisting of the prostaglandins, the thromboxanes, and the prostacyclins

Biosynthesis

catalyzes the conversion of the free essential fatty acids to prostanoids by a two-step process.
In the first step, two molecules of O2 are added as two peroxide linkages and a 5-member carbon ring is forged near the middle of the fatty acid chain. This forms the short-lived, unstable intermediate Prostaglandin G.
One of the peroxide linkages sheds a single oxygen, forming PGH. .
All other prostanoids originate from PGH.
The image at right shows how PGH2 is converted:
The three classes of prostanoids have distinctive rings in the center of the molecule. They differ in their structures. The PGH compounds have a 5-carbon ring, bridged by two oxygens 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.