prostaglandinendoperoxide

Prostaglandin endoperoxides are a class of short‑lived lipid intermediates formed during the biosynthesis of prostaglandins and thromboxanes. The primary representatives are prostaglandin G2 (PGG2) and prostaglandin H2 (PGH2). They are derived from arachidonic acid by the cyclooxygenase activity of prostaglandin-endoperoxide synthases. During the COX reaction, arachidonic acid is first converted to PGG2, which contains a 9,11‑endoperoxide ring, and is then reduced to PGH2 by the enzyme’s peroxidase activity. Both PGG2 and PGH2 are unstable and rapidly metabolized to downstream mediators.

In most tissues, PGH2 serves as a common substrate for downstream synthases that generate various prostaglandins and thromboxanes: PGE2, PGD2, PGF2α, prostacyclin (PGI2), and thromboxane A2 (TXA2). TXA2 promotes platelet aggregation and vasoconstriction, whereas PGE2 and PGI2 regulate inflammation, pain, fever, and vascular tone. PGD2 and PGF2α contribute to allergic responses, smooth muscle function, and other physiological processes.

Regulation and pharmacology: COX‑1 is constitutively expressed in many tissues, while COX‑2 is inducible during inflammation. Nonsteroidal anti‑inflammatory drugs (NSAIDs) inhibit COX enzymes, reducing synthesis of prostaglandin endoperoxides and downstream mediators, which underlies their analgesic and anti‑inflammatory effects.