Prostaglandin H₂ (PGH₂) !

PGH₂ is the unstable product of COX. Each cell type turns it into its own prostanoid: TXA₂, PGI₂, PGE₂, PGD₂ or PGF₂α.

Updated 2026-11-01

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Key facts

Made from PGG₂ by the peroxidase site of COX-1 or COX-2.
Its half-life is very short, so it is converted where it is made.
Thromboxane synthase makes TXA₂ from it in platelets; prostacyclin synthase makes PGI₂ in endothelium.

A cyclopentane ring bridged by an endoperoxide (–O–O–), with two side chains and a 15-hydroxyl.

All NSAIDs act upstream of PGH₂, so they lower every prostanoid.
The balance between TXA₂ and PGI₂ made from PGH₂ shapes clotting and vascular tone.

Think of the answer, then tap the question to see it.

Which enzyme activity makes PGH₂ from PGG₂?

The peroxidase activity of COX-1/COX-2.

Why do NSAIDs lower all prostanoids?

They block COX, which makes PGH₂, the common precursor of every prostanoid.

What do platelets and endothelium make from PGH₂?

Platelets make thromboxane A₂; endothelium makes prostacyclin (PGI₂).

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: Prostaglandin H2 (CID 445049) (PubChem, NCBI, 2026) · Public domain; Prostacyclin synthase (PTGIS) - Homo sapiens (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.