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[Biochemistry](https://durgical.com/en/biochemistry/) · Topic

# Eicosanoids: prostaglandins, thromboxanes and leukotrienes

Eicosanoids are local messengers made from arachidonic acid: they control inflammation, pain, fever, clotting and airways.

Updated 2026-11-01

## Key facts

- Phospholipase A₂ releases arachidonic acid (20 C, ω-6) from membranes; corticosteroids restrain it.
- Cyclooxygenase (COX-1/COX-2) branch: PGH₂ → prostaglandins, prostacyclin (PGI₂) and thromboxane A₂ (TXA₂).
- 5-Lipoxygenase branch: LTB₄ (attracts neutrophils) and LTC₄/D₄/E₄ (bronchoconstriction, leaky vessels).
- Aspirin acetylates COX irreversibly; in the anucleate platelet the antiplatelet effect lasts its lifespan (7–10 days).
- TXA₂ (platelet) aggregates and constricts vessels; PGI₂ (endothelium) does the opposite.

## In detail

- 1. A stimulus (injury, cytokines) activates phospholipase A₂, which cuts arachidonate from phospholipids.
- 2. COX performs two reactions: cyclooxygenase (forms PGG₂) and peroxidase (PGH₂).
- 3. Each tissue converts PGH₂ according to its enzymes: thromboxane in platelets, prostacyclin in endothelium, PGE₂ and PGF₂α in many tissues.
- 4. 5-Lipoxygenase, with its activating protein (FLAP), forms LTA₄, which gives LTB₄ and the cysteinyl leukotrienes.
- 5. NSAIDs block COX; coxibs mainly COX-2; zileuton inhibits 5-lipoxygenase and montelukast blocks the cysteinyl-leukotriene receptor.
- 6. ω-3 fatty acids (EPA) give series-3 eicosanoids, which are less inflammatory and less pro-aggregant.

**Also called**
Arachidonic acid derivatives, Prostanoids

## Clinical notes

- PGE₂ protects the gastric mucosa: that is why NSAIDs promote peptic ulcer.
- In the newborn, COX inhibitors close a patent ductus arteriosus and PGE₁ keeps it open.
- Cysteinyl leukotrienes cause bronchoconstriction in asthma; aspirin can trigger asthma in sensitive people.
- Uterine prostaglandins (PGF₂α, PGE₂) explain dysmenorrhoea and its response to NSAIDs.

## Pathways

- [Prostaglandin and thromboxane synthesis](https://durgical.com/en/biochemistry/pathways/prostaglandin-and-thromboxane-synthesis/)

## Related conditions

- [Asthma](https://durgical.com/en/conditions/asthma/)
- [Peptic ulcer disease](https://durgical.com/en/conditions/peptic-ulcer-disease/)
- [Myocardial Infarction (Heart Attack)](https://durgical.com/en/conditions/myocardial-infarction/)
- [Patent ductus arteriosus](https://durgical.com/en/conditions/patent-ductus-arteriosus/)
- [Dysmenorrhoea](https://durgical.com/en/conditions/dysmenorrhoea/)

## Related

- [Cyclooxygenase (COX-1 and COX-2)](https://durgical.com/en/biochemistry/enzymes/cyclooxygenase/)
- [Palmitate (palmitic acid)](https://durgical.com/en/biochemistry/molecules/palmitate/)
- [Fatty acid synthesis (lipogenesis)](https://durgical.com/en/biochemistry/pathways/fatty-acid-synthesis/)

## Test yourself

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

## Why does aspirin's antiplatelet effect last the platelet's whole life?

Aspirin acetylates COX irreversibly and the anucleate platelet cannot make new enzyme.

## Which eicosanoid attracts neutrophils?

Leukotriene B₄ (LTB₄).

## Which enzyme do corticosteroids restrain to lower all eicosanoids?

Phospholipase A₂ (via lipocortin/annexin A1), which releases arachidonic acid.

## Which prostanoids have opposite effects on platelet aggregation?

Thromboxane A₂ (platelets) promotes it and prostacyclin PGI₂ (endothelium) inhibits it.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/biochemistry/topics/eicosanoids-prostaglandins-thromboxanes-and-leukotrienes/)

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

Sources: [Arachidonate metabolism](https://reactome.org/PathwayBrowser/#/R-HSA-2142753) (Reactome, 2026); [Synthesis of Prostaglandins (PG) and Thromboxanes (TX)](https://reactome.org/PathwayBrowser/#/R-HSA-2162123) (Reactome, 2026); [Synthesis of Leukotrienes (LT) and Eoxins (EX)](https://reactome.org/PathwayBrowser/#/R-HSA-2142691) (Reactome, 2026); [Prostaglandin E2 (CID 5280360)](https://pubchem.ncbi.nlm.nih.gov/compound/5280360) (PubChem, NCBI, 2026) · Public domain; 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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/topics/eicosanoids-prostaglandins-thromboxanes-and-leukotrienes/