Eicosanoids

Biosynthesis and main classes

Eicosanoid synthesis begins when phospholipases release a 20-carbon fatty acid from membrane phospholipids. Specialized enzyme pathways then convert that fatty acid into distinct families. Major routes include cyclooxygenases (COX), lipoxygenases (LOX) and cytochrome P450 oxidases. The common classes are:

• Prostaglandins — regulate inflammation, fever, pain and smooth muscle tone.
• Thromboxanes — influence platelet aggregation and vascular constriction.
• Leukotrienes — potent in airway constriction and inflammatory cell recruitment.
• Lipoxins and specialized mediators — often involved in resolving inflammation.

Physiological roles and examples

Eicosanoids participate in many local control systems. They modulate growth responses after exercise, steer inflammation and coordinate components of immunity. They are released in response to harmful stimuli such as toxic compounds and invading pathogens, and they act as mediators of pain, vascular permeability, bronchial tone, uterine contraction and renal blood flow. Some eicosanoids also function within the central nervous system, influencing neurotransmission and local blood flow.

Clinical relevance and pharmacology

Because prostaglandins and thromboxanes are central to inflammation and platelet function, common drugs target their synthesis. Nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit COX enzymes and reduce prostaglandin formation, relieving pain and fever. Leukotriene pathway inhibitors are used in asthma and allergic disease. Research into eicosanoid pathways has informed therapies for cardiovascular disease, inflammatory disorders and pain management.

History, distinctions and notable features

The discovery and characterization of prostaglandins and related substances were major advances in 20th-century physiology and pharmacology, recognized by awards and sustained research interest. Eicosanoids are notable for acting mainly in an autocrine or paracrine manner, having very short half-lives in tissues, and for arising from common membrane lipids so that dietary or metabolic changes in fatty acid composition can influence their profiles. They differ from steroid hormones by acting locally rather than via long-range endocrine signaling.

Because eicosanoid networks intersect with many signaling pathways, their control systems are complex and context-dependent. Ongoing research continues to map specific receptors, signaling partners and roles in health and disease, making eicosanoids a central subject in inflammation biology, cardiovascular science and metabolic research.