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Prostaglandins

  • These three groups are collectively called eicosanoids, derived from arachidonic acid via the cyclooxygenase (COX) or lipoxygenase pathways.

  • Prostaglandins are a group of physiologically active lipid compounds derived from arachidonic acid via the cyclooxygenase (COX) pathway.

  • They act as autacoids, having diverse roles in inflammation, vascular function, and other processes.

Synthesis:

  • Arachidonic Acid Release: Phospholipase A2 releases arachidonic acid from membrane phospholipids.

  • COX Pathway: Cyclooxygenase enzymes (COX-1 and COX-2) convert arachidonic acid into prostaglandin H2 (PGH2).

  • Further Conversion: PGH2 is a precursor for various prostaglandins (e.g., PGE2, PGI2) and thromboxanes.

Arachidonic acid → (COX enzyme) → prostaglandin intermediates → PGD2, PGE2, PGF2α, PGI2 (prostacyclin).

Synthesis of Prostaglandins
Synthesis of Prostaglandins

Major Prostaglandins:

PGE2 (Prostaglandin E2):

  • Functions: Mediates inflammation, induces fever, modulates gastric mucosal protection, and regulates reproductive processes.

PGI2 (Prostacyclin):

  • Functions: Inhibits platelet aggregation, induces vasodilation, protects the endothelium.

PGD2 (Prostaglandin D2):

  • Functions: Involved in allergic responses and sleep regulation.

PGF2α (Prostaglandin F2α):

  • Functions: Stimulates uterine contractions, involved in the menstrual cycle.

Pharmacological Effects:

  • Inflammation Modulation: Promote vasodilation, increased vascular permeability, and sensitization of pain receptors, contributing to inflammation and pain.

  • Gastroprotective Actions: Maintain gastric mucosal integrity by stimulating mucus and bicarbonate secretion.

  • Renal Function: Regulate blood flow in the kidneys and influence sodium excretion.

  • Platelet Function: Some PGs inhibit platelet aggregation, balancing thromboxane effects.

  • Vascular Tone: Control vasodilation and vasoconstriction, impacting blood pressure.

  • Reproductive System: Induce uterine contractions during labor and regulate menstrual cycles.

Examples:

  • PGE₂: Mediates fever, pain, and inflammation; protects gastric lining.

  • PGI₂ (Prostacyclin): Inhibits platelet aggregation and causes vasodilation.


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