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The eicosinoids are locally acting hormones produced by Arachidonic Acid and include Prostaglandins (PGs), Thromboxanes (TXs), and Leukotrienes (LTs). The PGs and TXs are products of the Cyclooxygenase (COX) pathway and are known as prostanoids, whereas the LTs are byproducts of the 5-lipooxygenase pathway. Prostanoid receptors are all G-Protein linked, and their stimulation activates distinct cell-signalling pathways. Five main prostenoid receptors have been defined and cloned, and have been termed TP-, IP-, DP-, FP-, and EP-receptors. These receptors are the ligands for the natural prostenoids know as TXA2, PGI2, PGD2, PGF2a, and PGE2, respectively. EP-receptors can be divided into four subtypes, EP1-EP4. This webpage is a descriptive analysis of pain sensitivity in different types of EP-knockout mice; this is done in the hopes of eventually characterizing the roles of the different PGE2 receptors. Below is a simple diagram showing the biosynthesis of prostaglandins, and thromboxanes from Arachidonic Acid, that are clinically relevant.. Our focus, however, will be the prostaglandin PGE2, to which the EP-receptors bind.