Prostaglandin Structure and Function

PG synthesis involves four steps (Figme 2). The first two steps are common to all cells involved in prostaglandin synthesis while the final two steps are cell-specific (14-16). Release of the substrate, arachidonic acid, from membrane phospholipid stores by phospholipase is the initial event in prostaglandin synthesis, and this is followed by formation of the common PG intermediate, PGHj catalyzed by PGH synthase. At this point, rearrangement of PGH to form either stabk (PGD / Ej/ F, ) or unstable (platelet thromboxane - TxA, endothelial prostacyclin - PGy products takes place. The final step, also cell-specific, involves breakdown of the active compounds to irractive metabolites. 

Steps in prostaglandin (PG) biosynthesis PG synthesis involves four steps 1) Release of the substrate, arachidonic acid (20 4), firom membrane phospholipids by a phospholipase. 2) Formation of the common intermediate, PGHj, from arachi-donate by PGH synthase throu sequential cyclo-oxygenase and peroxidase activities, both ofwWch are present within the same enzyme. 3) Fonnation of cell-specific PG products, either stable (Dj, E, Fj,) or imstable (thromboxane, prostacyclin), by distinct enzymes formd in different cells and tissues. 4) Breakdown of active compoimds to inactive metabolites, using TxAj - TxB, and PGI - 6keto PGF as examples. 

Both platelet and endothelial cyclooxygenase appear to be equally sensitive to the effects of aspirin since they are identical products derived from the same gene. Hiis point has 

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