Production of prostaglandins. Arachidonic acid is released from the plasma membrane by phospholipase A2. The enzyme cycloxygenase catalyses the conversion of arachidonate to two prostanoid intermediates (PGH2 and PGG2). These are converted by specific enzymes into a number of different prostanoids as well as thromboxane (TXA2). The predominant prostaglandin produced varies with the cell type. In endothelial cells prostacyclin (PGI2) (in the circle) is the major metabolite of cycloxygenase activity. Prostacyclin, a potent vasodilator, is involved in the regulation of vascular tone. TXA2 is not produced in endothelial cells of normal kidneys but may be produced in increased amounts and contribute to the pathophysiology of some forms of acute renal failure (eg, cyclosporine A-induced nephrotoxicity). The production of all prostanoids and TXA2 is blocked by nonsteroidal anti-inflammatory agents (NSAIDs), which inhibit cycloxygenase activity.
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