The most important function of cyclooxygenases (also called prostaglandin synthases) is endogenous in that they metabolize arachidonic acid to prostaglandins (Figure 4). First, the incorporation of two molecules of oxygen into arachidonic acid generates a cyclic peroxide (endoperoxide) and a hydroperoxide substituent. The resulting intermediate is prostaglandin-G2. Then, the hydroperoxide substituent is reduced to a hydroxyl group. The resulting compound is prostaglandin-H2. Many sufficiently lipophilic drugs that have a low redox potential act as an oxygen acceptor or electron donor in this second reaction and several of them are toxified in this way. This includes many
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