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Introduction

Cyclooxygenase (COX) enzymes catalyze the rate-limiting step in the conversion of arachidonic acid to prostanoids (eg, prostaglandins, prostacyclin, thromboxane A2) ( Figure 1).  Prostanoids are involved in a wide range of physiologic (and potentially pathologic) responses (eg, gastric mucosal protection, smooth muscle contraction/dilation, platelet aggregation, inflammation), acting locally within the tissue in which they are produced.  COX enzymes exist in 2 isoforms with different roles: COX-1 and COX-2 ( Figure 2).

COX-1

COX-1 is constitutively expressed in most tissues and is involved primarily in maintaining normal physiologic functions, including:

  • Gastrointestinal (GI) effects:  In the GI tract, COX-1 synthesizes prostaglandins that protect GI mucosa by limiting gastric acid production, increasing mucosal blood flow, and increasing bicarbonate production.
  • Renal effects

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