BACKGROUND - Prostanoid synthesis via the action of cyclooxygenase-2 (COX-2) is a component of the inflammatory response. Prostacyclin, a product of COX-2 in vascular endothelium, has important physiological roles, such as increasing blood flow to injured tissues, reducing leukocyte adherence, and inhibiting platelet aggregation. We examined the possibility that selective COX-2 inhibition could suppress the protective effects of prostacyclin, resulting in an alteration of the hemostatic balance and vascular tone.
METHODS AND RESULTS - Circumflex coronary artery thrombosis was induced in dogs by vascular electrolytic injury. Orally administered celecoxib (COX-2 inhibition) or high-dose aspirin (HDA) (COX-1 and COX-2 inhibition) did not alter time to occlusive thrombus formation compared with controls (celecoxib 77.7+/-7.2 minutes, HDA 72.0+/-18.5 minutes, control 93.0+/-21.8 minutes). Oral HDA with an endothelial recovery period (HDA-ER) (COX-1 inhibition) produced a significant increase in time to vessel occlusion (257.0+/-41.6 minutes). The observed increase in time to occlusion was abolished when celecoxib was administered to animals dosed with HDA-ER (80.7+/-20.6 minutes). The vasomotor effect of endothelium-derived prostacyclin was examined by monitoring coronary flow during intracoronary administration of arachidonic acid or acetylcholine. In celecoxib-treated animals, vasodilation in response to arachidonic acid was reduced significantly compared with controls.
CONCLUSIONS - The results indicate important physiological roles for COX-2-derived prostacyclin and raise concerns regarding an increased risk of acute vascular events in patients receiving COX-2 inhibitors. The risk may be increased in individuals with underlying inflammatory disorders, including coronary artery disease.