Cyclooxygenase Isozyme Expression and Intimal Hyperplasia in a Rat Model of Balloon Angioplasty

Prostaglandin formation is enhanced in vascular disease, in part through induction of cyclooxygenase (COX-2) in vascular smooth muscle cells. Because COX regulates cell growth and migration, we examined whether the COX expression plays a role in the development of intimal hyperplasia after vascular injury. Rats undergoing balloon angioplasty of the carotid artery were randomized to receive a selective COX-2 inhibitor (SC-236), a selective COX-1 inhibitor (SC-560) or a combination of the two. Normal, uninjured vessels showed COX-1, but no COX-2 expression. Fourteen days after balloon injury, both COX-1 and COX-2 were expressed in the neointima. Balloon angioplasty resulted in a marked increase in the urinary excretion of prostaglandin (PG) E2, PGF2α, and thromboxane (TX) B2. Both the COX-1 inhibitor SC-560 and the COX-2 inhibitor SC-236 suppressed the generation of PGE2 and PGF2α, particularly when combined, suggesting a role for both isozymes in the generation of prostaglandins in this model. In contrast, TXA2 was markedly suppressed by the COX-1 inhibitor SC-560. COX-2 inhibition with SC-236 had no effect on intimal hyperplasia at day 14 (0 versus 8.5%; n = 7 in controls). In contrast, intimal hyperplasia was reduced by SC-560 when administered alone (by 42%; n = 7, p < 0.05) or in combination with SC-236 (by 40%; n = 7, p < 0.05). COX-1 may play a role in the development of intimal hyperplasia, potentially through the inhibition of platelet TXA2. Despite being expressed in the neointima, COX-2 does not play a role in the development of intimal hyperplasia after vascular injury.