Background - The Rho/Rho-associated kinase (Rho-kinase) system is implicated in various cellular functions, including migration, proliferation, and apoptosis. Because a possible role of the system is suggested in neointima formation after vascular injury, we sought to examine whether a new specific Rho-kinase inhibitor, Y27632, prevents neointima formation of the balloon-injured rat carotid artery, and if so, to investigate the effects of Y27632 on migration, proliferation, and apoptosis of smooth muscle cells (SMCs) in the injured artery. Methods and Results - Y27632 was administered intraperitoneally from 1 day before to 14 days after vascular injury. Treatment with Y27632 inhibited phenylephrine-induced Rho-kinase activation in the carotid artery on the basis of immunoblotting against the phosphorylated myosin-binding subunit of myosin phosphatase. Y27632 markedly prevented neointima formation at days 7 and 14. In controls, BrdU+ proliferating and TUNEL+ apoptotic SMCs were transiently and coincidentally increased in the neointima, with a peak at day 7. Y27632 significantly increased the neointimal TUNEL+ SMCs at days 7 and 14, but not BrdU+ SMCs. Y27642 significantly decreased the number of intimal SMCs at day 4, while not affecting the number of BrdU+ or TUNEL+ SMCs. Reendothelialization after balloon injury was not significantly affected by Y27632 at days 7 and 14. Conclusions - Y27632 inhibited neointima formation by enhancing SMC apoptosis and probably by suppressing early SMC migration. Therefore, a role of Rho-kinase is suggested in neointima formation after vascular injury.
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