Rho‐kinase inhibitors prevent agonist‐induced vasospasm in human internal mammary artery

Abstract

Vasospasm of arterial conduits used for coronary artery surgery is an important cause of graft failure and is likely to result partly from raised levels of vasoconstrictor substances such as thromboxane A₂ and endothelin‐1. Our aim was to find pharmacological agents that could prevent agonist‐induced vasospasm. Isometric tension was recorded from discarded segments of human left internal mammary artery (LIMA). Submaximal contraction evoked by the thromboxane A₂ mimetic U46619 (10 nM) was not inhibited by a blocker of store‐ and receptor‐operated Ca²⁺ channels (30 μM SKF96365) in the presence of diltiazem. Furthermore, contractions to 1 nM U46619 were preserved when extracellular Ca²⁺ was reduced from 2.5 mM to 60 nM. Thus, sustained U46619‐evoked contraction occurred without Ca²⁺ influx. We hypothesized that contraction might occur via Rho‐kinase‐mediated Ca²⁺‐sensitization of myofilaments. Inhibitors of Rho‐kinase (Y27632 and HA1077) were profound relaxants. If contraction was pre‐evoked by 10 nM U46619, Y27632 and HA1077 caused full relaxation with EC₅₀s of 1.67±0.22 μM and 3.58±0.35 μM respectively. Y27632 was also effective if applied before U46619, but was less potent. Y27632 abolished contraction evoked by endothelin‐1 and significantly reduced resting tone in the absence of a vasoconstrictor. Rho‐kinase‐mediated Ca²⁺‐sensitization appears to be a major mechanism of vasoconstriction in human LIMA. Rho‐kinase inhibitors may have an important role in preventing vasospasm in arterial grafts used for coronary artery surgery. British Journal of Pharmacology (2001) 132, 302–308; doi:10.1038/sj.bjp.0703809