Honokiol attenuates vascular contraction through the inhibition of the RhoA/Rho-kinase signalling pathway in rat aortic rings

Objectives Honokiol is a small-molecule polyphenol isolated from the species Magnolia obovata. We hypothesized that honokiol attenuated vascular contractions through the inhibition of the RhoA/Rho-kinase signalling pathway. Methods Rat aortic rings were denuded of endothelium, mounted in organ baths, and subjected to contraction or relaxation. Phosphorylation of 20 kDa myosin light chains (MLC ₂₀), myosin phosphatase targeting subunit 1 (MYPT1) and protein kinase C (PKC)-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase (MLCP) of 17 kDa (CPI17) were examined by immunoblot. We also measured the amount of guanosine triphosphate RhoA as a marker for RhoA activation. Key findings Pretreatment with honokiol dose-dependently inhibited the concentration-response curves in response to sodium fluoride (NaF) or thromboxane A ₂ agonist U46619. Honokiol decreased the phosphorylation levels of MLC ₂₀, MYPT1 _Thr855 and CPI17 _Thr38 as well as the activation of RhoA induced by 8.0 mm NaF or 30 nm U46619. Conclusions These results demonstrated that honokiol attenuated vascular contraction through the inhibition of the RhoA/Rho-kinase signalling pathway.