Abstract: OBJECTIVE To observe the effects of myo-endothelial gap junction(MEGJ) on the endothelium-dependent and -independent vasorelaxation/vasoconstriction of superior mesenteric artery(SMA) in hemorrhagic shock rats. METHODS With determined the changes of diameter of SMA by a intravital microscope system, the effects of 18α-glycyrrhetic acid(18α-GA), a uncoupling agent of MEGJ, on endothelium-independent vascular contractile response to norepinepherine(NE), endothelium- independent relaxation reactivity to sodium nitroprusside(SNP), and endothelium–dependent contractile response to myricetin, endothelium-dependent relaxation reactivity to acetylcholine(ACh) in hemorrhagic shock rats were observed. RESULTS After treatment with 18α-GA(2 mg·kg-1), the endothelium-independent vasorelaxation/vasoconstriction of SMA induced by SNP (10 μg·kg^-1) or NE(3 μg·kg^-1) in hemorrhagic shock rats had no significant changes. While 18α-GA pretreatment significantly blocked the endothelium-dependent relaxation reactivity to ACh(2 μg·kg^-1) and contractile response to myricetin(2 μg·kg^-1), the vascular relaxation/contractile response of SMA to ACh or myricetin in 18α-GA group were decreased to 35.1% and 26.8% of the control group, respectively(P<0.01). CONCLUSION MEGJ played important role in the regulation of endothelium-dependent vasorelaxation/vasoconstriction in hemorrhagic shock rats.