AimTo investigate the effect of laminaria polysaccharide (LP) on the vascular endothelium-dependent relaxation and contraction of rats induced by psychological stress.MethodsNormal adult rats are randomly divided into control group, LP high group (LP-H group), LP low group (LP-L group) and low molecular heparin group, which was to build psychological stress of rat model by using the stimulation of uncertainty empty bottle.After the stress, rats were reviewed by open-field test.Then aortic rings were isolated and put into organ bath.The tension of endothelium-dependent relaxation induced by acetylcholine (Ach), contraction induced by norepinephrine (NE) and relaxation induced by nitroglycerin (NTG) after adding in L-arginine methyl ester hydrochloride (L-NAME) were recorded.ResultsCompared with control group, the frequency of crossing and rearing behavior increased significantly in model group, LP-H group, LP-L group and low molecular heparin groups.The model group reduced Ach-induced relaxation (p<0.05) and enhanced NE-induced contraction (p<0.05) in comparison with control group.Compared with model group, the relaxa-