Abstract: AimTo observe the effects of ouabain on vascular smooth muscle (VSM) of the guinea pig and its interactions with Ca₂₊ and norepinephrine (NE). MethodsUsing isolated thoracic aortic ring of the guinea pig, the degrees of contractile activity of drugs were recorded. ResultsOuabain showed a direct contractile effect in a concentration-dependent manner on thoracic aortic ring of guinea pig. Ouabain shifted the NE dose-response curve to the left without changing in the maxium response. Ouabain shifted the CaCl₂dose-response curve to the left and upward, increased the maximum response to Ca₂₊; In Ca₂₊-free medium, the ouabain induced contraction was abolished, an increase in extracellular Ca₂₊ restored the response; nifedipine and verapamil abolished the ouabain induced contraction. ConclusionThe ouabain induced contraction is mainly dependent on the extracellular Ca₂₊ concentration, independent on the presence of endothelia of aorta, suggesting that Ca₂₊ antagonist may treat the hypertension induced by ouabain. Ouabain, NE and CaCl₂have synergetic contractile effects，　suggesting that the synergetic contractile effects of ouabain and NE may contribute to the generation and development of hypertension.