RESUMO
<p><b>AIM</b>To observe the effects of ouabain on vascular smooth muscle (VSM) of the guinea pig and its interactions with Ca2+ and norepinephrine (NE).</p><p><b>METHODS</b>Using isolated thoracic aortic ring of the guinea pig, the degrees of contractile activity of drugs were recorded.</p><p><b>RESULTS</b>Ouabain 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 CaCl2 dose-response curve to the left and upward, increased the maximum response to Ca2+; In Ca(2+)-free medium, the ouabain induced contraction was abolished, an increase in extracellular Ca2+ restored the response; nifedipine and verapamil abolished the ouabain induced contraction.</p><p><b>CONCLUSION</b>The 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 CaCl2 have synergetic contractile effects, suggesting that the synergetic contractile effects of ouabain and NE may contribute to the generation and development of hypertension.</p>