Objective   To investigate the relaxant effect and its mechanism of SO₂ derivatives(sulfite and bisulfite, 3:1 mol/L)on the isolated thoracic aorta rings in rats.

  Methods   Isolated rat aortic mucle rings were used to perfuse in chambers containing chemicals tested in Kerbs buffer and the ring tensions were recorded.

  Results   SO₂ derivatives had relaxant effects on thoracic aorta with and without endothelium.The contraction responses induced by norepinephrine(NE), potassium chloride(KCl), and Ca²⁺ were antagonized SO₂ derivatives in a non-competitive manner.The pD' ₂ values were 0.43, 2.03, 2.49 respectively.In Ca²⁺-free modified Krebs solution, the contraction of two components induced by NE were inhibited significantly by SO₂ derivatives.The effect features of SO₂ derivatives mentioned above were just like that of verapamil in the same experimental conditions.

  Conclusion   The relaxant effect of SO₂ derivatives on rat's thoracic aorta is not dependent on endothelium, and is closely related to the blockage of Ca²⁺ entry through both potential-deqendent calcium channel and receptor-operating calcium channel, and to the inhibition of intracellular Ca²⁺ release.